Riddle me this-wife's new bike can't coast

[sjbraun]

Okay, perhaps there was a bit of hyperbole in the title, but I need help trying to figure out why my wife's new bike is such a slug going downhill.
At first I didn't quite believe my wife's complaints, but then we did some testing. We'll be cruising along on a downhill and all will be well, but as soon as she stops pedaling, she immediately slows, not just a little, more like 2-3 mph.
I've checked her brake alignment, no rubbing that I can see. Is there anywhere besides her wheels that could cause this?
Her wheels at 1400gm clinchers: 28 hole Kinlin XR-200 laced to C-4 hubs.

Thanks

[bike22]

does she weigh less than you?

[thwart]

Wheel/tire rubbing chainstay. Or (much less likely) in front rubbing the fork.

If that's not it, throw in another rear wheel to see if there's some freehub dysfunction going on.

[Louis]

Assuming it's not the rear hub, then lack of potential energy (i.e. is she a featherweight?) seems to be the most likely reason.

[Richard]

If she takes her feet off the pedals, do the cranks keep turning? If so, there is an issue with the rear wheel and she is at risk for wrapping the chain and making quite a mess if it isn't fixed.

[rice rocket]

Did she buy a fixie? :D

[martinrjensen]

If the rear wheel quick release is not tight enough, the wheel will pull over to left side and rub on the chainstay. It won't make much noise either so it's easy to miss

[swg]

I hate to say it but there is a flaw in the C-4 hub. It requires a shim to allow the cassette to clear and for the freewheel to work properly. Contact C-4 and they will send you the shim and instruction on where to install the shim. Otherwise they have been good hubs.

[buldogge]

Also, make sure of the opposite and insure that the rear skewer is not overtightened and causing drag.

-Mark in St. Louis

[markie]

The scientist in me asks that you and your wife go the the top of a hill, switch bikes with your wife, and then see which bike is the fastest downhill.

As already asked, "do you weigh more than your wife?"

[sjbraun]

Yes, I weigh more than my wife. we realize that she's at a disadvantage due to her reduced mass, but at 135 pounds, she's not super small. What we see happening to her isn't something we see with other similarly massed riders.

I guess the wheels go back to Fairwheel today for a check.

Thanks to everyone for their suggestions.

[oldpotatoe]

I hate to say it but there is a flaw in the C-4 hub. It requires a shim to allow the cassette to clear and for the freewheel to work properly. Contact C-4 and they will send you the shim and instruction on where to install the shim. Otherwise they have been good hubs.

'Otherwise good hubs'.....really, how? If they have a defect?
Sorry, This seems like another case of product testing by the customer.

[zap]

does she weigh less than you?

My wife weighs quite a bit less than I do and I have a hard time keeping up.

Aerodynamics baby.

Hub would be my guess.

[Joachim]

I've had wheels with C-4 hubs. My rear hub had excessive drag due to a faulty (?) seal (the lip folded inside, increasing drag). It was replaced with a low-drag lip-less seal.

[fourflys]

My wife weighs quite a bit less than I do and I have a hard time keeping up.

Aerodynamics baby.

Hub would be my guess.

that's interesting because I weight about 190# and one of my riding buddies is about 250#... I can smoke him up hills, but on the otherside he'll come whizzing by me at a good 3-5mph faster than me...

[flydhest]

at 135 pounds, she's not super small.



Dude . . . are you really a slow learner? Talk about things not to say about the wife

How's this, "why yes, I do weigh more than she does. In fact, substantially so, because she is petite. Nevertheless, I was making the comparison to other, similarly willowly cyclists."

[joking, of course]

[William]

that's interesting because I weight about 190# and one of my riding buddies is about 250#... I can smoke him up hills, but on the otherside he'll come whizzing by me at a good 3-5mph faster than me...

Yeah, just get out of the way because I'm like a loose cannonball picking up speed. :) If there is a group, I have to pull out and move up front otherwise I'll be riding up on folks without even trying.



W.

[RPS]

My wife weighs quite a bit less than I do and I have a hard time keeping up.

Aerodynamics baby.

Hub would be my guess.
Exactly. The potential energy due to elevation is the same for everyone on a per-weight basis, so it’s just a matter of who has the lower wind drag on a per-weight basis (excluding differences in rolling friction which is normally minimal).

I think thin tall riders of equal weight tend to have more aerodynamic drag than fat short ones. Discussing weight alone is not enough IMO. Plus position on the bike is so important too.

[Richard]

"who has the lower wind drag on a per-weight basis " which always will favor a heavier rider over a lighter rider if both get in some form of tuck.

[William]

I understand what physics state....

But my real world experience has always been that I will gain speed faster if every one is coasting or soft pedaling. That's why in a group, unless I want to constantly be riding my brakes, I need to pull out and pull ahead which I can generally do without effort.

