996 17 Inch tyre fitment

[chappardababbar]

Perhaps I’m a little slow but I don’t feel this isn’t straightforward and I could do with some advice...

I’d like to buy 17 inch OZ allegerita wheels for a NB 996.1 C2.

The standard 17s are 7J front, 9J rear (although in some places I have read 8J). I’m going to stick with these sizes in OZ.
I believe standard offsets are ET50 front and ET65 rear

The question is, what is the correct tyre size for these wheels?

I think it should be 205/50/17 front, and 225/50/17 rear

Is this correct?

[gizlaroc]

205.50.17 F and 255.40.17 R

or

225.50.17F and 265.35.17 R

[g7jhp]

https://www.wheel-size.com/size/porsche/911/1997/#...

[chappardababbar]

g7jhp said:

https://www.wheel-size.com/size/porsche/911/1997/#...

Thank you both, if I understand this correctly does the front tyre at 50mm have a higher profiled (deeper sidewall) than the rear tyre at 40mm?

That can't be right can it?

[gizlaroc]

chappardababbar said:

Thank you both, if I understand this correctly does the front tyre at 50mm have a higher profiled (deeper sidewall) than the rear tyre at 40mm?

That can't be right can it?

The profile is a percentage of the width, being wider it has to be lower to keep the same circumference.

[stewart rix]

The sidewall depth will be the same for both front and back (otherwise the rotating circumference of the tyre would differ)
50% of 205 = 102.5mm
40% of 225 = 102.0mm

[Orangecurry]

chappardababbar said:

Perhaps I’m a little slow but I don’t feel this isn’t straightforward and I could do with some advice...

I’d like to buy 17 inch OZ allegerita wheels for a NB 996.1 C2.

The standard 17s are 7J front, 9J rear (although in some places I have read 8J). I’m going to stick with these sizes in OZ.
I believe standard offsets are ET50 front and ET65 rear

The question is, what is the correct tyre size for these wheels?

I think it should be 205/50/17 front, and 225/50/17 rear

Is this correct?

As above, factory sizes are 7J ET 50 or 55 and 205/50 - rears 9J ET 55 and 255/40.

However, if I were you, as you are choosing your own rims, I'd get 8J fronts and fit 225/45.

Why? Although these cars give telepathic feedback on 205 fronts, IMO/IME the front benefits from a little more grip.... better turn in, and less understeer.

And from a practical point of view, 225/45 tyres are much cheaper and you have a much much bigger choice.

[Scrump]

g7jhp said:

chappardababbar said:

Thank you both, if I understand this correctly does the front tyre at 50mm have a higher profiled (deeper sidewall) than the rear tyre at 40mm?

That can't be right can it?

Yes.

Front is taller but skinnier.
Rear is lower but wuder.

No. As already said the 40 or 50 is a percentage of the width so sidewall height should be almost the same.
The 40 or 50 does NOT mean 40mm and 50mm.

[chappardababbar]

Scrump said:

g7jhp said:

chappardababbar said:

Thank you both, if I understand this correctly does the front tyre at 50mm have a higher profiled (deeper sidewall) than the rear tyre at 40mm?

That can't be right can it?

Yes.

Front is taller but skinnier.
Rear is lower but wuder.

No. As already said the 40 or 50 is a percentage of the width so sidewall height should be almost the same.
The 40 or 50 does NOT mean 40mm and 50mm.

Thank you, I understand it a little better now

[chappardababbar]

Orangecurry said:

chappardababbar said:

Perhaps I’m a little slow but I don’t feel this isn’t straightforward and I could do with some advice...

I’d like to buy 17 inch OZ allegerita wheels for a NB 996.1 C2.

The standard 17s are 7J front, 9J rear (although in some places I have read 8J). I’m going to stick with these sizes in OZ.
I believe standard offsets are ET50 front and ET65 rear

The question is, what is the correct tyre size for these wheels?

I think it should be 205/50/17 front, and 225/50/17 rear

Is this correct?

As above, factory sizes are 7J ET 50 or 55 and 205/50 - rears 9J ET 55 and 255/40.

However, if I were you, as you are choosing your own rims, I'd get 8J fronts and fit 225/45.

Why? Although these cars give telepathic feedback on 205 fronts, IMO/IME the front benefits from a little more grip.... better turn in, and less understeer.

