According to evo magazine, the Sti and standard uk car suffered in their lap times considerably due to having 16s rather than the 17 of the RB5 and 22B. Has anyone changed and noticed this improvement on the road?
Does the ride suffer considerably?
Anyone tried 18s?

I am going to reply to my own message just so that it looks like someone was interested in my topic and that I am not a loner, with 0 in the replies column.

I have to say that I kept away from this one because I thought Mike Nunan might reply.

Mike http://bbs.scoobynet.co.uk/wink.gif

OK OK I'll reply as I've just done this change!

Had a Scoob before with 16s (205/50 P-Zeros) for two years and thought it was/they were the dogs danglies. It did have Prodrive suspension as well.

My latest Scoob (got second hand) had 16s with 205/45 tyres (not a misprint). Thought it handled very well, sharp turnin, lack of roll etc. Tyres were knackered so I put on (correct) 205/50 P-Zeros. Hmmm. Squashy feeling from the handling, more body roll. But less harsh ride - noticable even with that small change in profile.

Got 17s and fitted 215/40 A520s. Body roll much reduced, more grip, better turnin etc. Basically better all round. BUT the ride is harsher than before. Personally I can live with this as I prefer the better handling. And decent suspension would cancel most of this - I have stiffer Eibach springs on standard dampers - bit of a mismatch.

Hope that helps

Dave

Hi Adam,

There are three main things to consider when you move up to 17" rims:

1. Unsprung mass will increase by about 1kg per wheel. This causes a slight degradation of the ride quality.

2. You will usually drop the profile from 50 to 45 or maybe even 40. This will improve turn-in as noted, but also make the ride a bit harsher.

3. Because 205/45R17 tyres are not broadly available (Pirelli PZeros are the only option, basically) most people fit 215/40R17s. The extra width means that you will lose a bit of steering feel and suffer more tramlining. You won't get more grip unless you drop your tyre pressures (see previous discussions if you're interested -- we've done this one to death!)

Point 2 is the relevant one really. I've just fitted Goodyear Eagle F1s in 205/50R16 size and they feel less confidence inspiring than the original Bridgestones. I think this is down to sidewall flex. Many people have complained of similar problems with Bridgestone SO2 Pole Positions in that size. I'm planning to try a set of 17" boots at some point to see whether this really is the problem or if it's due to the setting changes that I made on the same day at the tyre fitters.

-= mike =-

(You were right Mike, I had to stick my oar in...)

[This message has been edited by mike_nunan (edited 06-09-1999).]

Hi,

Just to follow-up Mikes reply:

1) I anticipated this and weighed mine before and after. There was no difference in weight between the 16" wheel/tyre combo I had before (6.5x16 Speedline Safari and 205/50 P-Zeros) and the 17s I got. Mind you, the wheels weren't cheap!

2) agreed.

3) I'm sure Mike means 215/40-17....

Dave - in pedantic mode - quiet day at work

Got an STi - a lot of people say the first thing to do is sort the suspension. I disagree. Changing from 16s to 17s has made a huge difference.
Everything has improved, except the ride quality. But that's a small price to pay.
I changed the OE wheels for speedlines - I reckon there's know weight difference.
Only problem now is it needs more grunt!

Mike, there <I>are</I> other tyres available in 205/45x17. In addition to the Pirelli P-Zero Assimetrico, there is also the Yokohama A520, and (according to my local tyre specialist) the Dunlop D9000.

Having said that, as you say, there is a lot more choice in 215/40x17.

I stuck with 205 P-Zeros to keep a matched set.

Having never driven a car on 16"s, I can't make a comparison, but the 17"s seem fine for everyday use. The ride is superb compared to some so-called sports cars I have driven.

Andrew


[This message has been edited by Andrew Dixon (edited 03-09-1999).]

I have a set of 205/45 R17 Dunlop SP9000 on my 17" Superturmiso's. They are reasonable tyres, not great in the dry, not great in the wet, but they are brilliant aquaplaning according to the surveys. I've done nearly 10,000 miles so far, and there's still ample tread left on them.

