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I went to my local tire store today, needing to replace only two tires. I had replaced two about a year ago. The tires I put on a year ago were OEM Goodyear Forteras. Today, I had 2 Falken Pro G5s installed. The guy at the store said it was a bad idea to mix brands and to only replace two tires on a 4x4 vehicle. He said differences in traction between the two types of tires could lead to damage to the transfer case. Is this legit? Or was he just throwing some bull$hit, trying to sell me more tires?🤷‍♂️
 

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Throwing BS, for the most, but with that being said, not all tire sizes are actually the same size even if they are marked the same size. Some are true, while others are actually undersize. Plus the difference in tread pattern can affect braking and performance.
 

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In general, you need all four tires to be identical in diameter within a very small percentage for a 4x4 or AWD vehicle. To do otherwise CAN result in drivetrain damage. Therefore, it's a normal practice to replace all four unless they are nearly new. Mixing brands, in itself, isn't necessarily horrible, but different tires feel and perform differently so as you start to move through rotation for even wear, you will potentially end up with a situation that isn't the best for performance and stability. I recommend you go get two more of those Falken Pros for the other two positions for best results.
 

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I agree. It is a good idea to have 4 identical tires, but it's not the end of the world.
 

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03 WJ, 4.Slow, 3" IRO
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I went to my local tire store today, needing to replace only two tires. I had replaced two about a year ago. The tires I put on a year ago were OEM Goodyear Forteras. Today, I had 2 Falken Pro G5s installed. The guy at the store said it was a bad idea to mix brands and to only replace two tires on a 4x4 vehicle. He said differences in traction between the two types of tires could lead to damage to the transfer case. Is this legit? Or was he just throwing some bull$hit, trying to sell me more tires?🤷‍♂️
He is legit. How much damage depends on what type of 4x4 system your Jeep has. He was actually trying to save you money. You will likely wear your tires out quicker, as well. Another concern with mismatched tires, it can become dangerous when roads get slippery. If you are able to switch between four-wheel and two-wheel drive, driving in two wheel drive won't be a big concern.
 

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ow much damage depends on what type of 4x4 system your Jeep has
All three options for the JGC are based on the same drivetrain...no difference in the effect of mis-matched tire sizes.
 
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So the newer Forteras I already on there have 8/32 of tread left. If I swap out the Falkens for 2 new Goodyear Forteras, I'll be ok, correct? Because the tread depth is almost the same.
 

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03 WJ, 4.Slow, 3" IRO
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All three options for the JGC are based on the same drivetrain...no difference in the effect of mis-matched tire sizes.
I was making the statement more in general that to one specific system, hence my use of the words, "depends" and "how much". Someone that is easily misinformed could take this post as gospel and end up doing thousands of dollars worth of damage to their drivetrain or wrecking their vehicle. I have a feeling the tire shop guy was speaking in general terms as well. I would never expect a tire shop guy to know the ins-and-outs of every single four wheel drive vehicle that comes into his shop daily let alone yearly. He could be liable for selling the OP mismatched tires without the disclaimer.

I could go into a very lengthy post on the different types of four-wheel drive systems and how mismatched tires may or may not affect them. There are books written on this subject. It's even taught in college. I do realize everybody already knows, anybody that goes to college is really just an educated idiot, especially when they have an engineering degree...

Read your owner's manual. What does it say about mismatched tires? If you choose to do something different, that's on you.
 

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Guts, you are certainly correct in the bigger picture. But this is a MY11-MY20 Grand Cherokee specific sub-forum which is why I responded as I did.
 

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So the newer Forteras I already on there have 8/32 of tread left. If I swap out the Falkens for 2 new Goodyear Forteras, I'll be ok, correct? Because the tread depth is almost the same.
I'm going to stick my oar in and agree with you. I do agree with your tire guy about keeping makes of tire the same if you can, and also about changing all four tires at the same time. I think here though the tread height difference is minimal. If the tire shop did'nt advise you as they did and there was a problem it could come back on them.
 

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The drive train has no idea of what tread design is on the tire. All it knows is how many revolutions per mile the tire makes. How many revs is determined by the rolling diameter of the tire. It's recommended to replace all 4 so that all 4 have the same rolling diameter. There could be some handling differences with "missmatched" tires but if it's basically the same kind of tire and tread design it's not going to be enough difference to matter (other than tread depth) unless you are auto-crossing or racing. You can look up the revs/mile on sites like tirerack.com for various tires. If the tread depths are within a couple of 32's you should be fine if the revs/mile when new is essentially the same. It would not be usual for a worn set of "matched" tires to vary 2 to 4 32's between the 4 tires. IMHO people are way overthinking this. Naturally the people who sell tires are going to want to sell you four of them instead of two.
 

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Jim in PA, the OP's questions was rather generic for a MY11-MY20 Grand Cherokee specific sub-forum, every answer posted, including yours, was in general terms, that is why I responsed as I did. I apologize if I over stepped.
 

