benajah

Ive always been as much of a time trialist as a road racer, but I have never really compared how much advantage I gain from riding a aero TT bike versus a standard road bike on a flat course. I am now in a position that I need to make a certain average pace in a USAC sanctioned TT to get admitted to a certain athletic program (equates to about a sub hour 40k in speed but doesnt need to be as far), but I no longer own a TT bike (sold it when we had a kid to buy kid furniture, priorities), but I do have a pretty aero position on my current road bike.
Any idea how much speed you gain from aero bars, aero tubes, etc?
I honestly have never done a flat TT on a drop bar road bike, always dedicated TT bikes, so have none of my own data to compare the two, and I guess am hoping someone has some comparable data or a source for such.
Thanks,

Racer Ex 

How tall is a tree question. Anybody that gives you any kind of answer for you is talking out their ass, at best they can give you a comparison from their own time trialing. Even then unless the conditions and fitness were identical it's not going to be very precise.

FWIW this year I did a Merckx TT with aero wheels and a TT helmet and went 18:37 over 7.7 miles while I did 17:50 on a new untested TT bike with a bad wheel choice for conditions 6 months before. This jives with a minute over 7 miles slower a few years back when I flatted warming up on the TT rig and had to grab my road bike on a course I had ridden a bunch.

I wouldn't even venture a guess regarding the level of comparative fitness in either case. I'm a low drag guy who has spent hours testing in the field and the tunnel to optimize my TT position. Your mileage is going to vary.

I've seen people go slower on their TT bike than they do on their road bike for the same wattage because of a horrible set up and the fact they they only ride the TT bike once or twice a year.

Aerodynamics are highly interactive, so wind tunnel data on a particular bike or bike part doesn't mean that you'll produce the same gain/loss with a rider. And it's also speed contingent.

So the answer to your question is a giant shrug.

benajah

Thanks. Internally I probably was fishing for answer "you don't need skin suit, TT bike, you'll be fine"
real answer is more complex.

grwoolf

It seems like your real question is whether or not you can hit a certain pace (~25mph) over X distance on your road bike. Seems like a pretty easy thing to answer if you have said bike. Maybe you're asking because you know that pace you can hit on your road bike and want to know the adjusted TT bike pace?

As far as your original question, I just got a TT bike this year and my position needs a lot of work, but I still see at least 1mph difference on the TT bike (probably more like 1.5.

Why not just put some clip-on aero bars on the road bike and maybe push the saddle forward a bit? I'd think the aero bars would get you most of the gains you'd see with a TT bike.

Looigi

I would tend to agree with this...and probably raise the saddle a bit too. IMO, one major difference between riding with aero bars and a similarly low position in the drops is that you expend (waste) less energy with the upper body and back when supporting your elbows on the aero bars. Of course the arm position on aerobars is going to more aero than in the drops.

For short stretches you might ride in an aerobar-like position resting your forearms on the tops, but I find that gets painful fairly quickly, and certainly doesn't have the same security as gripping the bars.

Dean V

Wouldn't the obvious thing to do be to find a course similar to what you will be riding for the event and go and ride it on your road bike. Then you will have a good indication of if you are fast enough with what you have.

Debusama

That's just silly, what we really need is some kind of theoretical formula for how much time is gained when wearing a skin suit vs aero-bars vs tt bike so the op can spend a bunch of money on stuff without even knowing if he might be either fast enough to qualify as he is, or not fast enough to mater what bike he's on.

carpediemracing 

My understanding is the main benefit to a TT bike is the fact that it allows you to get into a good aero position.

On a standard road bike I think you'd need a Look Ergo stem or similar to get the bars in the right place. That's what it took for me to fit the two best TT riders I ever fit.

waterrockets 

Oh, well there's this then:

I'm guessing the OP isn't Uwe Peschel though.

Racer Ex 

Not really. I can replicate my TT position on any bike that's in the ballpark for size. I can't make my road frame as fast as my Shiv.

You're welcome. Need is a relative term. Will you be giving away time by not having an optimized TT bike and position with equipment that's been tested and works with your set up? Absolutely.

Will a slapped together bunch of bit make you faster than you would be on your road bike? Again, that's a big shrug. Like I said, I've seen a lot of people go slower on their "TT" bikes.

And the distance of the event matters. If you stick yourself in position that you're not used to riding you might be faster aerodynamically but there can be a really steep power drop off within 5-15 minutes; your "net" over a 40k might be a lot slower.

