Brake system downsizing question cause bigger isn't always better

Have a question for my favourite forum aboot brakes. I have an mk5 gti that I want to abuse but it has bigger brakes and I cant stuff a 15" rim on the front.

So my question is, if I put smaller front brakes on it from a normal golf, should I also put the smaller rears on from the golf? or can i just leave it? I can fit a 15" rim over the gti rear brakes...

I'm concerned about brake bias basically. I dont want to have to add a proportioning valve.

THanks!!!
Steve

Are the brakes any different between the two models? It seems sometimes they like the just make bigger front brakes with no changes in rear. I always assume they deal with rear bias with the proportioning valves when they upsize fronts and don't change rears, which would mean you should swap in the smaller front's rear prop valves.
What is the application?
Street car/rallycross car I'd probably just do the front brake swap and then go drive it and see how it is. If it's too much rear bias then go to a better pad in front or a softer pad in rear to get bias to a driveable state. Plenty of people do this same thing for stage cars.
Stage rally car I'd probably swap the front and rear brakes from donor car and go to a dual master cylinder setup.
The poorer option I would measure everything and put it into my bias calculator and figure out what the ideal combination of available masters and stock parts excluding the stock prop valve that would be to give me around 60-65% front bias and then put a line limiter/adjuster on rear to dial in just how much rear bias I want.
Of course, I'd also do all those measurements to determine which master cylinders in my dual master setup to achieve a 65% front bias which I can then fine tune with my balance bar.

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Grant Hughes

Yeah sorry the rears are also bigger then the standard golf rears. So both front and rears on my gti are bigger then standard.

I'm not doing stage rally, just street and rally x. My car doesn't have any kind of proportioning valve. I'm not wanting to add one, or a dual master. Cheap cheap is the way to go for me

Just throw it on there, you will be fine.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

i suppose theres no harm in trying

I installed Audi TT-Q (225) Front and rear brakes on my Mark IV, and was still able to fit 15" wheels. The braking is more than adequate, and I was actually advised against the bigger brakes on the forum while doing my build. I already had all of the parts sourced, so I went ahead with it, but it definitely was Not needed.

Yeah I read a bit of your build thread.

I'm trying to go smaller

turned rear rotors down to 11.25 then installed rear caliper to front on genny as everythong lined and bolted up, coincidently brake boas is better now no front lock up

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All bridges burnt, island life is beauty

Ummm....