Help with a tyre size question please!!

[steve.B]

Ive change my alloys from the standard 997 C2S on 295 tyres as they got damaged to the slightly wided turbo style which carry the 305 width tyres, I would like to know if anyone out there knows if the 305 tyres will fit on my car or do I go for the 295 as someone has said is ok to do.
I have to buy new tyres anyhow but don't want to make a costly mistake.
Thanks.

[sidicks]

steve.B said:

Ive change my alloys from the standard 997 C2S on 295 tyres as they got damaged to the slightly wided turbo style which carry the 305 width tyres, I would like to know if anyone out there knows if the 305 tyres will fit on my car or do I go for the 295 as someone has said is ok to do.
I have to buy new tyres anyhow but don't want to make a costly mistake.
Thanks.

Surely the tyres match the wheels, not the car, so if a turbo has 305 tyres on those wheels, then that is what you should buy.

I was previously under the impression that the C4S had 305 tyres and the C2S had 295s, but I'm sure I've read posts where some C2S owners stated that they had 305 tyres on standard wheels. I'm guessing that the 10mm difference therefore doesn't matter too much, but would suggest sticking with 305s!

Sidicks

[thegoose]

Super Ted said:

The width of your old C2S rim and the Turbo rim are the same - 11J.
So the 305 or 295 tyre will fit OK on the rim. If you bought a Carrera Sport wheel they have 305 tyres on a C2S from the factory.
But you have to make sure the offset is OK - you would have had ET67. Depending on whether your Turbo wheels came off a Turbo (offset ET51 I think) or off a C2S with Turbo wheels (offset ET67) will make a difference.
Potentially the wheels will stick out wider and you have a narrow wheel arch on your car.

Sounds like it's worth checking your new wheels to see how they compare to your olds ones. If they are the same width and offset and the fronts aren't changing then I would stick with what you've had before. I say this because I once changed to wider rear tyres on a 996 C4 because that's all they had available on the day (295 instead of 285 I think) and on the damp trip home down the lanes I could tell there was more grip than before because the car kept understeering - i.e. it had more rear grip than before but the balance was upset by this. Given the choice again I'd stick with the smaller size. Porsche have spend millions developing the car to decide the tyres sizes so their choice should be the best, unless you're changing other aspects of the car's set-up.

[steve.B]

Thanks for your replies, Well the tyres are ordered now and I thought it best to opt for the tyres to suit the rims ie 305's.
Where would I get the offset changed if I find there's a problem??
Footnote... wanted mich'Pilots tyres but would have to wait 4 weeks for the fronts and 2 weeks for the rears and thats from the largest tyre wholesaler in the south according to my local garage.

[Orangecurry]

steve.B said:

Thanks for your replies, Well the tyres are ordered now and I thought it best to opt for the tyres to suit the rims ie 305's.
Where would I get the offset changed if I find there's a problem??
Footnote... wanted mich'Pilots tyres but would have to wait 4 weeks for the fronts and 2 weeks for the rears and thats from the largest tyre wholesaler in the south according to my local garage.

you can't change offset - it is one of the characteristics of the wheel.

OK you CAN change offset by fitting spacers, but you'd have to be insane to put these on a 911.

ETA did you try any online tyre-suppliers?

Edited by Orangecurry on Monday 21st January 17:08

[thegoose]

Costco do Michelins, with a price match I think and at the moment (or v soon) are doing an extra £80 off a set of 4. They should have stock. Otherwise try Protyre Motorsport (official tyre supplier to Porsche Club GB race series), based in Stoke near the Michelin factory.

If the offset is the same as you already have and the rim width is the same as you already have, why risk altering the handling characteristics by changing the tyre width?

[steve.B]

thegoose said:

Costco do Michelins, with a price match I think and at the moment (or v soon) are doing an extra £80 off a set of 4. They should have stock. Otherwise try Protyre Motorsport (official tyre supplier to Porsche Club GB race series), based in Stoke near the Michelin factory.

