What difference does wheel size make?

[three sisters]

My car has 17" wheels at the moment. I see other CDTis with different sizes, what difference does wheel size make?

[stef_uk]

put simply going on the standard radius for the speedo to be correct

a smaller wheel 15" will have a bigger sidewall on the tyre producing a softer ride and less stability in cornering
were as a bigger wheel 18" will give a greatly reduced sidewall and a harsher rider but better handling

your 17" would be considered the best of both worlds...

the only other reason for bigger rims is they look alot better on the car and appear to fill the arches better.


hth stef

[Departed]

Another possible reason is unsprung weight. Tyres are heavy, compared to alloy wheels, especially ones with small spokes and big gaps. Though it has to be pointed out (before anyone thinks i didn't realise) that most of the weight is in the steel band under the tread, which is there on all tyres.

[Tim]

I've got 18"'s on my 75 and agree with Stef the ride is slightly harder but it takes corners much better and it does look the part (IMO)

[Dragrad]

15" wheels survive pot-holes and kerbing better that 18" wheels IMHO

You should see the roads around here!!!

[three sisters]

What about MPG and performance. And speedo etc. readings?

[GreyGhost]

As long as the overall radius (wheel plus tyre) is similar then speedo readings will be normal (accuracy is a moot point as all speedos are likely to be around 10% out).
MPG is unlikely to be affected to any degree, although larger wheels will be also be wider which will have some effect. Very difficult to quantify unless you do real world comparison tests, due to driving habits, road conditions, vehicle tune, etc.
Performance on larger wheels and tyres I think will be limited to handling, which will be greatly improved but harsher.

[Reebmit]

Another reason for fitting larger wheels can be to accomodate larger brakes

[M3NDEREZ]

Originally Posted by Dragrad

15" wheels survive pot-holes and kerbing better that 18" wheels IMHO

You should see the roads around here!!!

You'd never get away with my 19's then, Andrew?!

Thought I'd chip in on this one.. If you're putting 18's on a 75 instead of 17's, don't expect any hugh increase in handling.. The 75 (Saloon - Before the Tourer Touge crew have my b@lls) wallows in the corners something rotten.. However, the flipside of this is that you also don't lose a noticeable amount of ride quality by losing a little off the tyre wall either.. Both Merl and I went from 15's (on 65 tyre wall as I recall) to 18's on a 45 tyre wall, and neither of us noticed an loss in comfort. I then went even further, to 19's with a 35 tyre wall, and still, no real sense of any firmness in the ride.. I think perhaps it's because the 75 Saloon's suspension is so soft to start with..

Two things it really comes down to on a 75 as far as I'm concerned - 1) Vanity, in that bigger wheels unquestionably look better, and 2) Cost - I once had a full set of brand new 15" Federals fitted, balanced, and new valves for £118 - On the 19's I'm likely to pay around £70 each for the same tyres.. Or more like £120 per tyre for Eagles or PZero's.. If the look of 17's doesn't offend you, and you're not prepared to pay £100 extra for a set of tyres on 18's, I wouldn't bother upgrading..

[Merl]

Originally Posted by M3NDEREZ

You'd never get away with my 19's then, Andrew?!

Thought I'd chip in on this one.. If you're putting 18's on a 75 instead of 17's, don't expect any hugh increase in handling.. The 75 (Saloon - Before the Tourer Touge crew have my b@lls) wallows in the corners something rotten.. However, the flipside of this is that you also don't lose a noticeable amount of ride quality by losing a little off the tyre wall either.. Both Merl and I went from 15's (on 65 tyre wall as I recall) to 18's on a 45 tyre wall, and neither of us noticed an loss in comfort. I then went even further, to 19's with a 35 tyre wall, and still, no real sense of any firmness in the ride.. I think perhaps it's because the 75 Saloon's suspension is so soft to start with..

Two things it really comes down to on a 75 as far as I'm concerned - 1) Vanity, in that bigger wheels unquestionably look better, and 2) Cost - I once had a full set of brand new 15" Federals fitted, balanced, and new valves for £118 - On the 19's I'm likely to pay around £70 each for the same tyres.. Or more like £120 per tyre for Eagles or PZero's.. If the look of 17's doesn't offend you, and you're not prepared to pay £100 extra for a set of tyres on 18's, I wouldn't bother upgrading..

Basically what M3NDEREZ said goes....

I can't really feel any difference where bumps are concerned but it does hold the road better now.

I have found with 18" my speedo is now 5% out where before it was 10% which after speaking to a few owners seem to be the general ruling.

If you had 15's then i would say its well worth the purchase to 18's and as you can see below 18's do look better...