wheel work at above 30km/h?

Back by popular demand, the general all-things Road forum!

Moderator: robbosmans

bosco2814
Posts: 33
Joined: Wed Feb 17, 2016 4:21 am

by bosco2814

I am finding a new wheelset to replace my corima aero 47mm for criterium race.
Could please suggest some wheel for me?

I am focusing on two main things. 1. acceleration, 2. working speed

Does any wheel that work at the below speed?

30 - 45km/h?

35 - 45km/h?

35- 50km/h?


My corima aero is not work after 35km/h and i tried zipp 404, it will work after 35km/h but i think its acceleration is too slow for criterium race.

Thanks a lot.

ichobi
Posts: 1793
Joined: Thu Jan 19, 2012 11:30 pm

by ichobi

How about bora 35? Light, wide rim and instant acceleration with supersmooth hub. Might not help much at highspeed due to shallow depth but works wonder if you like quick response.


Sent from my iPhone using Tapatalk

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



Grill
Posts: 662
Joined: Mon Aug 20, 2012 12:12 pm
Location: Oop North

by Grill

Don't think I've ever heard of a crit slower than 35kph...

All wheels work at all speeds is just that watt savings increase at higher speeds. Go deep as you can handle as it's not like there are ever any climbs worth mentioning in crits. Reynolds Aero 72 are a personal favourite.

After that it isn't the wheels slowing your acceleration, it's you're legs.

bosco2814
Posts: 33
Joined: Wed Feb 17, 2016 4:21 am

by bosco2814

Grill wrote:Don't think I've ever heard of a crit slower than 35kph...

All wheels work at all speeds is just that watt savings increase at higher speeds. Go deep as you can handle as it's not like there are ever any climbs worth mentioning in crits. Reynolds Aero 72 are a personal favourite.

After that it isn't the wheels slowing your acceleration, it's you're legs.


I don't know how to describe, but I ride corima aero and zipp 404, I feel 404 is harder to acceleration than corima aero

bosco2814
Posts: 33
Joined: Wed Feb 17, 2016 4:21 am

by bosco2814

ichobi wrote:How about bora 35? Light, wide rim and instant acceleration with supersmooth hub. Might not help much at highspeed due to shallow depth but works wonder if you like quick response.

I think bora 35 will be no advantage in the breakaway because a breakaway in criterium at least 45km/h.

Sent from my iPhone using Tapatalk

Krackor
Posts: 257
Joined: Tue May 31, 2011 9:48 pm

by Krackor

Do the math on rotational inertia vs. aerodynamic drag. It would take an extreme case for acceleration to suffer in the case of a more aerodynamic wheel. Aerodynamics also help you accelerate because the wind resistance doesn't increase as much as you increase speed.

Here's some math I did, copy-pasted from an email conversation I had with a friend. The topic is a comparison of two wheels with different aero properties and different rim weights. The end result is that 150g of rim weight accounts for a difference of around 0.5W during an acceleration in a criterium. If your 150g heavier wheelset is at least 0.5W more aerodynamic, then it will actually save you energy during accelerations.

Let's figure out the kinetic energy difference between two rims. The approximate difference between 6.7s and 404s is 150g, primarily in the rims. I'll assume that's all concentrated at 700mm diameter, even though it's probably closer to 600mm. (The rim bed is 622mm.) Total kinetic energy of a hoop is m*v^2, half of that in rotational KE, half in linear KE. 15 meters per second is 33.5 mph, so we can plot the KE difference from 0 to 33.5 mph:

http://www.wolframalpha.com/share/clip? ... 4180sjn0tq

Vertical axis is in joules. If we want to calculate power difference say, from accelerating from 20 mph to 30 mph, we'd take the difference of that plot @30mph minus the plot @20mph divided by the time it takes for that acceleration to happen. At an intense crit, we might have to accelerate from 20 to 30 out of a corner in about 5s to keep up.

