How can I measure castor angle?

[tom16v]

I have bought some of the adjustable tie rods that Rob makes at Sprintspeed.
They look lovely, but I would like them to improve things rather than be detriment to the cars handling when I fit them.
At the moment I have lowered the car, but it is otherwise standard.
This has made slow speed steering much heavier, which if I understand things correctly, is likely because there is more negative camber with the suspension resting in the lowered position and this is increasing the scrub radius. I think I could cure this with either an extra camber shim, or raising it a little again.
The car has always dropped left a bit when you let go of the steering though. This has not changed. I wonder if this is due to unequal castor angles. I would like a little extra castor for straight line stability, but I would like to be able to measure it so that it is equal both sides so it doesn't make the car drop left or right.

Any ideas?

Anyone else run adjustable castor and have experience setting them up?

Thanks for your comments

Tom.

[gmsclassics]

I run caster 4.0, camber -3.2, toe 0.0 on the car I use on the track. That setup gives me stable neutral handling on fast sweeping corners. Hairpins are still understeer on entry so slow in and fast out remains the best option. Car can be quite twitchy in a straight line as it has lost some of the self centering ability in favour of much tighter turn into corners. What is best on the track, isn't best on the road and vice versa. Finding a compromise depends on what is most important to you.

Problem with the Dolomite suspension is that any adjustment other than steering tie rods, alters all three settings simultaneously, so it is a difficult / time consuming exercise. I run no shims at the top behind the suspension mounting bracket and then a longer bolt at the bottom so the vertical link can be pushed outwards to create more negative camber. I've also got washers between the lower ball joint and the vertical link (with longer bolts). If you want more/ less caster, just use the new tie rods to move it back or forward, remembering that you will simultaneously change camber and toe. I've found adjustable tie rods need quality uprated poly bushes - standard rip to pieces very quickly. The thickness of the bush also affects settings and soft bushes will also change geometry as you corner!

It is relatively easy to measure toe and camber (with the road wheels on) using bits of wood, a long spirit level, a cheap laser level and basic trigonometry. Not worked out how to do caster yet. I try to get camber where I want it then go down for a wheel alignment at a time when they are not busy and then work with them to get what I want. Helps if all the bolts/ nuts are well lubricated and I also take some of my tools to get at awkward ones.

Best place to start is get the adjustable tie rods to exactly the same length as standard ones (with the first bush on) and then play with adjusting from there.

Hope this helps

Geoff

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[soe8m]

I don't use adjustable's but replicate the ST ones with the 2000/2500 bushes. I also make sure the total length when fitted is about 15mm shorter than original. This gives for a roadcar the bests results i think discovered by trail and error.

I'm not a fan as in the picture above to use washers between the balljoint and hub. The balljoint is stressed more and it does influence your steering in a bad way because of moving the wheel centre away from the line of the upper and lower balljoint. This is not the way neg camber must be achieved, more hub angle compared to the balljoints. Only by removing shims at the top or putting washers between the subframe and lower mounting as in the upper picture you must use for more neg camber.

Jeroen