TT vs. Road bike. Pedal clearance?

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phourgenres
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Joined: Wed Sep 21, 2011 7:19 pm

by phourgenres

Trying to justify a TT purchase. Is the pedal clearance any lower on a TT bike (aka is the TT frame any lower on the road)? Otherwise, I can't find any other reason not to throw on clip aerobars on my road bike, and fit it like a TT bike.

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ergott
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by ergott

Generally a TT bike has a steeper seat tube angle. That gets the rider to rotate their position more forward and more weight on the arms. This position also allows for a flatter back thus more aero.

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Fiery
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by Fiery

TT position results in a drastically different weight distribution on the bike, affecting handling. This is exacerbated by the different hand positon (the aero bar). Unlike road frames, TT frames are built to handle properly in the TT position.

phourgenres
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by phourgenres

I'm aware. Slamming the saddle forward would mitigate that. ;)

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ergott
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by ergott

It won't change the geometry of the front end though.

deek
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by deek

TT bikes generally have a much slacker head tube angle, which leads to more trail so they are more stable in a straight line (conversely, don't handle as quick.) TT bikes also generally have a longer wheel base. BB drop is usually close.

The biggest benefit of a TT bike is being able to shift from the aerobars. You could do something dual purpose with a Di2 set up though. If you only want to use this bike for TT stuff, you might be okay.

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ITTY
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by ITTY

I have done the road bike conversion thing and it is the most awkward and uncomfortable I've ever felt on a bike, and it handled horribly. If you're going to be doing a fair amount of time trialing, I strongly recommend getting a proper TT frame. They are easier to get yourself into a proper time trial position via fit, and they are way more comfortable at speed in the TT position.

Edit to address your actual question:

I doubt most time trial bikes have significantly lower bottom brackets (mine doesn't), but even if they did, it shouldn't really affect you in a time trial. You won't be pedaling through tight corners very often in a TT.
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wingguy
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by wingguy

To echo what other's have said, STA is the killer. You can get a 0 offset post and you can slam the saddle forwards but rarely if ever will you be anywhere near as steep as a good fit on a TT specific bike. This has a big effect on your pedal stroke and how low a position you can sustain without losing power. It also has major knock on effects on the cockpit length - you'll be stretching significantly to rest into the pads. Not really an issue on 10 milers, but a 25 or over could get pretty difficult to sustain.

Compare an S3 54 with a P3 54 in a few metrics that have been mentioned: BB drop, P3 is 7mm lower. HTA, P3 is 0.6 degrees slacker. Fork offset, they're the same. All fairly neglible. But when it comes to fit: Stack: P3 is 33mm lower. Reach: P3 is 33mm longer. STA, the P3 is 6 degrees steeper. These are huge differences, and there is a good reason for it.

Bottom line is that yes, you can throw aerobars on your road bike and use it but no, you can't fit it like a TT bike.

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