ZX Tyres

furyspyder · Unread post by **furyspyder** » 30 Jul 2003, 16:54

I have a ZX 2.0 16V, and recently changed the original michelin rear tyres, after 72,000 miles (!!!) for a nice new set of michelin Exalto's (with the directional tread). Since the change (and I have done over 800 miles with them fitted, so they should be 'scrubbed in') the turn-in into corners has been nicer - smaller wheel movements required - but the stability through long fast corners in particular (such as on a fast 'A' road) has worsened. It seems to go from oversteer to understeer to oversteer etc etc, and I end up going around the corner in a series of straight lines !! Also, when at 80 on the motorway, the car always used to be as steady as a rock, the most stable car I have driven at speed, but now it seems very susceptible to unevenness in the road surface, camber, ruts etc and tends to wander more easily as a result of these road surface features. Tyre pressures are regularly checked, rear subframe bushes are new, front outer track rod ends are new, everything else is tight.
Any ideas? Does the ZX need a certain tread pattern type for the rear tyres because of the passive rear wheel steer?

VisaGTi16v · Unread post by **VisaGTi16v** » 30 Jul 2003, 17:14

Dont know about the tread patter but were they balanced properly? Also you would have been used to your old rear tyres so now you have new ones on the back, they will have more grip than the front ones that are part worn. This could explain the cornering. I know from experience of mine they are quite twitchy. ive just replaced my rear budget tyres with some pirreli p7000s but they are wearing in so no play time yet

Might be worth checking the wheel nuts? Had a friend who was complainging about his mr2's handling...then he did the nuts up tight

The movement regarding road surface is weird, guess different tyres will work differently. Check tyre pressures as well, garage may have done them wrong, think the manual says 31 front, 33 rear. Did you get the same profile as before/the front as well?

David W · Unread post by **David W** » 30 Jul 2003, 19:10

What tyre have you on the front fs? If I understand it that you've just bought a pair and they're a different type, well then all sorts of issues can arise for the enthusiastic driver.
I've just fitted a set of Goodyear Ventura's to my Xantia replacing the Michelins that were on it.....but interestingly I had a few hundred miles with a new pair of the Goodyears on the front while I waited to afford the new ones on the rear.
The handling was ruined with the Goodyears on the front only because they had a far less responsive dry road turn-in than the old Michelins...and I find the sharper the turn-in the more the rear axle seems to "self-steer".
Once I'd fitted the rear two Goodyears and run them in the balance mostly returned, the overall dry road grip is down on the Michelins though. Interestingly the ride, and bump-thump in particular, is far better on the Goodyears.
Our ZX TD is currently on Michelins front and new Firestones at the rear. This combination seems to match OK and it handles as it should.
David

furyspyder · Unread post by **furyspyder** » 30 Jul 2003, 20:10

Tyre pressures are fine. I have got into the habit of checking them every week since the old offside rear tyre had a slow puncture for the last couple of years!
Fronts are Michelin (Pilot??) MXV3's. These were the first set of fronts its had since the originals and I put them on about 35,000 miles ago, not long after I bought the car. Nowadays, the Michelin range has changed totally so I could no longer get these again to replace the rears. However, they are coming close to needing replaced and perhaps before the end of the year they will need changing. Lets hope Michelin don't change their range AGAIN in the meantime, so I can still get exalto's for the front to match the rears! Incedentally, the Exalto's have a directional tread with a sort of 'arrow' pattern leading to a central channel. The MXV3's have a more traditional block pattern.
I had wondered about asking the tyre fitters to change them for something else (at no extra cost to me) as they didn't seem to be fit for purpose. Also, after having bought them I read a review in Autocar comparing a few different tyres on a Mondeo and a BMW M3. The michelin tyres didn't come out very favourably at all. I think the Pirelli P7 came out tops in most situations/respects.
Not sure whether to wait until I need to replace the fronts and see what happens then with the Exaltos' on the front aswell, or get the tyre place to change the new Exalto rears for Pirellis and see how they do. I doubt they will just swap them for me though.

VisaGTi16v · Unread post by **VisaGTi16v** » 30 Jul 2003, 20:35

I sersiuosly doubt they will swap them just because you dont find them as good as the old ones. If they had some seriuos balance problem due to dodgy manufacturing perhaps they would.
I chose between the p7000's and yokohama a539s. Went for the pirelis in the end as they will last a bit longer and although I do some competition in the ZX its not enough to justify much shorter tyre life. Cost me £130 inc fitting for the pair. I am leaving my older front tyres on for now as it will be interesting with more grip on the back, might control it a bit more as the old knackered rears led to all sorts of interesting tail action

jeremy · Unread post by **jeremy** » 30 Jul 2003, 21:02

I think you are sufering from good old tramlining!
As the edge of tyre tread touches a longitudinal ridge in a road surface the tyre is deflected and in effect its rolling radius becomes less. Imagine your tyre as 2 separate discs and you will see what happens next - the tyre will try and turn toward and ride up the ridge.
this was a severe problem with cross ply tyres and I've driven cars that appear to go sideways on some forms of ridge, - eg gentle depressions at traffic lights, centre white lines etc.
On of the initial attractions of radial tyres was that due to their construction the tread was flat and they didn't suffer. I can well remember fitting some 165 x 14 michelins on a Morris Oxford and being amazed how it didn't react to anything.
Since then we have modified the radial design principally by lowering its profile and I think this has led to a return of tramlining to some extent - and I think the lower the profile the worse the problem.
The most interesting results couldbe obtained by mixing radials and crossplys. With crossplys all round the problem wasn't too bad as the whole car tended to move sideways and so pointed in about the right direction, but with radials on the back (the correct way round) the fronts would steer away on their own as usual and the back didn't join in - so the thing wandered all over the place.
I think what is happening to you is that the self steering of the tyres (not you ZX back subframe) is enhanced by their profile and by the fact that your tyres have nice new square shoulders on them. As you got 72 000 from your last set of back tyres this problem is going to be with you for a while.
Why not swap front and back and see if there is any difference?
jeremy

David W · Unread post by **David W** » 30 Jul 2003, 21:41

Now we've established you have a mix of old and new gereration Michelins, as Jeremy says, swap the pairs from front to rear and see what happens.
To be honest running radically different pairs front and rear can be a real reason for some twitchy behaviour.
David

furyspyder · Unread post by **furyspyder** » 31 Jul 2003, 01:17

Yeah, I had thought about swapping tyres front to back, but just hadn't found the time to do it recently. I'll give it a go when I next get a spare weekend and let you know what happens !!
(Just had another look at the fronts and they are actually Michelin Pilot HX tyres with the code MXV3 in smaller lettering)
Watch this space!
Many thanks for the help[:)]