18" vs 17"

[TorpedoCreative]

Im a little confused...
the 17" rims come with 215/45/17 tyres
the 18" rims (spec B) come with 215/45/18 tyres

does that mean the overall rolling diameter is bigger for the Spec B's? Does that have an affect the performance?

Im about to buy some spec B rims and want to know what size tyres I should be fitting to them? If I go smaller ie 40 series, will that have any adverse affects (eg the speedo accuracy etc)

cheers

James

[04GT]

I always thought 18s had the profile tires of 40s
then 19s profile of 35s
and 20s profile of 30s

[swingn]

In 2005 / 2006 the STI tuned models came with the 18's but still kept the 45 profile. By he sounds of it they are still doing the same thing. Guessing it has something to do with trying to keep the ride quality nice with all the lower & hard suspension... Can anyone shed anymore light on that one?

I'll see if I can find it in my old motor mags, but in their reviews they basically said that the standard GT's were quicker 0-100 because the rolling diameter was larger.

If your buying 18's I'd make sure you put the right profile on there i.e - 40. Its what I'll be doing when I eventually get rims

[tangcla]

The 18" Spec.B wheels I have now are 215/45/18 - when my new wheels come, I should be using 225/40/18.

[04GT]

If i had 18s, i'd put on 35s cos they look cool

but if i do end up getting 20s, i'll put 30s

[OzSTi]

Im a little confused...
the 17" rims come with 215/45/17 tyres
the 18" rims (spec B) come with 215/45/18 tyres

does that mean the overall rolling diameter is bigger for the Spec B's? Does that have an affect the performance?

Im about to buy some spec B rims and want to know what size tyres I should be fitting to them? If I go smaller ie 40 series, will that have any adverse affects (eg the speedo accuracy etc)

cheers

James

You're right that both the 17" and 18" rims had 45 profile tyres. I assumed Subaru had altered the final drive ratio to compensate. I wonder if they got the speedo calibration wrong and stuffed up our speedos in the process.

Anybody got a standard (non-spec B) GT out there? Can they comment on their speedo accuracy as it's now well documented how the spec B's are 'out' the best part of 10%.

When I replace my tyres I'll go up a bit to 225/45/18 although this wont even half fix the speedo error, it'll go some way.

[senator]

if your thinking 18"s get 45's, currently the 08 gt spec b tb sti come with 40's not the best option if you doing alot of kms on country roads.

[OzSTi]

if your thinking 18"s get 45's, currently the 08 gt spec b tb sti come with 40's not the best option if you doing alot of kms on country roads.

Are they 40 series? What width?

[CJ1177]

I asked a good snr Subaru mechanic prior to getting my 20s asking if there was any difference in the speedo or speed sensor computer settings etc, I gained his genuine interest & he got back to me with there all the same no matter what size wheels (17" or 18"), so the 17" wheels are the most inaccurate with the larger 18" taking up some difference.

& 04GT trust me unless you have had 30 series tires DONT get them

[Arith]

Are they 40 series? What width?

I think it was posted that the STi's came with 225/40-18.

[overl0ad]

http://www.miata.net/garage/tirecalc.html

wheel size calculator. really good as it tell you the difference and any variance in your speedo