[post updated 6/13/2017]

For most Jeep owners a tire upgrade is the first and biggest improvement that they can make to their vehicle. Tires offer improved on and off road performance, including better traction, clearance and float on lose surfaces, and they just look better.

However, everything comes with a cost, and the cost of bigger tires comes in the additional modifications that you’ll need to make to get those tires to fit your Jeep.

So, let’s start with common tire sizes and what’s required to run them on a Jeep JK. To do this we need to keep in mind both the tire height and width as each effects the clearance required to prevent your tires from rubbing suspension, fender or body parts.

32” x 10” – This is the biggest size that’s shipped stock from the factory, no changes are necessary to the wheels, suspension, fenders or body assuming that you still have factory sized wheels 6.25” of back spacing (or less/smaller number) that are 7.5” wide (or wider/bigger number)

33” x 10” pizza cutter – Will still fit on a stock JK and stock wheel as indicated above

33” x 11” – on the edge, they will probably work on the stock 6.25” back space wheels, however, they may rub slightly on the sway bar at full turn. This can usually be corrected by adding washers on the steering stops to slightly reduce the maximum turning ability.

33” x 11” – 33” x 11.5” – Will rub the front sway bars with the stock 6.25” back space wheels. As above this can be corrected by adding wheel spacers or buying new wheels with smaller back spacing (the wheel is located out / further from the chassis)

33” x 11.5 – 33” x 12.5” – Will rub the front and rear sway bars with the stock 6.25” back space wheels. In this case you will need less back spacing than the stock wheels provide. This will mean adding spacers to the stock wheels of buying new wheels with less back spacing. Optionally you can install a small lift or leveling kit, mostly to maintain the aggressive jeep look.

34” x 12” – Will rub the front and rear sway bars with the stock 6.25” back space wheels. In this case you will need less back spacing than the stock wheels provide. This will mean adding spacers to the stock wheels of buying new wheels with less back spacing. Additionally, the taller tires may contact the fenders at full flex. And, again, optionally you can install a small lift or leveling kit, mostly to maintain the aggressive jeep look.

35” x 12” – 35” x 14.5” – Will rub the front and rear sway bars with the stock 6.25” back space wheels. You will need less back spacing than the stock wheels provide. When you reach 35” tires the stock wheels are too narrow, so you should plan to buy new wheels with less back spacing. Additionally, the will now contact the fenders on bumps, hard corners or when flexing off road. This means that you will need to cut or replace the fenders, or you will need to add a small amount of lift (2” lift or leveling kit). Don’t discount cutting the fenders. It sounds scary first, but if you’re handy they can look nice and get you to 35” tires very inexpensively. With 35” tires you will notice a small reduction in power / acceleration, but it will be livable.

37” x 12.5” – 38″ x 14.5” – Will rub the front and rear sway bars. You will need new wider wheels with 4.5” back spacing. At this point there’s no avoiding lifting the suspension. Your suspension choices are: 3” of lift with slight rubbing, 3” of lift and trimming the pinch seam and fenders, or 3” of lift plus another 1” of body lift, or step up to a 4” suspension lift. Additionally, with a 37” tire you will need to change your differential gears to get your power back. Why would you add both a 3″ suspension lift and a 1″ body lift in stead of just adding a 4″ suspension lift? Because with 4″ or more comes additional modifications, including a new drive shaft, more advanced u-joints, and possibly exhaust cross over pipe changes. And, you’ll also need a new jack capable of lifting your Jeep high enough to slide in a 37″ tire in case you get a flat.

40″ x 13.5” – Everything said above to fit a 37″ tire is true, but with a 40″ tire you’ll need about a 6” lift or you’ll need to do some serious cutting on the body to create more clearance. You’ll also need more power and larger breaks to turn and stop such large, heavy wheels/tires.

Keep in mind that you and your passengers will need to live with what you’ve built. If you need to take grandma to church on Sunday she may not appreciate having to step on a bucket to get into your vehicle (true story). And, your wife may take issue with loading the kids and groceries into your monster Jeep. Just remember that each inch of body or suspension lift will increase the Jeep floor height by one inch, and that some spring lift kits actually lift the Jeep up to an inch more than the advertised lift amount. And, that each inch of tire lift will raise your Jeep by about one half the increase in tire height.

