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Aero trumps weight, until it doesn't

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Aero trumps weight, until it doesn't

Old 09-19-17, 06:39 PM
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blazin
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Aero trumps weight, until it doesn't

BMC time trial coach Marco Pinotti told Cyclingnews that a 2kg difference in bike weight could give a 20-second benefit, with other seconds gained thanks to the familiarity of riding on a road bike.
Bike change could be key to Worlds TT success | Cyclingnews.com

Apparently, racers in the world championship time trial plan to change from a TT bike to a road bike due to the benefit the lighter bike will produce over just a 3 km climb. The estimate of that benefit quoted above strikes as much more significant than the small numbers people seem to cite here frequently. I'd be interested, since most of us don't have the luxury of mid-life bike swaps, to know what the difference would be riding the whole course on just a TT or just a road bike. I imagine TT would still come out on top?
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Old 09-19-17, 06:53 PM
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Is there a descent? If not, and the climb is very significant, the balance could easily shift from zero to weight.
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Old 09-19-17, 06:55 PM
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If BMC's TT bikes really weigh 2kg/4.5 lbs more than their road bikes, I'd start looking as to why they have almost a 20 lb bike.

That's amateur-league.
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Old 09-19-17, 07:00 PM
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It takes 20 seconds to raise 2kg by 215 meters... if you're pedaling at 200W. And that's for otherwise like-for-like cases.

It seems like you'd really have to introduce very-case-specific biomechanical quirks, perhaps including gearing changes, to give a 2kg-lighter road bike a 20-second advantage on the climb.

Originally Posted by blazin View Post
I'd be interested, since most of us don't have the luxury of mid-life bike swaps, to know what the difference would be riding the whole course on just a TT or just a road bike. I imagine TT would still come out on top?
Yes, easily. For most people, the performance difference between a road bike and a TT bike on the flats is obvious. On a climb, not so much; grades often have to get pretty significant before the TT bike stops winning. And unless the gearing bottoms out no matter how steep the grade, a TT bike should never be that much slower than a road bike a few pounds lighter.

Last edited by HTupolev; 09-19-17 at 07:03 PM.
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Old 09-19-17, 07:06 PM
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I think it is more than just weight that handicaps a TT bike on a climb. The forward saddle and layout of the handlebars isn't helping either.
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Old 09-19-17, 07:11 PM
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Course ends at the top of the climb.


Last edited by blazin; 09-19-17 at 08:11 PM.
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Old 09-19-17, 11:11 PM
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For this year's Worlds Only this might all make sense. No descent, and anyone who misjudges power output could lose Huge time on that hill. The pro women's race was won by a Dutch woman who went marginally slower in the first third and saved extra for the climb---and they had to descend.

I am betting more than a few male riders will run out of steam two-thirds of the way up that hill. A five-second bike change could almost pay for itself given the steepness of the first three k of that climb.
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Old 09-20-17, 04:36 AM
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Your subject says it perfectly OP....and why bikes that aren't optimized for aerodynamics however do hit the UCI 15 lb weight limit...most standard race bikes have usual aero cues including slippery wheels...why Tarmac's, TCR's now shaped a bit more aero than before...and similar models still have a place in pro racing...also why almost nobody rides disk brakes. Weight matters if elevation changes.

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Old 09-20-17, 06:31 AM
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Originally Posted by blazin View Post
Course ends at the top of the climb.

That's a stiff hill at the end of a TT. It would be tough for me on any bike. 9% average over three kilometers.
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Old 09-20-17, 06:53 AM
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Of the first 20 or so riders through the course, most are opting not to change bikes. The first rider on the course had a poor change and ended up getting a push off the carpet. No word yet if he's disqualified, or what penalty he'll get.

EDIT: I'm following it here.

Last edited by Kevindale; 09-20-17 at 07:12 AM.
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Old 09-20-17, 07:29 AM
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Hey...no spoilers plis...I actually do have this being recorded at home. Man I love this new Olympic channel.

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Old 09-20-17, 08:03 AM
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It's streaming on YouTube. Looks like official feed, FWIW.
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Old 09-20-17, 08:29 AM
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Originally Posted by San Pedro View Post
It's streaming on YouTube. Looks like official feed, FWIW.
oooh....something to do at work. Wait...I'm not finding it...got a link?
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Old 09-20-17, 09:56 AM
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I think part of the difference might be the wider range and more smoother gear transitions you can put on just one bike nowadays. And with electronic shifting you don't have to suffer cadence hits because you didn't shift the front and back correctly to the next higher or lower ratio.

