15 replies to this topic

[burnz24]

First some background info, im currently part way through an x16xe build on my mini and im fast approaching the time to buy the brakes.

Now, most of the running gear is being replaced anyway so changing brake size is no trouble and im going to be using 4 pots so stopping is also not a problem but i want to use the biggest brakes that will fit under my chosen wheel size.. and there in lies my problem i cant choose what size of wheels to use with regards to handling; 10's, 12's or 13's, the car will have a decent suspension setup and decent tyres.

which size will give me the better handling and more importantly which size will handle the weight and power increase better.

For each size;

10's, with a 165/70 A008 tyre with a 5-6" rim

12's with a 165/55 A048R tyre on a 5-6" rim

13's with a 175/50 A048R tyre on a 6-7" rim

 

I am told 13's tend to give me out and out grip and road holding (by that i mean throw it into a corner and it sticks like glue) but may exagerate any torque steer and 10's give me a quicker response as well as agilty (would be better at a slalom) and 12's give me a mixture of both.

 

I should add ive only ever driven a mini on 12's however im not biased (at the moment) towards any size and looks are not a part of this, im a believer in function>form.

 

p.s. just to clarify is the max brake (from mini sport/spares anyway) sizes for each wheel size

10 - 7.5?

12 - 8.4?

13 - 8.4?

 

Anything ive missed? just ask and thanks in advance.

 

[HarrysMini]

You can fit 7.9" discs over 6x10 Revolutions. It varies between what wheel it is.

 

Also, you can get 10s thinner than 5" wide.

Edited by HarrysMini, 19 June 2013 - 09:46 PM.

[jaydee]

5x10 are perfect in terms of handling, 13" wheels are heavy and can give tramline/torque steer 

Use the A032R over the 008s, they offer much more traction and grip

[AVV IT]

Oh dear, sounds very much like some people are getting "Road Handling" confused with "Road Holding" again!!! Uncle Cooperman will no doubt be along shortly, to put you all right and to give you all a good ticking off!!! 

[jaydee]

No hes right, 13s give a slightly better road holding, its the handling that is not at its best

[burnz24]

I highly doubt 7.9 inch discs will fit 'over' 10x6 revs but they may fit under, but thanks I didn't know that, would the minisport 4pots fit? Or is that what you mean? I also know the steering will be Heavier with 13s
And torque steer is what I was worried about with 13s
Hopefully cooper man will sort me/us out..

[Cooperman]

Ok, here we go (again!)

Road-holding is the physical measurement of the centripetal force which a car can generate, measured in 'G' through a given corner. It is largely determined, these days, by the tyres. In the dry a wide tyre like the 175 section width as fitted to 13" wheels will tend to be better, but in the wet it will not be as good as a narrower tyre like a 165 or 145.

Handling is not the same at all. It is the way the car responds predictably to the dynamic inputs of steering, braking and the application of power.  

It is possible to have a car with very poor road-holding but excellent handling. I always allude to a Mini running on narrow forest tyres on a dry tarmac road. The road-holding will be atrocious, but the handling will be superb with predictable power-on understeer and controllable lift-off oversteer.

This is a simplification, of course, and overall vehicle dynamics is a complex subject.

My personal belief is that the best handling Mini will be on 3.5" x 10" wheels with 145 section tyres pumped up to around 34 psi all round.

However, for ultimate road-holding a 13" wheel with racing slicks will be best.

[tiger99]

And, of course, you need good handling to be able to exploit the roadholding! (A Formula 1 car is optimised for roadholding, with only minimal concessions to handling, which is why it takes the likes of Louis Hamilton to drive one, whereas the roadholding of the Mini was intentionally degraded at the design stage to allow the handling to be improved to make it safe in the hands of very mediocre drivers.) For that reason. I would prefer a slight reduction in roadholding, if it brought much better handling, as overall the car would be quicker in most situations, for most drivers, except when driving in a steady circle, which we tend not to do very often.

 

There is a lot of guff talked and written about torque steer, especially in the monthly comics, which I no longer read as they are mostly garbage and a few pretty pictures. It has NOTHING to do with the width or diameter of the wheel as such, and is totally dependent on the angular relationship of the stering axis to the wheel spindle and driveshaft, and the scrub radius (offset from the wheel contact patch centre to where the steering axis meets the ground). It only changes when the wheel diameter is changed because the wheel offset has not been set correctly to get the correct scrub radius. That happens because certain compromises are made to get wheel arch clearance etc.

