Great question, To which I have absolutely no answer but would love to know as well.

I'm currently "in the bike market" and have done a little research and "laying out" of frames. Drawing four frame geometries on top of each other revealed a few differences, although not consistant differences.

The top of the head tube on all of the road bikes were higher than the tri bike I laid in. 2 out of 3 head tubes on the road bikes were considerably behind the head tubes of the tri bike. 1 out of 3 of the road bikes had the head tube almost exactly in the same position as the tri bike.

All of the road bikes had a less of a seat angle than the road bikes, some not by much though.

I suspect that if I laid in more frames and more tri frames the differences would become even more blurred, so my conclusion. There are no standards. You have to shop by geometry. One companies "Road" bike may indeed be more "tri specific" than another companies "tri bike".

Of course none of this answer the question of feel or fit, merely were the geomtry is. I've no clue on the subject of fit and function and as evident by recent post completely confused...but hopefully learning.

~Matt

Owning both, I'm far from convinced that a tri bike always has advantages over a road bike with clip-ons and slightly forward geometry. As a roadie IMO you'd be at a disadvantage to suddenly hop on a tri bike for one race and expect to be faster. It takes time for your body to adapt to a new position. On a technical or hilly course the road bike is usually a better choice. Tri bikes are at their best on flatter courses.

For your current road bike it sounds like the shop put on aerobars that are too long. If this was a roadie shop this wouldn't surprise me since my experience is that they often don't have a clue regarding tri bike set ups. You need shorter road geometry specific aero bars. Keep away from the forward seat posts on a road bike as they just screw your handling up.

Here's another option for your road bike called the big slam position. read carefully

http://www.bicyclesports.com/Slam_Setup.html

Real tri-bike = Cool, converted road bike = not so cool.

I have to side with the Gopha on this one; a retrofitted road bike - especially one witha forward seat-post - just looks damn ugly. However, if you are comfortable in the new position, then go for it. I felt that my tri-fitted Trek handled really badly.

Slowman talks quite a bit about this subject on the ST main site. It basically comes down to a handling and safety issue. But I've known some pretty fast triathlete age-groupers on road bikes converted to "tri-bike" geometry -- it can be done with the limitations that Slowman discusses.

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FIST Certified Fitter
Salt Lake City, Utah

I used to ride my old carbon TCR with a forward post and whilst I went ok on it had some frankly frightening moments going downhill. If you can afford both types of bike, ride both and select the one for the course of the day. If this isn't an option choose one that you find the most comfortable. Whilst a TT geometry may not be ideal for large hills, comfort and history with an establisehd bike play greater dividends......

I wrote this a few years ago:

http://www.xtri.com/article.asp?id=126

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Tom Demerly
The Tri Shop.com

Thanks to everyone for the feedback. To address a couple of things mentioned:

The aero bars were fit by a good local tri shop. They recommended either the 'jammer' bar option or a more adjustable Profile something-or-other for my conversion. I went with the Profile's since they would be more useful should I ever decide to get a tri specific frame. I have them set up to the length of the 'jammer' bars. The FF seatpost was installed because, like mentioned in Tom's article, I was too cramped in the aero position with the seat in the normal location. I definitely noticed a shift in weight to the front of the bike with this change - evidenced by sore hands when trying to ride on the hoods.

As far as bike looks - my sense of style died a long time ago. Any chance of resurrection vanished the first time I put on lycra and a bike helmet, stepped out of the house and thought I looked good.

The 'slam' position seems like it might be the way to go. I can see a 'real' tri bike if my future, but I'm having a hard time justifying dropping significant money on a new bike given that I've never even done a sprint distance tri before - and I'm a master at justifying spending obscene amounts on money on bike stuff. I can get the R1000 Areo and add a base bar, bar end shifters and brake levers and have a total investment of under $200, with everything I buy transportable to a new frame if I do get obsessed with tri's. It wouldn't be any worse than my current road-bike-as-a-tri-bike setup, and would allow me to turn my road bike back into something usable outside the aero position.

Speaking of base bars - what would that provide over using the existing drop bars? It seems like it offers more usable hand positions and better access to the brake levers - is there anything else I'm missing? Any reason not to use them on a converted setup?

Thanks again!

