O/T - Motocross disk brake rotors

I have a friend who has two kids who are breaking into pro moto-cross racing and are sponsored by one of the big name motorcycle manufacturers. They glaze over a set of stock brake rotors every day on the track and they have gone to larger diameter aftermarket rotors and caliper extensions - still - less than 2 or 3 days of riding before brake rotors are glazed over or warped and then tossed.

The rotors appear to be made from a variety of different steels (I had an analysis done on one rotor and it was made from 410 stainless). The kids race on courses that have long up/down hills with water at the bottoms - so the brakes get really hot on the way down, then a dunk in the water/mud and then back up / down the hill - repeat a dozen times in a row for each heat.

Any thoughts on an alloy that would better resist warping / glazing? I don't really think they need to worry about corrosion - they will certainly replace the rotors before they begin to corrode.

They should try and get into contact with one of the big time teams that run the same make.
I think pad material would have something to do with it.
Yes from experience most rotors are some type stainless, from stock to aftermarket.
As an afterthought maybe the GNCC cross country guys would better answer as
they deal with wet conditions more than moto and supercross.
Slowmo Saturday - YouTube

sry can't help with the alloy. it sounds to me that either their brake pads are the wrong compound or they are dragging their brakes too much and over heating the disk. granted i know that dragging their brakes is used to help turn the bike. But i would tell them to put better pads on and don't drag brakes as much. i know that isn't the answer you were looking for but 99.9 percent of the riders i work with the only reason they change rotors are when they bend them from a wreck or to put oversized aftermarket rotors on.

Eric

Do some searching on what NASCAR uses for rotors and pads on the short tracks, they heat cycle the piss out of those things, Bright cherry red - mid corner and then cool down with fans and duct work on the straights. That has to be the most demanding application I can think of. Mike

I suspect there is better alloy than stainless.

Ive been road racing motorcycles for more then a few years, I use cast iron disks on my race bikes with organic compound pads from Porformance Friction Ive never had a glazzing problem even in rain races ... as Eric said above I would look at the pad compound there may be one better suited to use with a SS disk.
Cheers Don

Here's a company that resurfaces motorcycle disk brake rotors:
TrueDisk LLC - Motorcycle Brake Rotor Resurfacing and Grinding Services

Here's a company that resurfaces motorcycle disk brake rotors:
http://www.truedisk.net/

Some motorcycle braking system information:

Brake Pads & Parts
CycleBrakes.com - Motorcycle Brakes, Accessories, Motorcycle Parts, Brake Rotors, Pads, Lines, Discs, ATV Brakes, Wave Rotors, Braking Systems, Galfer, Sport-bike Brakes, Custom Steel-braided Brake Lines, Harley-Davidson, Dirt-bike MX Brakes, Perform
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Brake Calipers | Motorcycle Brake Calipers | Racing Brake Calipers | Engineering | Pretech, Reading, UK
http://www.apracing.com/info/index.asp?section=Motorcycle+Products_4
http://www.sbs.dk/index.dsp?area=98
DP Brakes
Spiegler Performance Parts - Motorcycle Performance Parts | Custom Motorcycle Accessories
ISR Brakes
Metal Gear
Motorcycle Archives - EBC Brakes
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http://www.apracing.com/info/produc...idecar+2+Piston+Caliper-CP2696-38E0_2536_1085

Can't they downshift to control speed downhill? That's SOP for truck drivers who would otherwise melt their brakes.

magneticanomaly said:

Can't they downshift to control speed downhill? That's SOP for truck drivers who would otherwise melt their brakes.

Click to expand...

Hard to get much engine braking on the front wheel. And down hill slowing down, that's the only wheel with any weight on it.

You should try M_X racing sometime, The stuff you are forced to do is quite eye opening. Love the adrenalin

I was involved in making a couple thousand of the oversize rotors per year for several years. Good work until offshoring killed the profit in it.

We used 410 SS, not because it was necessarily the best material for the application, but because people seem to want something that stays shiny. Analysis of a stock Japanese rotor showed the material to be closest to 410.

