Switched to 35's and feel like a brake upgrade is necessary - Page 3 - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > JK Jeep Wrangler Forum > JK General Discussion Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 10-20-2013, 03:16 PM   #61
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by Doctorsti View Post
Yeah, I doubt Mopar is putting out a kit that will some how damage my vehicle without braided lines or front track bar. AEV doesn't use one for 2.5" lift which ends up being around 3" unless you have armor or heavy bumpers. The 1/4" off center front axle was going to bother me so I did it. That was vanity more then performance. I highly doubt performance would suffer much from a 1/4" off front axle.

I'm guessing if Mopar's kit includes limit straps and doesn't include brake lines it's because the engineers that put it together wanted to make sure all of the critical items were included. I don't see many if any other kits include limit straps and have read plenty of threads of people whining about how a coil fell out. I'm also not sure they needed to include the 2.0 reservoir shocks but each piece is in the kit for a reason. Brake lines and front track bar are nice add-ons that they figure people may upgrade to at a later time.

Maybe Teraflex can comment on their testing and as to why they offer not only a performance rotor kit but also a performance brake kit. Few people would likely believe them and just rave about how they are all about the Benjamin's and trying to rape the Jeepers.
To be fair...the little bit of axle shift and lifts...while it may not cause "problems" it is the "good enough" mentality of modding. For some, its enough. For me, it's miles away, I want mine setup to be perfect, which is why I got the 2.5 AEV kit, and other things I felt it was lacking (like an adjustable front track bar.)

As for the brakes, I'd LOVE any of these brakes tested against OEM jeep brakes in a side by side comparison...same rigs, same wheels/tires/tread life.

NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 03:41 PM   #62
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by NFRs2000NYC View Post
To be fair...the little bit of axle shift and lifts...while it may not cause "problems" it is the "good enough" mentality of modding. For some, its enough. For me, it's miles away, I want mine setup to be perfect, which is why I got the 2.5 AEV kit, and other things I felt it was lacking (like an adjustable front track bar.)

As for the brakes, I'd LOVE any of these brakes tested against OEM jeep brakes in a side by side comparison...same rigs, same wheels/tires/tread life.
Don't let anyone find out your putting an AEV 2.5" lift, you'll get berated because garbage AEV didn't include brake lines or front track bar. God forbid you buy that instead of a "QUALITY" company who knows how to develop a lift with proper parts. Obviously tongue in cheek, so we're all clear.

When I get the larger rotors I'm going to compare 4-6 emergency stops and average their distance. I will attempt to do it mid day so ambient and surface temps can be close.

Teraflex shows the test for the performance rotor kit in a video unless you would suggest try are straight up lying.

| TeraFlex Suspensions

Looks like 20-25 feet shorter

Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 04:06 PM   #63
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by Doctorsti View Post
Don't let anyone find out your putting an AEV 2.5" lift, you'll get berated because garbage AEV didn't include brake lines or front track bar. God forbid you buy that instead of a "QUALITY" company who knows how to develop a lift with proper parts. Obviously tongue in cheek, so we're all clear.

When I get the larger rotors I'm going to compare 4-6 emergency stops and average their distance. I will attempt to do it mid day so ambient and surface temps can be close.

Teraflex shows the test for the performance rotor kit in a video unless you would suggest try are straight up lying.

| TeraFlex Suspensions

Looks like 20-25 feet shorter
Again, evidence can be manipulated 100 different ways. With a bigger brake kit, your test would indeed show that doing 4-6 emergency stops back to back are better on your new brakes rather than OEM brakes. However, what your test doesn't show is that the test is complete bunk, since no one does 4-6 emergency stops back to back. Just because the sky is blue, doesn't mean it doesn't get cloudy from time to time.
NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 04:19 PM   #64
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Just watched their video....

Ive been racing cars forever, and have been installing brake kits on most of them. I simply don't understand how the teraflex kit can improve anything. You have the same exact pad, touching the same amount of rotor, with the same amount of pressure. The only explanation I have for the video (end of it) would be the teraflex brakes were cold and the first test was done on warmer brakes.

BTW, you would gain a shorter stopping distance with drop brackets. That nose dive adds quite a bit of braking distance.
NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 04:55 PM   #65
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by NFRs2000NYC View Post
Just watched their video....

