13 replies to this topic

[Iain L]

I want to fit 10" wheels, so that means fitting the 7.5" conversion kit from my standard 8.4" setup.

Now logic would say that the 7.5" setup isn't going to be as good as the 8.4" but how much difference is there between the 2?

[davies145]

my 7.5 brakes are alot better than any of my mate standard ones, my dad is even amazed by how well they stop the car,

ashley

[charie t]

7.5" disc brakes are suprisingly good despite their size. A good set of pads and discs helps with it as well. The suspension can even have an effect as to how well the car brakes, but for every day useage (not race track use) good pads and discs

[Ethel]

0.9 inches

Actually that's not so glib. The braking effect is tied to the leverage of the disc & 8.4's have 0.9/7.5 more, or 12%.

7.5's do close the gap with pad area, and the average leverage (to the centre of the pads) will be somewhat less.

[Cater_Racer]

My 7.5" stop the wheels no problem, stopping the car is slightly more difficult, 10" wheels don't have enough grip even with "sticky" tyres to present the brakes with problems. On Classic Rally use I use Cooper S steel calipers and solid discs, and 4 pot alloy calipers and cross drilled 7.5's for track use. which have proved excellent even in demanding conditions.

Edited by Cater_Racer, 05 March 2011 - 04:35 PM.

[Dan]

Actually that's not so glib. The braking effect is tied to the leverage of the disc & 8.4's have 0.9/7.5 more, or 12%.

Halve that, the braking leverage is based on the disc radius not diameter. By the time the shape of the pads and offset of the caliper is taken into accout, I'd be surprised if there was much more than 4% difference.

[aston19uk]

you can go on about stats and as such. But for every day driving use. you wont notice the difference.

[Iain L]

So not much difference at all then, good to know.

Cheers

[Carlzilla]

Just gone from 8.4 to 7.5 on exactly the same pad compound, practically no noticable difference as yet.

[richieg]

I did the conversion last year and found that there is much better "feel" from the cooper s 7.5" setup. Just upgraded to grooved disks and green stuff pads and I think that's a big step up. much better bite and give a lot more confidence

[red_mini_MMM]

Are you going to use a servo?

[MRA]

Sorry guys it has nothing to do with radius or diameter of the disc, it has a lot to do with the mean radius and a comparison of the diameter against the radius is going to exactly the same, as a fraction, 8.4/7.5 = 4.2/3.75 ....

The simple formula, has a lot to do with .....

Clamping pressure, mean radius, number of pads/discs (mini = 2 as it has a single disc per corner) friction coefficient of the pad material, and pad swept area.

You are also using stlightly smaller diameter wheels and tyres, therefore the ratio of disc mean radius against tyre radius when measured to the road will possibly offset any disadvantage that your 7.5" disc brake setup will give you

[bmcecosse]

S discs are fine. I used them on Mull Rally with DS11 pads (no servo) and they never faded on me - perhaps just slightly at the Dervaig hairpins - where they were apparently glowing red...... You need to make sure the rear drums are doing their fair share of the braking - do the drums get hot ??

[Dan]

comparison of the diameter against the radius is going to exactly the same

Yes I had it in my head that the calculation above was comparing the diameter of one to the radius of the other but looking again I don't think it is. I went over it in my head a couple of times to check, still failed!

Concerns have been raised over anyone saying that any given set of brakes are fine, without knowing much about the installation and use in question.

Lets limit it to saying that S brakes, when fitted properly and plumbed correctly using appropriately sized wheels and tyres are adequate to brake the mass of a standard Mini. Whether they are the right choice for your particular installation is a lot more complex a question.

Incidentally there are other options for fitting 10" rims. Personally I dislike the Fiesta caliper or massive spacer route (including the spaced wheels available that sit next to the brake rather then over it). You can use 8.4" discs turned down to 7.9" or 7.75" though, many companies make very good 4 pot alloy calipers for these sizes.