So I am upgrading the front brakes on my MX-3 racecar. The OEM has 10 inch rotors and pretty small calipers and pads.
Being this is a "$500" lemons car, I am DIY a 'big brake kit' by using $30 11.6 inch Mini Cooper S rotors and JY $10 aluminum dual piston
1999+ Mustang calipers. To make this fit the MX-3 spindle I had to cut off one mounting ear and redrill it and make a mounting plate.
Got this all together, really excited about the setup, but I am a bit concerned about the tight clearance to my 15 inch wheels.
The stock mx-3 wheel are not going to fit without spacers at all. The miata wheels I use almost fit.
I can use a 1/4 spacer on the wheels to increase clearance, but would rather not if I can avoid it. I can grind the calipers some more,
but don't want to go too far, i've done maybe 1/16 of inch. They are aluminum so over 1/2 thick.
I could grind the wheels a bit too, but then I have to do all four.
How much space do I really need? They got hot when racing, so everything is going to expand in size.
Interesting..
Can you just add like an 1/8" spacer? Seems like that would do the trick and I see no downside.
The rotors will expand radially, the calipers not so much. To be honest, you will have more issues with the deflection in the bearing, hub, upright, and wheel, although these will be pulling the wheel mostly away from the caliper, not towards it.
Gut feeling is, if you can slip a ziptie past the caliper everywhere without it getting stuck, it's plenty good. If there is any contact at all, it will self-clearance. And clearance will only get better as the pads wear and the caliper retreats to the inside of the car.
What are you doing for maintenance? The Lemons racers I have seen who ran front-drivers would replace the whole upright/rotor/caliper assembly two or three times per race, as scheduled maintenance during a driver change.
Wow, I have not seen anything nearly that drastic in lemons or champcar.
That sounds expensive and time consuming!
I do know that a lot of competitive fwd cars are buying good name brand bearings and repacking them with neo grease now. Seems to last at least 12 hours on track.
In reply to wvumtnbkr :
It's really not THAT bad... if you have spares anyway, it doesn't take very long for a crew to do. I witnessed people doing it in the time it took to effect a normal driver change. "At least 12 hours" isn't enough when you're running for 24 
Knurled. said:
What are you doing for maintenance? The Lemons racers I have seen who ran front-drivers would replace the whole upright/rotor/caliper assembly two or three times per race, as scheduled maintenance during a driver change.
We change drivers, so we can maintain going around and around... . I've never heard nor seen of anyone doing as you describe,
Racing in Lemons is two days, so saturday evening you have time to work on the car before sunday racing starts back up.
IMO, If a car can't go 8 hours with a single hub assembly, there is something wrong. What the FWD cars seem to have trouble with is failing cv shafts.
I bought another set of hub/spindles for this brake upgrade, so I will have spares with the old stock setup.
I am going to put in new bearings and long studs while I'm doing this work on the new spindles.
With the longer studs, I can use a simple spacer, seems like the easy button here.
The car handles great so I am loath to change the geometry/scrub radius with spacers, but 1/4 to 1/2 probably has little effect?
I say "scrub radius" to pretend I know something about it, which I don't.
They break at night now?
I DID say it's been a while since I paid attention...
I think that if you've got 1/16" everywhere you should be OK. As Knurled indicated thermal expansion isn't going to be very significant, particularly compared to flex and freeplay.
Why are you making this change?
The reason I ask is I always looked at better cooling and pad compounds before going bigger. I never needed to go bigger when we were endurance racing. Cooling was always something we had to optimize and it was very track dependent.
Compound was related to temps and what the drivers wanted in terms of feel. Some wanted really strong initial bite while others wanted less initial bit but higher ultimate bite.
sorting that was always a three way rubix cube of balancing compound cooling and the track we were at.
dean1484 said:
Why are you making this change?
We had new Yellow Stuff pads front and rear at Buttonwillow, and they were worn out by Saturday. These pads are $100 each, so $200 in pads in one day, that is $400 in pads for a race, ouch!. IMO, it is going to be much better and cheaper to put in big brakes, that use Mustang pads that are 50% bigger, and widely available in all kinds of compounds vs mx-3 pads. And less weight. Figure the upgrade for like $200, it is a no-brainer! Right?? We could just drive slower, which is what we did on Sunday with stock pads, actually not much slower, maybe lost 5 seconds a lap, but that isn't why I am in the game, going faster for cheaper is what I enjoy. :) We have added cooling ducts. I'm also converting to manual brakes too, less weight, more consistency, and adding ability to adjust rear brake bias.
I can't argue with that. Are you wearing just the fronts or all the pads evenly?
could you not be getting enough heat in to the pads.
proper bedding being done?
That is a light car and I think there is something going on there. However the big brakes you are doing is a viable option especially at the cost!!!
What are you doing about a proportioning valve? Also have you looked at the sizing of the master and or the volume of the new caliper cylinders compared to the stock setup?
2GRX7
Reader
10/13/19 12:42 p.m.
Try this bit of info;
https://www.racetechnologies.com/article/how-measure-your-wheel-proper-brake-clearance
....under "wheel clearance" step 4. They also have good ideas to consider when visualizing exactly what you want to accomplish.
Hopefully, that helps.
Brakes wear roughly evenly for the most part. The OEM setup is crossed brakes, not front and back, so plumbing redo to change, then I will use a simple prop valve to the rear brakes. The car has not been able to lock up the front tires at speed. You know in lemons the cars tend to run in packs, so having great brakes is a safety issue.
Selected MC because it was cheap and light and 1 inch bore, from a dodge mini-van i think. Just going to be test it and see thing.
Never did any proper bedding of pads before, I understand that might help wear.
What car are you running in lemons?
I don't race any more. I raced from the early 80s until about 2012. Won a couple lemons events. (Nickles are really heavy). Also did some chump car.
We preferred endurance racing with SCCA and EMRA. 4, 8, 12, and 24 hour races were what we did. 4 hour races were really sprint races but they were good tune ups and test sessions for the real races.
The funny part is I have never done an autocross. I want to try that some day.
