CUP1 tyre sizes

[db@944s.co.uk]

Hi guys,

Just bought a set of Cup1's yesterday and having had a good look, I'm still not 100% sure of the tyre sizes to order.

The wheels are:

7J x 17 ET47
9J x 17 ET55

I'm thinking 205/55/17 and 245/40/17

Does anyone run these wheels and if so what size tyes do you have?

Thanks

 

[dlknight]

ORIGINAL: db@944s.co.uk

Hi guys,

Just bought a set of Cup1's yesterday and having had a good look, I'm still not 100% sure of the tyre sizes to order.

The wheels are:

7J x 17 ET47
9J x 17 ET55

I'm thinking 205/55/17 and 245/40/17

Does anyone run these wheels and if so what size tyes do you have?

Thanks

993 Cups come supplied with 205/50/17 and 255/40/17. I believe this is correct and maintains the same total rolling radius as standard wheels/tyres.

Regards

Dave K.

 

[944turboS]

You can use this link to check the results of any change in tyre size.

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

 

[Peter Empson]

When I bought my Cup ones they came with the same sizing as you mention (they came off a 911) and I didn't think they were really right for the 944. Nowhere near enough front end grip compared to the rear. I would try to reduce the front to back width difference, you can go as wide as 225's at the front and either stick with 255 at the rear or maybe 245. I ended up with the same tyre sizing as used on the 968 and it suits me perfectly (but i can't remember the exact sizing at the moment, but could check later on if it helps).
It will be worth getting the 968 caster mounts too if you haven't already, they will make a big difference.
Best regards,
Peter

 

[944turboS]

My 17" wheels have 215 fronts & 245 rears.

 

[Guest]

I don't know if Cup1s are the same size as my Boxster alloys on my S2, but I have 205/50s on the front with 255/40s at the back. When I bought it there were 215/45s, or something similar on the front, which were too wide for the wheel apparently.

I would be inclined to agree with Peter, the above sizings result in me being generally more likely to understeer than oversteer, but I can get both!

Graham

 

[mik_ok]

As per Peter - as I understand it the "correct" sizes should be as used on the 968 ~

225/45/17 front
255/40/17 rear

993's do indeed run 205/50 fronts as opposed to the 225's, but they only have approx 33% of the weight over the front.

 

[Peter Empson]

I've just checked mine (I have a terrible memory for numbers) and they are as posted above (thanks Mik).

I hate to add another suggestion, but it might be worth considering fitting some better arb's if you haven't already - you will have a lot more grip now than standard (unless you can find P6000's in this size []) and if you enjoy spirited driving you may find the roll gets a bit too much. They're not expensive either if you get a used set from a Turbo.
Best regrds,
Peter.

 

[JM1962]

I have the same wheel sizes on my S2. I currently have 205/50 and 255/40, but I would recommend 225/50 and 255/40 to help reduce understeer. This site has a lot of useful info on rims and tyres, rolling radius etc http://www.carbibles.com/tyre_bible.html

 

[dlknight]

ORIGINAL: mik_ok

As per Peter - as I understand it the "correct" sizes should be as used on the 968 ~

225/45/17 front
255/40/17 rear

993's do indeed run 205/50 fronts as opposed to the 225's, but they only have approx 33% of the weight over the front.

I was doing some research on this earlier (Porsche PET) and noticed that true 968 Cups are 7.5" x 17" up front, 993 wheels are 7" x 17" so the tyre sizes above may not be correct for 993 cups.

Dave K.

 

[db@944s.co.uk]

Hi Dave,

The wheels are cup 1's, not 993's. I think the front ones were first fitted to a 964 and are date stamped 1993. The rears are Mile Miglia's, date stamped 1998.

Having spoken to the firm we buy the tyres for the garage from and Mytyres.co.uk, they can't give me a definite size, so i'm no further forward.

Thanks for all the effort you guys have put into this thread.



Derek

 

[Peter Empson]

Dont worry about the fronts being 7" wide running 225's, that's exactly what I have as my wheels also came off a 911 and I know of several others using the same combination.
I use toyo T1-R's and on their website it gives the max width their tyres are safe to run on and this combination is listed as being fine (I've done many road and hard track miles and have had no issues either).
Best regards,
Peter.

 

[burrow01]

What would be the rolling diameter of the original wheels?

Ideally whatever tyre size you choose should not change the diameter, to ensure the ABS etc still functions correctly

There is a calculator here:

http://www.1010tires.com/TireSizeCalculator.asp

Pete

 

[Fen]

225 and 255 are the sizes to use. All 911 cup wheels are 7" front but that is big enough for 225 section tyres. The 968 7.5" cups have an offset that actually puts them further inboard in spite of that (by 3mm IIRC)

 

[mik_ok]

Link mentioned above for Toyo tyres and rim widths CLICK HERE

As stated by Fen & others, 225's are fine on a 7" front rim. (my Leon has also runs 225/50/16 on 7" rims for years without issue).

 

[Diver944]

ORIGINAL: mik_ok

As stated by Fen & others, 225's are fine on a 7" front rim.

and the narrower 7" rims are lighter.........................probably []