Ive been racing cars forever, and have been installing brake kits on most of them. I simply don't understand how the teraflex kit can improve anything. You have the same exact pad, touching the same amount of rotor, with the same amount of pressure. The only explanation I have for the video (end of it) would be the teraflex brakes were cold and the first test was done on warmer brakes.

BTW, you would gain a shorter stopping distance with drop brackets. That nose dive adds quite a bit of braking distance.
It's physics and mechanical advantage. Look up "moment arm." A larger radius to a brake disc the larger the moment arm. Yep, same swept area, same line pressure, same piston diameter BUT larger effective torque due to the longer moment arm. Where's Mr. Wizard when I need him!
Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 05:01 PM   #66
Supporting Member

WF Supporting Member
 
m998dna's Avatar
 
Join Date: Jan 2012
Posts: 2,955
Quote:
Originally Posted by Doctorsti View Post
I don't believe you are of any benefit to this thread and probably should troll elsewhere
I would like to see a purpose, scope, expected outcomes and ROI for this project.

Have you taken your Jeep off road yet?

.
__________________
2013 Wrangler JKUR10A 3.6L DOHC - MDH 032515
:: 2002 Chevrolet G3500 LWB 8.1L - motovan
:: 1991 Cherokee Laredo 4.0L HO - resto in-process
:: 2010 Cherokee SRT8 6.1L Hemi - sold
:: 1965 Plymouth Sedan 562ci Hemi - sold
m998dna is online now   Quote Quick Reply
Old 10-20-2013, 05:43 PM   #67
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by Doctorsti View Post
It's physics and mechanical advantage. Look up "moment arm." A larger radius to a brake disc the larger the moment arm. Yep, same swept area, same line pressure, same piston diameter BUT larger effective torque due to the longer moment arm. Where's Mr. Wizard when I need him!
I don't buy it. The rotor is only a smidge larger, so the performance gain would be minimal IMHO, even if there was one. Like I said, the elimination of nose dive would result in a better improvement than a rotor upgrade. I would love to see a side by side (2 jeeps) do a cold emergency stop to see the real effective difference. Couple that to the fact that 17" wheels are a must and it is a serious expense for many running 15s and 16s.

They way you make it sound is like going from a fred flinstone mobile to a ferrari. If there is a marginal braking improvement (lets say 3-5 feet), at that point, I'd rather have a steel bumper. You can't have your cake an eat it too. If you want large tires, your vehicle will need more time to come to a stop, so drive accordingly. I drive with a 5-10 car gap with my jeep, where as my with my s2000 I can drive with a 1/2 a car gap and not worry about rear ending someone. Lifting causes nose drive to be more pronounced, and as a result, poorer stopping distances. MT tires make for terrible stopping distances, etc. A jeep on 28" spinners and street rubber will stop better than a jeep on 16s and 35s. Your tires are the limiting factor, no matter how good your brakes are. If you have brakes that are too good for your tires, you'll just end up plowing them...which SOMETIMES might mean shorter stopping distance, but at the expense of zero vehicle control. Pick your poison.
NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 06:18 PM   #68
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by NFRs2000NYC View Post
I don't buy it.

They way you make it sound is like going from a fred flinstone mobile to a ferrari. If there is a marginal braking improvement (lets say 3-5 feet), at that point, I'd rather have a steel bumper. You can't have your cake an eat it too. If you want large tires, your vehicle will need more time to come to a stop, so drive accordingly. I drive with a 5-10 car gap with my jeep, where as my with my s2000 I can drive with a 1/2 a car gap and not worry about rear ending someone. Lifting causes nose drive to be more pronounced, and as a result, poorer stopping distances. MT tires make for terrible stopping distances, etc. A jeep on 28" spinners and street rubber will stop better than a jeep on 16s and 35s. Your tires are the limiting factor, no matter how good your brakes are. If you have brakes that are too good for your tires, you'll just end up plowing them...which SOMETIMES might mean shorter stopping distance, but at the expense of zero vehicle control. Pick your poison.
What are you talking about? It's fine if you "don't buy" hard science, that's cool with me. I guess it's easier to say you don't buy it then to learn something. But the rest of the post is just nonsense. I missed anywhere I mentioned a Ferrari. What or how you drive are not material to this thread and neither is going on about how the rubber is the limiting factor.