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The drive train has no idea of what tread design is on the tire. All it knows is how many revolutions per mile the tire makes. How many revs is determined by the rolling diameter of the tire. It's recommended to replace all 4 so that all 4 have the same rolling diameter. There could be some handling differences with "missmatched" tires but if it's basically the same kind of tire and tread design it's not going to be enough difference to matter (other than tread depth) unless you are auto-crossing or racing. You can look up the revs/mile on sites like tirerack.com for various tires. If the tread depths are within a couple of 32's you should be fine if the revs/mile when new is essentially the same. It would not be usual for a worn set of "matched" tires to vary 2 to 4 32's between the 4 tires. IMHO people are way overthinking this. Naturally the people who sell tires are going to want to sell you four of them instead of two.
Even if two different makes and models of a tire happened to be made the exact same size, would the rolling diameter be the same at the exact same tire pressures? Are the sidewalls the same stiffness? Do the tires flex the same? Do they have the same number of nylon and steel belts? All of these factors can add up to well over an inch in rolling diameter and be different when measured static or at speed.
 

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Does Jeep have a recommended tread depth difference tolerance (or rolling diameter tolerance) for GC 4x4s?
(new to the forum & haven’t yet bought a WK2, so slowly learning...)

I’ve read where other manufactures recommended that tread depth differences should be 4/32 or less for all tires on their 4x4s (I think Subaru might even recommend 2/32).

With my current 4x4, I do a 5-tire rotation which keeps all tires, including the spare, with similar tread depths and tire pressures.
Unfortunately, it looks like Jeep made it a pain to do a 5-tire rotation as the Grand Cherokee spare tire compartment is not large enough to fit the identical tire that on the vehicle (the “full-size” spare tire matches the overall diameter, but not the width).
So, I imagine most the time that folks have to use their “full-size” spare tire, the tread difference will be > 4/32 on a 4X4. Seems strange for a Jeep...

I’ve read where some folks do buy an identical tire for the spare, but they have to either raise the cargo floor or air-out the tire to make it fit.

(sorry, kinda deviated from the OP’s question to also include the spare tire...)
 

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On Allpar.com, Ed Sheaves, a retired Engineer for Jeep, said he had proved to management the difference in diameters of new tires and worn to the tread bars tires front/rear on full time 4WD for extended period of time would cause excessive wear on the transfer case.

Tire sizing is nominal, like a 2x4 doesn't really measure to be 2x4. Same brand and model, of the same size, yes will be exactly the same. But different brand and model, the true measurements can differ, enough to make a difference.....

Look at the detailed specs for both tires, the one you want is revolutions per mile. This is how many times the tire makes a full revolution over a mile, you can see tires of different brand and models, but the same nominal size, you can see more than a minor difference between them. But, if you have a mix of brands/models of tires, check the detailed specs for revs/mile, if they are same then the tires are identical in rolling diameter...

And it is not good to mix brands/models of tires on a car, it can be small difference, but the different tire characteristics can cause exaggerated handling characteristics for the vehicle.....
 

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Audi, Subaru, Porsche and a few others call out in the owner's manual specific conditions for replacement on AWD vehicles. For example, Audi states that "rolling radius of all 4 tires must remain the same or within 4/32-inch of each other in remaining tread depth". Subaru states that tires must be "within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth."

Having said that, since this is a Jeep forum, when I had a nail in the sidewall and the tire couldn't be repaired, I could not find anything in the Jeep manual stating how to handle this situation. I kept to the Audi guideline and ensured I was within 4/32".
 

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Can't say it enough, if you have a full time 4WD vehicle, like the WK2, you need to change all the tires at the same time. And yes, they are expensive, plan ahead, as your tires are approaching needing replacement, and you're going to have trouble affording it all at once. Then buy 2 and put them in the garage, until you can afford the other two and mounting and balancing. You can save money on good tires by buying online, like at tire rack.

Mixing brand and models is not wise, certainly do not be driving aggressively if you different brands and models. With 4WD, a different brand and model of the same size could actually have a different rolling radius and rpm than another brand/model. As well, the tires have different characteristics in wet/dry/snow/gravel, etc.... While your suspension is designed and setup for the same characteristics for all 4 tires.... ....So while its not likely, it is possible in bad weather or aggressive driving with different brand/models of tires, you get unpredictable handling and spin out....
 

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Most larger chain tire stores will not install just 2 tires on an AWD vehicle nor will they install mis-matched brands/types/construction. It's a major liability issue for them.

These tires are a significant mismatch and I'm surprised anyone put those Falkens on with the Forteras
Forteras are a T- speed rated tired in a standard load
The G5 is a V- speed rated tire and is an Extra Load tire.
Radically different construction. The tire store should never have installed those Falkens.

If you're going to drive on them, you need the lower performing tire on the front- the Fortera. With a stiff Falken on the front and a soft Fortera on the rear you could end up with a a very tail happy car in an emergency. Personally I'd go back to the tire store and have them swap off 2 of the tires and match them up but that's just my 2 cents worth, though I worked for Goodyear in the 80's and oversaw tire stores in 3 states.
 
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