The perimeter disc brake rotors on the “Vinnie” I wrote about yesterday do a nice job of keeping the wheel open for a very clean look and one comment asked the question why more motorcycle manufacturers don’t use them. Pretty good question in my mind since they seem to make a lot of sense and Buell is using them very effectively on their bikes. If you use only one disc you eliminate a lot of weight from the extra rotor, caliper, hoses and fluid, you lower the rotating mass and the position of the rotor would seem to make the caliper more effective. There may be some positive handling effects just from having the rotor out there to begin with instead of inboard, though that is outside of my knowledge, perhaps some engineers could weigh in on that one.
There have not been a lot of customs that I can think of with perimeter rotors, the bike built by LBF Cycles with the clear Lexan wheels had perimeter discs which they sourced from Krugger Motorcycles of Belgium, a custom builder who uses perimeter rotors on many of his bikes. After those and the Vinnie, who else?
When you look for aftermarket brake rotors, perimeter mounts don’t seem to be available. I don’t know where Matt Hotch got his, perhaps they were made just for him. Does Buell make their own? Hugo Van Waaijen, who works on the Bottpower project, pointed to Braking, a company over in Italy, that has an aftermarket kit with a 17 inch wheel and two perimeter disc brakes. Looks like a nice kit, something I haven’t seen around anywhere else, though I really am not a brake expert so we’re outside my area.
One thought I have is that perimeter rotors would have to be part of the wheel or mounted to a wheel with some attachment points built in and those are not available. No wheels, no brakes. But if they are effective, wouldn’t some wheel builders respond or some brake companies ask a wheel builder to make them? How about a company like Performance Machine? They make wheels and brakes, seems like a natural next step.
Are perimeter discs available from more companies? If so, who? If they are, why aren’t more builders using them? And, back to the original question, why aren’t more manufacturers using them? Inquiring minds want to know.
Link: Braking
Mark Savory says
There is an outfit in Colorado that does perimeter brakes that I’ve talked to last summer. (I can’t remember their URL) They have done brakes used for Goldhammer’s bikes and others.
The brake disk material is readily available — one just needs to make the phonecalls to track it down. Then its just a matter of getting it cut. That’s the easy part. Mounting calipers and mounting the disk to the wheel are the big challenges! (unless you have a girder-style fork)
I applaud Braking for their wheel/brake setup! Hopefully they can OEM them to a manufacturer.
Gary says
Well with regards to handling you want light weight and low moment of inertia. So if you go to a perimeter design and then are able to use one disc instead of two you can maybe (but I doubt it) save enough mass to make it practical. The problem is that the moment of inertia goes up with the 4th power of the radius. So sticking weight farther away from the axle like that could be bad news.
Buell claims that they are losing not only the weight of an additional disc, but also that they are losing weight by making the spokes of the wheel thinner since they don’t have to transfer braking force anymore. Its plausible enough and thats probably all that matters. I haven’t seen any numbers that back it up.
Personally, until I see it on a real race bike I think its just for show.
todd says
Think about cost. How much of the material in the center is thrown into the recycling bin? The other is inertia like Gary said. Losing unsprung weight isn’t as beneficial as reducing rotating mass. I think if one used a carbon fiber wheel rim then you’re way ahead on both accounts.
There’s a couple other ways to think about it too: the perimeter rotor is a Buell thing, putting one on your bike makes people think you copied Buell. Brakes of the current trend are already highly effective. Money spent on improving the motor, chassis, or suspension can be better appreciated.
-todd
Hugo says
I think a good solution would be brakes fixed to the rim (like BMW for instance) and then use ceramic discs. An American company, Braketech, is working on it and it saves a lot of unsprung weight. http://www.braketech.com/cmc.html
Yamaha OE 320mm stainless: 3lbs 3.0oz at 4.5mm thick [1446grams]
BrakeTech 320mm Iron: 2lbs 15.1oz at 5.0mm thick [1335grams]
BrakeTech 320mm CMC: 1lb 1.2oz at 5.0mm thick [488grams]
Hellllooooo that is 1kg less per disc! The price is still pretty high for a set, but for losing so much unsprung weight it is worth it (especialy compared to CF wheels). Slap on some magnesium rims and I don’t think you’ll recognize your own bike…
BTW Chris Cosentino designed his own bike ( http://www.cosentinoengineering.com/index_files/page0005.htm ) and used the braking perimeter disc rotor with good results I think. They now work on an interesting supermono: http://www.ti-racing.com/
Bob Horn says
AP Lockheed experimeted with perimeter rotors for racing and street use back in the early ’80’s. They wouldn’t produce the street version since they said it was prone to curb damage while parking. Keep in mind the tire widths of that era. As far as the racing version went, I have no idea.