If the offset is the same as you already have and the rim width is the same as you already have, why risk altering the handling characteristics by changing the tyre width?

Due to damaging two of my alloys I had the chance to buy a new set of turbo alloys which I've been advised by several people will fit my car, I was also told that you can put the 295's on these rims or the 305's the last thing I need is to have a set up problem but I don't know enough about these sorts of things. Am I better than to put the 295's on, are both the wheels the same size and will 10mm make a big difference if so in what way will I know.
Questions..Questions I know. Thanks in advance.

[thegoose]

OK, first you need to know the width and offset of each set of wheels. The width is given as a J number e.g. 11J is 11 inches wide. The offset is given as an ET number e.g. ET57. The widths will be different front/rear and probably the offset will be too.

Probably best to get this info, post it on here and go from there (others may have more experience to advise you, depending on what you tell us).

[steve.B]

Thanks 'thegoose' for your help

[Bob Haywood]

Resurrecting the issue slightly, but I have a particular problem with wider and larger 19" rims fitted to my 2002 3.6 C4, (I think that they are Turbo design); when the car is jacked up, the inner tyre wall hits the lower trailing arm suspension link as the wheel drops inwards and downwards. There is no problem when the suspension is loaded, but it is awkward to refit the wheel after removal. The rear tyres are 295/30/19. I had a similar problem on the front wheels (235/35/19) with new tyres hitting the suspension arm on the running area of the tyre; this was resolved by fitting 7mm spacers. I am wondering if fitting spacers on the rear wheels would assist and if so, what size is recommended? Has anybody faced this problem before?

[Orangecurry]

We cannot possibly help with this unless you tell us the width and offset of your actual wheels.

If they are OE then this will be stamped on the inside face, somewhere. That is your starting point.

Personally on a 996 I would find some 18" wheels, but you didn't ask for that advice.

[Pope]

Bob Haywood said:

Resurrecting the issue slightly, but I have a particular problem with wider and larger 19" rims fitted to my 2002 3.6 C4, (I think that they are Turbo design); when the car is jacked up, the inner tyre wall hits the lower trailing arm suspension link as the wheel drops inwards and downwards. There is no problem when the suspension is loaded, but it is awkward to refit the wheel after removal. The rear tyres are 295/30/19. I had a similar problem on the front wheels (235/35/19) with new tyres hitting the suspension arm on the running area of the tyre; this was resolved by fitting 7mm spacers. I am wondering if fitting spacers on the rear wheels would assist and if so, what size is recommended? Has anybody faced this problem before?

Not wishing to sound alarmist but If the wheel touches ANYTHING unloaded then do not use the car as is - if the suspension unloads naturally when driving, the contact could be much worse. The car would fail an MOT in that condition also.

If you have 10mm clearance from the body to the wheel / tyre on the outside then adding a 5mm spacer and corresponding longer bolts (from a GT3 - red spherical cap under the bolt denotes a 5mm longer threaded section) will resolve the clearance issue by moving the assembly 5mm outwards - statically.

Be wary though.....

The suspension has bushes that flex and twist under specific loads, moving the hub around in the wheel arch markedly - easily breaching a 5mm static clearance.

Taking it too far, you could remove the wheel, then the spring / damper unit and refit the wheel then run the suspension through its full range of movement on a jack - full extension to compression and see what hits / how much clearance you have to play with.

Is the car lowered? 19's would have the effect of bringing the car up slightly, negating the drop. Worth noting that on earlier cars Porsche issued bulletins on fitting larger wheels due to excessive wheel bearing loads (16's to 18's officially - but 19's weren't a thing in the late90's early 00's !!)

[Bob Haywood]

Thank you Orangecurry and Pope.
I can confirm that the rear rims are 11J with an offset of ET67, according to the information on the inside of the rim.
I too had considered going back to 18" rims, but having just spent circa £850 on 4 new Michelins, I was loathe to throw that away. Unless of course I can find anyone who wants to swap a set of eighteens for my nineteens, with almost new tyres!
With the car standing, the gap between the inside of the tyre wall and the rear suspension trailing link is about 25mm. I have to raise the body of the car by about 100mm before the tyre and suspension get too close.
I am quite happy to fit spacers, having now got them on the front wheels, but wonder if 5mm will be enough? Should I go for 7mm or 10mm to be on the safe side?

