WK Stock Scrub Radius - JeepForum.com
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post #1 of 7 Old 09-29-2018, 11:21 PM Thread Starter
KristopherR
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Join Date: Jul 2018
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WK Stock Scrub Radius

It's going to be a ballpark guess since the different wheel/tire combinations will move the number, but any idea on what the OEM Scrub Radius might be on a 2008 WK CRD 18" wheel option?

I'm going to have to guess it's likely zero or a touch negative.

I bought some JK wheels and the 255/75/17 tires along with 1.5" spacers. I was really hoping to keep the rubber inside the fenders for aesthetics but more practically because I don't want a ton of positive scrub. With this combination I end up with a little less scrub than the width of the spacer and less offset wheel simply due to taller tires.

I know a ton of guys have gone the same route with taller tires and less backspacing seemingly with no issues. Is this anything to worry about? If anyone says they have unpredictable handling under braking I am all ears. I'd hate to dial in more Toe In but that might help..and a 1.25" spacer also. At some point I will be towing a 27' RV so trying to minimise headaches.


Last edited by KristopherR; 09-29-2018 at 11:25 PM. Reason: spellingz
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post #2 of 7 Old 03-08-2019, 10:11 PM
voltquad
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A bit late of a response, but better late then never.

I've been driving my 2010 5.7 powered WK for several months with 1.5" spacers and 32.1" tires on JK wheels. The JK wheels have .25" less offset (6.35mm) and the increase in tire size puts my scrub radius increase to about 1⁵⁄₃₂" more positive than it was from stock. The increased scrub radius does negatively impact how well the WK drives, but it's not that bad.

The differences I noticed are:
  • increased feedback to the steering wheel.
  • greater steering wheel effort required to turn, especially when not moving.
  • less self-centering force when wheel is near center (not as bad as driving a vehicle with a live front axle)
  • hitting bumps with one tire with the sway bar connected gives a harsher feel
  • Absolutely no differences in braking.
  • Absolutely no torque steer.

I much prefer the way the Jeep handles without the spacers, but even with the spacers it drives better than a vehicle with a live front axle.

I used this site for my calculations:
Setting the larger tire's offset to 44 is as close as you can get to the actual JK wheel offset of 44.45.
Setting the larger tire's offset to 6 (6.35 mm rounded down) is what happens when you add the 1.5 inch spacers.
https://www.wheel-size.com/calc/?whe...wcl=4in&sr=0in
https://www.wheel-size.com/calc/?whe...wcl=4in&sr=0in
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post #3 of 7 Old 04-15-2019, 07:34 PM Thread Starter
KristopherR
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voltquad I appreciate the reply.

I have since changed tires and now my setup is the same as yours (255/70r18 KO2 on Sahara wheels) along with the 1.5" spacer.

Also found the exact same behaviour. It's predictable and drives just fine including tight radius' such as on/off ramps.
What I don't care for is the shuddering when in a slight bend over bridge deck expansion joints. I find this is when there is steering input and the wheel gets 'light' over the bumps which causes the driver to pull on the wheel more. It's probably aggravated because of the greater steering effort needed from the driver.

I've debated increasing the tire pressure to get them less bouncy but I have done the load calculations and this tire is carrying proper load at the stock pressure. And if I'm honest, my front struts are likely less than ideal.

I've not tried to disco the front sway.

2008 Jeep WK CRD 255/70r18 KO2 on Sahara 18s 2.5" level 1.5" spacer | 2010 Ford Flex ecoboost
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post #4 of 7 Old 04-16-2019, 04:12 AM
caulk04
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If you concerned about it, go with a thinner spacer. I have 1.25" spacers and I'd be perfectly find with a 1" or likely even a 3/4" if there's one available and trustworthy. Even a 3/4" spacer will get you the UCA clearance you need while also keeping more clearance to the pinch weld and minimizing scrub radius.

I've done many a hard brake application and noticed no scary traits.

Also, a 27' camper? Yoi!

08 Limited Hemi - wheels, tires, springs...ya know, stuff
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post #5 of 7 Old 04-16-2019, 08:30 AM
Ahaze
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Which Sahara wheels do you have? The 5 and 7 spoke 18s with 255s clear the brakes and upper ball joints without a spacer. I run the 5 spoke Saharas with a 3mm spacer to alleviate a slight tire rub on the frame rail at full lock.
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post #6 of 7 Old 04-16-2019, 11:32 AM
caulk04
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Width and offset are pretty much the same across all the wheels for a given platform, outside of something like the SRT8.

I run the polished 7-spoke wheels but have never tried to mount them without a spacer.

08 Limited Hemi - wheels, tires, springs...ya know, stuff
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post #7 of 7 Old 04-17-2019, 10:18 AM
Ahaze
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Yes, width and offset of all stock JK wheels is the same. Caliper clearance is not though. If scrub radius is a concern, the two wheels I mentioned clear the WK brakes without a spacer. With stock JK 255s, they clear the ball joint stud as well. The other wheel styles will need a very thin spacer to clear the front brakes. Any bolt on spacer is overkill as far as brake and ball joint clearance is concerned with 255 section width tires.
If you like the look of your tires hanging outside the fenders, that's fine but there is no need for anything more than a 3/16" or possibly even 1/8" spacer with any stock JK wheel/tire combo. Just be sure to confirm your lug nuts have enough thread engagement when using the thin slide-on style spacers.
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