Scrub forces at the contact patch

[michael2]

Negative scrub causes tires to toe in and positive scrub causes tires to toe out. What causes this?

Also, It seems to be a popular notion to examine scrub from front on section drawings. But when I perform rudimentary drawings in plan view, the point at which the SAI intersects the ground changes with respect to a turning tire. This is not pointed out in any literature that I have read. This must have something to do with how the tire is distorted in either case?

 

[michael2]

Joest,

I am an amateur for sure. But the notion that the most perfect set-up may be spoiled by some silly contact patch is certainly not lost by my brain. ...I tend to think Ferrari's trouble this year (may) have had something to do with tires.

I am left to the but dyno and my hands. The reason for beginning this topic about scrub was to retain or improve feel. knowing what the tires are doing...or not doing, is important to my consistency.

Sort of back on topic, I noticed something a bit peculiar about the orientation of the damper and hub assembly on my 05 Mini cooper. The damper does not follow the axis in side view to the ball joint, rather, it tilts forward of the axis as it meets the hub assembly. This causes some distortion at the bearing as the wheel is turned. I cannot figure out what geometric advantage this has...except for packaging - the damper housing is slightly flattened in the area that crosses the tire's section. Locating the damper in this way also stands the damping more upright in the front view. Any thoughts? I wondered of this might be connected to scrub or camber gain.


Thank you all,

Michael

 

[michael2]

"This causes some distortion at the bearing as the wheel is turned."

I mean the strut bearing, not the hub bearing.

 

[GregLocock]

"...Wow! Half the compliance from tires. "

On a race car, not a road car.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[michael2]

Greg,

That reads counter-intuitive. How come?

Michael

 

[GregLocock]

?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[michael2]

I sorted of expected road tires to be more compliant than race tires. My experience is very limited with near race DOT tires. These posses very stiff side walls, however.

F1 tires...

Michael

 

[Warpspeed]

Yes, but the compliance of the suspension (wheel rate) is going to be WAY lower on a production car too.

Michael2, I would not be discouraged about what a multi million dollar Formula One budget can achieve, just look on in awe, and let them fight it out among themselves.

Amateur weekend racers probably have more fun anyway, and you will be up against people with similar resources.

 

[michael2]

Warpspeed,

I've been a fan of red since about 6 years old. I had an opportunity to be at Fiorno last year to watch a 2005 F1 shake down test...wow - I am in awe! Controlling one of those things takes a wee bit of talent.

Okay, yes, I get it now. Wheel tate, and, aero forces too, yes?

michael

 

[GregLocock]

Typical production suspension will have a deflection of around 25mm per g, tires are about 210 N/mm. F1 cars are more like <5mm per g and I don't know what the tires are.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.