Again the mention of MT tires! Yes sir those darn MT's they are POOOOR on road... good thing I don't have them on the Jeep and they are sitting in the garage on the stock rims.
Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 06:28 PM   #69
Jeeper
 
Join Date: Aug 2013
Posts: 61
I am surprised that the stock brakes cannot lock up with 35" tires, regardless if they are all-season, summer tires or MT.

That is the most surprising aspect of this thread.


As for the ability to handle heat generated while braking the two ways of handling this are 1) being able to handle the heat (with more mass to absorb the heat), and 2) the ability to dissipate the heat with better cooling. Both techniques are employed on the track.

I guess that if the Jeep is going fast enough, and when braking without locking up (threshold), then you may generate enough heat during the stop to have a benefit if you can manage a larger rotor or have better cooling.

I am hoping to hear that the braking (without changing the tire) can be achieved with an upgrade to the braking system, but I am skeptical that it can be achieved.


For the record, what tires are you running on the Jeep DoctorSTi?
the_saint is offline   Quote Quick Reply
Old 10-20-2013, 06:32 PM   #70
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by the_saint View Post
I am surprised that the stock brakes cannot lock up with 35" tires, regardless if they are all-season, summer tires or MT.

That is the most surprising aspect of this thread.


As for the ability to handle heat generated while braking the two ways of handling this are 1) being able to handle the heat (with more mass to absorb the heat), and 2) the ability to dissipate the heat with better cooling. Both techniques are employed on the track.

I guess that if the Jeep is going fast enough, and when braking without locking up (threshold), then you may generate enough heat during the stop to have a benefit if you can manage a larger rotor or have better cooling.

I am hoping to hear that the braking (without changing the tire) can be achieved with an upgrade to the braking system, but I am skeptical that it can be achieved.


For the record, what tires are you running on the Jeep DoctorSTi?
Toyo Open Country AT2 35/12.5R17
Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 08:20 PM   #71
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by the_saint View Post
I am surprised that the stock brakes cannot lock up with 35" tires, regardless if they are all-season, summer tires or MT. That is the most surprising aspect of this thread. As for the ability to handle heat generated while braking the two ways of handling this are 1) being able to handle the heat (with more mass to absorb the heat), and 2) the ability to dissipate the heat with better cooling. Both techniques are employed on the track. I guess that if the Jeep is going fast enough, and when braking without locking up (threshold), then you may generate enough heat during the stop to have a benefit if you can manage a larger rotor or have better cooling. I am hoping to hear that the braking (without changing the tire) can be achieved with an upgrade to the braking system, but I am skeptical that it can be achieved. For the record, what tires are you running on the Jeep DoctorSTi?
Stock brakes can absolutely lock up 35" tires.
NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 08:37 PM   #72
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by Doctorsti View Post
What are you talking about? It's fine if you "don't buy" hard science, that's cool with me. I guess it's easier to say you don't buy it then to learn something. But the rest of the post is just nonsense. I missed anywhere I mentioned a Ferrari. What or how you drive are not material to this thread and neither is going on about how the rubber is the limiting factor. Again the mention of MT tires! Yes sir those darn MT's they are POOOOR on road... good thing I don't have them on the Jeep and they are sitting in the garage on the stock rims.
The MTs weren't directed at you, but for general thread discussion. Yes brake torque can be increased with a larger rotor. This is usually done by guys in cars like civics that have a 12.2" rotor and they slap on a 15" rotor on their 19" wheels. On the jeep, you will gain a little bit of brake torque with a larger rotor but it will generally be offset by all the other mods jeepers do that hurt braking performance. If you have money to throw around for a marginal improvement, by all means. However, it won't transform the jeep from what it is to even a normal car brakewise, let alone something like an STI. You posted this thread for what reason? To get opinions? You got some. If you are just going to knock all the opinions then why bother?
NFRs2000NYC is offline   Quote Quick Reply
Old 10-20-2013, 08:40 PM   #73
Moderator

WF Supporting Member
::WF Moderator::
 
jkjeeper06's Avatar
 
Join Date: Jul 2010
Posts: 3,486
Quote:
Originally Posted by NFRs2000NYC View Post

Stock brakes can absolutely lock up 35" tires.
Definitely.

