EK Civic scrub radius?

[nd55]

Hey,

does anybody know the scrub radius, king pin inclination or offset of an EK civic?

Nick.

[nd55]

Before anybody mentions it, I did search.....

[ECU-MAN]

this is the only specs honda have released in the tech guide.

you can check the workshop manual for more info if you find one on the web somewhere

Camber Front - 0° 00' ± 1°
Rear - 1° 00' ± 1°
Caster Front 1° 40'
Toe Front IN 1 ± 2 mm
Rear IN 2 (+ 2 -1) mm

[creativepunka]

Its the steering axis inclination as we dont have king pins, try search that.

[nd55]

did a search of "steering axis" + honda.


Results are the same, it's in everybodies glossary, but not real numbers.

Nick.

[nd55]

> Its the steering axis inclination as we dont have king pins,

This jogged my memory a bit.

I dug up a suspension printout done by "Spinning Wheel" (Woolloomooloo) a while back.

"Steering Axis inclination" is about 10.5 degrees.

Just trying to work out wheel/suspension details to minimize bump steer.

Thanks.
Nick.

[creativepunka]

dont quote me, but from memory doesnt the scrub radious depend on the the rim width, height and offset.

[nd55]

doesnt the scrub radious depend on the the rim width, height and offset.

Yes.

I'm trying to justify 16" or 17" wheels, but I can't make them match OEM scrub radius figures without resorting to ($$$$) low profile tyres.

Looks like I'll have to investigate 15" wheels.

I quick look through the Kumho dogalogue dosn't show much in 15's. ... but that's another thread I'm sure.

Nick.

[Muzz]

Just trying to work out wheel/suspension details to minimize bump steer.


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. 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.

Bump steer is caused by the steering arms changing angles in a way that pushes or pulls on the front hubs steering ball joints as the suspention is moved through its range of motion. Its one of those things you dont have to worry about at all unless your experiancing its negative effects.

The only thing thatll effect your bumpsteer that youll be changing, is your static ride height, which im guessing you wont be slamming since your after a good sussy setup. The only other way the bumpsteer will be altered is by changing the steering/suspension geometry, somthing that you wont be touching.

[xtc_romeo]

this is the only specs honda have released in the tech guide.

you can check the workshop manual for more info if you find one on the web somewhere

Camber Front - 0° 00' ± 1°
Rear - 1° 00' ± 1°
Caster Front 1° 40'
Toe Front IN 1 ± 2 mm
Rear IN 2 (+ 2 -1) mm


:thumbsup:

[nd55]

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!