[Orangecurry]

right erm... I don't know all the 996 numbers without doing a search, but a narrow-bodied 996 had 10J ET65 18" rears as one option, so using those figures as a starting point...

11J are really a WB fitment, but, if you really want to, according to
https://www.willtheyfit.com/index.php?width=265&am...

willtheyfit said:

Compared to your existing wheel, this new wheel will have an inner rim which is 14.7mm closer to the suspension strut. The outer rim will poke out 10.7mm more than before.

So I would think at least a 10mm spacer to be certain, but then will you hit the arches?

[Bob Haywood]

Thanks again Orangecurry.
I was not aware of the 'will they fit' website which looks very helpful.
Measuring by eye only, it looks as though I have about 10mm outward shift before the wheel arch comes into play.
I will probably order two sets of spacers, one 7mm set and one 10mm set and see how they both fit.
I don't want the car to be too far out of spec but I do like the look of the rims so would like to keep them, even taking into consideration the cost of buying 18" rims and new tyres.
It has been a salutary lesson, buying a car that has non-standard equipment fitted without recognising the problems that may ensue!

[Orangecurry]

You may well get away with it, but Pope is not wrong. It only takes one spirited drive, full compression followed by full extension and something may well 'give'.

OE 18" 996 wheels cost buttons, and the so-called MY02 wheel is not only very light (significantly lighter than the 19s you have), they also look great. 18" tyres are cheaper than 19s as well......... do the maths.

[Bob Haywood]

I am conscious of the safety issues, so will consider swapping my 19s for some good condition 18s. Does anybody have any ideas of anywhere I can look to effect this swap?

[Orangecurry]

Bob Haywood said:

I am conscious of the safety issues, so will consider swapping my 19s for some good condition 18s. Does anybody have any ideas of anywhere I can look to effect this swap?

A swap is unlikely, but you never know.

The OEM 19s should be worth a significant amount, if in good condition. I would try to sell them on PH at first. Put the widths, ET and part numbers in the advert.

For buying, as I doubt you are doing too many miles at the moment, I would take my time and watch places like ebay.

Here is your bible for OE wheels - thanks again to Florian Seibold for compiling.

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

Once you have decided which wheel-designs you like, keep a watch on the bay by searching for 'used' 'Porsche 18 wheel' and wade through the rubbish.

Be aware - split-rims may or may not appeal to you, but they cost much more to refurbish properly when the time comes, and may allegedly have been 'professionally' refurbed by an amateur with a rattle-can - they need to be taken apart, and put back together properly.. Which is why I recommended the lightweight single-piece so-called MY02 wheel, which is also period-correct (if you care about such things) on a 2003 car.
Also - boxster versions of the OE 911 wheels are common - they are 7.5/9J width pairs, whereas your car came on 8/10J pairs. Though if you fancy 17" wheels, the correct 996 factory offerings are usually 7/9J pairs, confusingly.

As a starter - there's a decent set of MY02s on the bay at 825 GBP at the moment. If needed, a proper professional refurb (if you go direct) should cost about 350 GBP incl VAT on 4x18 single-piece rims..

FYI - I have bought a ridiculous number of wheels from the bay over the years, and was only sent 1 u/s rim in all that time, and received a full refund when I pointed out the big crack in the barrel - although I have done my homework, and therefore am comfortable with identifying what I want.

Edited by Orangecurry on Monday 22 March 09:09

[Bob Haywood]

Thank you Orangecurry for the good advice.
I shall probably try and sell and buy on e-bay but will try a set of spacers pro-tem to avoid any nasty surprises!

[Orangecurry]

...good plan....

But I would never *sell* on ebay due to the ridiculous charges plus hideous ebay help-centre.... who only exist to tell you 'the computer says 'no'.....'