They are meant to stop 3500# of trailer(jk as same brakes as jku). If they couldn't stop an extra 60#(huge overestimation) per tire that just wouldn't mathematically make sense.

As far as moment arms go:
Yes it is rotational mass vs a force on the tire, but in reality a trailer a trailer applies more force to the tires as it applies its force at the full radius of the tire and creates a larger moment on the brakes than just larger tires would
jkjeeper06 is offline   Quote Quick Reply
Old 10-20-2013, 08:48 PM   #74
Jeeper
 
Join Date: Aug 2013
Posts: 61
Quote:
Originally Posted by NFRs2000NYC View Post
Stock brakes can absolutely lock up 35" tires.
This makes me suspect that there may be an issue with the doctor's Jeep's brakes.
the_saint is offline   Quote Quick Reply
Old 10-20-2013, 09:52 PM   #75
Supporting Member

WF Supporting Member
 
m998dna's Avatar
 
Join Date: Jan 2012
Posts: 2,955
Quote:
Originally Posted by the_saint View Post
This makes me suspect that there may be an issue with the doctor's Jeep's brakes.
Or the doctor's credibility...

.
__________________
2013 Wrangler JKUR10A 3.6L DOHC - MDH 032515
:: 2002 Chevrolet G3500 LWB 8.1L - motovan
:: 1991 Cherokee Laredo 4.0L HO - resto in-process
:: 2010 Cherokee SRT8 6.1L Hemi - sold
:: 1965 Plymouth Sedan 562ci Hemi - sold
m998dna is online now   Quote Quick Reply
Old 10-20-2013, 10:56 PM   #76
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by m998dna View Post
Or the doctor's credibility...



Lets add some facts to this thread, buckle in for some math on a Sunday night yall!

I will preface by saying this is hard physics and the laws of this planet so any rebuttals will only be applicable on some undiscovered world outside this universe.

Torque generated by the rotor = Force of friction from the caliper/pad x the effective radius of the rotor. Tr = Fc/Radr

Because the wheel/tire and brake rotor are coupled on the hub the Torque found in the wheel, the torque found in the tire, and the torque found in the rotor are the same (either positive or negative value). Tr = Tw = Tt

Now we are at the Tire’s contact to the ground.
Friction between the tire and the ground is equal to the torque on the tire divided by the effective rolling radius of the tire.
Looks like this: Ft = Tt/Radt

Friction force of the vehicle is equal to the sum of the friction forces of each tire.

Deceleration of a vehicle in motion is solved by the equation:
Accel (+/-) = Friction force total / mass of the vehicle

In a case of simply increasing tire radius:
Plug that in the calculations above and you will find that as tire radius goes up Friction force on tire goes down. As friction force goes down so does the sum of the friction forces total. As the sum of the friction forces total goes down and vehicle mass goes up you get a lower value for acceleration, which in this case due to friction being negative would be deceleration.

Now lets do this again for increasing the rotor radius with no change in tire size shall we:
Torque generated by rotor = force of caliper friction (will remain constant if same caliper/booster/etc..) x the effective radius of the rotor.
Friction force of the tire = torque of the rotor / radius of tire which in this case is remaining the same. Ft = Tr/Radt
For increasing rotor radius you get increased torque and as the numerator goes up the result also goes up. Simple math again.
Friction force of the tire goes up along with rotor radius
As total friction goes up and vehicle mass remains constant (or negligible change of 2 lbs per wheel) you will get larger values for acceleration which again in all of these will be deceleration as friction force is opposite the direction of travel which any self respecting physicist would make positive values.

From grade school math you can now see that as tire radius goes up and rotor torque remains the same (remember tire torque = wheel torque = rotor torque) the Friction on the tire is reduced and you get smaller deceleration values.

As brake rotor radius goes up you get larger values for friction between the tire and road surface and therefore larger deceleration values and faster stopping which we can all figure out pretty quickly results in shorter distances.
We can argue over who did what to their S2000/Mustang/Mall Crawler/sport bike but this is mathematical fact. It’s physics and I don’t think Newton cares how hardcore your rig is or what life experience you have.

