Car unsettled over bumps

[JeremyC]

My car gets unsettled over bumps, particularly if I cross the centre line or move between lanes.

Car is a 97, the right Yokohama Advans on the front, previous owner fitted Rotalla's to the rear just before I bought the car:(I had the tracking checked recently and had it set to the compromise values suggested in the table at the bottom here: http://mgf.ultimatemg.com/group2/suspen ... acking.htm It's only done 43k miles, it is entirely possible it's never had new bushes.

My thinking would be the next thing to look at would be the rear lower arm bushes, thoughts please?

On the subject of bushes there are clearly lots of vendors out there. On other cars I have previous good experience with PolyBush and PowerFlex. I'm keen to not make the ride any firmer. On my Sprite I used PolyBush blue and was very pleased with the results but they don't do a blue version of the F bushes. I'd value opinions on the best bushes for a good ride.

Many thanks in anticipation

[Reckless Rat]

Has the car had the hydragas spheres re-gassed? Is the ride height correct at 368mm (front) or has it been fitted with lowering pins?
I personally wouldn't run either make of tyre you mention. Toyo T1Rs are the dogs.

[RobboMC]

I think the conventional view is that these cars should have the same brand and pattern of tyre on the front and rear.
My son has Yokohama Advan 701's on his Toyota MR2 which has the same front/rear combo as the F, and he drives away from the pack on the club runs.

So my concern is that your car has different grip levels front and rear if the tread wear rating of the tyres is a lot different;
so you could be chasing an issue that's not in the bushes.

By all means replace the lower arm bushes, I have done front and rear on my car in last 12 months to keep it running straight.

Start with the easy things first.

[Rob Bell]

I'm with Rob - have a thought about changing the rear tyres (or replacing all four at the same time): squirrely handing often results from mismatched front/ rear tyres on mid-engined cars.

[JeremyC]

Thanks for your thoughts folks. Ride height is OK and I'm not aware of any modifications and the previous owners weren't those sort of people. I do recognise the mismatched tyres issue and the Rotalla's wouldn't have been my choice however I'm a little surprised that this effect would manifest at at lower speeds. It's not like I'm driving on the edge at a track day.

Changing tyres is much easier than fiddling round with bushes though so I suspect that's what I'll do.

[Steve55]

Have you tried jacking up each corner and seeing if there’s any play in the geometry/ bushes/bearings MOT style - hold wheel at 3 & 9 o clock then 12 & 6 o block and move back and forward checking for movement.

[Rob Bell]

Odd handling can appear very quickly and even at low speeds with mismatched tyres. It is certainly worth replacing all four.

Steve, I agree - worn rear wheel bearings can also cause untoward handling - and MGF/TF bearings don't seem to make noise when they fail (no idea why not!)

[Steve55]

Just replaced all the upper ball joints, front and back and it’s made a positive difference to the handling of my TF.

[JeremyC]

Thanks folks, I have had a wheel waggle but I might go round again a bit more brutally.

Just done my tax return and I've got a couple of hundred coming back so I might spend that on two Yokohama for the rear to match the six month old ones at the front.

[JeremyC]

OK, splashed out on a couple of Yokohamas to match the front, and based on a ten minute test drive the car's poise is much better. I have an Autosolo at the weekend so that will be the acid test.

Thanks for your contributions to the thread.

Jeremy

[JeremyC]

Acid test passed, car handled beautifully on dreadful West Sussex roads and the billiard smooth Goodwood circuit. I just want slightly better turn in now.