Handling Change after 1st service

After 2 years with a Boxter S I upgraded to a 996 C4S. What a difference. It is the best handling car I have ever driven. In 13,500 miles of pushing it hard it had hardly moved on the road until last week. I had only seen the PSM come into play on three occassions; once on mud, once on snow, and once when lifting off over a rise. Last week I had a full service and 2 new (Michelin Pilot) tyres fitted behind. Since then it has slid, slightly, once or twice in every journey. I have seen that PSM light flashing and felt the little slides on around 20 occassions in 1000 miles. Why is this? My guess is that it has to be something to do with having new tyres on the back and not on the front. I know it sounds mad but it has only slid on dry roads. It seems better in the wet. I have checked everything obvious (tyre pressure, wheel nuts, tyre direction etc.) and called the dealer. They said bring it back but didn't really sound like they believed me. They said they would road test it but, to be honest, this isn't going to happen inside the speed limit. M. Migration info. Legacy thread was 31127

New tyres dont perform to their best until they have done 300 to 500 miles. When brand new they are very slippery. This from the Continental tyres site.... Take time to break in your new tires New tires have to be driven a few hundred kilometers on dry roads to rid the tread of parting agents and antioxidants applied during production. Not until the tread has been slightly roughened will the tire be able to make its true gripping power felt. What's more, flooring it and slamming on the brakes can cause tire/rim slip in the first few hundred kilometers of tire use. That's because the lubricant used in mounting the tire has an initial tendency to reduce the adherence of these two parts. You are thus well advised to exercise care with new tires. And keep in mind that winter tires fresh out of the factory will need a bit of time to attain full winter suitability. Migration info. Legacy thread was 31130

You need to scrub in a new set of tyres. It usually takes a few hundred miles but can vary depending on the driving you do. Migration info. Legacy thread was 31152

Thanks for this but these tyres are now well and truly 'scrubbed' in. Does the fact that the back tyres are new and the front was worn (still well and truly legal), in itself, explain my problem. As I said above, it is strange that the car seems to performs better on wet roads. Is this because there is too much grip on the back relative to the front. The slides are minor (so far) but, nonetheless, disconcerting in a car which hardly ever faultered before. Mark. Migration info. Legacy thread was 31155

do you have the same tyres on the front as on the back? e.g. brand and N rating Migration info. Legacy thread was 31168

Yes. Same brand and N rating and same as when new but now 1000 miles on the back and 19000 on the front. What do you think? Mark. Migration info. Legacy thread was 31172

I changed my rears to proper N Pzeros asymmetrico. The first set made the car handle like a squirrel on speed. Got a second set and these are much better. Not as good as my worn out skins previously fitted. No comp from Pirelli... they claim their tires were made correctly. Bridgestones from now on... Pirelli will never again be fitted on my cars... forever. Migration info. Legacy thread was 31181

Maybe you are getting more comfortable with the handling! Migration info. Legacy thread was 31183

Hot dry day today and PSM is working overtime. Seems to be happening most on deceleration int corners rather than when accelerating out. On most severe occasion it felt as if PSM was breaking both front wheels simultaneously and car was standing on its nose a bit. Unless the dealer has made some adjustment to PSM at service (I don't know if that is possible), I feel this must be due to having more grip on the back than the front. If so, it should sort itself in time as the rear tyres wear much faster. Migration info. Legacy thread was 31199

Hi Mark, I had a similar issue with my 993 TT and everyone was pointing at my driving skills.....however after checking the pressures and tread and so on I actually got the wheels re-alligned. This was done by a specialist and the report showed the rear center of gravity pointing just off center. I remember power sliding a roundabout which looked really flash, but this was not intended and although I pushed her it wasn't at the point where I expected the back to slide. Once re-alligned, believe you me this made all the difference. The car felt so tight, like it was just out of the showroom. Maybe worth a try, this can cost up to £200 + from OPC, but well worth it. rgds Rammy '97 993 TT (Black/Black lthr) 408 Original Wild Bavarian Stallions Migration info. Legacy thread was 31200

