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So you want bigger tires

293K views 291 replies 105 participants last post by  KiwiScott 
#1 ·
So you want bigger tires

It seems as though every other question on the forum has to do with tires, specifically bigger tires. This is understandable because bigger tires without a doubt can make a Jeep look really good but at what cost?

Besides the fact that larger tires cost a lot more than your stock tires, what else is there to consider?

This post aims to detail the multiple factors involved with running bigger tires. This isn’t meant to scare you away from bigger tires, it’s just meant to give some insight into what the effects are so you can plan accordingly.


The effects of extra tire height
If you haven’t already thought this through you’ll come realize that these bigger tires don’t fit so well under the fenders.

Thirty-three inch (33s) tires will fit with minimal rub on a stock suspension (see sticky about largest tire on stock) but anything larger will require a lift (or a lot of trimming) in order to not cause rubbing.

Time to lift the jeep to accommodate those bigger tires! See sticky about things to consider when lifting your Jeep and also get out the wallet! A 2.5” lift is considered the maximum safelift height that won’t require even more modification to keep it running safely and enjoyably. A decent 2.5” lift kit will cost about $1000 USD.


The effect of extra tire width
Those bigger tires just aren’t taller (in most cases) but they’re also wider. Now you need new wheels with appropriate backspacing to accommodate them or you’ll need to buy wheel spacers.

This site can help you figure out what your new setup will look like and whether or not they’ll fit.

Custom rims, wheel tire packages for your ride - RIMSnTIRES.com

This site will help you calculate backspace from offset and vice versa.

Wheel/Tire Calculators | Custom Offsets

The consensus is that 4.5” of backspace on a 17” rim is the magic number to fit a tire up to 12.5 inches wide.

Stock (sport/rubicon) info for reference:
Tire size: 255/75/17
Rim size: 17x7.5 6.25” backspacing (which is approx. 51mm offset)


The effects of the extra weight
A short lesson in unsprung weight.
Unsprung weight is the weight (mass) on a vehicle that is not supported by suspension. Essentially, unsprung weight is the weight of your wheels and tires. Since this weight is not supported by the vehicle’s suspension, and the fact that it has rotational inertia, adding more unsprung weight is not the same as adding sprung weight.

There are calculators available that can help you determine exactly how much unsprung weight would equal in sprung weight but I will give you a quick example.

The Effects of Rotational Inertia on Automotive Acceleration

Stock Tire Baseline:

Calculator: Tire Rotational Inertia
Enter tire size: 255/75 R17 (Stock Tire Size)
Mass: 16.3 KG (36 lbs - ie 32" Goodyear SRA)
Tread to sidewall thickness ratio: 2

Results:
Tire equivalent mass is 30.464 kg (67 lbs) per tire
Equivalent mass ratio 1.87

Larger DuraTrac 35” Tire:

Calculator: Tire Rotational Inertia
Enter tire size: 315/70 R17
Mass: 27.21 KG (60 lbs - ie 35" DuraTrac)
Tread to sidewall thickness ratio: 2

Results:
Tire equivalent mass is 50.891 kg (112 lbs) per tire
Equivalent mass ratio 1.87

So that means the stock running weight is 67 lbs per tire whereas going with 35" DuraTracs would have a running weight of 112 lbs per tire. That's a difference of 45 lbs.
45 x 4 = 180 lbs

So essentially it's like carry an NFL wide receiver with you in the passenger seat when you add a bigger tire of this size and weight.

So who cares? My jeep can handle the extra weight, right?

Well, yes, it can handle the extra weight but at a cost. First, you’ll notice a bit of sluggishness in your Jeep’s ability to accelerate. It now has more mass to turn. Adding bigger tires essentially reduces your gear ratio, which also reduces your crawl ratio and robs your Jeep of power. This can be corrected by upgrading your gearing.

This site will help figure out what gearing you need in order to get you back to your original ratio.

4Lo.com :: Tire Size Change, New Gear Ratio Calculator

Example: You have 3.73 gearing and have 32” tires. You upgrade to 35” tires. You have now effectively reduced your gearing to 3.41. To return to the previous performance level you would need to upgrade to ~4.10 gears.

