Muzz, that you? we meet again.


> Hey there bud, the wheels you run, nor the scrub radius will effect you bump
> steer. The bump steer is purely caused by the suspension geometry.

OK. I hear you.

I know when I put 205/50R16, 42mm offset wheels on my EK civic, tramlining was a big issue.

I'd disconnected the power steering, cause I prefer some feedback.

Tolerable, but not sure I want lend the car to a friend/family member.

I realize this is not bump steer.

but ...

> What wheels are mounted to the hub will have 0 effect on bumpsteer if nothing > else is changed, even with an altered scrub radius from different offset wheels.

My theory is:

On OEM tyres/suspension the tyre centreline and the wheel pivot axis are kinda on a straight line, separated a little (fore and aft) beause of caster.

With a slightly larger tyre radius and different wheel offset the tyre centreline moves (outside in this case), causing a torque reaction between the tyre patch
center and suspension pivot axis.

This is usually cancelled because the effect is equal and opposite on either side of the vehicle.

On bumps or sporty cornering, the two sides of the card (drvr & psgr) are doing different things, thereby causing the car to be unbalanced.



Like I said at the beginning of the thread I prefer to keep the larger wheels, cause I like the look and was therefore looking to see if anybody had done anything to mitigate the handling issues.

Anybody know what limits ADR's place on increasing tyre diameter - assuming speedo correction and relevant eng. certs are taken care of?
I've seen one reference to about 15-20mm.... but desperately need some help.

I'm currently thinking 205/45R16's and/or camber are the only solution.

Nick.



Lets see, some calculations I came up with.

OEM 14inch wheel/tyre:

Wheel offset: 48mm (spec), 50mm (measured).
Steering axis incination: 10.5 degrees.
tyre radius: 0.288 meters (measured)
camber: 0 degrees.

205/50R16 wheel/tyre:
Wheel offset: 42mm (spec)
tyre radius: 0.32 meters (measured)
Steering axis: 10.5 degrees (no change)
camber: 0 degrees


suspension pivot point (OEM wheel): tan (10.5) * 0.288 = 0.052m

suspension pivot point (16" wheel): tan (10.5) * 0.33 = 0.061m

0.061 - 0.052 = 9mm.

Bigger wheels push the wheel track outwards of the different offset.
48mm - 42mm = 6mm.

Total change = 9mm + 6mm = 15mm.



:Flame suit on, quick!:

Ok, fire away!