how will different size wheels affect gearing?

[V8Smith]

Just got the new Chimaera wheels with 16inch wheels at the rear and they came with 225/16ZR55 S-O2 tyres! This makes the wheels bigger than the old 15inch as to keep the same size you need 45 or 50 series (not sure which one?). The tyres have lots of life in them so dont want to change them straight away if I can help it, how will this affect the cars performance in the meantime?? It also makes it very tight in the wheel arch!

Mike

[bugsy]

Mike
If the overall diameter of the wheel and tyre is larger, then I'm certain that your car will be slightly higher geared.
If I understand it right, it doesn't normally matter because the profile is smaller on these low profile tyres but in your case you haven't gone this route.

Derek

[M@H]

Thats a slightly bizzare rear tyre size isn't it..? (IMMSMC)

I had 205/55/15's on the front of my old chim and 245/45/16's on the back.. a 225/55/16 is quite a tall tyre, what have you got on the fronts..?

Cheers,
Matt

[V8Smith]

M@H said:

Thats a slightly bizzare rear tyre size isn't it..? (IMMSMC) I had 205/55/15's on the front of my old chim and 245/45/16's on the back.. a 225/55/16 is quite a tall tyre, what have you got on the fronts..? Cheers, Matt

Yes I thought it was an unusual size, I assumed it would be 225/50/16! On the fronts I have the normal 205/60/15!

Mike

[19560]

V8Smith said:

16inch wheels at the rear and they came with 225/16ZR55 S-O2 tyres! This makes the wheels bigger than the old 15inch as to keep the same size you need 45 or 50 series (not sure which one?).

50 series for 16" wheels and 45 series for 15" wheels, both assuming that you keep 205/60/15 on the front.

V8Smith said:

The tyres have lots of life in them so dont want to change them straight away if I can help it, how will this affect the cars performance in the meantime?? It also makes it very tight in the wheel arch!

It makes a 4% error which is generally condsidered to be too much. You need to decide what you want to end up with finally. If you fit 205/55/15s to the front then you may want 225/45/16s on the rear.

>> Edited by 19560 on Wednesday 2nd March 06:58

[NicBowman]

Hi Mike - 205/60/15 should be diameter 627mm, 225/55/16 will be 654mm. You will therefore reduce the revs by 4% ish, so 2500rpm in top will now become 2400 at teh same speed. This will put the speedo out by the same percentage. The car will also be 1/2 inch furher from the ground!

Nic

[Rockey]

If you want a definitive answer use this link
www.miata.net/garage/tirecalc.html

[V8Smith]

Thanks guys yes I thought it would be 45 series, but according to that website its 50 series (or 45 series if I fit 245 width tyres) so will buy them when needs must, but will leave it for now knowing its 4% out? I know this will make the car have a faster top end but will it make it accelerate 4% faster or is there more to it than that?

Cheers

Mike


>> Edited by V8Smith on Tuesday 1st March 14:40

[19560]

V8Smith said:

Thanks guys yes I thought it would be 45 series, but according to that website its 50 series (or 45 series if I fit 245 width tyres) so will buy them when needs must, but will leave it for now knowing its 4% out? I know this will make the car have a faster top end but will it make it accelerate 4% faster or is there more to it than that?

Hi, I had a bit of a blip yesterday lunchtime but edited now. It's doubtful that your rims will take the 245 width. Your car will now accelerate more slowly (approx 4% but torque curves come into play,) and the suspension angles will be upset and won't work as well. As long as the tyre doesn't rub and you don't drive too fast then you should be OK. J

[NicBowman]

accelerate 4% slower I'm afraid. But relaxed cruising.

Nic

[M@H]

19560 said:

Hi, I had a bit of a blip yesterday lunchtime but edited now. It's doubtful that your rims will take the 245 width.

I had 245's on my standard 16" rims.

[19560]

M@H said:

19560 said: Hi, I had a bit of a blip yesterday lunchtime but edited now. It's doubtful that your rims will take the 245 width. I had 245's on my standard 16" rims.

We don't know the rim width of V8Smith's wheels but the 350i and V8S both run 7" rims and 245 is too much of a stretch to fit.

Ideally a 245/45 will run an 8.5 or 9" rim.

The Griff/Chimp was designed for and originally had fitted a 225 rear tyre. Later cars were fitted with as wide as the 245 but it is usually considered to be far from ideal.

[M@H]

OK I give up

(Mikes Got Chimaera wheels as per his post, therefore a 7.5" rear)

>> Edited by M@H on Wednesday 2nd March 16:00