Thanks Rammy, This car is still under warranty so shouldn't be any cost implications if there is something so severe wrong with allignment. She is due back at dealer next week because of an oil leak so, if they can't find an explanation for the handling change, I'll be having two new front tyres fitted. I'll then be able to tell you all if it was the tyres causing it. Regards, Mark. Migration info. Legacy thread was 31308

Been in to be checked. They have put a software update on the PSM. Still coming into play when least expected on the way home (e.g. at 55mph on a bend behind a renault people-carrier). Surely it must have something to do with having new tyres on the back. Mark. Migration info. Legacy thread was 31641

I was wondering if you'd learned more on this, as this exact same thing has just happened to my BMW 330Ci Sport after having some new Dunlops fitted... I get the DSC light (v similar to PSM) flashing when going through bends at typical speeds- nothing too mad as I'm commuting! Oddly it happens most of all in higher speed bends on relatively neutral throttle rather than in lower speed bends with liberal stabs of throttle to deliberately unstick it to see what happens. I turned off the 1st stage of the DSC to see what was going on, and it was very obvious that it was oversteer rather than the front understeering. As the guys simply fitted the tyres and did nothing else to the car, I am assuming it is because they need to scrub in a bit. Although I have done about 400 miles since, most of it is on motorways where I suppose wear is at a minimum. I'll keep an eye on what happens. My theory is at higher speeds on a neutral throttle, weight transfer to the back is less and more pull to the outside of the bend, hence there is a bit less traction at the back on less sticky tyres. I doubt that changing the fronts would help. Migration info. Legacy thread was 31840

I've experienced exactly the same thing after having my rear tyres replaced on my BMW 325i Sport touring. Originally I had a different make of tyre (to that of the fronts) fitted , but the handling was soooooo wayward that I took the car back after about 1,000 miles and demanded another set of (same make as the front) tyres fitting. This was done at my expense, as I was convinced the original tyres I had fitted (Falken FK451's) were faulty. I had the Falkens sent back to Dunlop (who make them) for testing, but the results came back negative for defects. This wasn't exactly a surprise in the end, as the replacement new tyres (Dunlop sp sports) were just as bad!! I checked everything, and experimented with what must have been 8 to 10 different tyre pressure combinations between front and rear tyres in an attempt to restore my car's once faithful handling characteristics. I've now done about 3,000 miles on the new rear tyres and the situation has only improved marginally. The sensation is almost like the rear end being on castors! Very entertaining, but not good for the nerves! At low-ish speeds (up to 80 mph) the car feels ok, but above these speeds when you really need to start trusting your cars behaviour it's a nightmare! Bizarrely, this affliction seems worse on the left rear tyre than the right rear tyre i.e. through right hand bends. The DSC system, which I normally turn off because I hate it, simply cannot cope. I'm beginning to suspect it might, just might, be a balancing issue, although I can't detect any discernible vibration. A friend has suggested the problem arises when there is a large differential between the amount of tread-block movement between front and rear tyres, but this doesn't explain the difference between left and right hand corners. The car is going back to BMW soon (for good!) as I'm replacing it with a 993 (unlucky dogs!), but I would still be very interested in hearing any opinions on what, it would seem, is quite a common issue. I'm just sorry I can't shed any further light on the subject. Dean. Migration info. Legacy thread was 31846

Hmmmm. Interesting. It would indeed appear that there is a wider issue here. Especially annoying as my 330 was such a sweet handler before. It is discernably more nervous now- less stable through high speed bends and requiring constant adjustment. Then the dsc cuts is and it just feels dreadful and it means I can't carry decent speed through bends. Turning off the first stage of the DSC doesn't seem to help especially as nanny still cuts the power. I wouldn't trust the handling at this point enough to completely switch out the dsc as a high speed snap out of shape is not a good thing... plus there are a couple of times on ice/diesel where the dsc has saved my bacon so I will probably put up with it. The bizzare thing is it is a higher speed issue rather than a low speed one. I'm not optimistic that the dealer will sort it out. I can see the conversation with the dealer now- "our expert road tester technician guru tested it and noted no fault. You are clearly mad sir, kindly leave our premises..." I'll bet you'll be glad to get your 993! Migration info. Legacy thread was 31860