18 inch wheels on a 99 Chim
Discussion
The biggest problem is that drivability will be compromised.
The rears will be OK however snap-oversteer will be more likely. This is due to there not being as much lateral movement between tyre and rim under heavy cornering.
The fronts need to have a smaller overall diameter so the sidewall becomes very small. On bad road surfaces you will suffer rim bump. That’s where the metal rim bumps the inside of the treaded part of the tyre. You will also suffer tramlining and bump steer. These two effects occur because the tyre is no longer able to deform sideways. That sideways deformation is needed so that the treaded part of the tyre can absorb the pull of the road without pulling on the steering (tramlining). Bump steer occurs because the insufficient sideways deformation causes the tyre to bounce rather than deform.
Most people fit 18” rear & 17” front. That way they get the best of both worlds, good looks and a good handling
The rears will be OK however snap-oversteer will be more likely. This is due to there not being as much lateral movement between tyre and rim under heavy cornering.
The fronts need to have a smaller overall diameter so the sidewall becomes very small. On bad road surfaces you will suffer rim bump. That’s where the metal rim bumps the inside of the treaded part of the tyre. You will also suffer tramlining and bump steer. These two effects occur because the tyre is no longer able to deform sideways. That sideways deformation is needed so that the treaded part of the tyre can absorb the pull of the road without pulling on the steering (tramlining). Bump steer occurs because the insufficient sideways deformation causes the tyre to bounce rather than deform.
Most people fit 18” rear & 17” front. That way they get the best of both worlds, good looks and a good handling
Sorry to disagree but 18" fronts on country roads is not a good combination, there's plenty of comment on this subject on PH, you'll soon find that big front rims do bugger the drivability. That's event true for the straight six's.
If you're putting 18's on is to make the car look good then so be it but don't be fooled, 18" fronts will make your car drive worse.
ETA yes I have had 18" on mine, I put the five stud conversion on. I soon swaped mine for 16's all round, the car drives great on those.
If you're putting 18's on is to make the car look good then so be it but don't be fooled, 18" fronts will make your car drive worse.
ETA yes I have had 18" on mine, I put the five stud conversion on. I soon swaped mine for 16's all round, the car drives great on those.
Edited by bobfather on Sunday 15th January 22:18
I had 17`s and all four corners,even 17`s on the front are to large ,215/40/17`s have a very small wall height so i sold the front wheels and now running 16" fronts 17" rears,a very good compromise.
this is a picture of the 17" front wheel you can see the wall height ,2" less than standard setup..
For best handling stick with the factory sizes..
look how close the rim is to the floor ,it will be even worse with 18"s and tyres get alot more expensive.
Neal1980 and Maceb have 18" spiders ,ask them !
Don`t understand why more people dont go 16"front 17"rear..
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this is a picture of the 17" front wheel you can see the wall height ,2" less than standard setup..
For best handling stick with the factory sizes..
look how close the rim is to the floor ,it will be even worse with 18"s and tyres get alot more expensive.
Neal1980 and Maceb have 18" spiders ,ask them !
Don`t understand why more people dont go 16"front 17"rear..
[f
Edited by SILICONEKID340HP on Sunday 15th January 23:50
Thanks Martin, those with 18" will defend them and the debate has got a little heated on here in the past. A good example of this issue is the two types of BMW driver, those that are happy with run flats and those that change them for normal types at the first opportunity. Same issue, run flats have very rigid side walls, the effect is the same as reducing side wall. If you like to use your car at the limit on occasion then you need some sidewall flexibility. I've read on here that some people with 18" fronts reduce the tyre pressure to increase flexibility, I'm sure that works but it also means that rim bump becomes more likely.
As you can see already there are three people each with different opinions. Tyres and rims are a personal choice and there are a number of factors that can create different results. I can only report no tramlining or bump steer and a slightly harder ride after changing from 15/16 to 18 all round. Tyre sizes are front 215/35. And rear 225/40.
Never going to be as good as the smaller rims but still acceptable in my book 
Chilliman said:
I see HM's bonnet is up as usual 
I'm waiting for a one off cam, any day now then I can finish the engine.Anyhoo, I have SH Q/R hinges and it's off.....
My road wheels are 17" fronts with 40 profile tyres and tramlines like a b#stard!
My 17" track tyres have 45 profile and are much better, even with the stiffer sidewall.
haircutmike said:
Chilliman said:
I see HM's bonnet is up as usual
I'm waiting for a one off cam, any day now then I can finish the engine.Anyhoo, I have SH Q/R hinges and it's off.....
My road wheels are 17" fronts with 40 profile tyres and tramlines like a b#stard!
My 17" track tyres have 45 profile and are much better, even with the stiffer sidewall.
Edited by CHIMV8 on Thursday 19th January 07:26
Mine was on 18s all round when I first had it. I will say first off that I don't know whether the previous owner had done his homework with regards offsets and wheel weights (they were a lot heavier than the standard Estorils, which aren't particularly light themselves I'm led to believe...) but it was pretty attrocious. The steering (non-PAS) was ridiculously heavy and gained all sorts of unwanted bumps and shakes, the ride was all over the place, the front wheels rubbed on full lock, and to my eyes they simply looked too big on the car.
I've now gone back to stock 15/16s, all the problems above have been sorted and there's no significant loss of grip from the smaller contact patch. Tyres may be harder to get hold of in 15-inch, but they are generally cheaper.
Like I say, it may have been a poorly thought out job on the part of the previous owner, but at the very least it proves you need to do your homework carefully. Personally I'm much happier on the stock sizes.
I've now gone back to stock 15/16s, all the problems above have been sorted and there's no significant loss of grip from the smaller contact patch. Tyres may be harder to get hold of in 15-inch, but they are generally cheaper.
Like I say, it may have been a poorly thought out job on the part of the previous owner, but at the very least it proves you need to do your homework carefully. Personally I'm much happier on the stock sizes.
Edited by Chris71 on Thursday 19th January 09:48
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