Scrub radius

[Midding]

Thanks for the reply. Yep, only switching wheels, keeping same tire and all else staying stock.

I never considered this aspect of wheel buying, shame on me.

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[Kevin32199]

Thanks for the reply. Yep, only switching wheels, keeping same tire and all else staying stock.

I never considered this aspect of wheel buying, shame on me.

Heres a couple ways to think about it. 1) You would be increasing your scrub radius about +2.25" over what would be considered ideal according to the chart matrix. 2) As +25 offset seems to be an agreed upon acceptable upgrade from OEM, by going to -18 youd be increasing your scrub radius just under +1.75" over that. These figures I have made in inches would be the same as adding the same thickness spacer ( 25 + 18 = 43 = 1.69" ). These are not insignificant changes. I will be very interested to see what the difference is in handling.

 

[Headbarcode]

If I didn't have a very flexible 3.5" Gamechanger lift and tall 38's, I wouldn't have chosen 17x9 wheels with -12mm offset and 4.53" backspace. I fully agree with what's been previously mentioned, as far as a taller diameter tire helping to counter the change of scrub radius.

 

[Midding]

So would I be wrong thinking that it’s the length of the tire (from front to rear) and not the tire height (ground to top of tire) that reduces a some percent of scrub radius? Same thing I know just makes more sense in my head.

Thank you for the education, I appreciate it.

 

[Yellow Cake Kid]

This illustration shows a stock 33" tire as black, while the shaded area represents a generic 37"x12.5" tire, which is positioned coincidental to the same wheel.

You can see that the Steering Inclination Angle line extends downward to and through a point where it intersects the center line of the wheel.

The distance between the points where the Steering Inclination Angle and Wheel Centerline cross the horizontal ground plane may be positive, zero, or negative.

If everything else remains the same, increasing the tire diameter decreases the value of the scrub radius dimension.

 

[Midding]

This illustration shows a stock 33" tire as black, while the shaded area represents a generic 37"x12.5" tire, which is positioned coincidental to the same wheel.

You can see that the Steering Inclination Angle line extends downward to and through a point where it intersects the center line of the wheel.

The distance between the points where the Steering Inclination Angle and Wheel Centerline cross the horizontal plane where the tire contacts the ground may be positive, zero, or negative.

If everything else remains the same, increasing the tire diameter decreases the value of the scrub radius dimension.

Ah, that makes perfect sense, thank you!

 

[Yellow Cake Kid]

I am still trying to learn the specifics of the axles in the JL series Jeeps. In the meantime, I have been using this technical drawing as a reference.

 

[dginz]

Need some help here! Found this thread when I was researching why my JLU is shimmying all over the place way worse since putting on my new wheels/tires. I have Method 701s in 17x9 et12 on Cooper discoverer 33in tires. Sahara, no lift. I love the way these look but ever since installing them the Jeep feels like it’s all over place. I’m being throw around over the smallest bumps.

Is this all because of the more aggressive width and offset creating an incorrect scrub radius? I’m eventually going either mopar or dynatrac 2in lift w/ 35’s- though not sure this will help my problem obviously. I’ll go stock width and/or offset if I can get the ride back to normal.

Pic attached for reference. Any help/ advice is greatly appreciated!

 

[MSparks909]

Need some help here! Found this thread when I was researching why my JLU is shimmying all over the place way worse since putting on my new wheels/tires. I have Method 701s in 17x9 et12 on Cooper discoverer 33in tires. Sahara, no lift. I love the way these look but ever since installing them the Jeep feels like it’s all over place. I’m being throw around over the smallest bumps.

Is this all because of the more aggressive width and offset creating an incorrect scrub radius? I’m eventually going either mopar or dynatrac 2in lift w/ 35’s- though not sure this will help my problem obviously. I’ll go stock width and/or offset if I can get the ride back to normal.

Pic attached for reference. Any help/ advice is greatly appreciated!

What psi are the tires at?

 

[dginz]

What psi are the tires at?

I told them to do 34psi but looks like TPMS says 36.

 

[Yawnie'sPapa]

Need some help here! Found this thread when I was researching why my JLU is shimmying all over the place way worse since putting on my new wheels/tires. I have Method 701s in 17x9 et12 on Cooper discoverer 33in tires. Sahara, no lift. I love the way these look but ever since installing them the Jeep feels like it’s all over place. I’m being throw around over the smallest bumps.

Is this all because of the more aggressive width and offset creating an incorrect scrub radius? I’m eventually going either mopar or dynatrac 2in lift w/ 35’s- though not sure this will help my problem obviously. I’ll go stock width and/or offset if I can get the ride back to normal.

Pic attached for reference. Any help/ advice is greatly appreciated!

Scrub radius impacts whether the wheels want to naturally toe in or toe out - and can impact shimmy and wobble, brake steer, bump steer, etc.
If it's 0, you get squirm and instability.

 

[blnewt]

Need some help here! Found this thread when I was researching why my JLU is shimmying all over the place way worse since putting on my new wheels/tires. I have Method 701s in 17x9 et12 on Cooper discoverer 33in tires. Sahara, no lift. I love the way these look but ever since installing them the Jeep feels like it’s all over place. I’m being throw around over the smallest bumps.

Is this all because of the more aggressive width and offset creating an incorrect scrub radius? I’m eventually going either mopar or dynatrac 2in lift w/ 35’s- though not sure this will help my problem obviously. I’ll go stock width and/or offset if I can get the ride back to normal.

Pic attached for reference. Any help/ advice is greatly appreciated!

17x9 w/ an offset of +12 is not a big hit to scrub radius vs many other offsets some going way into the negatives. I'd give a little more seat time w/ the tires, sometimes a new set that's larger in size or more aggressive w/ the tread will take some getting used to. Might also get your caster checked, might be on the lower side, want to get it around 5.5 to 6.5 for real good hwy manners.

 

[azwjowner]

17x9 w/ an offset of +12 is not a big hit to scrub radius vs many other offsets some going way into the negatives. I'd give a little more seat time w/ the tires, sometimes a new set that's larger in size or more aggressive w/ the tread will take some getting used to. Might also get your caster checked, might be on the lower side, want to get it around 5.5 to 6.5 for real good hwy manners.

He said 12 but those Methods are actually -12. Quite a difference.

 

[dginz]

He said 12 but those Methods are actually -12. Quite a difference.

CORRECT, to clarify it’s et -12 & a 9in wide wheel. You can see how much they poke in the pic.

 

[dginz]

Scrub radius impacts whether the wheels want to naturally toe in or toe out - and can impact shimmy and wobble, brake steer, bump steer, etc.
If it's 0, you get squirm and instability.

So would my assumption be correct with these wheels at-12 & 9in wide that they are impacting the shimmy/ wobble? Because it certainly feels like it.

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