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Old 08-25-06, 09:43 AM   #1
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Are aero shoe covers a good buy.

I bought one pair of aero shoe covers. Think they are made of some lycra/vinyl? like material. Made by Pearl Azumi. I must have worn them no more than 10 times. I look at the bottoms and they are ripped to shreds. Doubt there is much more life to them.
I see Voler has them on sale now. Anyone had good luck with their endurance. Mine cost like $29. I expect them to last longer than 10 times. I liked them for warmth. ANyone recommend them and if you do what brand. Probably if one races in them, it minimizes road contact. For recreational riders , WIth stopping/going traffic lights, you unclip lots. That is probably the problem. Would you use this or other type shoe covers for recreatoinal riders. ? Thanks.
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Old 08-25-06, 10:03 AM   #2
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If your objective is warmth and not aerodynamics, then there are other options.

I don't own them, but I will be considering a bootie when it gets colder... it is, for me, something to keep my foot warm. Reduced aero drag of my feet at my usual 15 mph is meaningless to me. YMMV.
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Old 08-25-06, 10:06 AM   #3
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Originally Posted by Little Darwin
If your objective is warmth and not aerodynamics, then there are other options.

I don't own them, but I will be considering a bootie when it gets colder... it is, for me, something to keep my foot warm. Reduced aero drag of my feet at my usual 15 mph is meaningless to me. YMMV.
+1 on the bootie for warmth, but I find that the neoprene ones seem pretty aero anyway.

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Old 08-25-06, 10:27 AM   #4
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Aero shoe covers? Unless you're consistently riding 40kph+, they won't be of any use to you whatsoever. Now if you're using them for warmth, other posters have already covered that.
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Old 08-25-06, 10:48 AM   #5
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Good options mentioned here. . I bought the aero, not that they were aero; but I was at a store and they were on sale. They have kept my feet warm, just 10 rides and they are ripped to shreds, makes them pretty uncomfortable. Wondering if a similiar construction by another brand might be a stronger blend of material. Will give the neoprene's a try.
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Old 08-25-06, 12:41 PM   #6
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Hmm. Walking with them on pavement does shred them. I used to pull up the toe and heal parts as I came to a stop so they wouldn't touch the ground when walking, and the central band part was elevated by the heal bumper and cleat so it didn't touch the ground either.

The trackstand would be another tactic to prolonging the life of them at stoplights.

Usefulness? If you ride in a lot of grime, they could extend shoe life, I guess. And warmthwise, they are not warm or waterproof like neoprene, but then they are nowhere near as heavy or bulky.

Aerodynamics? Debateable. If you've already squeezed down to a no-wind-flapping jersey fit and are running a good low position on somewhat aero equipment, they are probably the next low-cost step.

Last edited by ghettocruiser; 08-25-06 at 12:48 PM.
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Old 08-25-06, 01:30 PM   #7
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Wonder if neoprene will shred like lycra shoe covers?
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Old 08-25-06, 01:57 PM   #8
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Originally Posted by operator
Aero shoe covers? Unless you're consistently riding 40kph+, they won't be of any use to you whatsoever. Now if you're using them for warmth, other posters have already covered that.
I've said it before, now I'll say it again; if the objective is to save time, aero equipment saves more time for a slower rider than a faster one. (www.analyticcycling.com) Shoe covers are just as effective at reducing drag for a 15 km/hr rider as they are for the 40 km/hr one. What magical transformation do you think happens at 40 km/hr or thereabouts?
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Old 08-25-06, 02:47 PM   #9
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I think maybe at 15 km/hr there are factors bigger than the aerodynamics of your shoes that affect your speed.
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Old 08-25-06, 03:50 PM   #10
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Originally Posted by asgelle
I've said it before, now I'll say it again; if the objective is to save time, aero equipment saves more time for a slower rider than a faster one. (www.analyticcycling.com) Shoe covers are just as effective at reducing drag for a 15 km/hr rider as they are for the 40 km/hr one. What magical transformation do you think happens at 40 km/hr or thereabouts?
That looks like an interesting site. Doesn't drag increase proportional to the square of velocity?
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Old 08-25-06, 04:03 PM   #11
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Originally Posted by sivat
That looks like an interesting site. Doesn't drag increase proportional to the square of velocity?
Yes, but drag is linear in frontal area and drag coefficient. Further, for normal cycling speeds, as long as the rider doesn't change position, frontal area and drag coefficient are constant and don't depend on speed.
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Old 08-26-06, 10:52 PM   #12
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Originally Posted by asgelle
Yes, but drag is linear in frontal area and drag coefficient. Further, for normal cycling speeds, as long as the rider doesn't change position, frontal area and drag coefficient are constant and don't depend on speed.
But the drag force is the drag coefficient times the velocity squared. So while the actual drag increases linearly, the force the rider has to exert to overcome the drag increases exponentially.
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Old 08-27-06, 12:10 AM   #13
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Originally Posted by asgelle
Shoe covers are just as effective at reducing drag for a 15 km/hr rider as they are for the 40 km/hr one.
You need to work on your comprehension. If you want to nitpick this isn't the place to do it. And besides that statement is wrong.

Quote:
What magical transformation do you think happens at 40 km/hr or thereabouts?
General figure to make a point. Thanks for playing.
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Old 08-27-06, 07:03 AM   #14
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Originally Posted by operator
You need to work on your comprehension. If you want to nitpick this isn't the place to do it. And besides that statement is wrong.



