NA MX5 geometry limits with standard ride height.

[Kozy]

I'm looking to add some negative camber onto my MX5 to combat some serious outer edge wear after autotesting. The suspension is completely standard, sitting at 14" rear and 13" front ('94 1.8iS).

 

How much negative camber will the adjusters allow? 

[Tony]

The rear will give around -1 degree 45', the front around -1 degree, more if you don't mind a low castor value.

[Kozy]

Well, that throws my idea right out of the window then, I think it must be maxed out already.

 

Just going to have to live with it I guess.

[Tony]

What numbers do you have for the camber?

[andyelcomb]

I'm surprised you are getting heavy outer edge tyre wear doing autotests - surely the rears are wearing level and you shouldn't be getting too much on the front unless you are getting chronic understeer for some reason.

 

I would have thought that running the pressures too low would have more of an effect than too little camber.

If you want the car to have better turn in then set the rear to give a tad toe-out. That'll make the thing spin like a top but also be very dodgy on the road.

 

I've run Tony's fast road settings on my S Spec for a few years now and its a very good all-round compromise. Have done track days, sprints, autosolos and targa rallies on sealed surfaces and the odd grass autotest as well and outer edge tyre wear just doesn't happen.

 

All I do is wear the rears quite quickly as I'm steering it mostly on the throttle and trying to limit the amount of steering wheel input.

 

[Kozy]

 

 

What numbers do you have for the camber?

It's not going on a machine until beginning of next month but when I bought it I was told it had a Flyin' Miata alignment on it, which I believe is -1°/-1.5°. I was hoping to get a little more up front, maybe 1.5 to 1.8° for some extra front end grip and to reduce the wear. The tyres were brand new Uniroyal RainExpert 185/60/14 and after two events there the tread has been totally scrubbed off the shoulder.

 

I was running some odd pressures recommended by the previous owner, about 35psi rear and 25psi front, to get the car nice and loose. I think the low pressure is what is causing the tyre to fold over, however I'm wary of adding more pressure as it tends to increase understeer

 

 

 

I'm surprised you are getting heavy outer edge tyre wear doing autotests - surely the rears are wearing level and you shouldn't be getting too much on the front unless you are getting chronic understeer for some reason.

 

I would have thought that running the pressures too low would have more of an effect than too little camber.

If you want the car to have better turn in then set the rear to give a tad toe-out. That'll make the thing spin like a top but also be very dodgy on the road.

 

The rears are certainly wearing more evenly, but still showing signs of accelerated shoulder wear even with high pressures.

 

It's undoubtedly the low front pressure which is causing the fronts to wear faster, but as I said, I'd rather counter it with more camber than more pressure. One can never have enough front end grip!

[andyelcomb]

I take it these are smooth tarmac autotests then?

Unfortunately I'd expect any new tyres to suffer quite badly as the tread will be deep and the blocks move about and wear quickly.

The Uniroyals are fairly soft too which won't help.

 

As you say, you can never have enough front end grip, which is why on one dry autosolo I ran 195/50/15s on the front and old 185/50/14 winter tyres on the rear - oversteer? You've never seen anything like it!

 

One thought - have you tried disconnecting the front anti-roll bar? That ought to help with turn in and/or increase oversteer.

Also, what type of diff are you using? I find my high mileage standard viscous diff a bit loose and it won't normally allow tight donuts on grippy tarmac.

[Kozy]

We do both tarmac and 'unsealed' events,  though it's really the tarmac ones I want to set it up for.

 

ARB might be worth a go, but the body roll is already quite high so I'd be wary of increasing it further.

 

It's got a T1 Torsen AFAIK.