20mph = 9 m/s = 12J
30mph = 13.5 m/s = 27J
(27J-12J)/5s = 3W

So the 404s would save 3W for the duration of each 5s acceleration. For comparison, a rider + bike will be in the ballpark of 7000J total KE at 20mph and 16000J at 30mph, and accelerating in 5s would take about 1800W. So that's maybe an unrealistic time spent accelerating. More realistic would perhaps be 15s, which would mean a 600W effort to get up to speed. Over 15s, the 404s would save 1W, or 0.17%. Now that I think about it, that's actually excluding air resistance. So the rider's total effort would be more like 600W + whatever it takes to hold constant speed integrated from 20mph to 30mph, but we can average that to be @25mph, which is probably something like 300W? So ~900W total. Still overestimating the average acceleration out of a criterium corner. Looking at some of my past race data, my accelerations out of corners are on the order of 450-550W which would probably cut the power advantage of weight by half to about 500mW.

User avatar
DMF
Posts: 1062
Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden

by DMF

I think what you are feeling at high speed is that a heavy wheel will carry its speed in a way that a lighter wheel doesn't. That's where you're getting a lot of this feeling that a wheel is fast at high speeds. Ofcourse acceleration will suffer massively, so take your pick as you're not getting both. Best compromise is to go as light as possible with as high a profile as possible to get the aero effect at least as you'll have to give up the effect of carrying momentum if you want acceleration.

That said, there is something to be said about a two kilo wheelset if you have the power to keep them running. They do fly on the straights...

Grill
Posts: 662
Joined: Mon Aug 20, 2012 12:12 pm
Location: Oop North

by Grill

DMF wrote:I think what you are feeling at high speed is that a heavy wheel will carry its speed in a way that a lighter wheel doesn't. That's where you're getting a lot of this feeling that a wheel is fast at high speeds. Ofcourse acceleration will suffer massively, so take your pick as you're not getting both. Best compromise is to go as light as possible with as high a profile as possible to get the aero effect at least as you'll have to give up the effect of carrying momentum if you want acceleration.

That said, there is something to be said about a two kilo wheelset if you have the power to keep them running. They do fly on the straights...


:lol: :lol: :lol:
Go on, tell me another!

NiFTY
Posts: 1493
Joined: Sat May 26, 2012 11:26 pm

by NiFTY

DMF there is so much pseudo science in that post. Weight and top speed have nigh on sweet *f##k* all to do with each other. And microacceleration in rims have been debunked. When accelerating, you are accelerating the whole bike+rider unit, not just the rim.
Evo 4.9kg SL3 6.64kg Slice RS 8.89kg viewtopic.php?f=10&t=110579" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

User avatar
DMF
Posts: 1062
Joined: Sat Dec 06, 2008 10:14 am
Location: Sweden

by DMF

Okey let's call it the "feeling" of acceleration, my bad thinking that was sort of implied. A light wheel will feel very zippy to get up to speed, out of a corner for example when the initial speed is low. A heavy wheel will feel sluggish at that same scenario. Pulling 700g of weight off my rims or emptying one water bottle will not bring the same sensation.

That's what I meant.

But I agree with th OP, keeping a light wheel rolling at high speed is a lot of work. You're not getting that sensation of the bike just rolling along by itself that other (IME heavier) wheels give you.

This has been discussed at length too...

Krackor
Posts: 257
Joined: Tue May 31, 2011 9:48 pm

by Krackor

The feeling of acceleration is misleading. Your butt dyno is not to be trusted here. Do the math.

bosco2814
Posts: 33
Joined: Wed Feb 17, 2016 4:21 am

by bosco2814

Krackor wrote:Do the math on rotational inertia vs. aerodynamic drag. It would take an extreme case for acceleration to suffer in the case of a more aerodynamic wheel. Aerodynamics also help you accelerate because the wind resistance doesn't increase as much as you increase speed.

