Rear bump steer

Bump/roll steer check on the rears for the first time, using a laser level on the brake disc and a mirror. I don't know why I haven't done this before. It turned out they (the rears) had quite a lot of toe in bump steer dialled in.

Apparently it is common to set up road cars for understeer and stability by inducing a bit of bump steer - toe in on the rears and toe out on the fronts. On race cars close to zero bump steer is preferred if possible, for maximum absolute grip and less scrub.

I reduced the bump steer by simply switching place of the bump steer spacers and it was significantly reduced. Not quite zero but I leave it there. Now the larger 9mm spacer is up and the smaller 5mm is down - opposite of the top image. (the top image is from the CSR Assembly Guide Supplement document)

I did the fronts for quite some time ago but without the mirror. I must say the mirror method is both simpler and more accurate. The basic idea is to put the laser level on the brake disc and point it forwards or rearwards to a mirror that reflect the beam back to the same point. If the point moves sideways relative to the origin when you raise the wheel - you don't have zero bump steer. Adjust the spacers and repeat.

Camber calculator

An easy way to measure camber is to use a spirit and a ruler. It is really important that the car is standing on a completely flat surface for this to work. Accurate? Well, accurate enough for me anyway.

Simple camber calculator:

Rim	mm
D1	mm
D2	mm
Camber	degrees

Adjusting Camber

Adjusting rear Camber
Rear camber is really easy to adjust, and can be done in just a few minutes.

1. Remove the wheel. 
2. Loosen the four small bolts (unlike the picture, normally two of them are hex bolts).
3. Add or remove shim plates as necessary. Silver = 1deg, red =0.75, blue=0.5 and black 0.25. You can buy them from Caterham parts.
4. Be careful not to over tight the bolts, especially the vertical ones. 

Beware that if having a cross-ply setup with not much camber, be sure you have enough threads left on the horizontal bolts, or the wheels may fall off!

Adjusting front camber
Adjusting front camber can be a pain, especially the first time.

1. Undo the camber lock nut at the end of the upper wishbone.
2. Remove the wheel
3. Remove the wing stay by loosen upper ball joint nut, and then removing the stub axle nut. The indicator wires prevent from complete removal, but tuck the wing stay out of the way and try not to scrape the wishbone paint.
4. Undo the top ball joint nut until the nut is on the end of the thread.
5. Now split the tapered joint. This can be done in several ways. Personally I use a cheap tool which fits perfect used up-side-down! See picture. I've read about others who use a hammer!? Some use a bolt with two nuts against the hub (never tried it).
6. Remove nut completely and adjust camber. One turn equals .25 degrees of camber.
7. If you feel lucky, put copaslip on for easier dismantle next time. But beware - copaslip can make it really painful to screw back the wishbone to upright nut!
8. Stub axle 82Nm
9. Upright top ball joint 52Nm. 
10. Wheel 74Nm
11. Tighten camber lock nut

Note that camber affects toe, so if you adjust camber, you must recheck your tracking!

Wheel alignment check

My current wheel alignment, measured in my garage. Cross-ply setup.

	Front	Rear
Toe	0.5° out	0.7° in	per wheel
Camber	-1.25°	-0.25°	±0.25°
ARB	Hard setting	-
Tyre	195/45-15	215/40-15	ACB10 road legal
Pressure	19 psi	19 psi	warm
Rims	6.5"-15	9"-15

Rear left wear

Front left wear

The wear in the middle came after running a bit too high pressure on Mantorp earlier this year. I think 19 psi is just right. I know that sounds low, but it works for me.

My rear 9" rims are too wide for the ACB10 according to Avon, but it works ok.