Maybe this is more in-line of what is going on....

The magnitude of terminal velocity depends on the weight of the falling body. For a heavy object, the terminal velocity is generally greater than a light object. This is because air resistance is proportional to the falling body's velocity squared. For an object to experience terminal velocity, air resistance must balance weight. An example that shows this phenomenon was the classic illustration of a rock and a feather being dropped simultaneously. In a vacuum with zero air resistance, these two objects will experience the same acceleration. But on the earth this is not true. Air resistance will equal weight more quickly for the feather than it would for the rock. Thus the rock would accelerate longer and experience a terminal velocity greater than the feather.




William

[RPS]

OK, let me word it differently:

It’s not that small riders don’t weigh enough, it’s that they have too much aero drag. :rolleyes:

[William]

OK, let me word it differently:

It’s not that small riders don’t weigh enough, it’s that they have too much aero drag. :rolleyes:

That's why they always try to suck my wheel. :bike:

:D



William

[Fixed]

I've had wheels with C-4 hubs. My rear hub had excessive drag due to a faulty (?) seal (the lip folded inside, increasing drag). It was replaced with a low-drag lip-less seal.

rear hub blues
imho

[swg]

'Otherwise good hubs'.....really, how? If they have a defect?
Sorry, This seems like another case of product testing by the customer.

So far the shim is working and have about 2500 miles on them. You have a good point & I agree it should not be required & looks like anther case of product testing. I just have too many other things in life to take care of right now and need all the time I can get my hands on for riding. So as long as their running I'm riding :)

[rustychisel]

rear hub blues
imho

Alex the seal

http://www.youtube.com/watch?v=QrYM2Gt9sMw

[sjbraun]

So this morning, me and the missus went for a ride. I switched out her wheels for a set of mine, DT Swiss 240s hubs laced to DT Swiss 1.1 rims, Michelin Pro 2 Race tires. What a difference!
I thought something was weird (in a good way,) when she took off at the beginning of the ride. On a mostly flat stretch, she rode comfortably at 17-18 mph. (Lately, she's been working to ride the same stretch at 15 mph.)
when we got to the downhills, she flew!?!
Instead of slowing when she coasted or needing to pedal to keep up, she coasted right along with me, even speeding up as she coasted down steeper pitches.
I still don't understand how the old wheels could have that much resistance, but
a different set seemed to make a huge difference.
I took her other wheels to Fairwheel. They switched out a seal and lubed the hubs. I think I'll let her ride my DT Swiss wheelset for a bit longer and then switch back to her C-4 hub wheels.
I don't understand what happened, but at least she was pleased to be riding better.

Steve

[bobswire]

So this morning, me and the missus went for a ride. I switched out her wheels for a set of mine, DT Swiss 240s hubs laced to DT Swiss 1.1 rims, Michelin Pro 2 Race tires. What a difference!
I thought something was weird (in a good way,) when she took off at the beginning of the ride. On a mostly flat stretch, she rode comfortably at 17-18 mph. (Lately, she's been working to ride the same stretch at 15 mph.)
when we got to the downhills, she flew!?!
Instead of slowing when she coasted or needing to pedal to keep up, she coasted right along with me, even speeding up as she coasted down steeper pitches.
I still don't understand how the old wheels could have that much resistance, but
a different set seemed to make a huge difference.
I took her other wheels to Fairwheel. They switched out a seal and lubed the hubs. I think I'll let her ride my DT Swiss wheelset for a bit longer and then switch back to her C-4 hub wheels.
I don't understand what happened, but at least she was pleased to be riding better.

Steve

Good luck trying to get those wheels back from her.

[sjbraun]

That's how I'll get a new wheelset!!

[Louis]

Thanks for the update. I was wondering how this was resolved.

It brings up something that I've wondered about in the past, but haven't figured out:

Is there a scientific, quantifiable way to measure wheel and / or drivetrain drag?

I would think that something that was as bad as the OP's wife's problem could be diagnosed simply by either a) lifting the rear wheel off the ground, giving the cranks a few turns, then seeing how the wheel spun down, or b) removing the wheel and spinning the axle / freehub with your fingers.

However, neither of those methods is terribly accurate, and based more on your "feel" for what's good and what isn't.

If anyone out there has a better way to do it, please share.

(The same question applies to the drag induced by the crank + chain + r-der jockey wheels.)

Louis

[swg]

'Otherwise good hubs'.....really, how? If they have a defect?
Sorry, This seems like another case of product testing by the customer.


I was contacted by C-4 requesting that I send my wheel back to them and they would take care of any issues. Sent it back to them and they rebuilt the hub. Took it out for the first time since getting it returned and it worked great. We will see how it holds up.

Thanks to C-4 for stepping up.