Will becoming more aero help a slower rider?

[Yorlik]

Will becoming more aero help a slower rider more than a fast rider? I'm old and slow and TT at ~23mph. Is there any way for me to determine how much time I could save on average with a rear disc wheel? I'm currently racing on an Open Pro Powertap wheel.

This is copied from a coach's post in another forum:
"An article in this year's VeloNews Buyer's Guide outlined the time savings by implementing various aerodynamic equipment options. The results were based on a 40k TT being covered in 48min (about 50km/hr or 31+mph). While the time savings would be greater the longer it takes you to cover the 40k, the time savings would not be linear since effort to increase speed rises exponentially. In other words, if it took you twice as long to cover the 40k, you would not necessarily realize double the time savings since you would be more than halving the amount of wind resistance you create to go 15.5mph versus 31mph. Hope this makes sense.

"In any case, the results are quite surprising..
Shoe Covers ($30) save 30sec over regular shoes
Skin suit ($250) saves 134sec over standard bibs/jersey
Aero helmet ($165) saves 67sec over regular bike helmet
Aero front wheel (up to $1000) saves 42sec over spoked training wheel
Aero rear wheel (up to $1500) saves 29sec over spoked training wheel
Aero bike (up to $12,000) saves 17sec over round tube TT bike"


Thanks,


Pat

 

[alienator]

Define "more." Aero always helps, but it's up to the rider to decide how little aero help they're willing to pay for. There is no definite answer.

FWIW, the figures you quote for aero benefits of various pieces and parts is only for one particular rider, one aero cross section, one wind condition, and one particular wind tunnel. Actually the figures are pretty useless without information on how the data was collected, but the figures might have some low order approximation value.

You have to know that the biggest influence on aero drag is body position. As for a disc wheel, the difference between it and just a deep rimmed wheel (say, a 50-60 mm rim) is going to be pretty small. Also one disc wheel is not necessarily the same as another disc wheel, but I assume you know that.

 

[gman0482]

Well here's my $.02 cents....

In order to spend all that dough just to shave little over 5 minutes off my time, my sponsors would have to be threatening me to rip up my $1 million dollar contract I have with them. Short of that, I'll be happy to be 5 minutes slower .

 

[daveryanwyoming]

Will becoming more aero help a slower rider more than a fast rider?...

In pure time terms yes, slower riders benefit more in absolute time savings than faster riders in part because they're out on the course longer. For instance:

If two riders (same: weight, rolling resistance, etc.) both drop their CdA from 0.25 to 0.22 on a flat 40k course at sea level then ignoring the start and turnaround:

A rider averaging 200 watts drops their time from 66.01 minutes to 63.49 minutes or a time savings of ~2.5 minutes by lowering their CdA.

A rider averaging 350 watts drops their time from 53.42 minutes to 51.32 minutes or a times savings of ~ 2.1 minutes for the same drop in CdA.

So in absolute terms the slower rider gets more time benefit but it's not a huge difference and I'll bet it makes a bigger difference in terms of race placings to the higher power rider.

But in terms of getting that CdA savings the big takeaway from your data is the relative importance of different items. It looks to me like your numbers reflect what the folks at MIT have published that aero helmets are the big bang for your buck along with pocketless skinsuits.

But the most important thing that dwarfs all the high price items on your list is rider position (which can be helped by a properly sized TT frame). So before you mortgage the farm to get trick wheels have you worked on optimizing your position and trained to ride in an aggressive TT position? And of course more power to throw at the course is the best thing in terms of lowering your times so are you training as well as you can and doing dedicated Threshold work regularly (hopefully some of it in your TT position)?

-Dave

 

[frenchyge]

Yes, but....

The flip side of this is that aerodynamic effects become more pronounced at higher speeds, and Cd is somewhat dependent upon the speed of flow around the object. So, depending upon the difference in speed, a slower rider will not realize the same Cd delta for a given piece of equipment that a 30+ mph rider will see.

 

[daveryanwyoming]

Fair enough, but my main points were:

- Slow riders don't gain so much more (even if the CdA deltas were the same) that it results in magic in terms of finishing times

- Position changes are the biggest place to save aerodynamically but lot's of folks buy multi thousand dollar wheelsets before they work on their flexibility or lowering their front end.

- Given a reasonably aero position, power still determines who stands on the podium or at least whether you finish among the top riders. So training trumps gear all and all assuming you've at least got some clip on bars and a relatively aero position.

-Dave

 

[alienator]

Dave's got it. For cycling, the thing to remember is that power varies with the velocity cubed. In simple terms, if you want to go a little bit faster, you have to put out a lot more power. At the speeds you're talking about increasing power by x magnitude causes a bigger change in velocity than aero equipment would at the initial speed.

The two things that are cheapest to improve--power and position--are the two things that effect the biggest changes.

 

[pat5319]

I've heard from reliable sources that an aero helmet will help more than a disc wheel (stay away form front discs-they'r dangerous as wind can "catch them" and steer you off course as the fornt wheel pivots)

 

[frenchyge]

Fair enough, but my main points were:

Oh definitely. My point was that despite spending more time on the course, a slower rider might not even see as much time benefit as the marketing would indicate for a particular piece of gear because all wind tunnel testing is done at faster speeds.

 

[daveryanwyoming]

Oh definitely. My point was that despite spending more time on the course, a slower rider might not even see as much time benefit as the marketing would indicate for a particular piece of gear because all wind tunnel testing is done at faster speeds.

I see what you mean, I tend to ignore the 'X watts saved' kind of advertising as I'm more interested in the aerodynamics of the whole system than a wheel or handlebar in isolation.

Heck if we added up all the marketing claims for light weight, low friction and aero gear the bike would ride itself

-Dave

 

[baker3]

I've heard from reliable sources that an aero helmet will help more than a disc wheel (stay away form front discs-they'r dangerous as wind can "catch them" and steer you off course as the fornt wheel pivots)

Anything from "reliable sources" will always be right. Nobody in their right mind would use a front disc in a road time trial, is this another reliable source?