Light reading on this subject can be found here:
http://www.stoptech.com/docs/media-c...raking-systems

And we didn’t even get into brake balance yet. YeeHaaa
Judging by the numerous threads on how JK rear brake pads go quicker then the front just suggests even more the fronts are not producing enough torque and are being overcome requiring the rears to pick up the slack. I didn’t get into the math on that but analytically that makes sense.

Oh and for the braided line crew all of these equations assume hard lines from the master cylinder to the caliper as line bulge is a negligible value and not worth solving for. Adding hard lines as has been discussed 1-2 times in this thread simply reduces the delay of the full line pressure on the caliper. There is deflection in the caliper along with warping of the knuckle also as confounding variables. I concede adding lines will make me feel better but I'm looking to bring my deceleration value back to where it started before the radius of the tire increased along with weight.
Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 11:08 PM   #77
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Oh and we were talking about stopping distance which is Velocity divided by 2x the acceleration value. Here again denominator increasing in value you will get smaller value for stopping distance.
Doctorsti is offline   Quote Quick Reply
Old 10-20-2013, 11:22 PM   #78
Jeeper
 
mckey73's Avatar
 
Join Date: Mar 2012
Location: Downstream from Hanford
Posts: 9,993
Talk about some overachievers. Sheesh.
__________________
“Animals don't hate, and we're supposed to be better than them.”

-Elvis Presley
mckey73 is offline   Quote Quick Reply
Old 10-20-2013, 11:46 PM   #79
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by mckey73 View Post
Talk about some overachievers. Sheesh.
didn't need to come to that but we obviously are having a hard time with mixing two arguments.

1st argument: physics of braking systems, larger rotors produce stronger braking forces and therefore shorter stopping distance. This is physics and not really an argument unless arguing 2+2=5 is your thing.

2nd argument: "improved" braking based on user need and situational use. Bigger rotors might not be "better" braking dependent on user style and preference whereas brake feel may make them just as happy or happier.

Throwing 35's on a stock Jeep affects it in many ways (which I don't need an orientation on) and I would find it hard to believe anyone would not expect some loss in performance or braking distance. The record will show I didn't start a thread about unsprung weight and it's affects on vehicle dynamics and handling although there is a massive change there too. The thread's intent was to express my personal feeling on that reduction in brake force and my desire to gain back on the other side of the equation as well as to see what others have done in this situation. Clearly some added braided lines from their "elite" lift manufacturers and that's great. Others have improved brake torque and still others have done both.

Hopefully in the end this will be a learning experience for all and we can even get some input from those that make braking systems a profession.
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 12:20 AM   #80
Race Car Dave

WF Supporting Member
 
NFRs2000NYC's Avatar
 
Join Date: Nov 2011
Location: NYC
Posts: 6,955
Quote:
Originally Posted by Doctorsti View Post
didn't need to come to that but we obviously are having a hard time with mixing two arguments. 1st argument: physics of braking systems, larger rotors produce stronger braking forces and therefore shorter stopping distance. This is physics and not really an argument unless arguing 2+2=5 is your thing. 2nd argument: "improved" braking based on user need and situational use. Bigger rotors might not be "better" braking dependent on user style and preference whereas brake feel may make them just as happy or happier. Throwing 35's on a stock Jeep affects it in many ways (which I don't need an orientation on) and I would find it hard to believe anyone would not expect some loss in performance or braking distance. The record will show I didn't start a thread about unsprung weight and it's affects on vehicle dynamics and handling although there is a massive change there too. The thread's intent was to express my personal feeling on that reduction in brake force and my desire to gain back on the other side of the equation as well as to see what others have done in this situation. Clearly some added braided lines from their "elite" lift manufacturers and that's great. Others have improved brake torque and still others have done both. Hopefully in the end this will be a learning experience for all and we can even get some input from those that make braking systems a profession.
Your math is great (although I'd love to see you run it with actual numbers (stock tires and stock brakes, 35" tires and stock brakes and 35" tires with upgraded rotors) I think tire compound is fairly important as are nosedive forces. You obviously know physics better than I do, so by all means, run the numbers for all of the above scenarios. I am plenty man enough to admit that I am wrong if the evidence stacks up. No one is immune from leaning something new, including me, so I'm all for the math run....although I don't know how you can find out the tire compound/friction values or the nose dive/weight transfer numbers. The problem is cars aren't run in a lab or in a vacuum so oftentimes simple math doesn't paint the whole picture.
NFRs2000NYC is offline   Quote Quick Reply
Old 10-21-2013, 12:35 AM   #81
Jeeper
 
