different tyre sizes and profiles
Discussion
Chaps,
Can anyone help with this dillemma.
I run a 1991 Porsche Carrera 2, and want to purchase some Dunlop super sport race tyres, after all the good press I have heard about them on this forum.
The only problem is that the tyre size and profile for the front is not exactly the same size as oe fitment.
Standard size is 205/50/zr/17.
The smallest size Dunlop do is 215/45/17, which actually measures 219mm with a diameter of 620. I dont know the actual measurement of my current tyre which is a Pirelli Rosso N3. i just dont want to mess up that great steering.....
any advice would be great
Thanks
Can anyone help with this dillemma.
I run a 1991 Porsche Carrera 2, and want to purchase some Dunlop super sport race tyres, after all the good press I have heard about them on this forum.
The only problem is that the tyre size and profile for the front is not exactly the same size as oe fitment.
Standard size is 205/50/zr/17.
The smallest size Dunlop do is 215/45/17, which actually measures 219mm with a diameter of 620. I dont know the actual measurement of my current tyre which is a Pirelli Rosso N3. i just dont want to mess up that great steering.....
any advice would be great
Thanks
Will,
I'm about to make exactly the same purchase. I don't think the fitment will be a problem. There is a slight possibility that the fronts may rub on the inside (wheel arch clearance should be fine), but if you have the 10mm steering stop upgrade (if your car came from the factory with 17" wheels then you will have the upgrade - if not then who knows ???), then it should be ok. Also there is no 255/40/17 for the rears, so you'll have to use the 245/40/17 - which again should fit fine.
There are two issues here :
1.) The handling dynamics will change subtly as the ratio of front to rear width is changed - should help turn in, but possibly will make it more nervous and prone to oversteer.
2.) These tyre sizes mean that the rolling diameter of the wheel is reduced slightly due to shorter sidewalls. This may make the ride more harsh (depends on the stiffness of the sidewalls). There will be a tiny improvement in accleration (gearing effect) and your speedo will over-read by a greater margin.
Have a look at this handy site - v. helpful for comparing tyre and wheel sizes.
www.miatanet.com/garage/tirecalc.html
Overall I think it's worth trying out as the Super Races are so cheap.
Good luck !
Jamie
>> Edited by Jamie Summers on Monday 28th February 14:21
I'm about to make exactly the same purchase. I don't think the fitment will be a problem. There is a slight possibility that the fronts may rub on the inside (wheel arch clearance should be fine), but if you have the 10mm steering stop upgrade (if your car came from the factory with 17" wheels then you will have the upgrade - if not then who knows ???), then it should be ok. Also there is no 255/40/17 for the rears, so you'll have to use the 245/40/17 - which again should fit fine.
There are two issues here :
1.) The handling dynamics will change subtly as the ratio of front to rear width is changed - should help turn in, but possibly will make it more nervous and prone to oversteer.
2.) These tyre sizes mean that the rolling diameter of the wheel is reduced slightly due to shorter sidewalls. This may make the ride more harsh (depends on the stiffness of the sidewalls). There will be a tiny improvement in accleration (gearing effect) and your speedo will over-read by a greater margin.
Have a look at this handy site - v. helpful for comparing tyre and wheel sizes.
www.miatanet.com/garage/tirecalc.html
Overall I think it's worth trying out as the Super Races are so cheap.
Good luck !
Jamie
>> Edited by Jamie Summers on Monday 28th February 14:21
Thanks for that jamie, but I am not that convinced about more oversteer and the wheel rubbing on the inside doesn't fill me with much confidence.
I already think the thing wants to swap ends at the best of times! But i am running crap tyres at the rear....
Just as I posted my question I found this tyre calculator on this site(who are supposed to be good for porsche tyres by the way)
www.montyswheelsandtyres.co.uk.
Have you fitted the Dunlop SSR's to your nine yet? and if so, what does it feel like?
Thanks
Will
I already think the thing wants to swap ends at the best of times! But i am running crap tyres at the rear....
Just as I posted my question I found this tyre calculator on this site(who are supposed to be good for porsche tyres by the way)
www.montyswheelsandtyres.co.uk.
Have you fitted the Dunlop SSR's to your nine yet? and if so, what does it feel like?