And from a practical point of view, 225/45 tyres are much cheaper and you have a much much bigger choice.

Thank you, great insight. I'm going to read up on this a little more.

[chappardababbar]

gizlaroc said:

chappardababbar said:

Thank you both, if I understand this correctly does the front tyre at 50mm have a higher profiled (deeper sidewall) than the rear tyre at 40mm?

That can't be right can it?

The profile is a percentage of the width, being wider it has to be lower to keep the same circumference.

Got it!

[Orangecurry]

chappardababbar said:

Thank you, great insight.

You are welcome but I can take no credit for this - many people have said as such - I am simply agreeing.

chappardababbar said:

I'm going to read up on this a little more.

A very good idea - you will need to understand a bit about offset as well if you stray from factory sizes.

Another thing many owners do to the OE wheels is to add spacers, especially on the front, to push the effective tyre-patch out slightly wider. However, most people do this for looks (rather than dynamics) as the appearance of the wheel in the wheelarch is less 'inset'.

On the 996, you would decrease the ET number to move the wheel further out.

So for example if you take the factory 7J ET55 front, if you reduce the ET to 50, the wheel would sit 5mm further 'out'. And indeed Porsche did this for the lightweight 10-spoke they put onto the 996.2 as well.

BTW, this is your OE wheel bible, which lists all of the weights as well. Useful for seeing what offsets and widths Porsche chose for the cars.

http://www.944racing.de/wheelweights.php

Thanks again to Florian Seibold for compiling.

[chappardababbar]

Orangecurry said:

chappardababbar said:

Thank you, great insight.

You are welcome but I can take no credit for this - many people have said as such - I am simply agreeing.

chappardababbar said:

I'm going to read up on this a little more.

A very good idea - you will need to understand a bit about offset as well if you stray from factory sizes.

Another thing many owners do to the OE wheels is to add spacers, especially on the front, to push the effective tyre-patch out slightly wider. However, most people do this for looks (rather than dynamics) as the appearance of the wheel in the wheelarch is less 'inset'.

On the 996, you would decrease the ET number to move the wheel further out.

So for example if you take the factory 7J ET55 front, if you reduce the ET to 50, the wheel would sit 5mm further 'out'. And indeed Porsche did this for the lightweight 10-spoke they put onto the 996.2 as well.

BTW, this is your OE wheel bible, which lists all of the weights as well. Useful for seeing what offsets and widths Porsche chose for the cars.

http://www.944racing.de/wheelweights.php

Thanks again to Florian Seibold for compiling.

From a driving point of view - my goal is to maintain or even enhance steering feel so my initial thought is that a wider front wheel, or indeed increasing spacing will take something away from this. This is what I meant but reading up on it more - to better understand the impact of these changes. I want to increase ride plushness as well.

From an aesthetic point of view - I like a chunky sidewall that is slightly inset (pretty much factory inset in fact), with factory ride height.

I'll read up on the 944 page - thank you!

[Orangecurry]

chappardababbar said:

From a driving point of view - my goal is to maintain or even enhance steering feel so my initial thought is that a wider front wheel, or indeed increasing spacing will take something away from this. This is what I meant but reading up on it more - to better understand the impact of these changes. I want to increase ride plushness as well.

From an aesthetic point of view - I like a chunky sidewall that is slightly inset (pretty much factory inset in fact), with factory ride height.

I'll read up on the 944 page - thank you!

Factory sounds perfect for you, and let's face it, Porsche do know a little bit about this subject.

I meant it when I said 205/50 is telepathic - but so few tyres are made in that size now, the trade-off to 225/45 makes a case to consider. Many people on Rennlist for instance simply fit 225/45 to 7J rims, but I never have so cannot comment.

[gizlaroc]

On the 986 I went the other way, I kept the 205 front but dropped the rear to 235 from 255, it felt lighter on its feet, less tramlining and took out 95% of the understeer and made it feel far better balanced over all.

I would happily go 225 front from 205 on the 996, which would keep overall grip levels but also reduce understeer nicely.

I think on 18s I have 235 F and 265 R, same thing really.


You will often get more difference between tyre size wise than you will going 205 to 225, or nearly as much anyway.



Putting on a modern tyre like the PS4 would probably be a proper nice upgrade regardless.