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Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

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Old 12-31-06, 01:39 PM   #1
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coaster brakes "burn out at high speed"?

I'm considering building up a coaster brake beater/commuter for some grimy city riding. In the 12/12/06 "coaster brake specs" discussion, nycbikes noted that coaster hubs are liable to "burn out at high speeds". Does this mean that the hub might burn out if you e-break at high speeds? Or is there some concern with internal friction/centripetal doom that means that the braking mechanism might burn out simply from the stress of fast riding?
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Old 12-31-06, 01:43 PM   #2
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email them to find out.
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Old 12-31-06, 01:55 PM   #3
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there seems to be disagreement on this question, so i'm curious to see what different folks have to say.
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Old 12-31-06, 02:52 PM   #4
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Back in the day we used the same coaster brake hubs for years with no problems. They were used when we got them and then were handed down from brother to brother for 5 iterations. One of them had the added wear and tear of hauling heavy newspapers in moderately hilly conditions year after year.

I don't know that you would call it high speed riding. The bikes were heavy and had fat tires so speed was somewhat limited. OTOH: We did get going pretty good on the downhills.
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Old 12-31-06, 04:00 PM   #5
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They get too hot when braking hard for too long. This can cook the grease in the bearings. A steep long hill can be a problem. You might have to repack the hubs after one long hill.
Thus the name "Repack Hill" when MTB's were just modified fat tire bikes. The ones with coaster brakes had to be repacked after one downhill ride I believe. Rim brakes are a lot better. However in the city on mostly flat roads, I don't see a problem with overheating but they don't stop fast. Compared to a bike with rim brakes front and rear you lose a lot more than half your stopping power. If you are careful you can get used to it. If you want to go very fast in traffic you would be much better off with two rim brakes. I have a few coaster brake bikes and I love them, but I keep off the long steep downhills.
Just going fast is fine, it's the hard braking that's a problem.

I built one with 700c wheels and thin tires, I love it.
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Old 12-31-06, 06:27 PM   #6
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coaster brakes

I agree with 2manybikes in that your primary concern is hills. All that height will be converted to heat which has to go somewhere. It can be dissipated through your hub but only so fast. If you manage your descent, you should be ok, but I prefer also having a front caliper brake so I can build up more speed, and not worry about hurting the coaster. As a data point, today I didn't touch the caliper brake despite descending my favorite climbing hill.

I doubt that you could ride fast enough and brake often enough to cause any significant heat build up in level traffic. The time in between will cool off the hub. Besides, if you're going between sprinting and hard stopping, something's wrong. And of course, if you skid, there's no heat build up (in the hub.)
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Old 12-31-06, 09:35 PM   #7
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The only concern with a coaster brake is if you let the let the heat build up on a long downhill until the lubrication boils or burns. They actually start to smoke after a while. That is a sign, much like when the magic smoke comes out of your tv or stereo, that it needs to be taken apart and fixed.

I've yet to burn one out like that, but I once dropped some water on the coaster hub of my Steamroller (before I put a drum brake on the front) after a very steep two block hill and it sizzled like it was on a frying pan.

There are a lot of factors that contribute to when overheating happens. Wheel size, rider weight, length of hill, skidding/skipping vs gradual braking, etc.

All that being said, coaster hubs are still my transmission of choice.
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Old 12-31-06, 10:23 PM   #8
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Good information on coater brake overhaul can be found in older editons of Sutherland's Handbook for bicycle mechanics. It's a good idea to pull them apart now and again and repack the hub internals with fresh grease every now and again. The frequency really depends on your riding; if you're doing a lot of descents or braking for long skids 24/7, you'll need to repack a lot. If you just bumming around, much less frequency.

One of the advantages to Sutherland's is it gives you detailed step by step diagrams of how to disassemble and then rebuild most older brands of coaster. Older Sutherland's editions can be found for 25-35$ on ebuy, at least they could a couple years agao.
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Old 01-01-07, 01:42 PM   #9
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I have a question:
If you skid with a coaster brake, will it still cook? I'm thinking a long skid down a long steep hill. I'm curious after reading the above post. It seems like since the wheel isn't turning, the brake is actually not building as much heat as it would if you just lightly rode the brake the whole way.
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Old 01-01-07, 01:55 PM   #10
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Braking only produces heat when there is movement and friction. If the hub is locked or spinning freely, then it will not produce heat.

I just put a S/A 3 speed hub with a coaster brake on an old peugoet frame. Unfortunately, I stripped an axel nut, so I can't try it out until I can find a new one.
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Old 01-01-07, 03:29 PM   #11
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Quote:
Originally Posted by fix
I have a question:
If you skid with a coaster brake, will it still cook? I'm thinking a long skid down a long steep hill. I'm curious after reading the above post. It seems like since the wheel isn't turning, the brake is actually not building as much heat as it would if you just lightly rode the brake the whole way.
in this case, the energy will be dissipated between the tire and the road, instead of within the hub...the tire will heat up, and it will wear rapidly...also, unless the rider puts most of his or her weight on the front wheel, it won't be possible to skid for very long before coming to a complete stop...

on very long, fast decents, the best way to avoid heat build up (which with rim brakes, can lead to tire blowouts) is to descend without braking, as aerodynamic drag is proportional to the square of speed...it also helps to put yourself in a more upright position
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Old 01-01-07, 04:32 PM   #12
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Yeah, when going down, catch as much air as you can with your arms and chest.

The main killer with coaster brakes is that there's not a supergood way for the heat to radiate away - it's all on the hub shell rather than on the rim, so considerations of surface area and such aren't so favorable. Also aluminum is a pretty good conductor of heat.

I'd be more concerned about a coaster brake being my only brake more with considerations of wholly inadequate braking rather than smoking the sucker out. But if you had a front brake and a coaster, life would be good. A front brake and a coaster and a rear brake, man, ready for the Alps.
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Old 01-05-07, 08:44 PM   #13
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Sorry I missed the post earlier. I concur with most. I live and have my shop next to a bridge off of which you can build good speed, and good heat if you're riding the brake. I'm not saying it's a frequent occurence that they burn out, I'm just saying it's good citizenship to cover others with a front brake for the just in case.

Physics also says that if you can only lock up one wheel your stopping distance is more than double (three times without a front brake I believe), so even the best coaster brake (or skid stopper) is putting others needlessly at risk.

Just a thought.
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