I just went thru the same issues, love my road bike, fits me well, wanted to be more aero for 1/2IM and IM racing (plus some TT races). Aerobars on current road set-up left me way too stretched out. My cheap solution? I bought a shorty stem and WHAMO great position achieved, no seat post change. Granted I ride middle & back of the saddle in my road set-up, but I can sit on the front of the saddle in this aero set-up, my knees almost touch my elbows, very comfy. Stem cost me oh $15. ;-)

You might want to do some research on the Cannondale R1000 Aero beofre you buy. Just because it has "aero" tubing doesn't make it a "tri bike". In fact, the R1000 Aero has roughly the same geometry as your road bike: something in the range of a 73-74 seat tube angle. Don't confuse these models with their tri models.

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Are you being hearing the sound of thunder?

What advantages does a purpose built tri frame with a steep seat tube angle have over a frame using standard road bike geometry, but using a zero offset or 'fast forward' seat post to provide a steeper seat tube angle? Is there any advantage if I can duplicate the positions?


Short answer: you can usually replicate a tri position on a road frame, but the handling of the bike will be very squirrelly because the wheels are in the wrong placxe relative to your center of gravity.

Longer answer:

Your body position on a bike is controlled by three points in space: your butt, your hands on the bar or elbows in the pads, and your feet. Ignore the bike for a second and just think about your body: if you're more flexible you can be more "folded up" than the next person, and you are said to have a tighter hip angle. If you are less flexible the angle between your torso and thigh has to be wider.

Your bike should be set up to accomodate your body by giving you the correct hip angle. If it's not, you'll be uncomfortable and lose power and have lower back problems and all kinds of other bad things will happen. When in doubt, a more obtuse angle is usually easier to handle, and you can always make your position more "aggressive" by bringing your torso closer to your thigh.

But you can have the same hip angle with your back vertical to the ground (as you might in a recumbant bike) or with your back horizontal to the ground (as you might on a very aggressive tri/tt setup). The general effect of being rotated further forward is that you support more of your weight on your elbows, so your upper body muscles can relax. Additionally, and more important to faster racers, you're generally more aerodynamic because you present a smaller front profile and you're more elongated.

A "steep" seat tube allows you to rotate your whole body forward and down, without forcing you into a very tight hip angle.

To get a position that's rotated far foward, you need the saddle to be higher than the elbow pads and closer to the handlebar. One difference between a tri frame and a road frame is the geometry makes this arrangement easier. As you point out It's possible to accomplish this on a road bike by using a longer seatpost with a zero or negative setback, combined with a shorter steering tube and flat stem.

However, picture the difference between a road position and a tri position. In road position, your butt is on the saddle, behind the bottom bracket, your torso is behind the head tube, and your hands are the only thing over the front wheel. On a road bike, your center of gravity is pretty far back, so you need a longer chainstay to divide your weight appropriately between the wheels. There are also steering issues that are dealt with by controlling the rake of the fork and the length of the stem.

In an aggressive tri position, your butt is almost right above the bottom bracket, your torso is spread out over the top tube, your head and elbows are over the front wheel and your hands are in front of the front wheel (well, in front of the axle.) On a road frame, that puts a LOT of your weight on the front wheel, which is one of the reasons your handling is tricky and descending is scary on a road bike with aerobars. On a tri bike, the rear wheel is brought in much closer underneath the rider. That's why many tri specific bikes have the rear wheel faired under the seat tube. The P3 is an extreme example. The position of the front wheel, fork rake, and (ideally) stem length are also different to accomodate the way you steer when your elbows are resting on the pads.

So: yes, you can replicate the same body position on a road bike but the handling will suffer. A tri bike will get you rotated further forward without sacrificing handling and power transfer.

Lee Silverman
JackRabbit Sports
Park Slope, Brooklyn

Excellent explanation Lee. Like many, I did the modified road bike thing for a while but one of other downsides is that you have a compromised bike. Assuming you put on a forward post and aero bars, you now have neigher a road bike or tri bike. I love having both since when I want to go do some climbing I want a road bike set up as a road bike. Both best when used as designed.

Thanks for the info.

After messing around with the bike some more, I don't think running a FF seatpost is an option. The seat tube of the Cannondale extends way beyond the top of the TT - the the point that I don't think I could get my seat height where I'd want it given the maximum insertion length on the FF seatpost due to the 'bend'. I could run a Thomson or other zero offset post and scoot the seat forward and get most of the way there, continue to run the aero bars in shorter position. I'll have to try that and see if it's comfortable.

Are there any steep decents on the Vineman course? From what I've read and seen, there's not a lot of climbing so I assume there aren't a lot of hairy decents, either...

You guys are going to enable my justifaction of a new bike, you know. I'll just send my wife here when she starts to complain...