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· It's all ball bearings
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Discussion Starter · #1 ·
This is admittedly going to be a dorky question/discussion:

Regarding "time-saving equipment" for time trials (aerobars, aero helmet, skinsuit, disc wheels, etc), how much of an effect does rider speed have on the absolute number of minutes/seconds saved on a time trial course of a given length?

Here's what I'm getting at: as we all probably know, there are a number of webpages that list the supposed time savings that correspond to different pieces of equipment, typically determined in wind tunnel tests and based on a 40K flat TT riding at 30mph, and assuming all other variables are equal. My question is, how much would those time savings estimates change if the rider averaged 25mph over the same course instead of 30? Or even 20 mph instead of 30?

Upon thinking about it for a bit, it dawned on me that the total number of minutes/seconds saved might not be very different for the slower riders (or time saved might even increase for slower riders?). It seems like the main difference would be that the proportion of time saved to the total ride time would be the only significant change.

In other words, if rider A rides a 40K at 30mph (50 minutes) and saves 2 minutes with aero wheels, the 2 minutes savings translates to a 4% savings in his overall ride time. If rider B rides the same course in the same conditions at 25mph (60 minutes), the aero wheels would only have to save him 3.3% of his total ride time to get the same 2 minute absolute time savings. Am I thinking about this correctly or am I way off? Does anyone know of a way to work this out mathematically, that accounts for the reduced drag imparted upon the slower rider?

My overall question is this: will an inherently slow rider benefit from going out and buying all the aero kit the same that an inherently fast rider will benefit from it, in terms of number of minutes saved in a TT (rather than percentage of time saved)?
 

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Since air resistance rises at the cube of air speed over the object, aerodynamic time savings would significantly increase at higher riding speeds. If you can produce enough watts, aero equipment can save time (vs lightweight equipment) on a fairly significant grade.

There are a number of articles looking at aerodynamics in the various _Cycling Science_ books (sorry no cite, books are at home). They're worth reading if you worry about this sort of thing. Or if you need help getting to sleep at night.
 

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ericm979 said:
Since air resistance rises at the cube of air speed over the object, aerodynamic time savings would significantly increase at higher riding speeds. If you can produce enough watts, aero equipment can save time (vs lightweight equipment) on a fairly significant grade.
Aerodynamic resistance (drag) goes as speed squared. Power to overcome drag goes as speed cubed. But that has little to do with the subject here. Aero equipment reduces frontal area, drag coefficient, or both and these are independent of speed at normal cycling speeds. What this means is that ignoring other forces (gravity, rolling resistance, etc.) speed will increase as the reduction in drag coefficient times area to the 1/3 power. As a result, the slower rider will save more time covering a fixed distance than a faster one. This can easily be demonstrated by a few calculations at analyticcycling.com.
 

· It's all ball bearings
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Discussion Starter · #4 ·
asgelle said:
speed will increase as the reduction in drag coefficient times area to the 1/3 power. As a result, the slower rider will save more time covering a fixed distance than a faster one. This can easily be demonstrated by a few calculations at analyticcycling.com.
aHA! This is what I was wondering. Thanks asgelle.
 

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My research agrees

asgelle said:
As a result, the slower rider will save more time covering a fixed distance than a faster one..
One of my favorite "what would happen if..." cycling books is "High Performance Cycling" by Jeukendrup, ed.

In it, various aerodynamic effects are considered. Comparing, for instance, standard wheels to a disc rear / tri-spoke front setup:
A rider producing 100 watts saves 1:30 over 40k
A rider producing 200 watts saves 1:11
A rider producing 300 watts saves 1:03
A rider producing 400 watts saves 0:57

Hope that helps.
 

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Some numbers

BenWA said:
Regarding "time-saving equipment" for time trials (aerobars, aero helmet, skinsuit, disc wheels, etc), how much of an effect does rider speed have on the absolute number of minutes/seconds saved on a time trial course of a given length?
As an example, the most aero wheels available will increase speed 0.4 mph at 25 mph. At 20 mph, this will give you 0,3 mph, and at 30 mph, it is 0.5 mph. So the % increase in speed is not constant.

The 20 mph rider would save 53 seconds in covering 20 miles, the 25 mph rider would save 46 seconds over the same distance, and the 30 mph rider would save 39 seconds. Of course the faster riders would cover the 20 miles much faster, so their time savings would be much smaller. Their time savings for an hour would be 57 seconds at 25 mph and 59 seconds at 30 mph.
 

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Competition is competition

Any time you're competing and you put time and effort into training and put money into gear and entry fees and all that it's a real shame not to look for every advantage you can find. Especially when you're talking about the difference of a minute. It's all a cost benefit thing. I'd spend $100 for 10 seconds and I'd pay $500 for a minute, that's what it's worth to me. Just because I don't get paid to ride a bike doesn't mean I don't want to compete to the fullest. I've lost way to many TTs and placings with a gap of less than 20 seconds not to take little things seriously.

How do the above numbers compare when viewed as a percentage of overall time?
 

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Discussion Starter · #9 ·
Agree.

triple shot espresso said:
Any time you're competing and you put time and effort into training and put money into gear and entry fees and all that it's a real shame not to look for every advantage you can find. Especially when you're talking about the difference of a minute. It's all a cost benefit thing. I'd spend $100 for 10 seconds and I'd pay $500 for a minute, that's what it's worth to me. Just because I don't get paid to ride a bike doesn't mean I don't want to compete to the fullest. I've lost way to many TTs and placings with a gap of less than 20 seconds not to take little things seriously.