 

If you increase the wheel diameter without changing the offset, the wheel centre will be higher off the ground, so the steering axis will intersect the ground further out, decreasing the scrub radius. Too low is bad for the handling, but most modern cars have it zero or negative, so that ABS brakes do not cause serious instability. A bigger wheel needs to have less offset, so the contact patch moves outwards (wider track is obtained too, which is useful) to keep the scrub radius correct, but then it will not fit under the arches, and will overhang the wheel bearings so far that they will be overstressed and have a short life.

 

On the other hand, bigger wheels of the same width, with lower profile tyres, don't necessarily change the scrub radius very much, as the tyre diameter does not change all that much. The wheel is only the bit of metal in the middle. Think about where the outer surface of the tyre will be when making comparisons between wheels.

 

The subject is much more complex than that, and you really should find a good book on suspension design if you want to know more. Most of what you read on the web is as untrustworthy as the monthly comics, as it is all regurgitated form the same sources.

 

Personally, I agree with Cooperman and prefer the feel of a Mini on standard 10" wheels, exactly as Issigonis designed it, but they will not be adequate for modern high power engines.

[Cooperman]

One other thing in terms of performance which always surprises people is why the original Cooper 'S' with c.75 bhp was so much faster in terms of top speed than the later cars.

Well, apart from the 'S' being lower geared, it had much less aerodynamic drag with its 145 section width tyres, no wheel arch extensions and no wing mirrors.

The Sport-pack wheels and wheel arches must add at least 50 sq. ins. to the frontal area and the wide wing mirrors add another 40+ sq. ins. That's an extra 90 sq. ins. to be pushed through the air. Try holding a 10" x 9" board flat into the airstream and see how much drag it creates.

So that is another reason for fitting standard width wheels and not fitting arch extensions. Then make both road-holding and handling as good as you can and the car will have a vastly improved overall performance capability.

[tiger99]

I think I would prefer to have wing mirrors, rather than wide wheels and arches, if it was a choice between one and the other! You can get "aerodynamic" mirrors, with a suitably shaped casing to get a lower drag coefficient than a standard mirror, but because the glass face has to be almost flat there is a limit to how good they can be. I wonder if it would be legal to use a tiny CCTV camera on an aerodynamically shaped arm, with a screen on the dashboard at each side, to keep the external area to a minimum?

 

On the subject of aerodynamics, has anyone tried an undertray to smooth out the rear subframe area?

[burnz24]

Well in that case I think a set of 165 10s will work, im kind of limited to sizes as I need the grip the better tyres give me.. All of that does actually make sense cooperman thanks for that, and thanks to everyone else for advice.

[ikissminis]

Another important point to consider is the condition of today's roads. In the 10 years I have been driving they have deteriorated significantly, to the extent that riding smaller 10" wheels can now be very uncomfortable as they feel they effects of bumps and recess much more; indeed some roads around my area are just not worth the discomfort!

 

That said, I have driven minis with all different kinds of set ups, and let's face it, we all like minis because we like driving go-karts.

 

Go for 10" wheels. 12" wheels are the sensible option, 13" wheels are far too compromised. 10" wheels is where the fun is at.

[jaydee]

 to the extent that riding smaller 10"  low profile 13" wheels can now be very uncomfortable as they feel they effects of bumps and recess much more; indeed some roads around my area are just not worth the discomfort!

 

 

Fixed for you 

Edited by jaydee, 23 June 2013 - 01:15 PM.

[JustSteve]

I have recently changed from 12's to 10's, both on 165's... I can tell you than the 10's are far more comfortable!

I will definately not return to 12/13'' on a road mini

[burnz24]

i hadnt even considered comfort until nw , if 10s are going to be more comfortable and give me better road handling then that seems the logical choice?

and ive only been driving for 3 years and i have noticed a very sharp increase in the crudyness (is that even a word??) of our roads, to the point where i do more miles due to the fact i weave around potholes/drains and completely avoid some roads, adding to my journey time.. and im pretty sure im not alone in this?

 

once again thanks to all for the advice on this