datlas 

I follow some tri forums. Don't hate.

Anyway, some of the folks in those forums claim that they are seeing 2-3 MPH improvements when going from an allegedly properly set-up road bike to a TT/Tri bike.

I am looking to hear from the 41 members who have BOTH a road bike set up for performance (ie. decent saddle-bar drop) AND a TT bike. Ideally also a PM.

I am NOT looking for wind tunnel data.

How much of a difference in MPH do you get at the same power level, assume somewhere just south of LT?

I am guessing somewhere between 0.3 and 0.6 MPH. I am not buying the 3 MPH claims but I am also open-minded.

rpeterson

Only changing the bike, so same wheels helmet and kit, I've got 2-4 mph at ftp depending on the wind conditions.

My aero position is a little ridiculous though.

jrobe

I have used my Powertap wheel to compare speeds on my favorite 1 hour TT ride with both my Cervelo R3 and my Cervelo TT bike. With the same average power output, I gain about 1- 1.3 mph with my TT bike. It is definitely not anywhere near 2-3 mph and my TT bike is set up to in a very aggressive aero position (to the point where I couldn't ride it comfortably for more than 1-2 hrs).

1 mph may not seem like a lot but that would be a 1 mile lead at 1 hour in a race - which is huge. The TT bike is really fun to ride. It seems like it is rocket fast compared to the road bike.

hhnngg1

Assuming a good fit specifically for the road bike and a good (but slightly different) fit for the TT bike, you'll get MAX 1.0mph from the aerobars effect. The aero tubing itself contributes almost nothing, so can be essentially be ignored despite all those claims of Cervelo, etc. saying that their aero tubing really makes a difference. The TT bike's added speed comes down almost entirely down to the lower aero-position on the aerobars.

If you're getting more than a 1.0mph difference, you either:
1) Had a terrible road bike fit, so it's not a fair comparison
or
2) Are using other TT-gear to augment the speed gains (like speedsuit, wheels, helmet). Even with all those goodies though, you're talking MAX 2.0mph of speed, and more likely closer to 1.0mph gain unless your roadbike position was horrible.

I ride my TT and roadbike about equally and have time trialed both with a powertap, so I can also attest to this effect.

asgelle

There is so much data available saying this is wrong that I don't even feel like posting references. Whether it's wind tunnel or field testing, the data show about the same improvement from aero tubing as aero wheels; roughly 1/2 mph form worst to best.

rpeterson

With no wind those aero tubes really don't do much, but with a strong wind at high yaw they make a pretty significant difference. Some of the variability between bikes is easy to test, go out on a calm day and ride at 25mph on a road and tt bike, the power difference won't be that great. Now go out on a day with some significant wind and ride into it at 20mph, the power difference between the two bikes will be quite a lot larger. At high speeds and low yaw angles you're not going to be seeing too big of a difference, but if you live somewhere with constant winds and you aren't that fast the differences are going to be much larger.

asgelle

That's like saying there's no difference between 1" and 1.5" because I used a 10 foot measuring stick.

hhnngg1

I'd love to see the data using real-world riders on a real-world course. NOT a wind-tunnel and nonmoving mannequin, which is how most of these inflated aero tubing speed gain frames are computed.

I'd strongly expect any bike company that could prove that their frame was 0.5mph faster than a round tube frame in REAL world conditions with a REAL rider, would be trumpeting it all over their advertising. As is, almost all the aero claims are limited to wind tunnel testing, and the differences there are still small. Small enough to be mostly negligible in the variance of outdoor conditions.

Bah Humbug

I've consistently seen ~1.5mph from my friends. The body position change makes a big difference.

I just wish I could figure out how to balance on the aero bars.

datlas 

This may be correct, but I wonder if they are set up aggressively on their road bikes. I am thinking that the folks who report relatively large increases are not set up properly for performance on the road bike.

datlas 

Where is LowCel when we need him??

JustinHorne

Are you even being serious right now? That's incredibly silly. What you call "Real World" conditions would be the LEAST accurate thing, because it's impossible to account for variables, which is literally what the wind-tunnel does.

Literally all a wind tunnel does is track the amount of force the bike (or object) is resisting against the wind, which is translated into a power equation, and that can be used to calculate how much slower or faster it makes you go. Because the force of the wind doesn't change in the wind tunnel all it's doing is seeing whether object A or object B resists more. For a more obvious example, imagine instead of bikes, it's determining whether a large sheet of plywood parallel or perpendicular to the wind resists more. Obviously it's the parallel one.


A "Real world" example would somehow need to make sure that you had two EXACTLY equal riders on the EXACT same path riding in the EXACT same position exerting the EXACT same amount of force. If somehow you did that, and literally the only variable between the two setups was the frame, one of which was more aero than the other, the aero one would be faster. Because that's insanely impractical, we use windtunnels.

hhnngg1

Yes, I'm dead serious.

Theroetical tiny advantages do NOT equal real world advantages. At least when you take into account the normal variables involved in riding.

Consider as a counterargument:

You definitely CAN measure (and quite easily and reproducibly) the aero advantages of:
- Aerobars
- Aero helmet
- Skinsuit
- Better position
All in REAL WORLD racing/TT conditions, even with the given variabilities of a course, as long as you try and keep things the same with the same rider.It's been done by Bikeradar where they compare the benefits of this gear, and many other places. You can measure real time advantages, with a regular stopwatch, outdoors, with reasonably similar conditions.

However, I'm not aware of any bike manufacturer that can reliably claim a measurable benefit with their aero frame outdoors, reproducibly. For sure, they can't claim it's as advantageous as aero wheels, or else every pro would be riding that particular bike.

Windtunnel data is helpful, but unless the speed gains are provable outdoors, it's still speculative. And I ride an aero framed bike.

rpeterson

One thing about my large increases is I'm considering my all day road position to all day TT position. My all day road position is pretty aggressive, but its still on the hoods and slightly relaxed, my only tt position is quite aero. If you consider the most aero I can get on a road bike vs my TT position it gets smaller of course.

rpeterson

https://forum.slowtwitch.com/forum/Sl...T!_P1802183-23

StanSeven

Good find! That's a very interesting and informative thread. Several of the contributors there (Andy Coggan, Rchung, etc.) used to frequent here. That was a long time ago. I guess people like Coggan didn't like his data challenged by people here saying "that's a bunch of BS", "it's just marketing","I know that's not true," etc.