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      10-29-2020, 09:31 AM   #1
bngcruiser
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Scrub Radius

Hey guys,

This is the first time I am making adjustments to my wheels/tires/suspension and actually worrying about what it is going to do to my vehicle (amazing right)?

A little background:

2013 WRX - Lowered on KW V1 Coilovers w/ stock wheel geometry
2014 STI - Lowered on KW V2 Coilovers w/ .5" wider wheel/tire geometry
2013 VW R - Lowered on KW V3 Coilovers w/ 1" wider/taller wheel/tire geometry
2018 BMW M2 - Lowered on KW V3 Coilovers (Looking to go: 19x9.5 et23 fr and 19x10.5 et34 Rr, MPSS 245/265)

I have been introduced to scrub radius for the first time during my research and I want to try to gain the best understanding of it.

This site has been a great resource as I have been trying to decide on the geometry of wheels to go with: https://www.wheel-size.com/calc/

I am looking to try and achieve a zero scrub radius relationship with the new wheels and rubber - the question I have is, can I affect the relationship by introducing camber/toe-in? I have Ground Control Camber Plates installed with my KW V3 Coilovers .. and if I am understanding the relationship correctly, I can add/subtract camber to influence the scrub radius along with increasing/decreasing the height of my Coilovers.

Thanks for any assistance .. I know I just asked a bunch of questions and introduced a ton of variables.

Cheers
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      10-30-2020, 05:25 PM   #2
Atsantone
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Found this on YouTube - a lot of great alignment information including scrub radius covered.
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      11-02-2020, 06:50 PM   #3
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You can completely skip all this. I don't know what the scrub radius of the stock suspension is but by going from 9" wide wheel with ET29 to 9.5" wheel with ET23 the centre of the tire remains in the same spot (because you are essentially adding the same amount of wheel/tire width on the outside as you do on the inside).

I'm running 15mm spacer and 1.85 degree camber with stock wheels and I'm not noticing any negative effects.
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      11-02-2020, 10:46 PM   #4
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Quote:
Originally Posted by mr_lab_rat View Post
You can completely skip all this. I don't know what the scrub radius of the stock suspension is but by going from 9" wide wheel with ET29 to 9.5" wheel with ET23 the centre of the tire remains in the same spot (because you are essentially adding the same amount of wheel/tire width on the outside as you do on the inside).

I'm running 15mm spacer and 1.85 degree camber with stock wheels and I'm not noticing any negative effects.

Not sure, maybe this is wrong:
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      11-03-2020, 05:15 AM   #5
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Yeah, it was wrong. Scrub radius isn't affected by wheel width but only by the offset value since that determines the location of the center of the tire (and contact patch). Notice how the calculator showed the scrub radius changed by exactly the ET (offset) change in the result.
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      11-03-2020, 07:06 AM   #6
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The video was very helpful.
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      11-05-2020, 12:24 PM   #7
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Continuing to try and better determine how adding positive scrub radius will affect the vehicle tracking down the road.

Does anyone know what our OEM Spec Scrub Radius for our vehicles? As a RWD vehicle, my understanding is we probably have positive scrub radius from factory with some toe in on the back.

I will be adding roughly 6mm of positive scrub radius, which will mean needing to add more toe in to keep the vehicle from changing the driving dynamics by a bunch.
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