sebbekk's Avatar
 
Join Date: Jan 2013
Location: Germany
Posts: 60
Just for the record, I think the physics behind brake torque are understood by many of us. The major caveat of those with substantial experience is that the friction coefficient between any kind of available 35" tire and paved ground is not even big enough to hold up to the brake torque of the stock rotor.

Initially I had chimed in because I am also concerned that my JK's brakes are not up to the task since I had upgraded to 35s (Goodyear Duratrac LT315/70R17 All Terrain).

Now if the stock brakes really cannot lock up 35" ATs as tested we must apply Newton's laws as explained above because the friction coefficient of the tire might be much higher than anticipated by those who are in favor of braided brake lines over bigger brakes.
__________________
'07 JKUR 3.8L, 6 Speed Manual (4.10 Axle), Superchips TrailDash, aFe PRO 5R Intake System, Gibson GP403S-C Performance Headers, Bulldog Alpha 9,300 Recovery Winch, Rugged Ridge XHD Bumpers, Rugged Ridge Aluminum Wheels, Goodyear DuraTrac 315/70R17, AEV DualSport SC 3.5", PureJeep C-Gussets, Nolden 7" Bi-LED Head Lights, ARB Twin Air Compressor, Hothead Headliners, Trektop NX
sebbekk is offline   Quote Quick Reply
Old 10-21-2013, 12:36 AM   #82
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by NFRs2000NYC View Post
Your math is great (although I'd love to see you run it with actual numbers (stock tires and stock brakes, 35" tires and stock brakes and 35" tires with upgraded rotors) I think tire compound is fairly important as are nosedive forces. You obviously know physics better than I do, so by all means, run the numbers for all of the above scenarios. I am plenty man enough to admit that I am wrong if the evidence stacks up. No one is immune from leaning something new, including me, so I'm all for the math run....although I don't know how you can find out the tire compound/friction values or the nose dive/weight transfer numbers. The problem is cars aren't run in a lab or in a vacuum so oftentimes simple math doesn't paint the whole picture.
I did just make the evidence stack up. Math and physics are how everything on this planet (and others for that matter) work. There's no seat of the pants changes to math which is why scientists assess change accounting for confounding variables. These are things that you don't have to figure out as they will be static. If you wanted to compare the braking distance between your rig and a buddies, where you ran Duratracs on 18" Sahara rims and he ran MT/R's on 15" beadlocks, you would have a hard time accounting for the variables. In this instance comparing your own vehicle with smaller diameter rotors to your vehicle again with only one variable changed you can assume the bulge in the lines, the coefficient of friction, the weight distribution, and weight transfer are the same.
No science would be publishable if naysayers jumped up and said... "well look noobie, what about if the tide is in and it rained 4 hours ago and you were sleepy, then what?" Geez minute gravity changes, coefficients of friction and reaction time just changed so yes your results will change in magnitude. My Jeep with 35's and 13" rotors will stop in more feet if it's rained or I'm tired but that if it just rained and I was exactly the same amount tired but had 11.9" rotors it would take me even longer to stop, get it?

In my specific case I changed one variable to ensure what I was experiencing was due to that variable alone. If I changed both at once I'd have a harder time proving anything. Even if a larger diameter rotor decreases my stopping distance 5 ft that is still 5ft less of a chance I mangle another human.

The other side of this argument that you also can't just toss numbers in will be driver reaction time. If you didn't sleep well the night before, had a brew or 2, or were on an antihistamine for example your total real world braking distance could be worse but it would have nothing to do with the vehicle.

Summary:
Stock Rubicon on 35" AT2s with 11.9" rotors takes longer to come to a stop then the same exact vehicle with 13" rotors. That's a hair over 10%, that's not negligible. It's irrefutable. You don't need to solve for the other variables as they don't change.
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 12:44 AM   #83
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by sebbekk View Post
Just for the record, I think the physics behind brake torque are understood by many of us. The major caveat of those with substantial experience is that the friction coefficient between any kind of available 35" tire is not even big enough to hold up to the brake torque of the stock rotor.