Next you’ll notice that it takes longer to stop and that your brakes are wearing quicker, so you may think about a upgrading to bigger brakes.

Before you know it, you’re out of gas! The accelerated decrease in Miles Per Gallon (MPG) simply due to needing to roll more mass around but most times bigger tires are also wider which means there is more friction to overcome as well. Your Jeep has to work hard to get things moving and to keep them moving.

You fill up your tank and you’re back on the road every time you hit a bump you feel more than before. That extra weight means the shocks and springs aren’t as effective as they were. Get out the wallet and get that coil spring lift kit if you didn’t already add that first! Note: Lifting the jeep is a whole other article with problems of its own!

All this harshness on the suspension has caused some effects of its own. Your wheel bearings, ball joints and other steering components are all wearing at an accelerated pace. Depending on the terrain, style of driving and the size tires you’ve upgraded to you may notice these parts failing sooner rather than later. If you have really big tires and do a lot of off road where one wheel hangs in the air, you may notice your axles are bending. Get out the wallet again, time to upgrade the ball joints, gusset the CV joints and sleeve the axle shafts (or upgrade to beefier ones). Throw on the steering stabilizer while you’re at it.

Note: These issues “wear and tear” issues are also compounded by the fact that you changed the backspacing on your wheels.

I hope this proves useful for anyone looking to run bigger tires so they can plan accordingly. I tried to be thorough and to ensure all my facts were straight, but I’m only human so feel free to add any additional information I may have missed or let me know if I made a mistake somewhere.
 
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#2 ·
You've got to pay to play with the big boys. Don't forget the tire carrier and Procal or the like.

But wait, don't you understand? This is an investment in your future. Having a lifted Jeep with bigger tires makes you taller, better looking, and more attractive. You get better jobs, make more money, and have more success in life because of your great decision making. You gain status, power, respect and even good health from all the great times you have driving that beautiful beast of yours. Now go get those 37's!
 
#4 ·
You've got to pay to play with the big boys. Don't forget the tire carrier and Procal or the like. But wait, don't you understand? This is an investment in your future. Having a lifted Jeep with bigger tires makes you taller, better looking, and more attractive. You get better jobs, make more money, and have more success in life because of your great decision making. You gain status, power, respect and even good health from all the great times you have driving that beautiful beast of yours. Now go get those 37's!
Thanks and good call on the ProCal for adjusting the computer for tire size and on tire carrier needing to be upgraded for sizes bigger than 33s. Adjusting the computer for the new tire size is important not to just fix the speedometer but also so the ESP system doesn't get confused and start applying the brakes for no reason.

I didn't even get into the handling effects caused by changing wheel offset.
 
#3 ·
Great post. Tire and wheel weights, rotational mass or not, vary quite a bit. A fifteen inch wheel might weigh 18-20 pounds and a 33x15 Duratrac or BFG AT weigh about 50 pounds. That's as light or lighter than stock set ups and will sit on your factory tire carrier no problem (weight wise, you will need to play with mounts and snubbies).

But a 17 inch wheels goes more like 25 to 30 pounds and a 35x17 mud tire might go 70 pounds or more. Now you are 85-100 pounds (and maybe much more as you will see) for the combo. I've seen members post weights as high as 119 pounds for a 35 inch tire!!

Tire weights are relatively easy to find, most tire manufacture website and many retailer sites have them. Wheels are harder. Not all manufacturers list them. Tread Depot has a lot of wheel weights and Pro Comp weights can be found in the other link:

Discount Tires for Sale - Tires, Wheels & Accessories | Tread Depot

http://www.procompusa.com/images/pdf/PCT_Wheel_Specs_Catalog.pdf

You can also use shipping weight to get an estimate. Amazon usually lists those.

Wheels, even aluminum, can get pretty heavy. 30-35 pound wheels aren't uncommon. Pro-comp 15 inch 1069's are only 16 pounds on the other hand!!! Don't assume a spindly looking wheels is light or a more solid looking wheel is heavy.

Tires vary a lot too. Look at these various popular all terrain tires, all 35x17 (315x17), all D-rated.

