Wich TT size is best (huge diff in BB drop !!) ?

Discuss light weight issues concerning road bikes & parts.
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LouisN
Posts: 2326
Joined: Mon Feb 19, 2007 3:44 am
Location: Canada

by LouisN

I'm shopping for a TT frameset and I can have a good deal on a Felt B14.

For the cyclist's height ( 1,65 m should fit on a size 51) and inseam ( 72 cm should fit on a size 47 cm) , the ideal sizing would be between the 47 and the 51.

Here's the geometry:

Size 47 51
Head Tube Angle 71 72.5
Seat Tube Angle 76.5 76
Top Tube Horizontal 490 518
Top Tube Center to Center - 515
Head Tube Length 115 115
Seat Tube Center to Top 470 510
Seat Tube Center to Center - -
Bottom Bracket Drop 45 70
Bottom Bracket Rise - -
Chainstay Length 375 395
Front Center 565 577
Wheelbase 935 961
Rake 40 40
Standover Height 703 743
Fork Length 345 370
Lower HS Stack 1 1
Reach 375 388
Stack 468 521

Unless it's an error, it seems like the size 47's BB drop (45 mm !!!) is very low compared to all the other sizes (70 mm).
Would this make the bike less stable in turns, switchbacks, etc...?
Or for such a tiny size the CG would be low enough to ensure good grip and stability ??

Better go small, lower size frame with a rider with shorter legs and longer torso, with a higher BB drop ?
or,
The bigger, longer TT frame, with a lower BB drop ?

Louis :)

by Weenie


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Calnago
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Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

I would be very surprised if that isn’t an error in the chart.
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

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kdawg
Posts: 85
Joined: Wed Nov 20, 2013 9:10 pm

by kdawg

The 47 is for 650 wheels so probably not a typo.

They are also almost a double gap in size - the larger frames are only 2cm apart.

The stack and reach is probably a more useful indicator of size.

47 stack 468 reach 375

51 stack 521 reach 388

So the 47 is a lot lower and a little shorter.
I'm left handed, if that matters.

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Calnago
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Joined: Sun Nov 07, 2010 9:14 pm

by Calnago

Ok. Makes sense if it’s for the smaller wheels
Colnago C64 - The Naked Build; Colnago C60 - PR99; Trek Koppenberg - Where Emonda and Domane Meet;
Unlinked Builds (searchable): Colnago C59 - 5 Years Later; Trek Emonda SL Campagnolo SR; Special Colnago EPQ

wingguy
Posts: 3738
Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

LouisN wrote:
Sun Jan 14, 2018 8:08 pm
Unless it's an error, it seems like the size 47's BB drop (45 mm !!!) is very low compared to all the other sizes (70 mm).
Check out the fork length yo. 650 wheels for shiz.

Also note there's a full 5 cm difference in stack. There's not really much 'in between sizes' going on there. You're gonna be one or the other.

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LouisN
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Joined: Mon Feb 19, 2007 3:44 am
Location: Canada

by LouisN

Oh, I missed that one .... :oops:

I was just thinking about the other brands's "smaller than 50cm" (like Cervelo's 48 cm) being built for 650 wheels.

OK that cancels the 47 for me then...

Thanks for enlightening me guys :beerchug:

Louis :)

wingguy
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Joined: Thu Mar 08, 2012 11:43 pm

by wingguy

LouisN wrote:
Sun Jan 14, 2018 10:09 pm
I was just thinking about the other brands's "smaller than 50cm" (like Cervelo's 48 cm) being built for 650 wheels.
Nah dude, the 48cm Cervelo P series are all normal wheels. The 44cm is 650c. Theoretically, anyway. Never actually seen one available from the distributor!

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LouisN
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Joined: Mon Feb 19, 2007 3:44 am
Location: Canada

by LouisN

All of the ones I saw are 650 ( I only checked the older models though...):
https://www.ebay.com/itm/Cervelo-P3C-Si ... Sw5eFZb1ot
but yes, anyways ... ;)

Louis :)

alcatraz
Posts: 841
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

I'm also shopping for a TT/tri frame.

I have long legs for my height and a short torso. I found that my "weakness" when choosing a frame is the top tube length. A frame suitable for my inseam has too long reach.

Also the seat angle I'd like to be 78 degrees as anything less can almost be achieved with road frames and sliding the seat forward or using a slight forward offset seatpost.

I'd say try to find your weakness and look for that to be right on the frame. You don't want to end up at the max of any adjustability so you have some room to adjust.

/a

by Weenie


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