The Honda “NAS” concept bike had one back in 2001 – the same time Buell released their production version.
I built mine back in 1989 by cutting out a rotor from stainless by hand. It mounted to a precisely located 5052 aluminum ring welded to a Akront Nervi rim. The calipers were two tiny PM units (like the NAS from 10+ years later). The brakes worked great, once race pads were installed. The high surface speeds ate the stock pads very quickly. The pad change was AP Lockheed’s suggestion – they were right. The rotor wore less after that!
They aren’t hard to make. But I’m getting a good laugh at those who think they are something new and/or original by Buell or whatever custom builder whose 15 minutes isn’t up yet.
hoyt says
excuse me if this is a silly question, but if the smaller discs are better why hasn’t the size of the disc been reduced and more pistons added? Say 8, instead of 6?
Have the engineers reached the magical size of the disc and consequently the proper placement & shape of the radial mounting with the current 6 piston calipers?
Or is the 8 piston caliper and ever smaller disc another evolutionary step yet to come?
p.s. very cool links Hugo. Single cylinder sportbikes are hopefully one of the next trends to be recycled for OEM street bikes. Maybe they will make custom kits for street use? Cagiva maybe coming out with a street bike using the Husky emissions-legal thumper.
hoyt says
…forgot to add:
considering all racebikes use “traditional” disc configurations instead of the radial mounted setup, I would venture to guess that the traditional setup is better for the intended application of performance bikes
chris says
i guess i learned what happens when you ask a question on here! thanks to Kneeslider for posting on this. personally – i now think it’s more of a styling exercise, but using a carbon or mag wheel and Braketech’s “magic” stuff – perimeters would be the way i’d go for performance. assuming it does all the magic they say it does. but the fact that the upper echelon’s of racing still stick to discs (even those with 4 wheels) makes me think it’s just less practical, if nothing else, to use a rim brake.
and hugo – those links are sweet. bring on the monocylinder performance bikes and i will be FIRST in line. especially if they have even half the tech of the TI Racing bike. that thing is brilliant. think they’ll make a street version?
Chris says
I saw Other Chris’s question in the other thread and ran some quick numbers. Assumptions I’m making here:
• neither rotor is drilled
• both rotors are perfect circles
• both rotors have identical thickness and are made of the same material
Mass is volume * density, and since we’re assuming thickness and density are the same, we can reduce the mass calculation to one of surface area.
Let’s say a “traditional” rotor is simply a solid disc of material for the sake of easy calculation. This may not be quite accurate, but it’ll give us a reasonable idea, and I’ll run the numbers for the other case in a second.
A “traditional” rotor, 10 inches in diameter, has a surface area of 314 in^2.
A perimeter rotor, 17 inches in outside diameter and 15 inches in inside diameter, has a surface area of 201 in^2. In terms of moment of inertia, this is essentially equivalent to mounting a 201-unit mass with 16-inch diameter on the wheel, giving it a moment of inertia of 16 * 201 * wheel speed, or about 3200 “inertia units” (where wheel speed is held constant).
A traditional rotor mounted on a lightweight (hypothetically weightless, for the sake of calculation) center, with a rotor O.D. of 12″ and rotor I.D. of 10″, has a surface area of 138 in^2. Inertia-wise, this is more like 1500 “inertia units”, assuming the same wheel speed as before.
The perimeter rotor obviously beats out 1970s-era solid rotor technology, but rotors on the latest sportbikes are much closer to the third example than the first, and they’re quite obviously superior in terms of overall mass and moment of inertia.
