Steering geometry check - a query.

My 996C4 suffers from a slightly jittery ride on motorways which I'd always put down to wide-tyre tramlining but have noted from other posts that it may be something more than that. I've tried tinkering with tyre pressures and find the manual's recommended 36/44 best. Various posters have stated that part worn Pirelli Zeros cause the problem - mine are down to 4.5mm and they are 5 years old. Others have said that a steering geometry check might be a remedy. My query is .......... Is it worth me getting a steering geometry check done with my car running on my part worn tyres?

This is my experience. My 2003 996 Carrera never tramlines which I was suprised as my previous car a BMW 3 series was terrible. I have just replaced my rear Pirelli P Zero Rossos 285/30/18 as they had 2mm of tread and they were fine. When I replaced the previous tyres I had a geometry check done by the OPC to make sure everything was OK on their recommendation and as the car was virtually spot on they only charged me half price.£100 instead of just over £200. I keep my tyre pressures at Porsche recommendation. Probably worth you having a geo check.

Might as well have a geo check- it won't be affected by new tyres as and when and it can only help, for peace of mind if nothing else.

Is it true that if the geo was significantly out then it would be apparent because you would get a unusual/ uneve tyre wear? Or is that complete tosh? Or sort of true but only if the geo was miles out?

Your are right in both cases! In 90% of cases, a car with abnormal geometry will have uneven or odd tyre wear. However, there are suitations where it is only slightly out, for example on the rear if there was a bit too much negative camber and a bit too much positive toe in then the tyres may wear evenly albeit quicker. Because the 911 has such a sensitive steering and responses, if the geo is slightly out you may feel the car behave differently even thought the geo is not miles out. Be careful where you take it though as some places are happy to set everything within limits which is probably fine in another car but in the 911, setting it to to the extremes of normal may still cause it to behave oddly.

:agree: with Min. A small amount of toe-out on the front or rear can make a 911 feel distinctly jittery, which may be the OPs problem.

Not a GEO expert at all but had my C2 done recently after a new steering assembly was fitted. I suppose I was just used to the previous set up but always felt a little nervous on fast sweeping bends, and it did feel like it was looking for every groove in the road to follow. Also noted that the rear tyres wore on unevenly on the inner side. After the GEO ( factory settings reset) the steering feels rock solid and fantastic, really gives so much more confidence. The only down side is the rear does not feel quite so unshakable as before. I suppose I am now wanting it slightly finer tuned. Finally I must be getting it? As a passing Q: what kind milage are people doing in theirs as a guide, I cover around 1200 a month. M :grin:

If the steering feels light at speed it's worth checking your ride heights as well...nose should be slightly lower than the rear. If the car just feels vague then a geos a good plan but checking ride heights is free :lol:

Thanks for all your comments chaps. My original post was made whilst my car was in an OPC for a major service. I deliberately didn't mention my query to them as I wanted to test the quality of their menu priced service without any prompting from me for potential 'add-ons'. I pre-booked a spark plug and brake fluid change as I had no evidence that this had been done in the previous four years. The only significant thing they raised was that 3 ignition coils were showing signs of perishing and might cause misfiring in damp weather. They quoted £121 incl vat and said they wouldn't charge any extra for labour so I had them done. Driving home the difference in the car was obvious and I looked forward to my regular Sunday morning empty road, cross country 'blat' with even more excitement than usual. I was not disappointed. A combination of far crisper engine response and far more effective braking made it seem like a new (or at least much newer car). The final point of my review was to see if the car felt any different at steady motorway speeds. Previously under acceleration all had been well but at any consistent speed the overall feel of the car had beeen disappointing. Nothing specific that I could describe properly but just 'not quite right' - hence my tyre wear/GEO query. On Sunday I spent 25 miles trying to replicate the issue - at various 2 digit steady speeds - and aside from a slight jiggle of the steering wheel, only evident through my palms when not gripping the wheel everything seemed fine. My conclusion therefore is that my car was just 'tired' and in need of some lubing and minor adjustments and/or that the engine was perhaps not firing at 100% on all cylinders. Given the above, the fact that I don't do much motorway driving anyway and that there's no sign of uneven tyre wear I'm going to postpone a GEO check for now but will get it done when I replace all 4 tyres next Spring. Thanks again. T8

Once again the views of the experts on here have proved to be spot-on. After getting caught out in the heavy rain last week and figuring that even if I don't do many miles in the next few months there's a good chance some/most will be in the wet I bit the bullet and replaced my knackered PZeros with new ones. As I'd shelled out nearly £700 the good lads at my local STS Tyrepros said they'd do any adjustments that their Corghi laser beams said were needed for £20 each. Sure enough the 'half-toe' on both the front and rear axles were well out and one other small adjustment was needed despite no obvious signs of uneven tyre wear. I don't normally enjoy motorway driving but as it was the simplest way to Windsor on Sunday I took the opportunity to run the tyres in a bit and looked forward to seeing if I could notice any difference. The result was amazing. The car felt 5 years newer. Quieter, completely stable and no jitters at all. I know that the geometry changes will not have been done perfectly but they are now within the Corghi databank tolerances and are way better than they were. For £60 I think I got a great deal. Thanks again all :thumb: