Low Profile Tyres - on a Dutton?

[James Doulton]

When I went to Castle Combe in August I was rather disappointed with my Legerra's road-holding. I was talking to another guy who had a stripped out Citroen Saxo VTS (he is actually the MOT inspector at the garage I use and did my car just a week before the meeting). His car was not really any faster than me in a straight line but went around the corners completely differently. He reckoned it was just down to tyres - he pointed out that almost everyone else was running Toyo R888's like he was.

According to my calculations (on a big Excel spreadsheet) a small increase in cornering power makes a huge difference to lap times, so it would be well worth improving the cornering, plus it would make me safer on the road if I had a bit more margin.

The trouble is that they don't seem to do them in 195/65 x 14, which is what I am currently using. I have had a look around and it seems that I can keep my existing gearing if I change my wheels and fit either 195/55 x 15's or 205/40 x 17's. I like the idea of the 17 inch wheels, there are quite a few 4 stud ones on fleabay from Focus ST's which would seem suitable.

But there have been comments before that Dutton's don't work well with low profile tyres and so I was wondering why. I can see two potential reasons:

• the first being the camber on the front wheels, mine is somewhere between 2.5 and 3.0 degrees. The camber means that the tyre is distorted more on the inside, by about 9mm, than on the outside. This would presumably matter more with low profile tyres as the side wall is shorter. But then you see kids driving around in lowered cars with MUCH more camber. They look stupid but you'd have thought that they'd correct them if they wore out quickly or handled badly, wouldn't you?
• The second reason that I can think of why low profile tyres might not be so good is that the tyres would probably be a lot less compliant and with a live rear axle that might mean that a bump under one wheel upsets the other one more than it would with a taller tyre. So bumps mid-bend might be more of an issue.

I would be interested to hear other peoples views and experiences with their Duttons.

[Jim (across the pond) Adamek]

Have you ever seen low profile tires on a race car?

[Steve Kerswell]

Like Adrian I have tried from 185/70x13 up to 245/45x17 with the dreaded pipe flanges to get the offset. Thought I had it right with 205/50x 15 until it rained very hard and I aquaplaned all the way home despite trying to ease it along. I've gone back to the13's and I'm very happy with my set up now, however its a (fastish) road car not a track day special. Intend to fiddle with the handling over the winter, if I'm able, Sierra build (the proper one) takes precedent.

[James Doulton]

Maybe I should go back to the 13" wheels that came with the car - the original Cobra ones that are shown in all the old publicity shots. I notice that Toyo do the R888R in 185/60x13 and, at £98.50 + fitting, they are a lot cheaper (or less expensive) than the 16" or 17" ones. That'd save me buying wheels as well.

If I fit the 3.54:1 rear axle then it would bring my gearing back to exactly what I have now with the 3.89:1 with the 185/65x14's.

I will probably have to jack up the suspension though to clear the stupid speed bumps that the local council have put everywhere. They have put lots of bolted down 'speed buttons' which I can just about ignore because they are only as wide as my track, so I can straddle them at the moment. Currently my sump and exhaust miss the top of them but those Toyos would make me nearly an inch lower.

[James Doulton]

It looks like good weather to check out the aquaplaning ... I might be a while.

[Steve Kerswell]

Fire into a big roundabout, that even upsets the Sierra :-)))