4 replies to this topic

[iwatkins]

Hi All,

Car is a 1990 Studio2 with a 1275 lump in it.

Running genuine HiLos and dampers for lowered usage. It's on 13x7 Supalites on 175/50/13 Yokos.

This is how we bought it.

Very grippy and very predictable on very smooth and dry surfaces. Totally unpredictable on bumpy, rough, damp or even a twig/leaf type surfaces.

Looks as though previous owner was going for looks or possibly track usage over being usable on the road. There is three inches of ground clearance between sump and road.

Most suspension components are getting close to the end of their life anyway looking at their condition so sorting the suspension is planned anyway.

However, I've raised the car nearly three inches at the rear and an nearly two inches at the front. I've dialled the dampers from full hard to much softer to give a better ride and to try and keep the wheels on the ground doing something useful. Car has now settled about 1/2 lower again all around.

This makes the car much more stable in all conditions with a nice waft of understeer if you push on too hard (safer for the wife). So it's closer to factory now.

However, a spirited drive today (first in a while) I was getting terrible bump steer. I nipped home, got the GoPro and fixed to the wing looking down at a front wheel.

I estimate from the incredibly boring video that I'm getting a good couple of degrees of toe out and toe in between hard acceleration and hard braking. I also tend to left foot brake when expecting understeer to transfer weight over the fronts but this was giving the same results.

Is there a known mod for this? E.g. Something like shimming the steering rack like we used to do with Subarus? Or does it require a more fundamental approach? I'll admit I haven't really spent much time looking into it as I've had more pressing stuff like all the electrics and emissions stuff.

Cheers

Ian

[mike.]

I would say a good portion of the problem is caused by 13x7 wheels. The big offset/dish is the problem, and mine is the same on rough roads. 

 

Also the age and condition of the cones won't help performance on rough roads and with low profile tyres like 13's, the cones need to be in top nick for the suspension to work properly.

[iwatkins]

Thanks Mike.

I kind of suspected so. I think the best idea is to return to stock then work from there?

Personally, I'd have a 10" wheel on there, but the wife's vanity rules over physics. Sob. ;)

Cheers

Ian

[mike.]

I prefer the look of 13's myself and the grip they provide is just huge. I also feel the wider wheels reduce bodyroll. 

 

But the roads are a lot worse now than a few years ago when I fitted the 13's and i'm considering going down to 10s myself! 

 

 

How much mileage has your car done? Just wondering how old the cones will be, because if they're worn out and collapsed the ride will be terrible with 13's and it will make your problems worse

[Algordo1100]

Its your wheels. Throw them over a bush!

Imagine a rod going down through the top ball joint and through the bottom ball joint all the way to the floor. The point where the rod hits the floor- that is where the cetre of the tyre contact patch would be in an ideal situation. 

Moving the contact patch out beyond that point means there is more leverage on the swivel hubs, so steering is harder and bump steer and torque steer are created. Torque steer happens because the tyre contact patch is further out then the axis of the swivel hubs, and one wheel will grip more than the other on uneven ground, so the driven wheel pulls the hub round , and literally pulls the steering over. As each wheel finds more or less grip on uneven surfaces, you experience this as wandering instability!

Yes, putting more rubber on the road will increase grip in simple terms, and a wider track  will give the centre of gravity more room to play with, so higher speed cornering may be achievable. However that is only in ideal situations, like a multi million pound, billiard table smooth racing circuit. Our roads certainly are NOT that!

 

So I would recommend to anyone, that they choose a more sensible wheel/tyre combination if they wan't their road going mini to be nicer to live with in the real world. There will also be far less wear on ball joints/ wheel bearings etc!  ,And you don't need to cut bits of wing away... and lets not get started on un-sprung mass!

 

So I would always chose:

 

Tens = 165/70/10 tyres on a rim with an offset of at least ET+15 (Cooper S replicas are ET 35 and can take that tyre) [exacton '1100 special' alloys are ET 15.5]

 

Twelves = 165/60/12 tyres on a rim with an offset of at least ET +14  (Rover 4.5X12's mini light style are ET +35 and run that tyre very nicely [RSP, 30, Cooper carb etc] )

 

Thirteens = Find a bush

 

Tens are the best in my experience, but some may want to keep the 8.4 brakes, so 12's are needed.

I think on those tyres,( if good quality rubbers are chosen), a normal, well set up road mini will be capable of cornering at speeds that will cause most people to soil their underwear. No further rubber required and a much nicer car to live with day to day.

Having owned Minis with all sorts of wheel/tyre combinations I can back this up with personal experience!

 

At least, thats what I reckon