And, Don’t forget

When you’re pricing/ordering tires that you may need 5 of everything (if you need a spare to match your new rubber).

[post updated 6/12/2017]

What are wheel spacers? Wheel spacers are rings typically made out of billet aluminum designed to be sandwiched between the axel’s wheel hub mounting surface and the wheel. A 1.5″ wheel spacer will work as an alternative to new wheels (6.25” wheel backspace with a 1.5” spacer equates to a total of 4.75” backspace) but many will argue that replacing your stock wheels is a more durable alternative.

pic 1

The use of spacers is an ongoing debate. If you plan to use spacers select a well-made hub-centric (described below) spacer with integrated lug that are 1.25″ ~ 1.50″ thick, and torque the lugs carefully. It’s probably also wise to periodically inspect the lugs to ensure that none have come loose.

High quality hub-centric spacer design with integrated lugs.

I would never use inexpensive spacers that use only the existing vehicle lugs. These reduce the threads remaining for your lug nuts to hold on to and they are more likely to result in lugs coming loose and wheel balancing issues.

[post updated 6/12/2017]

Tire Pressure Monitoring System (TPMS)

Weather you know it or not, your original factory Jeep JK comes with a Tire Pressure Monitoring System (or TPMS for short). The purpose of TPMS is to monitor your tire pressure and warn you if any one of your tires is significantly under-inflated and possibly causing an unsafe situation.

This device is actually a small electronic tire pressure gauge with a low powered radio that transmits its reading to the vehicle’s computer. The TPMS indicator is a yellow symbol that illuminates on the dashboard instrument panel of your Jeep and looks like the cross-section of your tire with an exclamation point.

Before this indicator light, knowing whether your air pressure was low using a tire gauge, or “eye balling” how much your tires bowed where they rest on the ground. This is especially difficult on large off road tires, and even more difficult with tires that are aired-down.

When replacing your wheels you’ll need to make a decision about the TPMS sensors that would be included on your factory wheels. These sensors typically last for 7 to 10 years. If you’re reusing your factory wheels you can just leave them in place. If you’re buying new wheels you have the option to (a) move them to the new wheels, (b) buy new ones (for about $45 a piece, and the spare has one too), of (c) eliminate them and just in stall regular valve stems.

I always ensure that the TPMS is operating when I upgrade a vehicle. I know that most vehicles will be driven on the highway / at high speeds, and I never know who might end-up driving the vehicle. Additionally, if you just replace the TPMS sensors with valve steps you will be faced with the annoying low pressure dash indicator.

The one down side of maintaining the TPMS is that some Jeep owners will choose to run their tires slightly under inflated (because it improves ride quality, offsetting the more firm ride that comes for higher load rated truck tires; or because they’re running a wheel that is on the narrow side and know that achieving even tire wear across the tread will require a little less air pressure)

 

[post updated 6/11/2017]

All About Jeep Wheels

The backspacing of factory wheels is large and designed to keep the tires under the fenders and keep you legal in all 50 states (even though many states have no laws preventing tires from extending beyond the fenders, a few do). Installing wider and taller tires on factory wheels can easily result in those new larger tires rubbing on suspension components. This is why most people opt to decrease their wheel backspacing in an effort to move their larger tires outward and away from any potential rubbing problems.

When buying new wheels for 12.5″ wide tires 4.7″ backspacing is the maximum (largest number, smallest amount of outward offset) necessary to prevent rubbing, and 4.5″ is recommended. For 14.5” wide tires 4″-3.75″ is necessary.

Smaller May Be Better?

(bigger sidewall looks bigger and smother ride)

Hub-Centric v. Lug Centric (Acorn Style Lugs)

This is almost not a question anymore. Back “in the day” most Jeep owners looked for hub-centric wheels. This means that the hole in the center of the wheel rests on the cylinder that protrudes from the axle. With Lug-Centric wheels the hole in the center of the wheel is larger than the cylinder protruding from the axle and the lug studs are all that keep the wheel centered on the axle. Hub centric wheel’s center made a snug fit, so the weight of the vehicle primarily sat on the center of the wheel instead of on the studs. While lug-centric wheel were fine, hub-centric provided that additional piece of mind knowing that any hard bumps would not be impact the lug studs.