Our rotors were laser cut from 11 ga sheet. Vacuum heat treated, jig tempered to Rc36-38, and blanchard ground to about .100 final thickness.

The rotors are thin to minimize rotational inertia as well as overall weight. IMO, ductile iron would likely be the best common material, but at that sort of thickness I doubt it would be reliable. We tested some non heat treated 410 rotors, and they didn't hold up well at all in cow pasture type testing. I was working with a 7X national enduro champion and AMA hall of famer on the parts, so the tester was pretty high on the legitimate testing scale. We used a lot of different patterns of slots and scalloped OD profiles to try to maximize the scraping effect to keep mud cleared from the pads. Some worked lots better than others, but I wasn't involved in that part of the work so I don't have any knowledge of what did or didn't work best.

If I was going to experiment with different steels, I'd start with abrasion resistant sheet and have the parts water jetted. That would bypass the hardening and tempering ops, which are a pain on pieces that large and thin. That would allow you to cut the part, grind for thickness and flatness, and do whatever necessary countersinking or spotfacing at the attachment points as the final operation. Probably try some AR360 first, and then something in the 300 range.

Considering the thickness of the rotors pretty much limits one to using steel rather than any other material, my gut instinct would be to concentrate on various pad materials as there's likely more difference there than what you'd find from one steel to another. All things considered, even the best combination is going to be a somewhat poor compromise as compared to a good brake design.

magneticanomaly said:

Can't they downshift to control speed downhill? That's SOP for truck drivers who would otherwise melt their brakes.

Click to expand...

REALLY?!

This is racing, not cross country shipping. If you want to win, you aren't on the brakes until the last possible second, and until that point, you're on the gas!

magneticanomaly said:

Can't they downshift to control speed downhill? That's SOP for truck drivers who would otherwise melt their brakes.

Click to expand...

Diesel engines do not have engine braking (they have no throttle plates to pull vacuum), they do not simply downshift to slow the truck down they use their Jakes.

What's a "brake rotor?"



Seriously though for competion my guess is the rotors and pads are consumable
items. Nascar? Those are carbon fiber rotors I think, and only have a decent
coefficient when dull red hot. Again, consumable item. Probably only one race
per set.

Carbon brakes in NASCAR? You'd be hauled out behind the woodshed for cheatin' like that.

I think even in Indycar, they only allowed carbon brakes on the super speedways, and cast iron on the road courses. Or I may have that backwards.

Motocross techniques are constantly evolving, things like scrubs and whips were
unheard of 20 years ago and now with four strokes still more new things.
A good technique I picked-up on a Gary Semics video is to use all 5 controls at once.
So as you go into a corner you are using both brakes to slow all the while already
shifting to proper gear, fanning the clutch while powering out. Makes for some
sweet seamless turns that are fast yet almost effortless. I can only imagine how
some aggresive kids work those rotors out.

Stainless for brake rotor?
Hopefully aircraft billet military grade ... sticker on it.
Stainless is quite a bad heat conductor, so it isn't really the best you can have.

Centuries ago, I have been enduro and MX racing. All of the brake rotors started to rust sooner or later. Except where the pad rubbed.
I really don't know the material, but certainly not SS.
I never ruined a brake rotor (except the bent ones) despite I very often used sinter metal pads.

In my eyes, SS is just a hype that will pass. But at least they sell a lot, if they have to replaced frequently.


Nick

magneticanomaly said:

Can't they downshift to control speed downhill? That's SOP for truck drivers who would otherwise melt their brakes.

Click to expand...

I don't know what they are riding but 2 strokes have very little compression braking. Not to mention what the others said.

I noted that the stock rotors appear to be equivalent to 9GU rear and 12GU front for stock and 11GU front and rear for the larger diameter aftermarket rotors. The only one with a ground finish is the OEM front rotor.

If using AR360 I could get 3/16" plate cut and blanchard ground - would localized heating associated with laser cutting be detrimental? I can get laser cutting done faster / cheaper than waterjet cutting.

Design is such that there are clearance holes for shoulder bolt style mounts - no countersinks and rotor appears to "float" side to side on fasteners.