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911 C4 GTS scary in heavy rain


PCGB Member
I've just returned from a great trip from the Midlands, in my 991.2 C4 GTS, to Lake Maggiore, a 2,500 mile trip, enjoying a great drive over the Simplon Pass. The car performed very well until I arrived back in the UK yesterday. The heavens opened and torrential rain came down with a lot of surface water on the M40. The car felt very scary then, it was tramlining and felt like at any point it was going to aquaplane. At the heaviest rain I kept the speed down to 60mph, but numerous vehicles, SUV's, Vans, small hatchbacks were passing me at speeds up to 90+mph, the visibility was still ok for those speeds. But I never felt safe to push the car any faster until the rain reduced. The tyres are all as OEM standard with lots of tread. I've read online it may be alignment, suspension or the traction control system that was making the car feel unstable to me. Can anyone offer any suggestions or should I be taking it into and OPC for a health check, the car has done approx. 20k miles. Thanks
I agree that it will be worth getting the geo checked but tyres may also be an issue.

I found that the Pirellis (N rated) were not very good in heavy rain and a change to Michelin PS4s has helped to improve wet weather stability. However, 315 tyres are never going to cut through standing water as well as normal size/narrower tyres!
Assuming you are confident you actually do have plenty of tread on all four tyres, there are still two vital bits of information missing from your post;

(1) what were your tyre pressures at that moment of time? (2) what is the actual make of tyre? OEM is not really helpful.

You have wide tyres on your vehicle (particularly at the rear). If tyre pressures are too low for the conditions it is possible for water to become trapped in the centre of the tread pattern which in turn can lead to aquaplaning at lower speeds than would otherwise be the case at correct tyre pressures. Some makes of tyre perform better than others in wet conditions. The softness of the rubber & the tread pattern are vital components in providing good performance in very wet conditions. However excessive surface water can overwhelm even the best tyres, so slowing down to a safe speed is always the best option.

If you slowed up to around 60 mph (very sensible), were you travelling in Lane 1 of the Motorway? If you were, most cars will "tramline" in lane one (even in the dry) because over loaded lorries have cause a rutted carriageway. In heavy rain, Surface Water builds up worse in lane 1 than lane 2 or 3. Even if you a slowing up to a safe/sensible speed, in these conditions I recommend that you travel in Lane 2 whenever possible (but still watch your mirrors) & only use Lane 1 when absolutely necessary.

Regardless of all of the above, it will be well worth getting a full geometry set-up done on your car. There are some skilled Independent Companies that will provide better advice & a better "set-up" to suit you than is generally available from an O.P.C.

If "white van man" thinks it is safe doing 90 mph in the wet, the only thing to do is stay well away from him & hope he is arrested before he causes a serious accident.

Best of luck

Gary Marsh

07768 997050
I had the tyres set before the trip to 32 front, 39 rear. They are Pirelli PZero (N). There were two on board and luggage in front trunk and on rear seats, baybe the tyres should have been on higher pressure? I was travelling in both lane 1 and lane 2 (when passing lorries). Thanks
garymarsh said:
Even if you a slowing up to a safe/sensible speed, in these conditions I recommend that you travel in Lane 2 whenever possible (but still watch your mirrors) & only use Lane 1 when absolutely necessary.

Great post Gary and I agree with everything you say, but isn't centre lane hogging illegal? :rolleyes:



Hi, I've been in touch with Center Gravity, they're extremely busy with earliest booking dates available being late August. Do you know of any other similar companies? Thanks
Suggest you book in for their first available date and ask for any cancellations, which they do get from time to time.

And whlle we're on the subject of wet weather driving, we were on the motorway system yesterday, M4/3/25, and the weather was also dreadful. And yet many cars had no lights on at all, but also many had their Daylight Driving Lights on at the front, but of course, no rear lights. Saw only one person with fog light on when it was particularly bad visibility.
I'm sure many drivers don't realise that when their daytime running lights are on their rear lights aren't, we also saw many of them.
As tscaptain and pwebb have suggested, you would be advised to book in with Chris Franklin at Center Gravity. Many seasoned PCGB campaigners have found significant improvements in both handling and roadholding once the magic has been worked.

It's an individual, bespoke service offered with the setup work persevered with until you're completely happy with the results. You will be impressed! [:)]



AndrewCS said:
Greenman986S said:
Scrounger said:
Suspension Secrets are the ones to use in the NW so I'm told.


maybe not...

No access permitted, can you post up the content / context please ?

Not my post but I have copied verbatim from

I had a full set of coilovers fitted to a 987 and during the installation needed numerous hubs as they couldn’t disassemble. The garage struggled to get the suspension apart. After a couple of delays the install was done.
On receipt of the car
* one of the rear brake shoe retaining clips was loose and chewing up the inside of the hub. The car was returned. They declared it’d been fixed but after 7 miles of driving home the same issue returned. I fixed it myself and got a token of compensation from the garage.
* All the suspension boots on coffin arms/toe arms etc that had been removed were either nicked or split in the process of disassembly. Some of the coffin arms were only 6 months old. Additionally the garage did not inform me about any of these problems either during or after the install but passed the work of as done.
One month prior to the install the car had passed it’s MOT.
In summary..
They damaged suspension parts which became an MOT failure.
The cost of fixing this was over £1600
They opted to hide the finished state and let the customer deal with an unroadworthy car
I believe that these guys can tweak setups and are probably good at doing so, but don’t have the ability to fit new parts with care or skill.

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