|   inverted disc rotors | bsenez
Sep 25, 2001 3:44 AM | | This is a pic of a buell with an inverted front rotor, i was wondering why this design isn't used on bikes. It seems like a good idea, you can build a lighter wheel, there will be less flex, and of course you have a ~24 inch rotor. |
| Ahhh that's an easy one | Pat T.®
Sep 25, 2001 3:56 AM | | One big hit with a rock and your rotor is either out of true, or toast all together. Plus it defeats the purpose of having your braking surface farther away from dirt, mud, and water.
Pat T.® MCM #69, MSPS #003 |
| Ahhh that's an easy one | bsenez
Sep 25, 2001 7:12 AM | | i think the rotor would be pretty tough since it is anchored on the outside by 6 bolts it would be hard to bend... it would get really dinged up if left exposed though. maybe a guard such as those used for the stanchions of inverted forks would be neccesary. i thick tough plastic piece that goes all around the the rim. it could even be slipped between the tires bead and the sidewall of the rim. as for heat, a huge rotor like that would diffuse it pretty quick. i have heard stories of roadies blowing a tire from heat on long descents, but this is a rotor which cools much quicker than a rim because it has less mass, although a good amount of heat may transfer to the rim and tire i do not think it would be enough to cause problems. maybe a ram air system to cool the caliper would help. |
| It's not worth the headache | Dave K
Sep 25, 2001 9:38 AM | | It's a solution for a problem that is not really that big a deal. A street motorcycle uses a big disc (or usually twin discs) because they need to slow a much bigger mass down much quicker (street tires can generate lots of traction). The 200-300 lbs of bicycle and rider do not require that much braking power. Motorcross bikes don't need that much braking power (too much braking force and the front tire is sliding) which is why they use single discs which are comparatively smaller than ones used by their road cousins.
Now back to bikes. If you put the rotor out at near the circumference of the wheel, you add a lot of weight. One, the rotor itself is going to be heavy (there is a lot of material there). Secondly, it's rotating weight that is made worse by the fact that it is situated out at that radius. Some second year physics will tell you that adding mass to the outer radius has a much larger gyroscopic effect than adding the same mass to near the center.
Heat transfer is not a huge problem in bike disc brakes as long as the system is designed well and used in the situation it was designed for. Using a light weight XC style disc brake (e.g. Hope Mini) on a long steep downhill will obviously overtax that system. That is why Gustavs, Purple Hayes and DH4's are used in those settings.
The Buell style brake was designed to use a large single rotor in place of 2 smaller discs. It's a neat idea for that motorcycle, but I don't see it translating into use for bicycles. We simply do not need the amount of braking power created by such a design. And if we did require that much power, there are simpler, lighter and more proven designs out there that would suit our needs better.
Dave |
| but it would be cool | bsenez
Sep 25, 2001 10:14 AM | | All of what you said is true, and i'll admit that there are very few bicycle application where it would be needed (tandems however do come to mind), but it would be pretty cool. you could probably even manage it with a stock fork and huge adapter, assuming the torque wouldn't just the adapter right the fork leg. you would probably want to add brace from the caliper to near the brake arch of the fork. yes, it all adds to more weight and complexity both things that are avoided. talk about one finger braking though :) i personally only weigh about 195 with my downhill bike but i've seen some guys at the mountain pushing 300lbs who look like they could use all the braking power they can get. |
| Not really | Pat T.®
Sep 25, 2001 3:59 PM | | With all that weight right on or near the front wheel your handling would be horrible. The strength issue is the worst part. Look how easy it is to bend a rim, and disc rotors bend fairly easy too, even from uneven torque on the bolts. Just to get a good system like that to work on a DH bike or Tandem would add probably 10lbs to the bike. My bike is at 42lbs right now, and that's with GustavM's, which I can stop on a dime, or do nose picks with one finger....plus I weigh 230. I think if DH'rs wanted to get more braking they would go with dual 140mm rotors, maybe 150mm. 205mm is the largest you can get right now....there may be a 215mm but I have not seen one. My front rotor is 190mm and that gets too close to the rocks sometimes. As far as using it on the road, I don't know any roadie that would add 10oz to their bike, let alone enough to get that brake to work on a tandem. Cool idea for the Buell, but not a good application for bicycles.
Pat T.® MCM #69, MSPS #003 |
| Even a Tandem wouldn't need.... | Dave K
Sep 25, 2001 6:07 PM | | a rotor that big. Your limiting factor is how much traction you have. No point in having a brake that will lock up your front tire as soon as you breathe on the lever. That is why motorcross brakes aren't as powerful as street bike brakes. There simply isn't enough traction in the dirt to require a twin disc set-up that is common on a street bike.
For tandems, you would probably be super happy with something like the Hope Enduro 4's or a Gustav. I have friends also pushing 300 lbs and they are more than satisfied with the current crop of high end DH brakes. Controllability along with power is the key. You have to be able to modulate the brake easily enough so as to not lock up the wheel.
In the end it is a waste of time to build a brake like the Buell design for bicycles. That is why it isn't cool. It would be a styling exercise and not any improvement on what is currently out on the market.
Dave |
| Well.. | Robert.
Sep 25, 2001 12:28 PM | | It will be able to be bent, thats the thing. Hit a rock and the thing will be dinged or knicked at least.
A huge rotor like that would add a lot of weight. So would ram air and a tough plastic peice.
The whole purpose of a brake system is to HAVE mass to absorb heat. Lighter masses absorb and release heat quicker but also heat up MUCH more and MUCH quicker. If you need to dissapate say 100 KW of energy a heavier mass may heat up to 300 degrees whereas a mass say 6 times lighter will still need to absorb the same amount of heat and will heat up to 1800 degrees enough to melt metal. As far as braking goes heavier the rotor the better.
Current disc brakes have enough power to lock the front wheel with little problems. This would be superflouous. Want extended Downhill Tandem heat capacity get a larger heavier rotor. |
| Real Reason | Torpedo
Sep 25, 2001 4:14 PM | | A super large rotor dispates heat better. So they did away with double rotors that are on some bikes for one big rotor. This is a street bike not a moto-x bike. You have significant amount of distance between tire and rotor and chances of hitting something is remote, now picture descending a rocky road, rocks bouncing all over the place, squeezing between big rocks that scrub the tire. And weight, I would suspect that for MTB use it would be heavier than what is being used. |
| Problem | Dougal THUG #1
Sep 25, 2001 4:32 PM | | The rotor is anchored to your rim. Your rim can dent pretty easily, thus bending the rotor.
Dougal.8m.com |
| heat transfer thru the rim... | Nonny
Sep 25, 2001 4:40 AM | | ...i'd think a design like that would seriously heat up the rim (and thus the tire) pretty darn quick under heavy use. Looks neat tho, but i'd hate to blow a tire out while braking down a mountainside cause of heat from the rotor cooking the tire.
Non. |
| I agree w/ Pat T | shiggy©®
Sep 25, 2001 8:00 AM | | We already have "inverted discs." They are called rim brakes. The moto style on the buell would have all of the disadvantages of both rim brakes and disc brakes and very few of the advantages of either |
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