At this time the point it moot, as it’s getting almost impossible to find hub-centric wheels. Wheel manufactures would prefer to not make different wheels for each hub diameter produced by the car manufactures. If you can find a hub-centric wheel (AES used to still make them) you will be greatly limiting your wheel choices to a few made by that manufacture.

 

But, 15″ May Be Too Small

A common question is: Do 15″ wheels fit a Jeep JK? You will find that 15” tires are significantly less expensive than any other tire alternative. This question is not easy to answer. The issue is that the smaller diameter wheel may not fit over the larger brake caliper on a Jeep JK. The ability to squeeze the smaller wheel on a JK is depends on the material that the wheel is made out of, the thickness of the material and the amount of backspace (very small backspacing may kick the wheel out far enough to clear the caliper). Generally speaking, steel wheels are made of thinner material, but are generally heavier than their lighter alloy cousins.

And, then there’s “Dubs”

And, while we’re talking about extremes, let get it out of the way; yes, you can run “dubs” (20″ wheels, or double-dubs – 22” wheels, or even 24” wheels) on a Jeep with the appropriate lift (I don’t judge, but you won’t get “the wave” with Dubs, I’m just saying …)

 

Pict 4

Bead Locks

Pros and Cons of Wheel Width

What are the pros and cons of wheel size? A larger wheel will reduce tire sidewall flexing and this will provide better handling on the pavement, and less sidewall can help to make you feel more stable in leaning situations as well. Small wheels will provide for more sidewall and will provide a smoother ride on the road and allow the tire to flex more providing better tread contact and more traction off road.

Q: How do you determine what size tire will fit what size rim correctly?
A: Typically, most off road tires come in a 12.50″ width and for the most part require an 8”-10″ wide rim. However, unless you are running beadlocks, I would recommend that you select a wheel that is 8″-9” in width or there about. When aired down for the trail, the narrower width will help prevent your tires from losing a bead.

Tire Pressure Monitoring System (TPMS)

Weather you know it or not, your original factory Jeep JK comes with a Tire Pressure Monitoring System or TPMS for short. The purpose of TPMS is to monitor your tire pressure and warn you if any one of your tires is significantly under-inflated and possibly causing an unsafe situation.

 

Pict 5

 

This device is actually a small electronic tire pressure gauge with a low powered radio that transmits its reading to the vehicle’s computer. The TPMS indicator is a yellow symbol that illuminates on the dashboard instrument panel of your Jeep and looks like the cross-section of your tire with an exclamation point.

 

Pict 6 – tire

 

Before this indicator light, knowing whether your air pressure was low using a tire gauge, or “eye balling” how much your tires bowed where they rest on the ground. This is especially difficult on large off road tires, and even more difficult with tires that are aired-down.

When replacing your wheels you’ll need to make a decision about the TPMS sensors that would be included on your factory wheels. These sensors typically last for 7 to 10 years. If you’re reusing your factory wheels you can just leave them in place. If you’re buying new wheels you have the option to (a) move them to the new wheels, (b) buy new ones (for about $45 a piece, and the spare has one too), of (c) eliminate them and just in stall regular valve stems.

I always ensure that the TPMS is operating when I upgrade a vehicle. I know that most vehicles will be driven on the highway / at high speeds, and I never know who might end-up driving the vehicle. Additionally, if you just replace the TPMS sensors with valve steps you will be faced with the annoying low pressure dash indicator.

The one down side of maintaining the TPMS is that some Jeep owners will choose to run their tires slightly under inflated (because it improves ride quality, offsetting the more firm ride that comes for higher load rated truck tires; or because they’re running a wheel that is on the narrow side and know that achieving even tire wear across the tread will require a little less air pressure)

Always remember

Don’t forget that you may need 5 wheels if you’re replacing the spare as well

And, don’t forget new lug nuts. New lug nuts are usually a good idea just to ensure that you’re getting the correct lug to match the wheels that you’re buying. Standard Jeep axles have 5 lugs each (for 20 total) and most spare tire carriers have 3 lugs to hold the spare (for a grand total of 23 lugs. If you live is a questionable neighborhood, or intend to leave the vehicle unattended you may also want to consider lock lugs to make it more difficult to steal you’re wheels while you’re sleeping or away (you may also want to consider moving; seriously, life is short, why spend it living around people that want to steal your expensive stuff).