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Discussion Starter · #1 ·
2018 TH - 1000 WHP

Forgive me if this is redundant & long but I searched extensively & couldn't find the answer.

Have a lot of tire spin I'm trying to get rid of. Bought Weld Laguna Beadlocks 20" (10.5x20) fronts & "17 (10x17) Rears. Buying Mickey Thompsons Street Rs on the rear for the track & will run 20" Welds, MT Street SS's on the front.

Issue: I see some folks run 315x50x17 MTs (rear) so I'm guessing they work fine. I havent seen anyone running 315x55x17's which is the concern.

Issue is the tire size comparison sites show that the 55's line up better than the 50's (attached & below). Plus it's more sidewall so my question is will this work?

Weld cant/won't take a stand on the right size & MT did the same thing claiming legal ramifications.

Here are some metrics. Are the 50's within the variance range?? Or are the 55's the right fight?? Stressing over this.

Rear Street R's 315x50x17 =
Size 1 = Fronts Street SS's (305x45x20)
Size 2 = Rears Street R's (315x50x17)
Size 1 Size 2
Diameter. 30.8" 29.4"
Width 12.0" 12.4"
Sidewall. 5.4" 6.2"
Circum. 96.7" 92.3"
Revs/Mile 655 686 (is this withing the transfer case variance range??)

Rear Street R's 315x55x17 =
Size 1 Size 2
Diameter. 30.8" 30.6"
Width 12.0" 12.4"
Sidewall. 5.4" 6.8"
Circum. 96.7" 96.2"
Revs/Mile 655 659

The 55's clearly line up better yet I can't find a single TH running them so I must be missing something...Thoughts?
 

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You don’t want different diameters on the front and rear, they all need to be the same. I’m not aware of a way to reprogram the jeep for a new diameter tire either so you’ll be putting more miles on the odometer than you actually travel (if smaller than stock). Sorry, that’s all I know.
 

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OK thanks. Would .2 Diameter difference be that big of a deal? I have no clue.
I have no definitive evidence one way or the other but I’ve had AWD vehicles since 2005 and I’ve always been told you don’t even replace just one tire if you get a flat, you need to do them all because any difference will cause added wear to the TC and differentials.
 

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2019, Jeep, Trackhawk, Granite Crystal
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The problem with tire size si to respect front and rear ratios. What happens is the center diff needs to compensate the difference of ratios so the awd doesn’t bind. Perfect example are the mechanical center diffs, when running different size tires or have old fronts/rears with new front/rears you would feel a jerk every “x” miles. Its the tires slipping unbinding the 4wd drivetrain. Our awd has a clutch pack in the center diff to change how much power is transfered to the front, but doesn not compensate for different ratios. Ratios are changed either by swapping front or rear diff ring/pinion gears or by tire size. The worst that can happen is busting your center diff
 

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I have no definitive evidence one way or the other but I’ve had AWD vehicles since 2005 and I’ve always been told you don’t even replace just one tire if you get a flat, you need to do them all because any difference will cause added wear to the TC and differentials.
I was told this recently at Dodge when 3 of my PZero's were almost shot and one was still very usable.
 

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Discussion Starter · #8 ·
Thx Vanguish. Here is additional info from tirecomparison.com on the two tire sizes. Both show a different gear ratio would be needed. I do not know about ratios but it looks to me that the 315x55 is again the better fit. What do you think?

315x50x17

And the 315x55x17:
"Gear Ratio Calculator

Screenshots attached.
 

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2019, Jeep, Trackhawk, Granite Crystal
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Thx Vanguish. Here is additional info from tirecomparison.com on the two tire sizes. Both show a different gear ratio would be needed. I do not know about ratios but it looks to me that the 315x55 is again the better fit. What do you think?

315x50x17

And the 315x55x17:
"Gear Ratio Calculator

Screenshots attached.
As long as the fronts and rears have the same ratio or within a really extremely close ratio you should not have any problems. I mean our tires to do not wear evening unless you methodically rotate your wheels to even out the wear. The central diff can handle the small tolerences created by uneven wear. I would seriously recommend having all 4 wheels with identical ratios between front and rear. Don’t worry about the size or width, just make sure they fit. Worry only about front and rear circumferences being identical which will lead to identical ratios. If all 4 are smaller or taller than stock, your only issue will be the incorrent speedo reading.
 

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Discussion Starter · #10 ·
As long as the fronts and rears have the same ratio or within a really extremely close ratio you should not have any problems. I mean our tires to do not wear evening unless you methodically rotate your wheels to even out the wear. The central diff can handle the small tolerences created by uneven wear. I would seriously recommend having all 4 wheels with identical ratios between front and rear. Don’t worry about the size or width, just make sure they fit. Worry only about front and rear circumferences being identical which will lead to identical ratios. If all 4 are smaller or taller than stock, your only issue will be the incorrent speedo reading.
 
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