Road to TT bike transition advice

[artemidorus]

I'm competing in a team TT in a month,and have already worked out a reasonably comfortable position on my road frame with clip ons and a reversed Thomson set-back seatpost (stack 602, reach 412, stem -6deg 120mm, no steerer spacers). My clip-ons are on the 80cm UCI limit, so can't go any further forward. I might be able to go a little lower on the stack with a new bike, but have already taken a 10% hit in threshold power, so am not too keen to do so.

I'm keen to get a Cervelo P2 or P3 (have always wanted a Cervelo), but find that the frames approaching my current stack (ie P2 or P3 61cm frames) are much longer than my current bike (ie P2 61 cm has stack 577, reach 448, P3 61 cm even longer and lower).

An obvious solution is to get a 61cm P2 or P3 and simply use a 70-80mm stem instead, and perhaps, if only until I get more powerful in the lower position, a +17deg stem or some of those aerodynamic aero bar risers. Is this a rational thing to do? Is there a penalty to a longer frame that I haven't anticipated? Advice much appreciated.

 

[daveryanwyoming]

Way too many unknowns about your current fit to know if the large P2/P3 frames are good fits for you. But sure if you can set up the Cervelos with a 70mm or 80mm stem and obtain the cockpit length you need then it's not a big deal you don't need to run a 90 or 100mm stem to get a good TT fit as long as you can get the elbow pads where you want them.

Are you confident in your current stack and reach based on fitting your road bike? The power drop isn't huge for the initial transition to a TT bke but it's high enough that it begs the question of whether you've achieved your best functional fit and the best balance of sustainable power, comfort, and aerodynamics. Be careful that you don't base too much on a sub-optimal road bike conversion as you shop for dedicated TT frames.

 

[artemidorus]

Dave, thanks for your advice. I guess that a more general question would be, why do they make these frames so long? I'm already as far forward as the uci will let me go - I suppose that the extra reach is most useful for non-uci events like triathlons. Maybe I should add that my road bike is one of the longest on the market and I'm 193cm/ 6'3".

 

[daveryanwyoming]

Well through most of their size runs the Cervelo P2/P3/P4 line run pretty long and tend towards the low and long end of the TT bike spectrum but actually the biggest frame (the 61) less so as it has less proportional reach for its stack. Here's a pretty good article and graphic laying out TT/Tri bike geometries in those terms: http://www.slowtwitch.com/Bike_Fit/Geometry_and_Handling/Graphing_geometric_themes_1321.html

But I don't think of even the mid sized Cervelo's as being too long in the cockpit and it's usually not hard to establish a UCI legal reach to the aero bar tips. It makes me wonder if you're riding with a lot of extension relative to the elbow pads, IOW are your elbow joints resting directly on the pads or do your elbows hang out in space a few cm behind where your forearms rest on the pads. The latter is usually preferred for long distance comfort.

And of course it begs questions about your overall fit in terms of things like shoulder angle and how open your position is as well as how steep and low you are or are not riding.

The UCI regs are pretty arbitrary and do penalize very tall and very short riders. The morph exceptions including the 80cm extension morph rule help but it's still a lame system based on rectangular coordinates instead of joint angles. A few years ago we could take both the saddle setback and the extension morph exceptions which helped a lot of folks but they've changed that rule to one or the other.

So I can't say why the Cervelo's you're looking at are built so long. I can say I've fitted several folks onto them and have not had problems satisfying the UCI position limits with stems in the 80-120mm range and stock front end assemblies and bar extensions. For taller riders we almost always end up taking the bar reach morph exception and running at least 5cm of saddle setback (often with an Adamo saddle) as the UCI pushes tall riders pretty hard when it comes to reach.

-Dave

 

[artemidorus]

Dave, once again, thanks. My aero bar positon is a long way back (maybe 4-5cm) from where I would put them in the absence of UCI rules. My elbows do hang ~2cm off the back of the pad even with my fingers curled over the end of the bar.

For taller riders, the uci-legal fit process seems to be:

1. put the aero bars where you think they should go
2. move the saddle nose forward to the 5cm limit
3. try out the fit and find that it's pretty comfortable
4. measure the bars and find that they're 5 cm too far forward (even for the 80cm exception)
5. move them back to the uci limit and then find that the saddle is now much too far forward
6. move the saddle most of the way back to its normal roadbike position
7. sigh and mutter about the stupid uci
8. see how low you can get the front end and still put out some power

I am certainly interested in finding a comfortable non-uci-legal position after my TT race, by moving the aero bars forward to where they feel right, and seeing what happens to my threshold power in a more instinctively correct position. To this end, getting a bike with a longer reach, like the Cervelos, would be useful.

Which Adamo saddle do taller riders tend to prefer?

Nick.

 

[artemidorus]

An update for anyone in a similar situation: I ended up getting the 61cm P2 and raced with an 80mm -17deg stem sitting on the headset and 50 mm aero bar risers, so same reach to the bull bars and the aero bars ended up 3mm higher than on the converted road bike.

For the moment the bike remains UCI legal with the bars at 80cm forward of the BB and the saddle as far aft as it will go, but I've dropped to 25 mm aero bar risers and am (slowly) getting used to them. This gives me a nearly 14cm drop from the saddle to the aero bar cups.

I'm thinking of forgetting the UCI for the moment and moving bars and saddle forward by 40-50mm, just to see what a triathlon position feels like, but will probably only ever race UCI events, so may keep things as they are.