Effects of increasing the track

Effects of increasing the track

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jaik

Original Poster:

2,001 posts

184 months

Thursday 8th February 2007
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I've heard all the horror stories of people wrecking wheel bearings and suchlike by fitting massive spacers and things. I was wondering whether it would be safe to push the wheels out by about 2" either side on my car (Suzuki Cappuccino). I'm not talking about using spacers or anything dodgy like that, but made-to-order wheels with the correct offset.

Also, with the wheel geometry setup properly, what kind of difference could I expect to feel in the handling?

Sam_68

9,939 posts

216 months

Friday 9th February 2007
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I've no experience of the Cappuccino, specifically, but general rules:

Firstly, 2" eash side is likely to require flared arches, for compliance with C&U regulations.

Increasing track reduces lateral weight transfer when cornering, so can increase grip.

It can increase loads on bearings and suspension joints, so expect reduced life on these components.

If you increase track at one end of the car only, it changes the diagonal weight transfer charactistics, which would result in more understeer (rear track increased) or oversteer (front track increased).

Assuming you increase the front and rear track by similar amounts, the basic effect on handling balance should be fairly minor BUT the effect on front end grip can be more significant, depending on Steering Axis Inclination, since you will be increasing the Steering Axis Offset. Steering Axis Offset has the effect of trying to lift one corner of the car when you turn the steering wheel, so if you increase the offset by fitting spacers, you will increase both the steering weight and the change in load on the tyre (hence increasing understeer), for a given amount of wheel movement. You will often find that tendency to tramline is increased, too.

Again, 2" each side is a fairly massive change, so will potentially result in big differences to steering weight/feel and steering characteristics.

You can tune out some of the negative effects by playing around with other elements of the chassis set-up, but it's a complicated juggling act and you need to know what you are doing to get it right.

Bottom line... if you need to ask the question, don't do it.

steve_d

13,478 posts

229 months

Saturday 10th February 2007
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Sam
Good reply. Thanks.
Would a better way forward for Jaik be to increase the rim and tyre width sharing it inside and outside to limit the offset. I accept this may reduce steering lock but a price to pay.

Steve

Sam_68

9,939 posts

216 months

Saturday 10th February 2007
quotequote all
Yes, if you make sure that the wheel offset (ie. distance from hub mounting face to centreling of wheel) is such that the extra width is shared equally inside and outside - so that the steering axis offset (distance between the axis around which the wheel turns and the centre of the contact patch) remains the same - then you have a good chance of upsetting things much less.

Obviously, steering will still become heavier, simply because of the increased tyre contact patch, but the other negative effectes won't be as severe.

Whilst again stressing that I know nothing about the Cappuccino, specifically, remember that bigger does not always mean better, where tyres are concerned, though. Bigger wheels & tyres means more unsprung weight (particularly significant on relatively small, light cars like the Suzuki). Also, if the suspension geometry was designed for narrower tyres, the camber variation in bump/roll might mean that it is alternating between the full contact patch being square to the road surface and riding on one edge as the suspension moves... if this is happening as the car rides bumps and ripples on the road surface around a corner, th result is unpredictable levels of grip.

My weekend toy (original Lotus Elan) is notorious for not responding well to tyres much bigger than the original 155 section - which look laughably narrow by modern standards - and Caterham's previous MD admitted in print that the cars would actually work better with smaller, narrower wheels & tyres but that fashion meant that buyers demanded low profile 'rubber bands' for their looks.

jaik

Original Poster:

2,001 posts

184 months

Saturday 10th February 2007
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Thanks guys. Currently I've got 195/45R15 tyres on rather than the standard 165/65R14 and they are much better. Like you say, the steering is heavier and it does try to tramline a little on occasion, but the extra grip is fantastic and the handling is still very predictable. I would be keeping the same tyre size and wheel width if the track were increased, just by getting wheels with a much lower offset.

The reason I ask is I've been looking at a fair few with wide-arch kits on recently and absolutely adore the look of them, but if it will make the handling worse then I won't bother.

bluespanner

3,383 posts

194 months

Wednesday 7th March 2007
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I have 215/45R17 tyres on my 306, with 25mm spacers no problem.