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Bike Drag

Old 06-19-09, 04:26 PM
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ChaosCon
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Bike Drag

Hey all -

Just upgraded from an old Schwinn World Sport to a Specialized Sirrus Sport. I've been noticing that on the Sirrus I seem to slow down faster from an equivalent coasting speed. Seems to me that one of 3 things is the problem:
  1. The bike's aerodynamics (seems unlikely, because I use the more upright riding position on the Schwinn, which is very similar to the Sirrus)
  2. A mis-calibrated part (also seems unlikely, due to the 'newness' of the bike)
  3. The bike's momentum (seems most probable in my opinion - Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth - Occam's Razor, etc...)

Since this is my first new bike, I was just wondering whether the small but noticeable difference in weight can make such a change in a bike's kinetics. Thanks for helpin' a n00b out!
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Old 06-19-09, 05:05 PM
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I have no idea what much of your post is refering to... mis-calibrated part? But check the wheels obviously. Put the bike on a stand on simply elevate the wheels and make sure the wheels spin easily and true. Give 'em a spin and they should spin on their own for a good while. No noisy bearings or anything. No brakes dragging either. Make sure the tires are inflated properly. If everything checks out O.K. then I'd say your deceleration rate is what it is. And yes, I'm aware of Occam's Razor.
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Old 06-19-09, 10:48 PM
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The 15-lb wheels on the Schwinn behaved like flywheels and helped it to maintain more momentum; the Sirrus's lighter wheels don't have the same flywheel effect.



More likely, though, is that something's out of adjustment, whether it's the brake calipers or something else. My bet is on a dragging brake pad.
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Old 06-20-09, 02:00 PM
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It could also be a difference in the tires; tire thickness can make a significant amount of difference in rolling efficiency. Thinner tires roll easier, but get flats easier too. If you had fairly-thin carcass tires on the first bike, and fairly-thick tires on the second, you can notice the difference in rolling resistance.
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Old 06-20-09, 02:29 PM
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Did the bike shop or manufacturer properly adjust the axle cones on the front and rear hub? If you grab the wheel and wiggle it side to side, there should be NO play to either side, front or rear wheel. If you raise a wheel off the ground and give it a light spin, it should spin easily and slow down gradually, coming to a stop with the valve at or nearly at the bottom of the wheel (closest to the ground). That's the heaviest part of the wheel so it will come to a stop in that position. It may even reverse direction if the valve goes beyond the bottom on the last revolution.

There is a remote possibility that the hubs and bearings on the old Schwinn are just better quality than the new ones. I think the World Sport may have been a model made by Panaonic in Japan and be far better quality than the Made-In-America Schwinn. If so, it will say, Made in Japan on the frame.

The other likely source of friction is the brake pads. If the brakes rub at any point as you turn the wheel, they are not properly adjusted. Open them up a tad and try to spin the wheel again. This all should have been checked by your LBS if they did a proper job of setting up the bike.

If you want to learn how to do it yourself, check out the Sheldon Brown website at Harris Cyclery. Just google on Sheldon Brown and it will come up. It is a simple job just taking a few minutes but is a lot easier if you have a set of cone wrenches, extra thin open end wrenches that are designed specifically for adjusting cones. They are not expensive and one set will last you a lifetime.
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Old 06-20-09, 07:27 PM
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A while back, I was on a group ride on my Worksman bike. I noticed on one downhill, a younger lighter guy was coasting down it on a newish road bike, hunched over in aero position, and I was sitting up but still gaining on him. So yes, weight can be noticeable at certain times.
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Old 06-20-09, 07:41 PM
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Thanks for the input guys!

I checked, double checked, and triple checked and it's definitely not a stuck brake pad Spun the wheels - no wiggle at all, and they did stop at the heaviest part. So I'm thinking it's the weight and my not being used to such a light craft I've got one more thing I need to have tweaked on it by the LBS, so I'll mention it when I go back, but I'm significantly more at ease now. Thanks!
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Old 06-20-09, 08:08 PM
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Originally Posted by ChaosCon View Post
Thanks for the input guys!

I checked, double checked, and triple checked and it's definitely not a stuck brake pad Spun the wheels - no wiggle at all, and they did stop at the heaviest part. So I'm thinking it's the weight and my not being used to such a light craft I've got one more thing I need to have tweaked on it by the LBS, so I'll mention it when I go back, but I'm significantly more at ease now. Thanks!
How long did they spin? The front should spin for a long, long time; the back will have a little drag from the freehub pawls. If the wheels' bearings are cone-and-cup instead of cartridge (which is my guess from looking at the pic at specialized.com), they could actually be too tight, creating some resistance of their own.
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Old 06-20-09, 11:41 PM
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Don't forget the tires. Different tires (even when similar types) have different rolling resistances.
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Old 06-21-09, 10:42 AM
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Originally Posted by BarracksSi View Post
How long did they spin? The front should spin for a long, long time; the back will have a little drag from the freehub pawls. If the wheels' bearings are cone-and-cup instead of cartridge (which is my guess from looking at the pic at specialized.com), they could actually be too tight, creating some resistance of their own.
Front one did indeed spin forever - about 30 seconds with a light push (certainly not anything like riding speed). The rear one did stop sooner - after about 12s with a similar push.
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Old 06-21-09, 11:47 AM
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Do the same with your other bike (assuming you still have it).
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Old 06-21-09, 11:59 AM
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Aha! Bingo! The front tires were comparable, but the old bike's rear tire spun 2 to 3x longer. Does that indeed suggest the bearings?


And thanks for taking the time to help me out! I really do appreciate it!!
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Old 06-21-09, 12:03 PM
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It might be the freehub. See what your LBS says about it, and whether other specimens of the same wheel do the same thing.
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