General figure to make a point. Thanks for playing.
Oh, come on play one more round. You say I'm wrong, prove it.
The drag force on a rider is
F_d = 1/2 rho Cd A v^2
where rho is the air density; Cd, the drag coefficient; A, frontal area; and v, rider velocity.

Shoe covers reduce drag by lowering Cd, leaving the other terms, unchanged. Now prove to me that Cd depends on velocity (for normal cycling speeds)? Otherwise the (proportional) change in drag will be the same regardless of speed.

Now, if you're saying I'm wrong that shoe covers lower Cd, beside being obvious on inspection, there are many tests where this has been measured to be true.
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Old 08-27-06, 02:29 PM   #15
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Lets just throw some numbers in here. Lets say shoe covers decrease Cd by .01. we'll call rho 2 and area 1. At 15mph, F_d will decrease 2.25. at 40mph, F_d will decrease by 16. That means for a speed increase of 2.67 times, the force to overcome the added drag will increase by 7.11 times. I would assume that the work needed is a more important factor than speed. You are right that the change in drag is independant of speed. The change in the work needed to overcome that drag over a given distance, however, is dependant on speed.
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Old 08-27-06, 02:58 PM   #16
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Originally Posted by sivat
The change in the work needed to overcome that drag over a given distance, however, is dependant on speed.
Work equals force times distance. If as you agree the change in drag (force) is independent of speed, then it follows that the change in work must also be independent of speed for a fixed distance.

As to your example, since you don't give the initial value of Cd, or bother with stating units on rho or A, (I can't believe you mean to say the air density is 2 gm/cm^3), there's no way to understand where your numbers come from much less check if they are correct.

But here's a simple example, Cd=1, A=1, rho=1, v=1 in some set of consistent units. Then F_d=1.
Reduce Cd by 5%; now F_d=0.95. The ratio 0.95/1=0.95

New case: Cd=1, A=1, rho=1, v=4; F_d=16. Reduce Cd to 0.95, now F_D=15.2.
New ratio is 15.2/16=0.95
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Old 08-27-06, 03:29 PM   #17
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In the winter, just work on logging base miles, speed doesn't matter as much. Therefore, worry more about keeping your feet warm, and less about the aerodynamics.
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Old 08-27-06, 05:15 PM   #18
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In the winter, just work on logging base miles, speed doesn't matter as much. Therefore, worry more about keeping your feet warm, and less about the aerodynamics.
California Dreaming on a winters' day.
There'd be no need for shoe covers.
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Old 08-27-06, 06:05 PM   #19
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Quote:
Originally Posted by asgelle
Work equals force times distance. If as you agree the change in drag (force) is independent of speed, then it follows that the change in work must also be independent of speed for a fixed distance.

As to your example, since you don't give the initial value of Cd, or bother with stating units on rho or A, (I can't believe you mean to say the air density is 2 gm/cm^3), there's no way to understand where your numbers come from much less check if they are correct.

But here's a simple example, Cd=1, A=1, rho=1, v=1 in some set of consistent units. Then F_d=1.
Reduce Cd by 5%; now F_d=0.95. The ratio 0.95/1=0.95

New case: Cd=1, A=1, rho=1, v=4; F_d=16. Reduce Cd to 0.95, now F_D=15.2.
New ratio is 15.2/16=0.95
The numbers were chosen to make the math simple. Units don't really matter. Anything can be converted to anything else with the right conversion factors. the equation, by the way, works for any fluid, not just air. Your example is assuming the same speed. First you said that speed didn't matter, now you're keeping speed constant. If speed is the same, then a change in cd is going to have a linear effect, but you asked why cd would matter more at 40kph than 15kph. And as speed increases, a small change in cd will have a greater effect than at lower speed. As I showed above. Since this no longer has anything to do with the OP, if you wish to debate this further, pm me and i'll school you privately.
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Old 08-27-06, 06:20 PM   #20
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the equation, by the way, works for any fluid, not just air.
Thanks for pointing that out. So far I've only experienced riding in air, but if I should ever find myself riding in some heavy liquid (density 2 gm/cm^3, or so), I'll remember your lesson. Of course you forgot to consider that if the density increases by 3 orders of magnitude, and you keep the velocity 40 mi/hr, the Reynolds number is way beyond anything seen in normal cycling.
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... if you wish to debate this further, pm me and i'll school you privately.
Given what you've written so far, I think I'm fine thanks.
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Old 08-27-06, 06:33 PM   #21
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First you said that speed didn't matter, now you're keeping speed constant.
You have to read the whole post. If you had, you would have seen that I considered 2 dimensionless velocities: 1 and 4. You would also have seen that reducing Cd 5% in both cases reduced drag force by 5%. Hence independent of velocity. I'll leave doing the calculations for other velocities as an exercise, though the result (5% reduction in drag) will hold for any velocity chosen.
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Old 08-28-06, 03:32 PM   #22
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Originally Posted by asgelle
You have to read the whole post. If you had, you would have seen that I considered 2 dimensionless velocities: 1 and 4. You would also have seen that reducing Cd 5% in both cases reduced drag force by 5%. Hence independent of velocity. I'll leave doing the calculations for other velocities as an exercise, though the result (5% reduction in drag) will hold for any velocity chosen.
At 15mph, non-aerodynamic sources of drag are a greater share of total drag than at 25mph.
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Old 08-28-06, 04:02 PM   #23
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Old 08-28-06, 07:55 PM   #24
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Originally Posted by NoRacer
+1 on the bootie for warmth, but I find that the neoprene ones seem pretty aero anyway.

wooo!

These rule,

although they did wear out a bit quick. Im thinking about trying the super warm PI's.
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