225 versus 235 Front Socks

Time to replace my first set of tyres on the 996. It's got 295/30/18 Pilot Sport 2 N3s on the rear; they're fine and don't need replacing. On the front it's got 225/40/R18 Contis. The fronts are not massively low but there is some inner wear. I had a full alignment done last year and can't remember if the wear was already there or not. Anyway, I'm finding that the car is a bit vague steering wise at the moment, and I noticed even doing some motorway driving that it was very twitchy. If you let go of the steering wheel the car stays pretty straight but the wheel really moves left and right a lot. My plan is to replace the front contis with some new PS2 / PS4s to match the rears. Question: does it matter if I put 225/40/R18 or 235/40/R18 on? I read that 235s could help with understeer a bit, but is there anything else I would need to do to accommodate the extra 10mm? I'm assuming not but wanted to check. Finally, does it matter if I put PS2, PS3 or PS4s on? Is there any significant difference between them?

It's up to you, the GT3 runs 295's at the rear and 235's at the front so if you have a C2 you are pretty much set up like a GT3 for the wheels except of course the GT3 has 8.5" rims at the front rather than 8" for the wider size, I understand on AWD models it can potentially be bad for your system and wear it out but having messed with sizes in my C4S I have had no negative long term effects from changing sizes. Regarding the steering, I'd first make sure your wheels are aligned and balanced but also a 996 is an old pretty analogue sports car, it has a lot of road feedback to the wheel and thats just the way they are, it's not modern electric steering, if you are dailying something more economy or comfort focused, or simply newer it may feel all over the place by comparison but is in fact the way it should be, most Porsche enthusiasts wish Porsche would go back to the old hydrolic steering saying the new cars lack feedback and your wheels are doing this anyway the new systems just make it so you don't feel it in the wheel. Personally I would not deviate from Porsche Specifications, I tried 305's and 315's on the rears of my C4S and both times resulted in the handling feeling somehow wrong and took my confidence away in the car till set back to 295's where is suddenly felt right again. Ultimately having been through messing with tyre sizes I would reccomend sticking to whats factory, I've in the past tried the K&N intake kit, different tire sizes and a host of other non Porsche mods just to end up now with a stock car again but for adding factory options and hollow spoke from the 996 turbo I found Porsche don't just bodge their engineering they optimised what they could and theirs no gains to be made without sacrifices somewhere else or spending alot of money and even though it would match a GT3 spec the rims would not may result in an imprecise feel at the front with more roll in the tire without the rim to support the wider size. Sorry for the long write up, but to conclude I think if you are having problems and don't mind buying tyres twice if you don't like the result go for it, I think they are only around £100 a side or better yet, go to a disount tyre place get both done for second hand cheap try it for a few weeks and decide if you prefer to buy new 235's or 225's. but also may want to try checking your alignment and balance, alignment is free to check at kwick fit and their system is state of the art designed for idiots to do it perfect and balancing is cheap to.

I toyed with the idea of putting 235 tyres on the front (I have 285 on the rear). I read that many comments about it creating masses of oversteer it put me off. If you're geo is correct but a large % of your tyres are worn on the inside (from previous geo) then you've not got full road contact and that will affect grip. Sounds to me more like your suspension needs a dose of looking at with how you've described the steering wheel wobbling, etc. What condition are your shocks in? Are they original or newish? Putting different tyres on won't fix a suspension issue.

Thanks for replies both. I will probably just stick to 225s then. Don't want to cause more niggles. esendia, I have a C4S (see sig). Looks like there is Michelin deal at the moment - £15 discount. Will get some ordered

I've got fairly new suspension, setup by Centre Gravity- the steering wheel does move around a lot when surfaces are less than perfect, but the car tracks straight. As has been said- it's what these cars do. FWIW I'm putting 235's on the front of mine, if of course my new wheels ever turn up. 285 at the back, 9 and 11 inch wheels.

Be interesting to see what the handling feels like.

Got two 225/40/R18 Y PS4s ordered off black circles with a £15 voucher code and mobile tyre fitter coming to my house on Wednesday. Total cost £206 - pleased with that!

with regard to the tyre diameter, you have already upset the front/rear ratio for the 4 wheel drive system with 295s on the rear, however the difference between 295s and 285s is only about 1% and tyre wear can be almost that.

Not sure what you mean - 225/295s are standard on the the C4S, no?

You're right, I have a narrow body C2 and I thought all facelift Carerras had 285s, the diameter difference obviously doesn't matter because the standard C4 has 285s.

When I got my turbo it had gt2 sized tyres,315 and 235. The handling was good. The rear felt unstickable and the car eventually understeered but not until you were really on it. One thing it did do was occasionally it would go into a fast left then right weave under full power. I did find a thread on one of the American forums where a few people had noticed the same. A quick lift stopped it though.Also the rear tyres very occasionally touched the arch liners on the inside. I decided I wanted to try the standard sizes so when my rears wore out I replaced with 295, still with 235 on the front. The car was quite different, the rear moved around more, it was probably more neutral but I had to be careful the back didn't get away from me. One area which was a problem was on hard cornering on long fast corners the psm stepped in too early, cutting power well before it needed too,this really was annoying.I think this was due to the over sized fronts and shows just how sensitive the PSM is to tyre diameter! When the fronts wore out I fitted 225s so back to standard sizes, and not surprisingly the car is neutral and moves around more and ultimate grip is down a bit, almost feels like the tyre pressure is a little low when compared to the gt2 sizes. The PSM is back to normal though and I'm happy with how it drives. One problem with the 315 tyres was they were often a few years old when bought, I think Michelin make them in batches and there are very few cars that use them. I did get a pair ridiculously cheap one time though! Mac