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Old 02-18-10, 01:33 AM   #1
guadzilla
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Converting road frame for TT use - seatpost and a few other things

Hi guys -

I am getting into TTs and my initial plan was to get a nice TT frameset. However, I have decided to convert a road frame I got for really cheap into a TT bike for now, and get a nicer frame later.

I have an Al seatpost with a slight setback - I was thinking of flipping it, so that it is set forward. This will steepen my effective STA. There have been a couple of other posts on it here at BF and no one seems to think it is a bad idea, but I thought I'd check and see anyway.

Any other tweaks that you guys recommend/suggest?

Thanks,
Vandit
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Old 02-18-10, 03:38 AM   #2
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I flipped my seatpost like that. I'm also fairly heavy (210 pounds) and I haven't had any problems after one season.

The only thing that might be a problem is that (depending on the seat and the post itself), you might not be able to get the seat as flat as you want. I had to dremel away a couple of millimetres of metal on part of the seatpost clamp to get the seat flat enough.
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Old 02-18-10, 06:23 AM   #3
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There are other problems with converting a road frame to a TT/Tri set up that have to be considered.

When you move the seat forward you have to extend the stem (assuming it was the correct length to start). This moves your entire body forward, placing far more weight on the front wheel than for a normal road or TT bike. TT/Tri bikes compensate for this by moving the back wheel forward under the seat (the cut out in the seat tube) and increasing the rake on the fork. You can't really do either with much effect on a road frame.

What this does it make the bike very "twitchy" in the steering and handling department. Depending on how much you move things and what you weight, it can be anything from annoying to dangerous.

If you are going to do this, and lot of people have, then be careful getting used to it.
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Old 02-18-10, 08:47 AM   #4
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Well, I cant get the seat level with the seatpost I have. Damn. Back to the drawing board.

exRunner - thanks for that info. I had read about it on Slowtwitch as well a while ago but it had sorta slipped my mind. I did have a practical experience of the twitchiness last year: had put clip on bars on my old Trek (which was 2 sizes too large for me and which I rode with a 60 or 70mm stem). Decided to try the aerobars at speed and promptly steered the bike into a roadside ditch. This bike is a little smaller in ETT than my regular road bikes, so atleast the stem will be more normal in size. I hope it will not be as twitchy!

V.
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Old 02-18-10, 09:09 AM   #5
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It isn't the length of the stem as much as it is your relationship between the wheels and your body. A smaller frame will actually make this worse. Like I said, be careful.
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Old 02-19-10, 02:27 AM   #6
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Originally Posted by exRunner View Post
It isn't the length of the stem as much as it is your relationship between the wheels and your body. A smaller frame will actually make this worse. Like I said, be careful.
Hmm, I had figured a longer stem would reduce the twitchiness, but yeah, I can see how that would stretch me out further. I have a 100mm stem on it right now and can probably drop down to 90mm or so. Will give that a shot. Is there a recommended stem size that is a good balance between twitchiness and weight forward?

I just tried my position on the bike and once I get a seat-forward post, it should be more or less fine. One other question - what part of the forearms go on the pads? Elbows (they ARE called elbow rests, after all) or is it ok to have the mid-forearm resting on the pads?

Eg, this shot:
http://www.bikingbis.com/_photos/LanceTTX.jpg (doesnt allow hotlinks)

V.
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Old 02-19-10, 01:28 PM   #7
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How much difference is there between riding in the drop bars vs riding on a TT bike? Let's say you ride 20mph in the drop bar. For the same effort what would riding a TT bike be? ANother mph or just a fraction?
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Old 02-19-10, 02:41 PM   #8
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How much difference is there between riding in the drop bars vs riding on a TT bike? Let's say you ride 20mph in the drop bar. For the same effort what would riding a TT bike be? ANother mph or just a fraction?
There is a lot more to it than that. The change in body position over the pedals saves the leg muscles that are required for running. A road bike uses many of the same muscles.

You can get very close to the same aero position on a road bike as on a Tri bike, but you loose the ability to support your upper body in a different manner, which is important when those muscles are tired from swimming.

As I write this I realize that I did all of last season's Tri's on my Allez (with aero wheels) because I was too lazy each race to get the P2 out and tune it up. Seems kind of silly now.
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Old 03-02-10, 05:15 PM   #9
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I reckon for the same power on a proper TT bike with the right geometry you are looking at 5kmh instantly when you get down in a good aero position !I instantly go from 35kmh to 41 kmh by getting down there.
A road bike on the drops may get you low but you must consider the 2 big pillars called your arms that are going to be either side of your torso causing massive amounts of drag as opposed to mostly in front of your body breaking up the air that your torso is about to go through.
In a pack on a road bike this is no big deal but when it's just you it makes a massive difference.
You also have to consider the effects of a road bikes geometry on the run .
Tri bikes place you in a position that uses more quad and less hamstring .
You are sure going to need your hams for running !
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