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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 09-14-08, 02:05 PM   #1
leerish
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uncommonly fast decents?

OK, strange bike behavior: it doesn't climb well or accelerate well, and descends faster than it probably should. It's a nice road bike that usually rides wonderfully, but just has been acting weird the past few weeks.

(When I was younger I had a mountain bike that behaved like this but to an extreme, so that descents were terrifying. I never did find out what was wrong with it, because I grew out of it so quickly anyway.)

What do you suppose the problem is, do I just need to make a trip to the LBS for a tune-up?
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Old 09-14-08, 02:20 PM   #2
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and the question is? uncommonly fast decents? compared to what and what do you consider fast? the up hill and accelerating is the engine for sure.
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Old 09-14-08, 02:30 PM   #3
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is this a riddle?
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Old 09-14-08, 02:39 PM   #4
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If you lose weight, it will climb faster and descent slower.

Remember, it's the rider, not the bike! :-P
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Old 09-14-08, 02:44 PM   #5
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Oohhh, busted Local Gravity Modulator. Too bad - gonna be expensive to fix. It's happened to your bikes before, eh? I'd get to the doctor - get a radiation emission eval. Of course, that could get expensive, too....

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Old 09-14-08, 03:04 PM   #6
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ummmmmmmm i'm 125 pounds, i don't think my weight is the issue. smartass. but seriously. doesn't accelerate well, and barrels down gradual slopes.

if anyone's got a constructive response, i'd like to hear it!
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Old 09-14-08, 03:10 PM   #7
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It's not as clear a problem as it might be. The whole point is to make the bicycle the best machine it can be: less friction, less drag, faster speed with less energy spent...and you are complaining that essentially the bike is working too well.

Is it that your brakes don't slow the bike enough going downhill?
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Old 09-14-08, 03:26 PM   #8
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my brakes seem fine, actually. anyway it's not just fast descents though, it's also that riding around on inclines or level ground is like dragging around a tank. been going on for about two weeks... never had issues with it before that. no, i did not gain weight.
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Old 09-14-08, 03:41 PM   #9
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Okay, thank you for the clarification. Do you maintain the same tire pressure as usual? Is it possible you have a brake dragging on the rim without it being noticeable? I've had that happen when my wheel went out-of-true and started rubbing the brake.

I would suggest the tires first. I understand some people find it funny to let a little air out of your tires when you're not looking, and then later they'll make jokes about your weight.
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Old 09-14-08, 04:06 PM   #10
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I understand some people find it funny to let a little air out of your tires when you're not looking, and then later they'll make jokes about your weight.
Won't be funny it you flat out a really fast descent, maybe in the corner.... won't be funny at all.
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Old 09-14-08, 04:27 PM   #11
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Originally Posted by relyt View Post
If you lose weight, it will climb faster and descent slower.

Remember, it's the rider, not the bike! :-P
Weight has nothing to do with how fast you descend. Gravity pulls you down at 32 ft/s no matter how fat you are.
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Old 09-14-08, 04:36 PM   #12
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pardon me for showing my dumb but does it have disc brakes if so check that part to see if the friction is to tight on the disc if it has regular brakes then check the wheel for wobble and placing undue pressure on the wheel
just some thoughts
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Old 09-14-08, 04:39 PM   #13
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I would suggest the tires first. I understand some people find it funny to let a little air out of your tires when you're not looking....
Wouldn't make it seem faster on downhills - at least, not while upright....

Are you indeed traveling faster (per your computer) on downhills than you did previously, or does it simply seem scary fast because the bike's handling has become sketchy? If the latter, or if you're not sure, I'd have the LBS give it a once-over, looking at wheel bearings, etc which might also make it feel sluggish on the flats - or worst case scenario, an injured frame issue. If the former, I stand by my gravity modulator postulate.
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Old 09-14-08, 05:30 PM   #14
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Originally Posted by Darkrider23 View Post
Weight has nothing to do with how fast you descend. Gravity pulls you down at 32 ft/s no matter how fat you are.


BBZZZZZZZZZZTTTT!!!!!

Oh! Sorry, but no.

Gravity accelerates things towards earth as a rate of 32 ft/s/s - every second that passes while an object is falling it gains another 32 ft/s of velocity...

But this is only really true in a vacuum with no other objects exerting force on the falling body. If you drop a feather and a bowling ball at the same time which will hit the ground first? In real life it is the bowling ball (aerodynamic resistance will play a large role in slowing the feather), but in a total vaccum they would hit the ground at the same time (in a vacuum no air = no aerodynamic resistance). If two riders are of approximately the same dimension but one is considerably heavier (like one rider has lead weights strapped all over his body) the heavier rider will be able to coast downhill faster.
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Old 09-14-08, 05:44 PM   #15
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Weight has nothing to do with how fast you descend. Gravity pulls you down at 32 ft/s no matter how fat you are.
Wrong.
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Old 09-14-08, 05:45 PM   #16
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If you are truly going down hill faster, and not just that it feels faster (as someone has asked) then I suspect that weight is somehow the issue.

Is there a chance that someone is playing a joke on you?

Is the bike heavier when you lift it?

Check your tires and frame tubes to see if anything has been added to make them heavier...

Did you just switch to tubes with slime in them to prevent flats?

Did anything change a couple of weeks ago? New tires/wheels etc?
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Old 09-14-08, 07:01 PM   #17
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probably a tire issue. but, it's possible that maybe your bottom bracket is not working correctly, which could mean when you pedal and you're not freewheeling it feels sluggish. and when you are freewheeling and the bottom bracket is not moving, you feel faster.

did anybody follow that?
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Old 09-14-08, 07:21 PM   #18
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One is mixing, or missing, air-drag into the gravity formulae. Personally I prefer 16T2. But unless one is planning to drop the bicycle off a tall building, I don't think it will apply.
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Old 09-15-08, 12:25 AM   #19
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probably a tire issue. but, it's possible that maybe your bottom bracket is not working correctly, which could mean when you pedal and you're not freewheeling it feels sluggish. and when you are freewheeling and the bottom bracket is not moving, you feel faster.

did anybody follow that?
Makes most sense of anything so far.
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Old 09-15-08, 03:07 AM   #20
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How can you ever go downhill too fast?
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