Coilover setup...tyres rubbing under braking.

[deviant]

Hi guys.

So my monster brakes now work extremely well. I also have brand spanking new tyres on the car and I have run in to a problem.

The car (NA8) is fitted with coilovers and has 205 / 50 / 16 tyres.

Under HARD braking the car is diving quite a lot and the front tyres are catching under the guards somewhere. I cant see where or what they are rubbing.

The tyres are also rubbing when going through / over large humps and compressions in the road.

Should I have a play with my coilovers at home or is this something to leave to the pro's? I am guessing I need to raise the car a touch and turn the stiffness up a couple of notches (front and rear to keep balance)? To be honest they are about as stiff as I would like them to be for the road, any stiffer and I think it would be bordering on uncomfortable and the suspension would not be controleld over rough surfaces...it would just jiggle and compromise handling.

Is it worth looking in to guard rolling?

The tyres that came off the car never rubbed at all. They were Goodyear's and the new ones are Bridgestones which to my eye look to have a much more rounded shoulder and sidewall...the Goodyears were 'square' so maybe they fit under the guards better?

[Hellmun]

First thing you need to do is see where it's rubbing. Then look at your available adjustments. Do the coilovers have adjustable perches? How low is the car? What's your alignment settings? What springrates are the coilovers? What offset are the wheels? What width are the wheels?

Otherwise it's hard to recommend anything.

[SPy vs. SPy]

I don't know about the NAs but the NBs have a plastic inner guard liner, there is a square block of plastic moulded into it which appears to be a sacrificial tell tail that your car is too low.

Have a look under the guards and see if you can see such a similar thing.

If it's too low you are possibly riding on the bump stops quite often too, this will cause bump steer if too excessive.

[emexv]

I don't know about the NAs but the NBs have a plastic inner guard liner, there is a square block of plastic moulded into it which appears to be a sacrificial tell tail that your car is too low.

Have a look under the guards and see if you can see such a similar thing.

If it's too low you are possibly riding on the bump stops quite often too, this will cause bump steer if too excessive.

I had a similar setup to yours and as SPY said my fronts rubbed on the plastic inner gaurd ( at least until they wore a big enought hole in the inner guard). It didn't do it on the road but definately on the track. It's easy enough to adjust your coilovers at home but if you play with the ride hight it will effect your camber.

[JBT]

Maybe your tyre/wheel combo is too big. According to this, your total wheel/tyre diameter is about 30-35 mm bigger than standard 185/60 14".

[deviant]

Thanks for the replies guys!

First thing you need to do is see where it's rubbing. Then look at your available adjustments. Do the coilovers have adjustable perches? How low is the car? What's your alignment settings? What springrates are the coilovers? What offset are the wheels? What width are the wheels?

Otherwise it's hard to recommend anything.

This all tells me...take it to a pro

I suspect the rubbing is on the lip of the guard towards the front of the car. There is no tyre damage and there appears to be no damage or rubber on the guard though. There are no guard liners.

The coilovers have adjustable perches but I do not know what the spring rates are, the last owner fitted them. I will try and contact the manufacturer though and see if they can help.

The car is low, they tyres are tucked up against the guard.

No idea what the wheel width / offest is.

[Benny]

If you want some help, take a few pertinent photos of the wheels and tyres on the car showing where they are rubbing.

At least then we can see what is happening and be able to give you some good advice.

However, if the rolling diameter of your tyres is too big, you'll have to jack it up like a 4X4 before it stops rubbing, and I'm sure you won't want to do that.

[deviant]

I will try and snap some pictures tonight.

I perhaps should have clarified that the tyres that came off the car were the same size and did not rub.

[Guran]

Might be worth sticking a spy cam up in the wheelarch somewhere and taking it for a short drive. With a bit of experimentation with placement of the cam, you should be able to pinpoint exactly where and what is rubbing, and have it all captured on video for posterity.

[Guran]

Maybe your tyre/wheel combo is too big. According to this, your total wheel/tyre diameter is about 30-35 mm bigger than standard 185/60 14".

+1

It's also worth adding that 205/50R16 is not a street legal size for an NA8. The calculated tyre diameter is 611mm versus 570mm for a stock NA8 (195/55R14); ie 41mm too big! Depending on which state you're in, the tyre diameter typically has to be within 15mm of the size stated on the tyre placard stuck inside your door (NSW). If you want to be legal and stick with 16" wheels, you need 205/40R16 (perfect match) or 195/45R16 (12mm too big) or 185/45R16 (3mm too big), if you can get them.

Also you should keep in mind that with your current tyres, your actual speed will be slightly more than what you see on the speedo eg. ~103km/hr at indicated 100km/hr. Take care around speed cameras!

[Guran]

After a bit of a search, I've discovered that tyre sizes are now under National regulation:

http://www.infrastructure.gov.au/roads/ ... eb2006.pdf

OVERALL DIAMETER

The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

The overall diameter of any tyre fitted to an off-road passenger vehicle or a commercial vehicle must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that model.

Speedometer accuracy must be maintained for the selected tyre and rim combination to within the degree of accuracy specified in ADR 18 where applicable.

Don't think your MX-5 qualifies as an off road vehicle.

[deviant]

Yes well...ahem...shuffle...cough...These wheels and tyres are used off road only...

I cant go down in wheel diameter due to my brake set up. In hind sight I should have looked at the 40 profile tyres however the 50 profiles that came off the car did not have any problems.

I'm not sure if I could get away with less width. This car is very capable of spinning it's wheels in several gears as it is so I am not sure how game I would be to go narrower!

According to my GPS the last lot of tyres were spot on but I suspect this set might not be so I will have to test that.

I went for a run last night and it was dark when I got home so could not get any pictures. I did buy a 'gum camera' a couple of weeks back so I could look at sticking it somewhere!

[Guran]

Sounds like 40 profile would be your best option once this set wears out . Shouldn't be too long with all that power.

There's lots of places in there that you could tape your gum camera onto. Just muck around with a few and I'm sure you'll pinpoint the problem.

[deviant]

A quick update to this...

Sorry I did not get around to taking pictures, snowed under at the moment and kept running out of time and inclination to do it.

I went ahead and had the guards rolled for a mere $40 per corner. They were rolled as much as possible before affecting panel gaps, paint and the shape of the wing. I knocked the coilovers front and rear two clicks closer to 'hard' and so far it looks like the rubbing has stopped. I have purposefully run over a few bits of road I used to go around because of the rubbing and there is none now. I have not been able to test out the super hard, howling tyres, brake test yet....that can be reserved for the trackday I am doing on Friday unless the wet weather forcast comes true!

[Patrick Bramston]

I have a na6 1.8 and tried to fit 205/50/16 because I had them. They were hitting everywhere,top, back and front of the wheel arch without driving the car out of the tyre fitting shop. I run 205/45/16 on the road and 205/50/15 on the track. The only scraping I get is the front mud flaps on the bitumen under braking.