Initially I had chimed in because I am also concerned that my JK's brakes are not up to the task since I had upgraded to 35s (Goodyear Duratrac LT315/70R17 All Terrain).

Now if the stock brakes really cannot lock up 35" ATs as tested we must apply Newton's laws as explained above because the friction coefficient of the tire might be much higher than anticipated by those who are in favor of braided brake lines over bigger brakes.
You are clear that braking even while the tire is rotating is caused by the tire compound slipping on the asphalt right? The slip is very very small and not something you see or feel. Each tread block that comes in contact with the road while the tire is rolling is slipping when you are braking just a little until it rolls off then the next and the next, etc.. When you lock the tire up you have produced more torque the tires can handle, yes, but you have also taken the brakes out of the equation and made the only equation tire compound coefficent of friction. In mine and your situation we went from a rubber contact patch of 9 or so inches up to 12 inches along with a rubber compound designed to maintain more friction with the road surface even when the coefficient of friction of the road surface goes down like in wet or snowy conditions. We have made our "brakes" more important.
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 12:53 AM   #84
Jeeper
 
sebbekk's Avatar
 
Join Date: Jan 2013
Location: Germany
Posts: 60
Like I said I believe the coefficient of friction between 35" ATs and paved ground might have been underestimated by those who don't believe in bigger brakes, no matter which of the two existent types of friction or a combination of those we are looking at. Interesting to me is that you have stated that you are not able to lock up your 35s which makes the maximum brake torque of your stock brakes relevant as a limitation in your brake system again, I agree.
__________________
'07 JKUR 3.8L, 6 Speed Manual (4.10 Axle), Superchips TrailDash, aFe PRO 5R Intake System, Gibson GP403S-C Performance Headers, Bulldog Alpha 9,300 Recovery Winch, Rugged Ridge XHD Bumpers, Rugged Ridge Aluminum Wheels, Goodyear DuraTrac 315/70R17, AEV DualSport SC 3.5", PureJeep C-Gussets, Nolden 7" Bi-LED Head Lights, ARB Twin Air Compressor, Hothead Headliners, Trektop NX
sebbekk is offline   Quote Quick Reply
Old 10-21-2013, 12:55 AM   #85
Supporting Member

WF Supporting Member
 
m998dna's Avatar
 
Join Date: Jan 2012
Posts: 2,955
OK so you're working on your PhD... I work with them all day long. Now the real world, put your helmet on and point your Jeep down a dirt hill and see if it will stop.

.
__________________
2013 Wrangler JKUR10A 3.6L DOHC - MDH 032515
:: 2002 Chevrolet G3500 LWB 8.1L - motovan
:: 1991 Cherokee Laredo 4.0L HO - resto in-process
:: 2010 Cherokee SRT8 6.1L Hemi - sold
:: 1965 Plymouth Sedan 562ci Hemi - sold
m998dna is online now   Quote Quick Reply
Old 10-21-2013, 12:56 AM   #86
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Another completely realistic response to this thread could be, upgrade the friction force at the caliper by changing pad compound and rotor material. That would also result in reductions in stopping distance.

What drives me nuts is this whole get brake lines to decrease stopping distance. It's just not accurate. If I was told "hey new guy, welcome and congrats on only learning to drive yesterday one vehicle in your whole life, try getting some pads with a higher coefficient of friction and you'll stop in less feet" I would have said thanks, good suggestion.
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 12:58 AM   #87
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by m998dna View Post
OK so you're working on your PhD... I work with them all day long. Now the real world, put your helmet on and point your Jeep down a dirt hill and see if it will stop.

