MX-5 OC Forum

So I'm moved from having a set of 16's to a set of 15's but for some reason this seems to have upset the balance of the car. When coming off the throttle, the car noticeably jerks to the right and under hard throttle, only noticeable really at motorway speeds, when it would jerk to the left.

My initial thought was that this was due to tyre pressures so I have checked that they are all identical, and they are all 30 psi.

Any thoughts? I am going to whack my old wheels back on tomorrow and drive down the same roads just to make sure it's not the car itself. Need to sort thsi ASAP as I'm off to the Ring next week!

Cheers

 Interesting, as far as I am aware the change in wheel sizes shouldnt have that kind of effect, so I am keen to know the outcome of the run on the older wheels. Sounds more like a brake in balance than anything else but what do I know, according to the wife every thing and nothing

Just a thought. But are all the tyres the right way round if they are directional ones

I recently had coilovers fitted but with the old wheels on I am sure it did not feel like this. So, I will put the old wheels back on and test that so I can rule the suspension out.

Thanks Mr Flea, I checked that and they are all directional tyres and all all facing forwards.

Thats a good idea. To try that first

 Out of interest why 30 psi? I`ve always run mine 5s at 26 psi whatever tyre size i`ve had.

Assuming they are all balanced up ok maybe time for a WIM alignment?

Morning Rael, are the 15" rims still fitted with the Barum tyres? If so I think thats where the problem may lay

Since fitting the Yokohama Parada2`s and the 4.3:1 Torsen diff, I just cant get the back end of `Lightning`  to un-stick at all, they are simply awesome

Dave - I can't really answer that with anything that would make a lot of sense - it's just a nice round number I suppose. They were at 36 before.

John - yes indeedio they are indeed those wheels/tyres. Are they not that great then?

I think what I will do is put my old ones on tonight, go out for a blast, and at least then I will know I have something to drive comfortably with. Thing is, they ideally need 2 new tyres and I am seriously running out of time before next week! I could also try swapping the current wheels/tyres front to rear to see if that makes any difference? It might just swap the jerking round to the opposite of what it currently is though.

OK so test complete...I have put the 16's back on and....the problem has gone away. So, what the bugger is it? I have a very limited amount of time to sort this situation before embarking on a trip to the Nurburgring and I absolutely cannot deal with a car that's wobbling all over the place.

I think my only option is to put 2 new tyres on my old wheels (2 are OK but 2 are unmatched and have seen better days) and use them for the journey. Annoying as I spent quite a bit of dosh on the little 15's!

Hi Rael, I do think it might be those Barum tyres on the 15" Wheels, thing is you can have 4 Toyo T1R`s from Camskill for the price of 2 of 16" tyres so I know what I would do.....

Yeah but I got no time to get that sorted now really, Camskill "might" be able to deliver them for Saturday but if not, then it's Monday and I'm at work all day during the day.

What a pain in the backside. Fancy the wheels John?!

I would take the wheels to a friendly local tyre fitter, have the new tyres delivered there, get them fitted and balanced for re-bolting to the car for Monday/Tuesday (maybe even have them delivered to a tyre fitter near to where you work)?

I do `fancy` the 15"s but have just ended up keeping the ones off my V-Spec II as the new owner was trying to keep the costs down, the I.L Motorsport style bar, Jackson Racing exhaust, front lip spoiler (now fitted to Lightning) and up-rated rear adjustable ARB (soon to be fitted to Lightning) were all `deleted` options.