No wonder my Sportster handling was "twitchy"...

I bought a new (to me) Sportster a few weeks ago Yesterday I went out for a blast with my wife as passenger (her first time out in it). To be honest, on the bumpy country roads around here, the handling was very challenging and not at all confidence inspiring, amd my wife did not enjoy the experience one bit! One reason was that I have just fitted new tyres and they were over-inflated. I asked the fitter for 24psi, but when I checked they were all at 32psi; so that didn't help. I stood there staring at the front end geometry, and noticed that to my "eyecrometer" there seemed to be far too much negative camber; seriously, noticably too much. I took some measurements using spirit level and ruler, and using my basic schoolboy trigonometry I worked out that front left wheel had 4.5 degrees of negative camber, whilst the front right had 3.6degrees.Way. way too much! For a fast road car I would not have wanted more than 1degree negative. It's almost as if the car was set up for lapping Silverstone (and then some!)

I then checked the rear camber. Both wheels have 3.5degrees negative . Again; way too much! So now I need to adjust those top front wishbones (luckily they are adjustable) to give me the required camber. How one does the Sierra-based rears is anyones guess! It's not a system I know at all, having been used to live axle hillclimb and sprint cars. Advice and comments most welcome! Thanks Chris.

[copperleaves11]

Hi Chris. Both Sportsters I have owned have been run with 18psi front and 20 psi rear, working on the principle that quite a bit of compliance in the suspension is in the sidewall of the tyres. I also found that a front anti-roll bar was not necessary either, for road use and I agree that 1degree neg camber is about right. The camber at the rear is adjusted by adjusting the upper spring seat. Hope that is of some help. Regards David.

[Patrick]

I have mine set to about 1.25 negative camber on the front, the rear is what it is to get it ride height right, probably a bit to much. Castor on the front I have 3 washers on the front, 4 on the back.

As for pressures I run mine realatively low on a 205/60/R15 bit more in the back than the front, little bit more than David is running right now but I'm trying it with more pressure to see what it's like.

[copperleaves11]

A further observation regarding castor and also it's effect on self-centring. Having had both Ford and BMW uprights my feelings are that the BMW units have more natural "rake" in their design, thus mounting the top wishbone centrally gives more self-centring effect than the Ford units which I found needed packing rearward and even then seemed to need more castor. Wonder if anyone else found this. Regards David.

[Patrick]

I spent a long time dialling in the self centre in order to pass SVA, E30 based sportster with modded E30 struts. The best self centre I could dial in was with the upper wishbone slightly back. This was all done by moving settings and driving it. It's been since 2009 when I got it through SVA. My memory is a bit hazy, ended up looked it up on my own website.

Many thanks for your replies. So on a Ford Sierra based rear end, am I right in assuming it uses the standard rear springs which may have been shortened? And you reclaim some positive camber by adding shims to the upper spring seat? Or maybe use a longer spring?
Thanks Chris.

[copperleaves11]

Hi Chris. On mine, and I think the Cabrio is the same, the top spring seat consists of a large diameter disc (5inch approx) which screws up and down a large captive thread. Regards David.

Hi Chris. On mine, and I think the Cabrio is the same, the top spring seat consists of a large diameter disc (5inch approx) which screws up and down a large captive thread. Regards David.

Thanks David. That simplifies things somewhat. I believe mine is the same.