[markcanderson]

My 9000 has standard ride-height (I think..) and on suspension bound the tyres sometimes rub on the plastic wheel arch extensions.. anyone else get that? 16'' Aero wheels with Dunlop SP9000 205/55zr16.

Am I running too high a section tyre? Does my car look lower than it should be?...hmmm

It's not a huge issue.. because it only happens if i'm going a little too quick over some speedbumps.

 

[wrighar]

I don't know which 9000 you are running, but according to saab, you could only ruin that size tyre from 1993 when the CS style came in.

the biggest saab approved size before then was 205/50*16.

Saying that though, I run 225/50*16 on my Aero with no additional rubbing other that an full lock.

Andrew

 

[saabman]

Mark do you mean the wheels hit the plastic sill cover or do you mean the arch moulding?
if it does hit the sill moulding you either have a caster problem or a bush problem as the wheel would have to be moving to far back to hit the sill

Sorry but if you mean the arch I have no idea
Edit: Cheers Mark for editing your post and making me look silly

 

[markcanderson]

The little plastic wheel arch extension lips are being hit.. (and broken in one case)..

It's a model year 1992, CD 2.3 Turbo.

Ahh.. so I should be on 205/50 not 205/55... well that explains it then.. hmmm (damn Saab specialist told me 205/55..)

I guess I'll need to wait until they're done.. and fit the correct size.

 

[1989agoodvintage]

Originally posted by Mark_A:
[qb]The little plastic wheel arch extension lips are being hit.. (and broken in one case)..

It's a model year 1992, CD 2.3 Turbo.

Ahh.. so I should be on 205/50 not 205/55... well that explains it then.. hmmm (damn Saab specialist told me 205/55..)

I guess I'll need to wait until they're done.. and fit the correct size. [/qb][/b]

Yeah, mines on 205/55 with 15 x 7" rims. I have no problems with these.

 

[wrighar]

Yeah, mines on 205/55 with 15 x 7" rims. I have no problems with these.  [/b]

You wouldn't they are 15's not 16's so your an inch smaller in diameter, and the extra 1/2 inch width may help as well pulling the tyre down in the corners.

The CS wheel areches were modded for bigger tyres compared to older 9000's

Andrew

 

[1989agoodvintage]

So a 205/50 R16 doesn't have the same outer diameter and width as a 205/55 R15?! I'm confused.

 

[wrighar]

So a 205/50 R16 doesn't have the same outer diameter and width as a 205/55 R15?! I'm confused.  [/b]

Correct.

The 205 is the set width of the tyre tread in mm based on a particular rim width.

The 50 is the %age tyre rim height of the sectional width (so 50% of 205 is 102.5 mm side wall height.

the 16" rim is exactly that and 16" *25.4 mm to a inch is 406mm.

So the diameter of

a 205/55*16 wheel is 2* (55% of 205) + 406mm = 631 mm, Giving an 1984mm circumference and 504 turns per KM

a 205/50*16 wheel is 2* (50% of 205) + 406mm = 611 mm, Giving an 1919.5mm circumference and 520 turns per KM

A 205/55*15 would be 2* (55% of 205) + 381mm = 606 mm, Giving an 1903mm circumference and 525 turns per KM.

A 205/50*15 would be 2* (50% of 205) + 381mm = 586 mm, Giving an 1841mm circumference and 543 turns per KM.

Also,

For a michelin tyre, in 205/50 ratios, michelin recommend 5.5, 6, 6.5 (optimal), 7 and 7.5 j rim widths,

these rim widths give a maximum inflated section width on the above tyre of 211, 216, 221, 226 and 231mm

Going to the extremes on the riom width will mean that the tyre will not perform as well as it can as it sidewalls will either be nipped or streatched to the rim, effecting the way the tyre lays to the road under load.

Andrew

 

[1989agoodvintage]

Cheers, I've been misunderstanding tyre sizes for the past 4 years. Good thing I don't have to buy too many

 

[wrighar]

That's pretty much it, it's a combination of the width and height.

The wider you go, the shorter they need to be as they stick out more and might hit the arches.

the old 185/65 * 15's were taller than most, but didn't hit as they were thin enough not to foul the edges. (622mm high).

Andrew

 

[mutungi]

With 16" wheels, you should be running on 205/50/16 tyres, it is the 55 which is the problem!

 

[markcanderson]

With 16" wheels, you should be running on 205/50/16 tyres, it is the 55 which is the problem!  [/b]

Yep, I've figured that.. ta!

however.. I'm a bit peeved at the (so-called)saabspecialist who told me to fit 55s instead of 50s...!

 

[southendsteve]

My 91 carlsson is running on 17inch wheels with 215/45/17 tyres with no rubbing at all?

 

[wrighar]

My 91 carlsson is running on 17inch wheels with 215/45/17 tyres with no rubbing at all[/b]

those would only be 625mm tall (somewhere between the height of 205/55 and 205/50 *16's, but becaue of the lowish profile, the absolute tyre width is only 215-220 mm on 7" rims.

So the outside dimentions (width and height) are hardly if at all bigger than other suitable fitments above, (so a valid size for a 9000)

Andrew

 

[Toby Mack]

to make life easy, go to http://www.miata.net/garage/tirecalc.html

lets you put in before and after tyres sizes and compare width and diameter. Also tells you how much your speedo will be affected.
Very useful if you are changing rims/tyres in an way.