Vibration at high speed

Hi, the car is absolutely fine around town at low speeds and then also on the back-roads driven spiritedly and again on the motorway at motorway speeds, but then when the opportunity allows and I get up to 100 (private road obviously) I start to get quite a bad vibration. Can't tell for certain if it's coming through the steering wheel or the wheels/suspension or if it's the car itself. The car is fine at 70, 80, 90 but then any more it starts to vibrate...? It's not the end of the world because obviously this situation doesn't happen very often, but the car surely is designed to do 170 and I wouldn't want to drive anywhere near these speeds on an autobahn or track with it.... Any ideas please?? (The brake discs & pads are new, as are all the coffin-arms & wishbones etc etc, it's got new tyres (presuming they've been balanced properly) it's also got new engine mounts. The only thing left is the shocks, springs & top-mounts which are getting replaced in a couple of weeks.) Thanks!

Sounds like the wheels haven't been balanced properly. If it's speed related and not engine rev related I'd rule out engine and possibly gearbox. Have you tried coasting in neutral at the speed it's doing it at and seeing if that makes any difference?

Thanks, if the wheels have been poorly balanced wouldn't this also show up at lower speeds under 100?? Good idea re coasting, will try that next time the situation allows. You'd assume if it were engine related that it would be rev dependent rather than speed and it doesn't vibrate at high revs at lower speeds. What about wheel bearings?? The car has done 77k so you'd presume these are still ok. Thanks again

I agree with Alex. The tyres will only be balanced to within a tolerance and the tolerance probably reflects normal road speeds. See if you can detect anything at half the speed you get the obvious vibration. Harmonics mean you might feel the vibration at half the frequency. You've had a lot of new stuff fitted so it's probably related. If it's not the wheels and tyres, get someone to go over all the fastners and check they're properly located and tight. If it's none of the above it could be a buckled wheel but not too bad if it's only very high speed you feel it.

I'd have thought wheel bearing would be a whine or drone and not vibration.. It it's wheel related you can usually define whether it's front or rear. Front has vibration and wobble of the steering wheel, rear feels more like your arse is on some whacky vibration plate.

Thanks, it's going to RPM Technic in a couple of weeks to have some KW V3's & new Porsche top mounts fitted, will ask them to go over everything else then. Will find out tomorrow if they balance wheels and if so ask them to take a look, otherwise will have to take the car to my local favourite tyre shop beforehand. The tyres were re-fitted elsewhere at a wheel refurbers, so there is the chance they weren't perfectly balanced. Absolutely no vibrations, or any other issues, up until magically the same speed around 100. Just googled it and all pretty much all mention wheel balancing although they say I should feel it at 60-70... One post mentioned CV joints..??

Bingo!

I've experienced this on a 996. Had to get to 140 plus, but could feel it. Took the car somewhere they could balance to a higher standard and it was fine. Some machines seem able to balance to save weights, rather than to a higher standard.

Thanks both, I'd say it was coming from the front and possibly also through the steering wheel. Definitely a vibration rather than whine so hopefully it's the balancing rather than bearings. Hopefully it's just the balancing and I can get them re-balanced at RPM to a tighter tolerance. What about CV joints??

Doubt it. Check your balancing first.

Thanks Alex, appreciate your help!

Balancing wheels is harder than it appears, despite the machines telling the operator what g and where to put the weight. Watch them do it if you can and check visually for any sign of the wheels being out of true. I know things like track rod end play can manifest in vibration but sounds like you're on top of the suspension.

Thanks, hopefully it's just the balancing and is an easy fix.... The track-rod ends have recently been replaced, along with everything else, so assuming they are all now ok and fitted ok it must be something else.... I'll report back once I've taken the car to RPM and had the wheels rebalanced.

I recently had a similar issue at around 90-100, just had all 4 wheels and tyres balanced, been out for a run and it's all sorted now (fingers crossed).

They are very sensitive in my experience. Spacers can also cause an issue.