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Old 03-04-09, 06:30 PM   #1
ldesfor1@ithaca
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Using a BMC TT02 as a road racing frame?

Has anyone successfully converted and raced a TT frame in RRs and Crits?

I currently race a CADD7 and want an aero road bike frame (as other posts of mine will show).

Many of the geometry points are the same on the 2 bikes so I think I could make it work, any obvious reasons not to do this?

I ride a 60cm Cdale and am looking at the Large 2007 BMC TT02.

thanks,

-L
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Old 03-04-09, 06:34 PM   #2
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It's got a pretty slack seat tube, I think it would be fine.
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Old 03-04-09, 06:54 PM   #3
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The ST is slack, so that should not be a problem. The HT is also slack, so it will handle a bit slow for a road bike. Most TT bikes are set up like this in the front end to keep the front stable when you have more weight forward in a TT setup. Swapping the fork out for one with less rake would help this some.
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Old 03-04-09, 07:01 PM   #4
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Can't think of a reason that it would not be ok. I have not ridden the aero EC90 fork so I have no idea how stiff it is.
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Old 03-05-09, 05:51 AM   #5
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Check the head tube lenght. TT bikes tend to have shorter head tube lenghts than road bikes. You'll either have a huge drop or too much stack height. Don't know exactly what the head tube lenght is on a CAAD7 but the C9 in a 60cm is 190mm vs 150mm on the BMC. I just went through this on a Fuji SST. I ended up with a 6.25in drop, 1.25in over my normal drop.

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Old 03-05-09, 08:43 AM   #6
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Quote:
Originally Posted by jamiewilson3 View Post
The ST is slack, so that should not be a problem. The HT is also slack, so it will handle a bit slow for a road bike. Most TT bikes are set up like this in the front end to keep the front stable when you have more weight forward in a TT setup. Swapping the fork out for one with more rake would help this some.
Corrected for you. More rake = less trail = faster handling.
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Old 03-05-09, 08:53 AM   #7
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Is there a reason you're trying to force this frame into an unintended use, as opposed to buying an aero frame that's designed to be a road bike?
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Old 03-05-09, 08:58 AM   #8
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Corrected for you. More rake = less trail = faster handling.
Right on.

Head tube angle and fork rake work against each other to get a bike's trail measurement into a range around a "sweet spot" (60mm of trail if I recall correctly). A lower-rake fork won't make the head-tube angle steeper. It will give you more trail, which will make the steering more stable combined with the already slowish steering of the slack head tube angle.

It's not a very desirable combination, in my opinion. I've ridden a bike with a slack HTA and a lowish rake fork. It felt silly.
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Old 03-05-09, 09:31 AM   #9
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...
It's not a very desirable combination, in my opinion. I've ridden a bike with a slack HTA and a lowish rake fork. It felt silly.
Most small bikes used to be made this way so that the front wheel clears more of your foot than it normally would (so you hit your toe, not the ball of your foot). My "crit/racing" designed bikes (Cdale, Spec) had 69-71 degree head tube angles. I was astounded at the handling improvement when I finally got on a 73 degree headtube angle bike (Giant TCR). The biggest difference was that I could initiate turns much quicker and I could also move laterally much easier when out of the saddle.

For regular cornering with a slack HT angle I'd just hunker down at my lean angle and hold it. But trying to change midstream wasn't natural.

cdr
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Old 03-05-09, 09:45 AM   #10
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COST. that's why I'm doing this.... and the BMC is dang sexy.

(i'm also supporting a shop I love to support and getting a great, very re-sellable frame with full ultegra and no extra parts to sell on ebay, meaning the value is even higher to me.)

Also, aside from the HT length, the specs are nearly identical to the Soloist team (which I also am looking at) which also has a 73degree HTA. So as long as I've got less than 3cm of spacers, I should be fine.

The saddle to BB is no problem.

The cdale has 1cm of spacers with a down-flipped 7degree 140mm stem. I'm guessing that an up-flipped stem is worth at least 1.5cm of spacers.

thanks for the replies, thus far.

-L
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Old 03-05-09, 09:49 AM   #11
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I have been on a test ride of that frame... It will not ride like a road bike.
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Old 03-05-09, 10:04 AM   #12
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any more info on that, fishmel?

-L
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Old 03-05-09, 01:43 PM   #13
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Originally Posted by carpediemracing View Post
Most small bikes used to be made this way so that the front wheel clears more of your foot than it normally would (so you hit your toe, not the ball of your foot). My "crit/racing" designed bikes (Cdale, Spec) had 69-71 degree head tube angles. I was astounded at the handling improvement when I finally got on a 73 degree headtube angle bike (Giant TCR). The biggest difference was that I could initiate turns much quicker and I could also move laterally much easier when out of the saddle.

For regular cornering with a slack HT angle I'd just hunker down at my lean angle and hold it. But trying to change midstream wasn't natural.

cdr
Jeez, 69-71? That's really low! I don't think I've ever ridden slacker than 71.5ish.
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Old 03-05-09, 01:53 PM   #14
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Corrected for you. More rake = less trail = faster handling.
Thanks. Mistype on my part. You are 100% correct.
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Old 03-05-09, 03:52 PM   #15
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Jeez, 69-71? That's really low! I don't think I've ever ridden slacker than 71.5ish.
Ride 48-51 cm frames and you'll see all sorts of weird things. I actually didn't buy a frame I ordered (the shop guys were even leery of having me buy it and they were the ones who suggested not buying it) because the frame looked so weird. I bought the next size up because I didn't want the weird looking first gen Cdale 48 (after that I rode a 50 for 4 frames).

Then add my uber-long upper body (14 cm stem back in the day, even 15 cm, due to the ridiculously short TTs) and the bike looks totally wrong. Still does actually, with 52 ST, 53.5 TT, and 12 cm stem. Looks about 5 or 8 cm too short in length for me.

I think that aero frames and designs will trickle down to the road racing scene, but I think the demand for that hasn't been created. If someone comes out and does some aero testing and proves that aero frames will help, then we'll see some good progress in frames etc. I say "etc" because bottles, bags, stems, brakes, they can all be part of the equation.

However, I wouldn't use a TT frame for mass start races, unless the geometry is the same (Stork and Fuji for a while are two that have the same geometry, not sure who else). The slower handling is much more of a trade off than a slight bit of wattage savings (or speed increase). Wrestling with shallow HT angles for so long made me appreciate normal HT angles. I'd choose a non-aero nice handling bike over an aero bike that requires significant effort to change lines mid-turn.

cdr
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