Here's some math I did, copy-pasted from an email conversation I had with a friend. The topic is a comparison of two wheels with different aero properties and different rim weights. The end result is that 150g of rim weight accounts for a difference of around 0.5W during an acceleration in a criterium. If your 150g heavier wheelset is at least 0.5W more aerodynamic, then it will actually save you energy during accelerations.

Let's figure out the kinetic energy difference between two rims. The approximate difference between 6.7s and 404s is 150g, primarily in the rims. I'll assume that's all concentrated at 700mm diameter, even though it's probably closer to 600mm. (The rim bed is 622mm.) Total kinetic energy of a hoop is m*v^2, half of that in rotational KE, half in linear KE. 15 meters per second is 33.5 mph, so we can plot the KE difference from 0 to 33.5 mph:

http://www.wolframalpha.com/share/clip? ... 4180sjn0tq

Vertical axis is in joules. If we want to calculate power difference say, from accelerating from 20 mph to 30 mph, we'd take the difference of that plot @30mph minus the plot @20mph divided by the time it takes for that acceleration to happen. At an intense crit, we might have to accelerate from 20 to 30 out of a corner in about 5s to keep up.

20mph = 9 m/s = 12J
30mph = 13.5 m/s = 27J
(27J-12J)/5s = 3W

So the 404s would save 3W for the duration of each 5s acceleration. For comparison, a rider + bike will be in the ballpark of 7000J total KE at 20mph and 16000J at 30mph, and accelerating in 5s would take about 1800W. So that's maybe an unrealistic time spent accelerating. More realistic would perhaps be 15s, which would mean a 600W effort to get up to speed. Over 15s, the 404s would save 1W, or 0.17%. Now that I think about it, that's actually excluding air resistance. So the rider's total effort would be more like 600W + whatever it takes to hold constant speed integrated from 20mph to 30mph, but we can average that to be @25mph, which is probably something like 300W? So ~900W total. Still overestimating the average acceleration out of a criterium corner. Looking at some of my past race data, my accelerations out of corners are on the order of 450-550W which would probably cut the power advantage of weight by half to about 500mW.


it means that 404 can be accelerate with less 0.5w?

bosco2814
Posts: 33
Joined: Wed Feb 17, 2016 4:21 am

by bosco2814

DMF wrote:Okey let's call it the "feeling" of acceleration, my bad thinking that was sort of implied. A light wheel will feel very zippy to get up to speed, out of a corner for example when the initial speed is low. A heavy wheel will feel sluggish at that same scenario. Pulling 700g of weight off my rims or emptying one water bottle will not bring the same sensation.

That's what I meant.

But I agree with th OP, keeping a light wheel rolling at high speed is a lot of work. You're not getting that sensation of the bike just rolling along by itself that other (IME heavier) wheels give you.

This has been discussed at length too...


So a rim around 50-60mm seems more suitable for me, the acceleration is just the feeling.

And except the finish line is 50m after the corner, the lightweight wheel will no advantage in a criterium that around 40-45km/h.

Krackor
Posts: 257
Joined: Tue May 31, 2011 9:48 pm

by Krackor

bosco2814 wrote:it means that 404 can be accelerate with less 0.5w?

No, not quite. It means the extra 150g of rim weight on the 6.7 accounts for an additional 0.5W required to accelerate it. However, the worse aerodynamics of the 404s account for an additional 6-7W required to maintain speed. When accelerating you have to spend both the sustained power and the acceleration power at the same time, so in total the 6.7s are faster than the 404s when accelerating by about 6W, even though the 6.7s are heavier.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



Krackor
Posts: 257
Joined: Tue May 31, 2011 9:48 pm

by Krackor

bosco2814 wrote:So a rim around 50-60mm seems more suitable for me, the acceleration is just the feeling.

And except the finish line is 50m after the corner, the lightweight wheel will no advantage in a criterium that around 40-45km/h.

Even if the finish is 50m from the corner, you have to be a very light rider (<50kg) and put out a huge sprint (>1500W) before the weight difference becomes as valuable as the aerodynamic difference.

Post Reply