2 very weird problems, any ideas? (996 C4)- resolved!

[orangecurry]

Glad you've got it sorted. :thumb:

What were the previous/new tyres? Same make/model/everything?

 

[FLGirl]

Glad you've got it sorted. :thumb:

What were the previous/new tyres? Same make/model/everything?

:bye: Hi mate. When the rears were changed it was to exactly the same make, and the fronts had plenty of wear left! No idea why that should unsettle the car so much, but it appears it did!

Just spent another 3 hours cleaning & polishing in preparation to meet some other Porks on Sunday, what are the chances of her staying gleaming on my drive up to London :grin:

Thanks again all.

 

[orangecurry]

Are they P-zeros by any chance? Did the garage/Paragon say how old the original ones were?

 

[clinchy993]

Glad you've got it sorted. :thumb:

What were the previous/new tyres? Same make/model/everything?

:bye: Hi mate. When the rears were changed it was to exactly the same make, and the fronts had plenty of wear left! No idea why that should unsettle the car so much, but it appears it did!

Just spent another 3 hours cleaning & polishing in preparation to meet some other Porks on Sunday, what are the chances of her staying gleaming on my drive up to London :grin:

Thanks again all.

What porky meet is this weekend :?:

 

[FLGirl]

Are they P-zeros by any chance? Did the garage/Paragon say how old the original ones were?

No, the tyres are Michelin Sport Contact 2 all round. The last invoice for tyre fitting is 2007 for new rears, so I guess the fronts were older, although they weren't massively worn.

clinchy993 - tis a mini meet organised on another forum I use. Is just a very small gathering this time

I'm just so happy to have my car back ance-Tap:

 

[Wattie]

Glad you got it sorted, but I am surprised it made this much difference just changing the tyres unless there was a big difference in tread depth and/or tread pattern.

However, the 4WD system on a Porsche is very sensitive to different levels of grip front to rear as it is set up to respond quickly at very high speeds to transfer more drive to the front. Most 4WD systems are designed for low speed response only and allow quite a lot of wheel slip before they lock up the centre diff, but the Porsche one is set up to respond quickly at speeds up to v-max!!!

I guess this is a lesson to us all to take the warning in the handbook seriously: It seems you can't mix tread types and/or depths between front and rear axles!

Just out of interest, are all the tyre sizes original spec? I know some people fit 295s on cars originally specified with 285s for example...

 

[FLGirl]

Glad you got it sorted, but I am surprised it made this much difference just changing the tyres unless there was a big difference in tread depth and/or tread pattern.

However, the 4WD system on a Porsche is very sensitive to different levels of grip front to rear as it is set up to respond quickly at very high speeds to transfer more drive to the front. Most 4WD systems are designed for low speed response only and allow quite a lot of wheel slip before they lock up the centre diff, but the Porsche one is set up to respond quickly at speeds up to v-max!!!

I guess this is a lesson to us all to take the warning in the handbook seriously: It seems you can't mix tread types and/or depths between front and rear axles!

Just out of interest, are all the tyre sizes original spec? I know some people fit 295s on cars originally specified with 285s for example...

My italics, but this is pretty much what Paragon said. In fairness now I've double checked, the fronts were at least 3 years old & although the tread looked fine I guess it was enough of a difference to unsettle the car.

Tyres are original size (posted up on pg3).

Now I'm getting excited about taking her again

 

[clinchy993]

Are they P-zeros by any chance? Did the garage/Paragon say how old the original ones were?

No, the tyres are Michelin Sport Contact 2 all round. The last invoice for tyre fitting is 2007 for new rears, so I guess the fronts were older, although they weren't massively worn.

clinchy993 - tis a mini meet organised on another forum I use. Is just a very small gathering this time

I'm just so happy to have my car back ance-Tap:

Ahh the PH London meet (10 only),Give me twisty country roads any day much more fun

:grin:

Have a good one :thumbs:

 

[Nick B]

FLG - glad to hear the matters have been sorted. I've followed the thread out of interest since driving a 4wd variant myself and had very isolated PSM intervention on the whole.
Thanks for comprehensively updating the outcome, it's so annoying when threads just seem to 'hang' with no closure.

 

[JRR1967]

Interesting thread.

I noticed some difference in behaviour when putting new rears on my 4S a few months ago, but nothing quite as extreme as that.

Useful info.

 

[FLGirl]

Well, I can comprehensively say the issue has gone

After the mini meet yesterday, which included plenty of twisty Sussex roads and following another C4 through bends at speeds that were a little hair raising to say the least, the car was 100% footsure & felt exactly as it is should. Phew!

Glad this thread has been of some use to others as well.

 

[smj043]

My 1999 C4 Cabrio had 2 new rears fitted recently then this exact problem was happening at roundabouts and corners. Scary I would describe it as when it happens. PSM light flashes briefly. They are continental sport contact 3 on rear and older continental sport contact 2 on the front with little wear. Always replaced tyres with same size and make generally speaking.

thanks to the forum and OP I think I know what to do to solve it and stop pooing my pants thinking the front wheels are falling off.

thanks.

 

[gizlaroc]

I always make sure I have the same front and rear.

I learnt my lesson with my M3 CSL years ago. It was only 3 years old and 13k miles at the time.
It was super twitchy. I just knew it was not right.

BMW swapped every suspension component, did the geo numerous times and still got the back end feeling loose.

After all that someone from BMW Colchester was covering in Norwich and they got him to take my car out. First roundabout he said "Different tyres front and rear."

I was adamant they were PS2's all round. Turns out they were PS2 rear and PS front, went back, put the proper tyres on the front and suddenly completely planted.


I must say that with Porsches it is not as extreme, but now I know what to look for you can easily notice the tell tale signs of mismatched tyres, either different patterns or different levels of grip front to rear.