[GreenMachine13]

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.

 

[American Jeeper]

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!

 

[flyfishnevada]

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.

 

[GreenMachine13]

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.

 

[yacc]

But according to half the guys on the forum, they lifted their jeep and put 35s on and the gas mileage stayed the same. Physics and math be damned!

 

[American Jeeper]

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.

Absolutely. Offset and tire width can change handling. While wider tires are good in some conditions, they can cause problems in others. Rain and ice can be of particular issue due to the vehicle weight being spread out, causing it to "float" and slip rather than dig down and make better contact with the driving surface.

 

[GreenMachine13]

Flyfishnevada, thanks for adding the useful information regarding tire and wheel weights and how to find them.

 

[kjeeper10]

Finding a shop to balance them big ol tires. Wider/tready tires following every rut in the road.
Load Rating E's .. Yep I'm ready for a 37" lol

 

[flyfishnevada]

Flyfishnevada, thanks for adding the useful information regarding tire and wheel weights and how to find them.

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.

 

[American Jeeper]

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.

The benefits of what amounts to one additional inch of ground clearance going from 33's to 35's are far outweighed by the costs in my opinion.

Oh yeah and add bent axle flange to the list. I did it with stock tires and the bigger you go the more leverage you have to do it.

 

[GreenMachine13]

The benefits of what amounts to one additional inch of ground clearance going from 33's to 35's are far outweighed by the costs in my opinion. Oh yeah and add bent axle flange to the list. I did it with stock tires and the bigger you go the more leverage you have to do it.

It really is a lot of expense for that extra inch or two of clearance.

 

[WatchThis!]

The benefits of what amounts to one additional inch of ground clearance going from 33's to 35's are far outweighed by the costs in my opinion.

Oh yeah and add bent axle flange to the list. I did it with stock tires and the bigger you go the more leverage you have to do it.

Until you find yourself in a lot of situations where you needed just 1/2 inch of clearance.

 

[GreenMachine13]

Until you find yourself in a lot of situations where you needed just 1/2 inch of clearance.

And after you get that you find yourself in situations where just another half inch needed... And the cycle continues.

 

[Screeper]

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.

 

[GreenMachine13]

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.

 

[Screeper]

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.

I appreciate that and enjoy the conversation. These boards would be pretty boring without a few different perspectives. Al

 

[American Jeeper]

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.

 

[flyfishnevada]

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.

 

[MacCTD]

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...

 

[thedawgshow]

What a great thread to come across, as I am just starting my build and gathering up as much info as I can before I start. THANKS!!!!