BFG AT KO = 60 lbs
Duratrac = 60 lbs
Cooper Discoverer S/T = 68 (Maxx version = 67)
General Grabber AT2 = 74

Mud tires? All E-rated except the BFG which is D-rated:

BFG KM2 = 66 pounds
Cooper SST = 67
General Grabber Extreme = 79
Toyo Open Country =83!!!

That Grabber extreme and Toyo weigh more than my stock Rubicon wheel and tire COMBINED! Six and ten pounds more respectively, just for the tire. Some added weight is OK but know what your getting and how much it weighs. All tires and wheels combos are not created equal and few dollars saved on tires might cost you thousands later due to breakage and wear.

Lastly, 15 inch wheels and tires are the lightest. Rubber and air weigh less than aluminum. That's physics. 17's are usually the heaviest combo. 16's are nice but most 16 inch tires are E-Rated. That adds weight and makes for a stiff sidewall and poor ride. It's counter intuitive but even though a 17 inch tire has less rubber than a similar sized 15, they weigh more. C-rated vs D and E. Mud tires are usually more than all terrains. Again you'd think a denser tread would be heavier but its the interior construction that does it.
 
#7 ·
Flyfishnevada, thanks for adding the useful information regarding tire and wheel weights and how to find them.
 
#9 ·
Sure. I didn't think about it until I read another thread. I couldn't believe how heavy the combos could get. I don't think most of us consider that and we probably don't blame the tire and wheel weight when our "C" cracks or bearings go out. We blame Jeep but 35's are some big tires by any standard and we routinely slap them on without a second thought.

I'm not ready for C gussets, heavy duty ball joints, etc. That's why I'm going with 33's for now at least.
 
#14 ·
I appreciate the argument but the same could be made for not going off road at all. That off roading gets expensive. Your gonna need four wheel drive, and that means transfer cases and off road tires. Gas mileage is gonna be garbage and don't even get me started on the handling of one of those 4X4's. There are few places you can't get into that you can't get to on a road. etc etc.

I think you should build it the way that makes you smile. If it breaks upgrade it. Its an expensive hobby any way you slice it on 35's or 37's or even 40's. As long as you are smiling thats all that matters. One nice thing about these boards is it seems everyone is happy with their Jeep which is why these trucks rock.
 
#15 ·
I appreciate the argument but the same could be made for not going off road at all. That off roading gets expensive. Your gonna need four wheel drive, and that means transfer cases and off road tires. Gas mileage is gonna be garbage and don't even get me started on the handling of one of those 4X4's. There are few places you can't get into that you can't get to on a road. etc etc. I think you should build it the way that makes you smile. If it breaks upgrade it. Its an expensive hobby any way you slice it on 35's or 37's or even 40's. As long as you are smiling thats all that matters. One nice thing about these boards is it seems everyone is happy with their Jeep which is why these trucks rock.
Thanks for the comment. I agree, do whatever makes you happy.

Wasn't trying to make an argument as much as trying to provide information to all the folks that have tire upgrade questions.

I hope it's helpful for them to see the effects and what can be done to counteract some of the problem areas. Also wanted to provide useful links to sites that help you determine what would work or not work.
 
#17 ·
Screeper you are right they do rock and it is a great thing Jeeps are so versatile and can be modified to meet the needs of it's owner. Some people keep them bone stock, others build off-road only rock crushing montsters, and most are somewhere in between. What works for one may not for another, but hopefully people sharing their ideas and opinions will help others make good informed decisions on what will likely work best for their rig based on it's intended purpose.
 
#18 ·
It is a trade off. You gotta pay to play. But it is important to know what your getting into when you upgrade. If you wheel and want that inch of ground clearance, great. But know the potential cost. I think a lot of Jeepers read a couple of threads stating 2.5 inches of lift and 35's is the sweet set up (and it is a nice set up and lots of owners run that with no problems) and do it. Then they don't understand why their drive line fails or their ball joints need replacement at 20k.

This isn't about advocating for one set up or another, just information. A quality 2.5 inch lift or leveling kit and 33's will get most of where we want to go and more. It's important to understand that.
 
#276 ·
It is a trade off. You gotta pay to play. But it is important to know what your getting into when you upgrade. If you wheel and want that inch of ground clearance, great. But know the potential cost. I think a lot of Jeepers read a couple of threads stating 2.5 inches of lift and 35's is the sweet set up (and it is a nice set up and lots of owners run that with no problems) and do it. Then they don't understand why their drive line fails or their ball joints need replacement at 20k.

This isn't about advocating for one set up or another, just information. A quality 2.5 inch lift or leveling kit and 33's will get most of where we want to go and more. It's important to understand that.
:wavey:
 
#19 ·
Regarding lifts and larger tires, looks for posts on the forums from people who have the actual setup you are looking to use, it seems to me there are a lot of people repeating information they read with no first hand knowledge. Couple examples would be tailgate damage caused by a larger spare tire, sure everyone says it will happen but it is hard to find actual number of cases of it, same with bent front axles from 35" tires ect...
 
#24 ·
The internet is full or regurgitated info and this forum is no different. Things do get lost/distorted in translation. That one time something happens to someone becomes the normal risk of doing something.

That said I have bent an axle flange and rotor wheeling with stock 32" tires and wheels on rear rubicon Dana 44 and I bet I could do it with a a front Dana 30 and 35's. Of course I am just one example:

 
#22 ·
Anything over 35" is the big jump. Thats big money. You're talking mandatory gearing (if you actually wheel), axle issues, bad mileage, bad brakes, tire carrier, etc. You ideally want just enough lift to clear a decent tire to carry you through most trails. My 2dr with the stuff in my sig walks most things. I will do 35"s when they wear down, but thats all I should need. This post should be a sticky.
 
#25 ·
This is a GREAT post! Thanks to the OP, and those how added additional information. As a track rat, unsprung weight it a big deal. It hurts "performance" (acceleration, handling, turn in, braking, ride quality, etc.) in many ways. Whether you are tuned in enough to your ride to recognize this, and whether you care are both up to the individual Jeeper. It is valuable, though, to have this info available.
 
#26 ·
Ok, great post! I probably won't be doing much more than mild wheeling in my mostly DD, maybe 4-5 times a year. I think I'll skip the leveling kit. And the 33s. Will keep my SR-As and then get stock size Duratracs in a couple of years.
 
#27 ·
Good post, I'm planning on going to 32's on new rims with 5" BS when I finally destroy the 30's on my Sport and that's it.. no need of bigger, just figure if I'm buying tires might as well get 32's... already have a flashpaq.

Couple of folks on the largest tire thread have measured Rubicon and Sport S wheels at 6" BS, I believe the first post in that thread says stock rims are 6.5".
 
#29 ·
Thanks!

I believe these are the stock wheel dimensions, as far as I've been able to gather.

Sport:
16X7 (5.75" backspace)

Rubicon / Sport S / Willys:
17x7.5 (6.25" backspace)

Sahara:
18x7.5 (6" backspace)
 
#30 ·
It would be nice to add various stock wheel and tire weights too for comparison. Near as I can tell, the 2014 Rubicon wheel is 27 lbs. I think that covers other models like the Willy's too. The stock BFG KM 255/75/17 is 48 lbs. That's 75 lbs total. As for others, I don't know. It was hard enough to find the 27 lbs wheel weight and I'm still not sure that's correct.

I'm going to agree that 35's are probably the break even point in most configurations. But as my post above illustrated, you easily go over 100 lbs with a 35 inch set up. But if you're concerned, you can stay pretty light too though mud tires are out. Then again, if you don't do serious mud or your off roading tends to be less than extreme, the Duratrac and BFG AT tires are both good choices. Very light tires and both have great reputations for wear and handling. Of course, you will still be dealing with the larger size and the issues that can cause.

My wishlist? A 35x15 Duratrac. The BFG AT 35x15 weighs a modest 54 pounds and Duratracs across the line are as light or even a bit lighter than the BFGs. A 20 pound or less wheel and you'd be looking at a 35 inch set up with a fairly aggressive tread that's lighter than my stock Rubicon combo. If you don't mind a real AT tread and a bit of a balloon look, the 35x15 BFG AT can do that now.

In the near future, the BFG AT KO2 should be out later this year. They've added some sidewall tread which should help break up that broad sidewall in a 35x15 and I'm hoping the tread proves to be a bit more off road friendly without sacrificing the on road handling. Even so, that might be my next tire after the 33's. I just can't handle the current BFG AT 35's on a fifteen inch wheel. I tried, really tried, but that's too much bare sidewall for me.
 
#32 ·
#34 ·
Sounds like gussets are pretty much a no-brainer. Sleeves sound like extra insurance, not really necessary but as long as you've got it torn apart kind of thing. I do love me a JKU with 37's. I get the itch every time I watch a WayofLife or Teraflex YouTube video. Maybe someday. Teralflex axles, 3.5 inch lift, drive shafts, new axles shafts, big old 37's. Ahh! *Going to go play lottery* :D

That's the key. Do what you want. Pay to play, break and upgrade, or keep it tame. As long as it's not dangerous, who cares? Run what you want and have fun. But knowledge will help you do it smart.
 
#35 ·
...

That's the key. Do what you want. Pay to play, break and upgrade, or keep it tame. As long as it's not dangerous, who cares? Run what you want and have fun. But knowledge will help you do it smart.
I think the knowledge part is where forums often fail. It's much easier to just spit out some forum dogma without questioning it. I think this thread goes a very long way toward helping people understand the tradeoffs and make educated decisions for themselves.:beerdrinking:
 
#36 ·
Forums are definitely a source of both good and bad advice. Lot's of dearly held misconceptions and flat out denial lead people to hand out questionable advise. Even consensus opinion can be a bad idea. Always on the owner to do what they feel comfortable doing and to use their common sense. We don't have to pay for the new parts, the owner does.
 
#65 ·
The one problem with forums, such as this, is they are often filled with anecdotal info - i.e. "I put 35 inch wheels on 9 inch width rims and they work fine with only a little trimming on a 1.5 inch leveling kit."

It's fine, it works for someone in their usage parameters. Not everyone will have the same parameters. Ultimately the forums should be treated as your beginning point in seeking knowledge, not necessarily the end point - though for some things the forum populace will be able to answer reliably.

I've been following this thread since it's inception and find it answers some questions, but breeds dozens more. I'm deep in research on the wheel question (what tires, which rim, how will it fit in my targeted 3.5 inch lift, etc.)

Back in the days or yore I was frustrated with how little actual math or science was involved in articles in hot rodding magazines. Most of these people just did stuff and it seemed to work for them, but the thing is they didn't really know why they got more power or torque, they just wrote, contributed or followed rules of thumb. That was OK when I was a kid on minimum wage and busting my knuckles under the hood of a muscle car. That's not good enough now that I'm considering a JKUR as an investment for purely recreational purposes and want harder information that people back then had. Now we have access to educated and trained mechanics, references on specific materials and often an actual mechanical engineer. That's pretty awesome compared to the days of yore. I've got a lot out of this thread and if and when I have more to contribute on the original subject, I'll be happy to chime in.

Now, rather than suffering a lack of info and an overload of anecdote, we've got such a staggering amount of information to wade through, we wonder when we are done. Can I make my decision now? Do I have the facts as I need them? Fortunately manufacturers are a lot more knowledgeable, too and are plenty happy to work with us through our research.

Better to enter a project well armed than going trial by error.
 
#37 ·
#38 ·
For anyone interested, I weighed my Rubicon spare. My scale says 73 lbs with .2 pounds of weight so 72.8. I went with BFG's weight for the stock KM's at 46.4 pounds (brand new never been on the ground, Tire Depot lists it as 47 and Tire Rack as 48)

So the stock Rubi (and Willy's, X, etc.) wheel weighs about 26.4 pounds. I've seen it listed as 27 so right in there.
 
#39 ·
For anyone interested, I weighed my Rubicon spare. My scale says 73 lbs with .2 pounds of weight so 72.8. I went with BFG's weight for the stock KM's at 46.4 pounds (brand new never been on the ground, Tire Depot lists it as 47 and Tire Rack as 48) So the stock Rubi (and Willy's, X, etc.) wheel weighs about 26.4 pounds. I've seen it listed as 27 so right in there.
Good info! Thanks for posting this.

The stock size Goodyear DuraTracs weigh in right around 40. Add the wheel 40+27=67 lbs and I'm coming in at less than the Rubicon/Wiilys setup.

The Goodyear SRA Setup would be 36+27=63 lbs
 
#40 ·
Well the title was so you want bigger tires. My answer is I already have bigger tires and would not go back. Its nice to have all that info and it helps some people but scares others.
I have the money to make my Jeep what I want and if it breaks I will fix, change, upgrade or do whatever it takes because anyone can buy a stock Jeep, there are millions of them. Mine is mine. I appreciate the post but I already have big tires and love every minute of it.
 
#41 ·
Well the title was so you want bigger tires. My answer is I already have bigger tires and would not go back. Its nice to have all that info and it helps some people but scares others. I have the money to make my Jeep what I want and if it breaks I will fix, change, upgrade or do whatever it takes because anyone can buy a stock Jeep, there are millions of them. Mine is mine. I appreciate the post but I already have big tires and love every minute of it.
X2. Agreed. Well said
 
#43 ·
Heck, for all my worries about tire weight, I'm still not totally against 17's and 35 inch Duratracs. It's only six or eight pounds. If I can manage to make a little more money this fall, I might just pull the trigger and maybe get gussets and new ball joints (as long as I have them out anyway). But mine is a weekend warrior more than a DD.

Some guys have jobs and kids and bills and they'd rather have a reliable Jeep on 33's than one more likely to end up in the shop on 35's. Just a factor of safety for them. Nothing wrong with that either.
 
#44 ·
Just some RAW DATA...

Wheel and tire weights

I had some downtime today and thought I would weigh my stock rubicon wheels and tires and compare them to my AEV wheels whit BFG KM2s in 35x12.5.

The last (2) photos are AEV Savegre and Pintler wheel weights only that I found on another thread.

My new wheel combination is 28.3 pounds heavier than the stock rubicon config.

Hope this info can help any one out.

By knowing this one can be prepared for things to wear faster. My plan are to upgrade to stronger components as the need arrises.
 
#45 ·
Just some RAW DATA... Wheel and tire weights I had some downtime today and thought I would weigh my stock rubicon wheels and tires and compare them to my AEV wheels whit BFG KM2s in 35x12.5. The last (2) photos are AEV Savegre and Pintler wheel weights only that I found on another thread. My new wheel combination is 28.3 pounds heavier than the stock rubicon config. Hope this info can help any one out. By knowing this one can be prepared for things to wear faster. My plan are to upgrade to stronger components as the need arrises.
That is a popular combo. I'm sure someone will find it useful! Thanks for sharing.
 
#46 ·
Found another interesting article about tires, in general, but there is a part of the article that talks about "void ratio" of the tire tread in relation the vehicles weight.

Essentially, the tire size (and tread void ratio) you choose should factor in your vehicles overall weight.

Off-Road Tires - Technical Articles - Four Wheeler Magazine

SIZE DOES MATTER

What tread type is the best for trail use on a given vehicle depends largely on tire size and vehicle weight. Here the goal is to get the correct contact pressure (weight per square inch), which is largely a function of tread void ratio. As the name implies, tread void is the relative amount of open space between the tread blocks, and it doesn't matter if there are a few large tread blocks or many small knobs. A high void ratio will put more of the vehicle weight on a smaller amount of rubber, increasing the contact pressure. A larger tire with the same tread will decrease contact pressure, although the void ratio remains the same.

Likewise, a lighter vehicle will have less contact pressure than a heavier one with the same tire. The two extremes would be a heavy vehicle on small, narrow tires with a high void ratio and a light four-by on big fat tires with a low void ratio. In one case, there’s too much contact pressure, in the other there’s not enough for optimum traction.

So how do you know when there’s too much and when there’s not enough? Try going up a hill of moderately packed dirt. If the tires start spinning but do not dig down much, the contact pressure is likely too low. You’ll want to try a smaller tire or one with a higher void ratio, or else air up a bit. Should the tires try to trench more so than go forward, chances are the contact pressure is too high. In that case try a larger tire or one with less void ratio, or air down more.
 
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