How do the above numbers compare when viewed as a percentage of overall time?
If you are going to race, you might as well give it your all.

The one thing that bugs me a little (okay, a lot) about time trials is that to be competitive, you have to keep up with the Jones's so to speak...you have to buy as much of the aero kit that the best guy has as you can afford to have any chance of catching him on the clock. This hurts when you only plan on doing a few TT's a year, because you are essentially spending thousands on kit for just a few races. And if you don't spend those thousands, you don't have a glimmer of hope in being competitive, unless you are physiologically some genetic freak who can stomp the field even without the equipment aids. I, personally, am no genetic freak, so I need all the help I can get. I'm just having trouble rationalizing spending the money for a few TTs a season (which is generally all I have time for). It seems that when it comes down to it, the TT is a battle of wealth as much as it is fitness and cycling talent.

Okay, I'm done with my peeing and moaning rant. :cryin:
 

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You are right that you've got to spend $$$, but you can get pretty aero on the cheap. How do I know? That's what I did. Total expenditures:

1. Used Full Ultegra GT ZR2000 from Ebay for $365.
2. Sold Ultegra brifters for $100.
3. Purchased aerobars from Performance for $60, cowhorn from Chucksbikes.com for $12.50, brake levers from Chucksbikes.com for $20, and barcons on Ebay for $60 (net $52 out of pocket).
4. Purchased chaero disk cover from excel for $60.

So there, for under $500, I built myself up a pretty aero starter TT bike. Remember, it's the first dollars that go the farthest (i.e. aerobars are good for a couple of minutes in a 40K, and they're under $100).

Since the initial buildup, I've purchased a used HED Deep (similar to the JET 90) front wheel for $250, and I've swapped out frames (net cost $150). For a TT rig, especially one built from a converted roadie, my personal experience is that you need to go down a frame size in order to get the saddle to bar drop necessary to get your back flat. The whole ballgame is about reducing your frontal area, position-wise, so just switching frames can make a big difference, even between two "non aero" models.

I'm still well under $1K out of pocket, and my bike is likely 97% as fast as the $6K rigs.
 

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Discussion Starter · #11 · (Edited)
good points shawndog

So you are currently using the CH aero disc cover in back and HED deep front? How is that CH aero working for you? That is one of my bigger concerns in terms of spending $$$: finding affordable wheels.

I have most of the other stuff on the list (except an aero frame/fork...I'm using my normal road bike with a quick handle bar/parts swap for every TT). My road bike is on the small side, so I think it is pretty good in terms of bar drop when I have it set up for TT's.


Regarding my original inquiry, it sounds like the take-home message is that when one refers to the claimed time-savings of aero parts/accessories based on a 40K TT @ 30mph, they can expect at least that much savings in minutes/seconds if they ride considerably slower than 30mph. Sounds like pretty good news for slowpokes like me!
 

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BenWA said:
So you are currently using the CH aero disc cover in back and HED deep front? How is that CH aero working for you? That is one of my bigger concerns in terms of spending $$$: finding affordable wheels.
I'm informed, though I haven't actually seen the report, that there's windtunnel data out there somewhere about the CHAero cover being very close to a disc that costs ten times more. Maybe someone else can chime in there. The downside, of course, is that it's added weight.

I've been happy with the cover. It's pretty easy to set up (takes about 10-15 minutes, but that includes cleaning off the cassette body since it's usually the only time I'll have my cassette off). If nothing else, it FEELS fast, and I'm a firm believer in the importance of the placebo effect for time trialing. In order to go fast, you need to believe that you can.

That said, the other thing to remember is that the front wheel is much more important than the back. The rear disc looks cool, but it's the front wheel that's taking the brunt of the wind.
 

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BenWA said:
I have most of the other stuff on the list (except an aero frame/fork...I'm using my normal road bike with a quick handle bar/parts swap for every TT). My road bike is on the small side, so I think it is pretty good in terms of bar drop when I have it set up for TT's.
One more thing to think about -- getting into an aero position is generally not going to be comfortable. Making power in that position is a bit of an aquired taste. You may be better served by buying a cheapo frame-fork that you can leave set up as a TT rig all the time. I think you need to ride it at least an hour a week to develop/maintain the ability to make power in the aero position.

Stated another way, I know a guy who is moderately fast and has a $6000 Litespeed Blade TT bike with a disc and trispoke. The only time he ever rides it is when he shows up to a TT. And his times reflect his lack of practice.
 

· It's all ball bearings
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Discussion Starter · #14 ·
shawndoggy said:
That said, the other thing to remember is that the front wheel is much more important than the back. The rear disc looks cool, but it's the front wheel that's taking the brunt of the wind.

I just ordered a ch areo from from excel. It's the front wheel that's gonna be the tough sandwich to eat, $$$wise.

Regarding the practice in the TT position, I have clip on aerobars and a flat base bar...I can clip the aerobars on my normal road bars and get the same exact position as when I swap the road bars with the base bar and clip the aerobars onto the base bar. In other words, I can practice riding in my TT position with minimal bike change and I can race TT with a bit more bike change.

Good point you had about keeping practiced, in any case.
 

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Sometimes it is all about the engine. Train to be your best and then see how many you can beat at the TT. Last year I only had a $300 Gaint mountain bike I put slicks on it and clipless pedals and I came in 58 out of 120 riders for the year. My best was 41:31 for a 21.7 average in a 15 mile TT. This year I got a road bike but it was fun beating guys on expensive road bikes with my cheap mountain bike.
 
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