.
Again with the troll response. Really guy? Going gets tough so you resort to ridicule. By the way you don't need a PhD to understand physics. It's taught in high school. Do you just tell your colleagues they have 4 eyes when you don't understand what they are talking about?
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 01:03 AM   #88
Jeeper
 
Join Date: Jan 2013
Location: Newark DE
Posts: 1,259
Quote:
Originally Posted by sebbekk View Post
Like I said I believe the coefficient of friction obetween 35" ATs and paved ground might have been underestimated by those who don't believe in bigger brakes, no matter which of the two existent types of friction or a combination of those we are looking at. Interesting to me is that you have stated that you are not able to lock up your 35s which makes the maximum brake torque of your stock brakes relevant as a limitation in your brake system again, I agree.
I tried pretty damn hard to lock em up this morning. Only chirps I got were when the tire lost contact with the ground over a bit of a dip and some gravel. Maximum brake torque is one thing but through the whole deceleration process a larger lever arm makes a difference not just at the limits of traction (notice I didn't say friction).
Doctorsti is offline   Quote Quick Reply
Old 10-21-2013, 01:08 AM   #89
Jeeper
 
spinlock's Avatar
 
Join Date: Sep 2013
Location: 37.9° N, 121.7° W
Posts: 3,626
Quote:
Originally Posted by Doctorsti View Post
I did just make the evidence stack up. Math and physics are how everything on this planet (and others for that matter) work. There's no seat of the pants changes to math which is why scientists assess change accounting for confounding variables. These are things that you don't have to figure out as they will be static. If you wanted to compare the braking distance between your rig and a buddies, where you ran Duratracs on 18" Sahara rims and he ran MT/R's on 15" beadlocks, you would have a hard time accounting for the variables. In this instance comparing your own vehicle with smaller diameter rotors to your vehicle again with only one variable changed you can assume the bulge in the lines, the coefficient of friction, the weight distribution, and weight transfer are the same.
No science would be publishable if naysayers jumped up and said... "well look noobie, what about if the tide is in and it rained 4 hours ago and you were sleepy, then what?" Geez minute gravity changes, coefficients of friction and reaction time just changed so yes your results will change in magnitude. My Jeep with 35's and 13" rotors will stop in more feet if it's rained or I'm tired but that if it just rained and I was exactly the same amount tired but had 11.9" rotors it would take me even longer to stop, get it?

In my specific case I changed one variable to ensure what I was experiencing was due to that variable alone. If I changed both at once I'd have a harder time proving anything. Even if a larger diameter rotor decreases my stopping distance 5 ft that is still 5ft less of a chance I mangle another human.

The other side of this argument that you also can't just toss numbers in will be driver reaction time. If you didn't sleep well the night before, had a brew or 2, or were on an antihistamine for example your total real world braking distance could be worse but it would have nothing to do with the vehicle.

Summary:
Stock Rubicon on 35" AT2s with 11.9" rotors takes longer to come to a stop then the same exact vehicle with 13" rotors. That's a hair over 10%, that's not negligible. It's irrefutable. You don't need to solve for the other variables as they don't change.
10% is not negligible by any means because although the lever arm of the brake pads increase linearly as the radius of the rotor increases, the braking force created by the brake pads, their friction coefficient and the swept area of the rotor increases by the radius squared. Assuming the brake calipers on both rotors are able to generate the same amount of pressure (which is probably not true) on the pads, the braking force generated by the larger rotors/calipers will be significantly greater.
spinlock is online now   Quote Quick Reply
Old 10-21-2013, 01:09 AM   #90
Supporting Member

WF Supporting Member
 
m998dna's Avatar
 
Join Date: Jan 2012
Posts: 2,955
Quote:
Originally Posted by Doctorsti View Post
Again with the troll response. Really guy? Going gets tough so you resort to ridicule. By the way you don't need a PhD to understand physics. It's taught in high school.
Yes, really.. you're way over thinking this. The problem has been solved long before you bought a Jeep.

I think you're in for some long nights... remember, you've only installed tires.

Good luck.

.

__________________
2013 Wrangler JKUR10A 3.6L DOHC - MDH 032515
:: 2002 Chevrolet G3500 LWB 8.1L - motovan
:: 1991 Cherokee Laredo 4.0L HO - resto in-process
:: 2010 Cherokee SRT8 6.1L Hemi - sold
:: 1965 Plymouth Sedan 562ci Hemi - sold
m998dna is online now   Quote Quick Reply
Reply

Tags
brake , brakes , mopar brakes , rotor diameter , teraflex

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off




Download our Mobile App

» Featured Product

All times are GMT -5. The time now is 02:20 AM.



Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC