logicfactory
logicfactory New Reader
2/11/12 1:58 p.m.

do you think 5lb 231mm solid rotors on each corner with wilwood dynapro singles can meet the following criteria?

needing to stop 65mph-0 without issue and at most 2x within one minute and the other would be 130mph-0 once every 10 minutes or so.

i doubt these questions can be answered directly so i will also ask has anyone ever autocrossed with such a minimalist setup in a similarly weight vehicle?

Keith
Keith SuperDork
2/11/12 3:05 p.m.

My Mini weighs 1450 lbs, and I've run it two-up in autocrosses so there was a total weight of at least 1800 lbs. It had solid 8.4" rotors up front with single-piston sliding calipers and drums in the rear. With heavy front weight bias, the fronts did pretty much 100% of the work.

The first time I ran it was in as-received condition, and the fluid in the LF caliper boiled. That's right where the radiator heat gets dumped in a Mini. With fresh fluid, I never had another problem although I have since swapped the brakes out to smaller vented discs and four-pot alloy calipers. I've never tried braking from 130 mph though, it seems an unlikely scenario

If you've got a low CG and rear weight bias, you'll probably be fine, especially if you can arrange for cold air blowing on the rotors instead of hot.

Knurled
Knurled Dork
2/11/12 4:08 p.m.
logicfactory wrote: do you think 5lb 231mm solid rotors on each corner with wilwood dynapro singles can meet the following criteria? needing to stop 65mph-0 without issue and at most 2x within one minute and the other would be 130mph-0 once every 10 minutes or so.

I see ~3000lb drag cars that turn 10-second times running that kind of setup. Some of them get regular street duty, as well.

i doubt these questions can be answered directly so i will also ask has anyone ever autocrossed with such a minimalist setup in a similarly weight vehicle?

Well, there's one way to find out. I can't see it really being a problem, autocrossing barely puts any heat into brakes.

I've been eyeing those funky looking rotors that Kawasaki uses. The rear rotors look just the right diameter for car use, and they're loads less expensive than similarly sized rotors made for Sprint cars.

mad_machine
mad_machine SuperDork
2/11/12 4:14 p.m.

not sure if you would call it lightweight.. but the fiat 124 (and exxie) used 9 inch solid discs all around..

logicfactory
logicfactory New Reader
2/11/12 4:36 p.m.

thank you for the feedback!

keith: your experiences may have in themselves solidified this decision but because it is many months out i will continue to seek opinions as it should only help make this decision.

what rotors and calipers are you using on the more recent setup if you do not mind sharing. i could not find any aluminum caliper options for a ~9" rotor; at least not recommended.

knurled: i do know some domestics run a strang engineering setup on the street i do not know why i overlooked this information; thank you.

the reason i brought autox up is i think the environment is much more demanding on brakes than the other i intend to use it in.

you have a link for these kawasaki rotors you mention? are they for motorcyles? im guessing because you mention funky they are some variate of a scalloped rotor.

mad_machine: thank you, it brings comfort to know that a car manufacturer with a reputation on the line and potential law suits to go belly up choose a similar brake setup oem and i imagine the car is a good deal heavier than my application.

Keith
Keith SuperDork
2/11/12 5:01 p.m.

The Mini is now running on calipers made specifically for the Mini, they're the cutest little things. They're from Mini Sport in the UK. However, we've been noodling around with Wilwood Powerlites on a 9" and 10" Miata rotor. They're tight on the former, but they will work. I haven't tried it on a solid disc and we're still in the prototyping stage so we haven't actually run the car yet, but I see no reason why it wouldn't work.

I've also seen a National level CSP Miata running Wilwood GP320s on 9" rotors, but he did have trouble keeping brakes in it. I'm not sure what the weight of that car is, probably in the 2000 lb range with about 175 hp at the wheels.

logicfactory
logicfactory New Reader
2/11/12 6:14 p.m.

keith: both options you mention i have crossed paths with. the gp320 were easier for me to dismiss with the ~ 230 price tag.
the powerlites i will have a better idea if i can make them work in a couple months when i have some rotors on a hub; being a radial mount i am kinda limited with mounted options on the knuckles i am using; as i do not want go wilwood hats because of cost. i am going to look into the weight and cost of the calipers you mention from mini. thank you.

Keith
Keith SuperDork
2/11/12 8:34 p.m.

If you think the GP320s were too expensive, don't even bother looking at the Mini Sport alloy ones

However, I have a set of stock Mini calipers and rotors if that suits your needs. 8.4" solid discs with a 4x4" bolt pattern, could be redrilled. The caliper mount might work better for you, too. One single 2" piston, cast iron. Drop me an email if you're interested.

tr8todd
tr8todd Reader
2/12/12 8:32 a.m.

If you want to see minimal brakes, just look at British sports cars. The TR7 and MG midget had some of the smallest brakes I have ever seen, and they seem to work OK most of the time. Back in the day, the TR7 was known for bad brakes in SCCA showroom stock racing. Changing out the pads and taking care of them enabled you to make it through a race, and an autoX is much less demanding. If what you have compares favorably to either of the above cars, I'd say your more than good on an 1800 pound autoX car. Just make sure you use good high friction pads.

Knurled
Knurled Dork
2/12/12 2:30 p.m.

FWIW, I had a Nissan with solid rotors in the 2300lb range. With extreme amounts of left foot braking, I could get the brakes to smoke gloriously, and the rotors were an interesting shade of purple, but they wouldn't fade.

And there were loads and loads of VWs out there with 9.4" solid rotors on the front. They were used up into the Mk3 Jetta range. Those cars weighed a lot more than 1800lb.

Yes, the rotors I'm thinking of are slotted and scalloped and generally have a lot of metal missing. I'm glad you are familiar with Strange brakes, those were the ones I'm thinking of. I think an entire corner - front hub, rotor, and caliper - weighs less than a Moraine caliper all by its lonesome, and definitely less than a stock rotor. They are also Not Cheap with a capital OMG.

I wouldn't do track day with the setup, mind you. Or even hot street driving without some kind of brake ducting. But for short runs on tires grippy enough that you can use cornering loads to do much of the work to slow the car down, I still think they'd do alright.

chandlerGTi
chandlerGTi Reader
2/12/12 3:31 p.m.

When I bought my Datsun 1200 GTLite car it had one wildwood rear brake on the passenger side. The guy who ran it said it was plenty for the rear. I've wondered about that but it was run competitively in the southwest.

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