DDK - Die Deutschen Klassiker

I have been through this once before in some detail, but would like to discuss the events of yesterday and today in my 987.2 2.9 Boxster.
Let's hear what you think as I'm at a loss.
A few salient details first:
987.2 Boxster, 91K miles, mine for the last 10 years.
2009 (March) full service history, does around 5K miles/year. Had the transmission oil changed about 6 years ago as part of a major service at Zuffenhaus. (who service the car now for 6 years, maybe 7).
Used for touring, rarely red-lined, no track drives etc.
19" rims Bridgestone tyres, same grade on all corners and N rated. 32 psi Fr and 34 psi Rr. Fr tyres are 6 years old and lots of tread, rears are 2 years old, and lots of tread.
Exhaust is the original unit from new and is fine.

We have just been into deep Wales, 280 miles round trip, overnight stay. Up until this pre trip point the transmission/car were normal, lots of road noise and shift action a bit heavy but fine.

The Noise:
A hard humming starts at 41 mph (very repeatable) seemingly in the rear and continues to about 60 mph when I think road noise is louder so drowns the humming out.
Did this for the last 2 days.
The humming happens with the engine on load, or off load or just keeping the car moving at the speeds. Gears choice makes no difference. Will do it in 3rd or 6th etc, makes no difference, thus I think the engine/clutch has nothing to do with it. You cannot feel any harshness/vibration in the chassis.
Going round turns gently or hard in the 40/60 mph speed range the noise does not change, so feel wheel bearings are ok.
Apply the brakes at 60 (say and gently) and the noise just runs down until 40 mph and it disappears.
Slow turns in reverse and forward, no CV clicking, all silent and smooth as it has always been.

Last time I had this same thing was before the rear tyres were changed when I had the wheels refurbished, so 2 years ago. It came on suddenly then, just as yesterday.

The tyres then were quite worn, far more worn than the current tyres. (they were Bridgestones, same spec as now)

This all points to the rear tyres, but any other thoughts please?
Thank you.

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Assuming that the F&R tyres are the same size, maybe swap F-->R & see if it makes any difference ?


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Andy the tyres are different sizes on the 987. It could be a wheel balance issue on the rears, might be worth getting them checked.

Yes, the wheels are very different sizes, but interesting about balance.
There is zero wobble on the steering but also nothing on the 'chassis' but a good idea and worth the try.
Wheels all coming off soon for a pre-MoT jet wash, so could pop them down to the local tyre place.
Thanks for the replies.

I had this before on a Subaru Impreza, drove me mad. Car was under warranty, and went into the dealership, who agreed something was amiss. They changed the rear drive shafts complete with joints - still there. Changed the diff - still there - In the end they swapped the tyres over from a car in the show room.......noise and vibration went.
It was the Bridgestone tyres! Apparently once they wear, they seem to go down to a different compound level and cause this issue, and can go out of roundness............never fitted a pair on any car since.
Last time you posted this, I think I mentioned the same then. If you had the same problem with Bridgestone’s previously why fit them again?


Last time I had this same thing was before the rear tyres were changed when I had the wheels refurbished, so 2 years ago. It came on suddenly then, just as yesterday.

The tyres then were quite worn, far more worn than the current tyres. (they were Bridgestones, same spec as now)

Thanks as ever!
I changed to Bridgestone on the rears because the good fronts were Bridgestone and I wanted the same make all round (a weakness of mine).
My only way out of this is a new set at around £800…
But the noise drives us mad, so may be the only solution.

This trip was marred even more by the crazy potholes everywhere, makes a sports car unbearable…

Or borrow a set of wheels with different tyres and do test drive?

That would be the ideal, but not so easy to do!

I can buy 2 new tyres for £128 with a strange brand name off ebay. A cheaper experiment than new tyres and would prove a point.

I've wasted £150 on worse things...

Or just buy 2 good quality rears and keep the front Bridgestones, but £500.
Tyres are now expensive!

Budget tyres are dangerous in my opinion - you could solve one problem and create another Graham.I would change the rears for something proper but non Bridgestone


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shift action ... We've replaced the shift cables on my spyder as porsche upgraded the design as the original was prone to failure due to the way it curved too sharply around the engine

Wayne, it was just to drive a few times between 40/60 mph to see if the drone had gone away. I would never run any car 'full-time' on unknown tyres.

James, there is a large steel wheel bolted to the side of the trans mounted on a large bolt and the wheel rotates on this bolt.
The wheel is connected to the bellcrank at the end of the cables by a delicate plastic link. Sometimes the rotation of the wheel tightens with grunge and grit and can impart a 1 to 2 and 3 to 4 and 5to 6 movement.

I think this must be some kind of a vibration 'damper'. I know someone who had the shift action go really hard, he disconnected the link, removed the shoulder bolt, cleaned and re-greased and the shift is "perfect".
Cables were fine!

Take it to James’s. Swap his rear wheels on. If it goes quiet then it’s your tyres.

Why not give Chris at "Center Gravity" a call, I reckon if anyone can give a valid opinion and has encountered this before it's going to be him.

Always been extremely helpful when he's worked on my cars before ( Porsches and others ) a phone call is likely to be far cheaper than a trial and error new set of tyres !

Good luck, hope you get it sorted out

Thanks for the idea, but I've only met James once and he is long way away.

A friend has a 996 C4S with I think the same wheel/tyres as my rears and is 40 mins away. Will contact him and see if they might fit.

Seems Michelin PS4 are the go-to tyre and around £900 the car set....
That is about 10% of what the car is worth on Webuyanycar.com.

Might be better to get a younger lower miles AUDI TT instead! But I bet they have a list of issues too.

Centre Gravity are worth the call mind.

Tyre technology has moved on enormously since the stance on finding a good brand and fitting them to all four corners.
If you find a decent premium set of tyres for the rear that are a different make, just change them to those. But before buying or committing yourself..................

Your simple way to find out if the rear tyres are causing the issue, is just try another set from another 987/996.