And yeah, you’d be in much better shape just using a lighter rim and ceramic rotors. 🙂
cl
hoyt says
Chris – the more I read, the more apparent traditional rotors are the way to go for powerful racebikes…
…but, Please clarify: your calculations above include comparing 1 traditional rotor against 1 perimeter rotor, right? As you may know, Buells use just one perimeter rotor, not 2. Whereas, all OEM Japanese sportbikes use 2 traditional rotors.
Is this where Buell is making up for reduced weight and inertia?
hoyt says
oops, I just re-read your comment, 2 traditional rotors at 1500 inertia units is still under one, 3200 inertia unit perimeter rotor.
maybe a Buell engineer will chime in
Chris says
Hoyt: right. I haven’t done any real-world calculations to figure out how much rotational inertia we’re actually dealing with here, and I don’t know enough to say for certain whether the ~10% increase would be noticeable or not, nor do I have complete confidence that a single perimeter rotor would be as effective in all cases as twin traditional rotors. If it is, that’s the only way I can see perimeter rotors even making a little sense, since you can eliminate the weight of the second caliper and brake line, plus the associated fittings, and possibly use a smaller master cylinder.
All other things being equal, though, I can’t see much of a case for perimeter rotors, and I’m certain that the major bike manufacturers have given this much more thought than I have, being that racing consumes a major part of their R&D budget and the goal of racing is to have the fastest bike out there.
cl
chris says
well now. i think that quite concisely answers the question. perimeters lose. barely in my opinion. but they still lose. on a custom bike – where performance isn’t of ABSOLUTE importance – i like the look. but it just doesn’t make sense for a performance bike when you look at the numbers. except for that silly old Buell.
Bob Horn says
Tony Foale had them on his QL and Q2 bike projects. They work great on swing-arm based front ends – they allow a lot more design freedom in the hub area. Which is why I used one.
Philscbx says
It’s simple logic.
Perimeter braking flat out will cost more to engineer and apply.
On the other hand the larger the diameter, the more power you have available and less heat. With pads the same size.
Braking systems complete with all parts combined in both packages, and perimeter is going to weight a lot less. If not half as much.
As for racing, that’s another deal altogether. Perimeter more than likely can’t apply here because of the compact design of components.
But if kept in realm of a normal street cruiser, I’d bet some serious cash it works great. Just in the upgraded performance response of the suspension.
Street cruisers are not slamming the brakes every 1000ft at mach II.
I think this is where people confuse topics comparing oranges to raisins.
In actual reality, a common sense rider on a cruiser maybe uses the brakes the last 100ft after downshifting.
Those who don’t downshift are not qualified riders in any category.
I just happened to be at the International Bike Show in Mpls Mn.
Beautiful customs had perimeter braking on both wheels.
Sean says
Perimeter’s are good, for improving stopping power. It’s simple physics, the closer the brake to the fulcrum the more power will be needed to equal the brake further from the fulcrum. They do, unfortunately, increase rotational inertia, which makes turning harder. As with everything on a motorcycle, you can’t have the best of both worlds, it’s one or the other.
Bob Horn says
Here’s some info on the subject:
http://buell.com/en_us/buell_way/buelltech/pdf_0102_2003.pdf
Robert Skipper says
I came across this old discussion while doing a search for perimeter disc brakes. My logic is simple enough – if I’m going to shell out several thousand bucks for a set of wheels, I want to see them. It’s not for a performance bike. Soooo…In the year and a half that have passed since this discussion, are more companies out there making them?
todd says
Robert, you should also check out this hub-brake post:
http://thekneeslider.com/archives/2007/05/16/360-brake-by-baldwin-wilson-development-corporation/
-todd
Robert Skipper says
Todd,
Thanks for the reply. I’ve looked into a few options, and until last week had decided to go with a tranny brake on the rear and no brake up front. Common sense prevailed, thankfully. Since I want to get started on the bike, I’ll worry about the more exotic setups another time. Besides, a certain well known chopper company refused to produce my wheel design, saying their software would not allow for unbalanced designs. I know the wheels were going to be asymmetrical, but thought they could be balanced with aluminum weights welded inside the wheels on the light side. Turns out I was right, and there is a company who will do them. But for now I’m going with a standard setup so that I can hopefully be uo and running in a few months.