A skin suit that fits will never lose you time over a regular kit. TT helmet...good bet this will help. Beyond that it gets pretty murky.

Jancouver

"Like I said, I've seen a lot of people go slower on their "TT" bikes"

tetonrider

TT helmet...good bet this will help. [/QUOTE]
just wanted to chime in with an example to underscore racer ex's point. i was fortunate enough to have a number of aero helmets available to me, so i decided to go out and actually test them on the road. rather than describe the entire process, i basically did multiple trial runs with each helmet, as well as with a road helmet for control. all were done on the same day, same wheels, same stretch of road. conditions were not perfect, but i made the best of them and the imperfections affected all runs.

i projected the results out to a 40k.

just by picking ANY of the aero helmets was good enough for a savings of 1' over the course of a 40k. that's fairly in line with what people expect.

what was SURPRISING was the difference from the best to the worst of the AERO helmets: it was also about 1 minute. i was testing for relative differences and don't take those time differences as gospel, but the test showed me a couple things that are worth being mindful of:
1) just using aero gear may help (in this case, it definitely does)
2) using the RIGHT aero gear vs the wrong aero gear can have as big an impact. (if you were willing to spend $x on a helmet to save n seconds, wouldn't you prefer to spend $x for the right helmet and save 2*n seconds?)
3) testing one's setup can be pretty easy and can pay off. i talked to lots of people since doing those quick tests, and it was very rare for me to hear of people that actually did ANY sort of test on their own gear. most often their rationale for purchasing boiled down to 'it looks aero'.

i have some thoughts as to why the aero savings was so big for me from one helmet to another, but that's really the topic of another thread.

carpediemracing 

From what I can tell, assuming a rear disk is about as aero as a TriSpoke (debatable either way but most would concede the disk is more aero), it seems like there's about a 25w difference between the Stevens road bike and Cervelo (assume some TT frame).

Based on the two numbers for a TriSpoke front or TriSpoke + Disk (8w diff), the difference between a rear disk and rear TriSpoke would be somewhere in that range. Therefore the difference between a TriSpoke and a disk would result in, at most, an 8w difference.

I'm not saying that there's not a difference in frames, I'm saying that the position is what saved the first 60-odd watts and that the frame isn't a big part of those 60 watts.

The last 27 watts was due to rider stuff - helmet, speed suit, and, interestingly enough, moving the saddle back.

The frame, then, seems to have saved about 25w. At my level that's not significant - I'd go from "really slow" to "almost really slow". For a top level athlete I think that's huge. To save 60w + 25w (rounding down and starting from the drops position) for the position + aero equipment, that's huge - it's almost exactly 40% of my FTP.

It almost makes me want to try a TT

tetonrider

i won't say that the difference between top-level TT frames is insignificant, but the biggest benefit of a TT frame is in enabling one to get in a proper aero position. that capability (proper fitting TT bike) is going to dwarf the differences between frames.

tunnel data i've seen shows the difference between a trispoke vs disc (with trispoke front) ~5W @ 30mph, depending on yaw (0 yaw is ~1W, 12.5 & up is 10W). the difference is less as speed decreases. of course, at lower speed one will typically see higher yaw, so the two are not mutually exclusive.

carpediemracing 

Understood on the frame. I've fit (two) higher level TT riders on road bikes (their request) using Look Ergo stems. I think it's possible to fit someone to a TT position on a road bike with an unusual stem like that but it compromises control a bit. One of the two riders, a national level duathlete, actually went back to the "TT fitted road bike" for at least two new bikes' worth of sponsors/seasons - he received new equipment/bikes but didn't like the fit or something as much.

I also think TT frame effectiveness may be related to rider height or specifically leg length. For me, on essentially an invisible-to-the-wind frame (it's so small), making the 9.5 cm headtube a bit more aero probably won't change things much, or the 40 cm seat tube, etc, at least relative to the rider (I ain't small). Someone on a frame 20 cm taller may/should see a slightly larger difference between a non-aero and aero frame.

I've never ridden one of the Stinger type discs but I used to race on a tapered side prototype rear disc (from that national level TT rider actually) as well as TriSpokes. I personally found TriSpokes to be faster in very specific situations (cross tailwinds) but the disc was so much lighter I used it in many (crit) races where acceleration counted. I actually tried to track down the disc wheel to buy it back - I traded my TT bike, complete with disc, for a beater mtb - but with no luck.