How much positive scrub radius until screwing things up?

[ajc209]

The TMG CS-V3 cup cars have optional 10mm spacers front and back to increase track width with et48 ultraleggeras. In case you didn't know, TMG are Toyota's offical motorsport team in Europe that build the le mans cars and won all those rally championships in the Celicas.... if they say its okay to run those spacers. ...

[solidONE]

I've run stock (+48), +45, +40 and +35 offset wheels from 0 camber to -3.2* degrees and there was very little difference in steering effort required between the different offsets. Not sure how much effect it has on tire wear characteristics, but steering effort, not so much.

[Ultramaroon]

Originally Posted by 7thgear

curious about this as well

Negative effects of excessive scrub radius are rarely written about.

A personal very negative effect for me is the greatly increased possibility of turning what would be minor curb rash into a catastrophic accident.

I don't remember how much positive scrub I had on my 240Z but whenever I barely touched a curb it would rip the steering wheel right out of my hands. I was always afraid of tapping a curb at any speed over a creep.

[MaximeT]

Originally Posted by Ultramaroon

A personal very negative effect for me is the greatly increased possibility of turning what would be minor curb rash into a catastrophic accident.

I don't remember how much positive scrub I had on my 240Z but whenever I barely touched a curb it would rip the steering wheel right out of my hands. I was always afraid of tapping a curb at any speed over a creep.

That's how I understand the possible troubles with scrub radius. The curb could suck your steering wheel and makes you turn more than what you want.

The question is: when does trouble start ?

[Ultramaroon]

Originally Posted by MaximeT

The question is: when does trouble start?

Good question. No idea but I have first-hand experience of when it's over the top.

[MaximeT]

Originally Posted by Ultramaroon

Good question. No idea but I have first-hand experience of when it's over the top.

My only experience is with LFS simulator. The only one I know where you can test different scrub radius.
The effect is scary.

[JDM4E]

Originally Posted by ajc209

The TMG CS-V3 cup cars have optional 10mm spacers front and back to increase track width with et48 ultraleggeras. In case you didn't know, TMG are Toyota's offical motorsport team in Europe that build the le mans cars and won all those rally championships in the Celicas.... if they say its okay to run those spacers. ...

good call, I couldn't find the 10mm info tho. How do you know? Anyway I agree that if it is good for them...

[ajc209]

Originally Posted by JDM4E

good call, I couldn't find the 10mm info tho. How do you know? Anyway I agree that if it is good for them...

10mm spacers.

First mentioned here:
http://www.toyota-motorsport.com/mot...tmg-gt86-cs-v3

and can be seen here on page 55 of the user manual:
https://www.google.co.uk/url?sa=t&rc...nTTLlxtcbYPbyQ

[7thgear]

Originally Posted by solidONE

I've run stock (+48), +45, +40 and +35 offset wheels from 0 camber to -3.2* degrees and there was very little difference in steering effort required between the different offsets. Not sure how much effect it has on tire wear characteristics, but steering effort, not so much.

depending on how the camber is achieved, you might actually be angling the strut to compensate for the increased offset so the actual effect on scrub is much smaller than the raw offset value.

[solidONE]

Originally Posted by 7thgear

depending on how the camber is achieved, you might actually be angling the strut to compensate for the increased offset so the actual effect on scrub is much smaller than the raw offset value.

The camber was added from camber bolts, so the increased negative camber probably had the opposite effect of increasing scrub radius a little, if anything.

[Swift]

Originally Posted by 7thgear

depending on how the camber is achieved, you might actually be angling the strut to compensate for the increased offset so the actual effect on scrub is much smaller than the raw offset value.

This.

[ajc209]

Originally Posted by 7thgear

depending on how the camber is achieved, you might actually be angling the strut to compensate for the increased offset so the actual effect on scrub is much smaller than the raw offset value.

Exactly. IIRC 2 degrees of negative camber (strut camber not bolts) at the front moves the scrub radius out by about 5mm. I cant find my friggin spreadsheet now actually I need it


So you might actually want spacers if you add significant camber depending on the wheel offset.

[NissanGuy]

I believe I've found it easier to lift a rear wheel just by adding 10mm spacers. Of course, we're talking about hauling ass up steep driveways. The other thing I noticed is bigger scrub radius exacerbates body roll. Even at standstill, turning the wheel lock to lock causes noticeable roll. Maybe 1-1.5" as measured at the roof?

[Ultramaroon]

Originally Posted by 7thgear

depending on how the camber is achieved, you might actually be angling the strut to compensate for the increased offset so the actual effect on scrub is much smaller than the raw offset value.

I'm not picturing this unless you're talking about changing, what is it with camber plates fore-aft, rake?

...well, plates in the strut tower that can do both.