For grand tours it lets the same bike be used for both flats and mountains. You don't see bike changes for mountains like we did in the past. I don't do TT, so I can't say if that's part of it.

New gearing technology is probably causing a lot of rethinking.
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Old 09-20-17, 10:16 AM
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Originally Posted by rubiksoval View Post
If BMC's TT bikes really weigh 2kg/4.5 lbs more than their road bikes, I'd start looking as to why they have almost a 20 lb bike.

That's amateur-league.
That's actually pretty normal -- because of the wheels, seatpost, and frameset. The PRO rear disc wheel ALONE weighs more than their road bikes' complete wheelset. It's a very heavy wheel. The wheels account for more than 1kg extra. The TM01 frameset probably has at least .5kg on the SLR01 frameset. Pro triathlon and TT bikes routinely weigh 20.5 to 22 pounds, ready to race. On a flat course, it doesn't matter.
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Old 09-20-17, 12:28 PM
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Originally Posted by Dean V View Post
I think it is more than just weight that handicaps a TT bike on a climb. The forward saddle and layout of the handlebars isn't helping either.
Climbing on a TT bike is like climbing on a road bike one size too small. Nothing is in the right place in my albeit brief experience.
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Old 09-20-17, 05:52 PM
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Originally Posted by Grasschopper View Post
oooh....something to do at work. Wait...I'm not finding it...got a link?
Sorry, fell asleep.


UCI channel.

It just popped up on my homepage last night.
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Old 09-20-17, 06:13 PM
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So how did Primoz Roglič, Wilco Kelderman and Nelson Oliveira do after changing bikes for the final ascent?
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Old 09-20-17, 07:40 PM
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Originally Posted by blazin View Post
Bike change could be key to Worlds TT success | Cyclingnews.com

Apparently, racers in the world championship time trial plan to change from a TT bike to a road bike due to the benefit the lighter bike will produce over just a 3 km climb. The estimate of that benefit quoted above strikes as much more significant than the small numbers people seem to cite here frequently.
Oh? I'm not so sure about that.

Using the good ol' Kreuzotter: 140lb rider, 200 watts, 20lb bike, 9% grade, 3.4km = 19m 46s. Chop the bike down to 15 lbs, and it's 19m 11s. Assume you lose 15s to the bike change, and that's still a 20s gain.

That's a big advantage in a pro TT. Amateur TT, less so. Club ride, nah.


I'd be interested, since most of us don't have the luxury of mid-life bike swaps, to know what the difference would be riding the whole course on just a TT or just a road bike. I imagine TT would still come out on top?
Uhhhhh.... yeah.

On the flat part of the course, a TT bike will smoke a standard road bike, even an aero road bike.... that is, by the standards of pro racing. That's why riders tend to use TT bikes on flat TT courses.
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Old 09-20-17, 09:21 PM
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Your numbers would be closer if you used 400w instead of 200w.
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Old 09-20-17, 09:40 PM
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Originally Posted by Athens80 View Post
So how did Primoz Roglič, Wilco Kelderman and Nelson Oliveira do after changing bikes for the final ascent?
Primoz Roglič gained time on the climb after switching bikes according to Velonews. There were cobbles on the climb as well.
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Old 09-20-17, 09:42 PM
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Originally Posted by rpenmanparker View Post
Is there a descent? If not, and the climb is very significant, the balance could easily shift from zero to weight.
No.
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Old 09-20-17, 09:43 PM
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Originally Posted by San Pedro View Post
Primoz Roglič gained time on the climb after switching bikes according to Velonews. There were cobbles on the climb as well.
Look him up. Became a pro at 25. Was in a big ski crash @ 21.
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Old 09-20-17, 09:47 PM
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Thing is all bike should be darn close to 6.8kg and measured. Unless I missed the press, that requirement should be there for both bikes. So if the TT bike was 16 lbs, and climbing bike was 15lbs, I expect it is wheels that is making the difference.
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Old 09-20-17, 09:49 PM
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Originally Posted by rubiksoval View Post
If BMC's TT bikes really weigh 2kg/4.5 lbs more than their road bikes, I'd start looking as to why they have almost a 20 lb bike.

That's amateur-league.
Our (kids TT bike is under 16). But wheels are the primary factor. His TT bike with his climbing wheels means add weight.

I would not change bikes.
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