Dunno why this just popped into my head, but it did: everyone seems to agree that a mini looks and handles the best on 10" rims (well ok not everyone agrees on the 'looks' bit but those that rate 12" and 13" wouldn't go for steelies).

So why did BMC make the switch to 8.4" brakes, forcing the change to 12" rims?? Or did they switch to 12" rims for some other reason, and that allowed them to go to 8.4"?

Kinda curious

no idea, But They should have gone 7.5" 4 pot calipers...

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12" wheels here and in UK came in with the 8.4" discs. We only got them on the 1275LS, in 1978.

Discs became standard on all Minis in UK when their Clubman 1275GT switched to 12" wheels, before that their GT had 10s with 5.5" S brakes, and all common Minis were still on 10s. I'm not sure of the change date....

Note none of the 8.4s back then had a servo fitted, this was changed however on the later Rovers. OTOH, all the 7.5" discs had one. I'd say they went for 8.4 discs originally to save the cost of a servo.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The change to 8.4" was driven my the legal requirement to have duel circuit brakes(around 1977?) which mean you could no longer fit a remote servo. Without the servo the brake efforts were considered too high for 7.5" discs. (Early 1275 GT's had 7.5' discs and servos.)

Standard non 1275 GT minis only got discs from about 1988 I think. Certainly the Mini 25 had drum brakes and 10" wheels...

The Rover servo setup was developed when the Mini became so popular in Japan in the late 1980's, Japanese drivers found the brakes too hard even on 8.4" discs...

matbe something to do with left over morris 1100 brakes?

Nope they were 8".
Different calipers, rotors, swivel hubs, everything except CVs.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

oops,,, never fear,,, i was just speaking dribble, edited now to make sure i didn`t look too much like the fool that i am

move along , nothing to see here

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

and a new european regulation was known to come up with a specific pedal force to give a specific brake force

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Rover 214 atm ....

Did it also have anything to do with the braking efficiency of competitor cars getting markedly better. ????

There was a time when a BMW was hugely expensive to insure because they stopped so well that they were rear ended with other cars that had inferior brakes.

Since then the brakes of most cars improved dramatically and the mini manufacturer (under the various corporate name) had to be seen to improving the braking systems. ??? Token attempts maybe but.......

I reckon it'd have something to do with making the rotors cheaper to manufacture - an 8.4" rotor is a much simpler device than a 7.5"... and it's more 'normal' when compared with other rotor/drive flange setups

just a thought