That said, next time I'll be looking for 215/40 R17 Yokohama A520's! Sod tyre wear, I want grip!!

Andy

Dave -

Aha; that's a very interesting and useful bit of info regarding "point 1". What 17" rims did you choose, BTW?

Oh, and thanks for the erratum (message duly amended now http://bbs.scoobynet.co.uk/wink.gif

AndrewD -

Are you running 205 or 215 width? Also, what d'you mean "keep a matched set"?

-= mike =-

Hi,

What happens to speedo accuracy if you change the tyre size and profile from standard (205/50-16) to 205/45-17 or 215/40-17

CJ

Hi there,

Nothing will happen to the speedo (nothing noticable) because the outside diameter (rolling diameter) stays the same (virtually).

Thats why the larger the tyre size (15, 16, 17) the smaller the profile (30, 35, 40, 45, 50). But the profile is a percentage of the tyres width. Some alloys allow you to change up a size on the width (205 - 215).

Cheers,

J.

CJ,

the difference between 205/50 x16 and 215/40x17 (or 205/45 x 17) is so small that it's not worth bothering about. Both are within 3% (ie less than the difference between a new set of tyres and a half worn set).

The following URL is an excellent little utility for calculating differences in tyre sizes, and their effects in rolling radius etc.

Hi Mike,

I went from Prodrive Speedline Safaris (6.5 x 16) with P-Zeros to Oz Superturismo Evolutions (ala Evo VI and Saj..) with 215/40x17 A520s. The Oz wheels are VERY light. Bugger to clean properly as I found yesterday...

As for speedo accuracy, the overall wheel/tyre diameter does not change enough to put it out. You can calculate the overall diameter yourself from:

D=(WxPx2) + (Sx25.4) mm
where: D = overall diamter in mm
W = tyre width. e.g. 215 or 205
P = profile as fraction. e.g. 0.40
S = wheel size in inches.

So, for a 215/40x17 we have:

D = (215x0.4x2) + (17x25.4) = 603.8mm

I'll leave the rest as an exercise for the reader...

This is the theoretical diameter. In practice they are different. You'll find that the tyre companies can provide you with the actual rolling diamter/circumference of their tyres - they actually measure them.

Dave

Thanks Dave,

Final question: what width are your 17s, 6.5 or 7 inch? Also, have you got LEDA or any other lowered suspension? Just wondering how much you can get away with in terms of wheel-arch clearance.

-= mike =-

Hi Mike,

Wheels are 7x17 ET48 - the same offset as the Safaris I replaced. I also have stiffer, lowered Eibach springs on standard dampers (don't ask - the first owner put them on - I wouldn't have) which, I believe, lower the car by 30mm. I haven't found any problems with wheel arch clearence as yet. Famous last words....

Dave

Cheers. If you're 30mm lower and you're not getting problems, those Eibach springs must be pretty knobbly ;o)

-= mike =-

I have 17" x 7" Speedline Superturmiso wheels with the 205/45 R17 Dunlop SP9000 tyres.

The was lowered by the previous owner using the Prodrive kit. The car was sitting low anyway, then I added some wood and stereo in the boot (anyone who has seen teh car will know) The car sits quite low at the back. The edge tyre is level with the rear arch. With people in the back, you lose some of the tyre in the arch, but there is no rubbing. (except for the ScoobySport backbox on some speed bumps at anything less than a crawl!)

Don't worry about the clearance. If you buy the right offset there will be no problems, even if you do lower it!

Andy

Dave,

Another final question for you http://bbs.scoobynet.co.uk/wink.gif

Did you find out how much the OZs weigh? Elite have told me 20kg, which sounds wrong. Perhaps that's the weight in lbs.

TIA

-= mike =-

Hi Mike,

God it's slow today....

Anyhow, the Oz wheels I have weighed 9kg on my trusty spring balance (nearly new). The tyres (A520s) weighed 9.1kg (according to Yokohama) so Elites number was probably for the combo. I can imagine the Superturismos being lighter than the Polaris wheels.

Cheers

Dave

Thanks Dave.