Thanks
Will
Will,
I don't think that the differences will be that dramatic. Overall the increase in overall grip should outweigh any issues at road speeds. The change in dynamics I imagine will only really be apparent at the limits on track. I just don't think it's worth worrying too much about.
I haven't bought the tyres yet, but intend to in time for the Bedford trackday on Mar 25th.
Jamie
I don't think that the differences will be that dramatic. Overall the increase in overall grip should outweigh any issues at road speeds. The change in dynamics I imagine will only really be apparent at the limits on track. I just don't think it's worth worrying too much about.
I haven't bought the tyres yet, but intend to in time for the Bedford trackday on Mar 25th.
Jamie
Jamie,
I was thinking of doing that track day too at Beds on the 25th, with my girlfriend in her mint 968CS! maybe I sit behind you for a few laps and check your progress.
The car is running Pirelli Rossos at the front, and Pirelli P6000 at the rear shock horror! and feels particularly nasty.
These were put on brand new when I bought the car from a so called "specialist" dealer put on probably to get rid of me out of the showroom no doubt.
I havent written the Dunlop idea completely out though.
I am no tyre purist extolling the virtues of this and that brand, when the average layman driver probably couldnt tell the difference anyway unless as you say they are
a) On a circuit
b) At the limit
c) A very consistent driver
I just want something that grips well, feels good at most speeds and lasts a reasonable amount of time.
Are you going to the Oulton Park track day on the 5th?I understand there may be quite a few 964 rs and other nines punting around.
I am in the area so and may go and watch.
Regards
Will
I was thinking of doing that track day too at Beds on the 25th, with my girlfriend in her mint 968CS! maybe I sit behind you for a few laps and check your progress.
The car is running Pirelli Rossos at the front, and Pirelli P6000 at the rear shock horror! and feels particularly nasty.
These were put on brand new when I bought the car from a so called "specialist" dealer put on probably to get rid of me out of the showroom no doubt.
I havent written the Dunlop idea completely out though.
I am no tyre purist extolling the virtues of this and that brand, when the average layman driver probably couldnt tell the difference anyway unless as you say they are
a) On a circuit
b) At the limit
c) A very consistent driver
I just want something that grips well, feels good at most speeds and lasts a reasonable amount of time.
Are you going to the Oulton Park track day on the 5th?I understand there may be quite a few 964 rs and other nines punting around.
I am in the area so and may go and watch.
Regards
Will
Will,
Oulton's a bit of trek for me, but will see you at Bedford on the 25th. I think the Dunlops might not be such a geat idea for road only use. Granted they are very cheap, but they only have 6mm tread from new and certainly won't be as good in the wet on the road as a 'normal' road tyre and will wear pretty quickly. I decided to go for the Super Races because I'm bored with changing wheels over for trackdays - so they're a bit of a compromise for track and road use - but I'm well aware of the likely limitations.
Come and say hi at Bedford and jump in for a lap or two if you want. Slate grey C2 reg G747 CHP.
I've got some pretty tired 'Rossos' on my car at the moment which seem fine. If your tyres are new I'd be tempted to buy a new set of Rosso rears and try to sell the P6000s. I need to change all four as they're on the wear bars, so thought I'd try something new.
Jamie
>> Edited by Jamie Summers on Tuesday 1st March 17:45
Oulton's a bit of trek for me, but will see you at Bedford on the 25th. I think the Dunlops might not be such a geat idea for road only use. Granted they are very cheap, but they only have 6mm tread from new and certainly won't be as good in the wet on the road as a 'normal' road tyre and will wear pretty quickly. I decided to go for the Super Races because I'm bored with changing wheels over for trackdays - so they're a bit of a compromise for track and road use - but I'm well aware of the likely limitations.
Come and say hi at Bedford and jump in for a lap or two if you want. Slate grey C2 reg G747 CHP.
I've got some pretty tired 'Rossos' on my car at the moment which seem fine. If your tyres are new I'd be tempted to buy a new set of Rosso rears and try to sell the P6000s. I need to change all four as they're on the wear bars, so thought I'd try something new.
Jamie
>> Edited by Jamie Summers on Tuesday 1st March 17:45
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