Which frame size and stem length?

Discuss light weight issues concerning road bikes & parts.
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TonyM
Posts: 2578
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Hi,

I will most probably buy a BMC Roadmachine02 as my winter and rai bike and I would need your opinion concerning the right size of the frame and of the stem length.

I am 170cm (5'7") with an inseam of 79cm (2'6";67 inches).

Currently I ride a Colnago C60 in 48S:
- Reach: 383mm
- Stack: 528mm
- Top tube: 530mm
- Stem: 11 cm

The BMC Roadmachine02 has a dual head tube cap "dual stack" that allows two positions (low or high) in order to achieve a different reach/ stack.

http://www.bmc-switzerland.com/int-en/b ... -02-three/

Image

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If I see it right, I would basically have the choice between the two following frame sizes:

A/ Size 47 cm (high position)
- Reach: 369
- Stack: 530mm
- Top tube: 522

OR

B/ Size 51 cm (low position)
- Reach: 378mm
- Stack: 539mm
- Top tube: 532

So here my questions:

-> Which size do you think would be the best for me (so that it is the closest to my Colnago C60)?

-> And which stem length should I have ? 13cm for the 47cm and 12cm for the 51cm?

Rudi
Posts: 137
Joined: Tue Apr 08, 2014 6:43 pm

by Rudi

Hi TonyM

Which is nearer to the Colnago? Neither. One is similar in reach and the other in stack. So I think there are compromises to be made.

How many spacers do you have on the Colnago and how tall is the top cap? And what angle is your stem?

If you are looking for exacts then the 51 low is 11mm too tall at the front. If you have a 10mm spacer in there currently or a tall top cap, then you can probably fit on this one fine - and the reach is probably better than the 47 high option. Also if you have a positive angle on the stem you could make it negative and so on. If you are already slammed on -17 and a "slam that stem" cover then you'll be higher on this (you'll need to decide if it is too high).

You don't say what stem length you currently have, so purely on the reach you'd need an extra 14mm for the 47 and 5mm for the 51. Not a lot of stems come in 5mm increments that I know of.

Personally, if you can deal with the 11mm extra height at the front (spacers, different angle stem etc.) then I'd go with the 51. If not the 47 with a longer stem.
Cervelo R3 - 5.4kg viewtopic.php?f=10&t=142420

by Weenie


topflightpro
Posts: 825
Joined: Tue Jan 13, 2009 2:35 am

by topflightpro

Try punching the numbers in to Bikegeo.net to really check things out. It compares three bikes at a time.

So far, it's been pretty accurate for me. And it's a lot easier to use than some of the other calculators.

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TonyM
Posts: 2578
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Rudi wrote:Hi TonyM

Which is nearer to the Colnago? Neither. One is similar in reach and the other in stack. So I think there are compromises to be made.

How many spacers do you have on the Colnago and how tall is the top cap? And what angle is your stem?

If you are looking for exacts then the 51 low is 11mm too tall at the front. If you have a 10mm spacer in there currently or a tall top cap, then you can probably fit on this one fine - and the reach is probably better than the 47 high option. Also if you have a positive angle on the stem you could make it negative and so on. If you are already slammed on -17 and a "slam that stem" cover then you'll be higher on this (you'll need to decide if it is too high).

You don't say what stem length you currently have, so purely on the reach you'd need an extra 14mm for the 47 and 5mm for the 51. Not a lot of stems come in 5mm increments that I know of.

Personally, if you can deal with the 11mm extra height at the front (spacers, different angle stem etc.) then I'd go with the 51. If not the 47 with a longer stem.


On my C60 I have a 82 degrees stem. No spacers.

The RM02 in 47/51 comes with a 9cm stem.

The negative stem on the 51 could indeed be an option. Any recommendation maybe?

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TonyM
Posts: 2578
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

topflightpro wrote:Try punching the numbers in to Bikegeo.net to really check things out. It compares three bikes at a time.

So far, it's been pretty accurate for me. And it's a lot easier to use than some of the other calculators.


Thanks :thumbup:
I am looking at it and it helps indeed!


I found therefore the result -> BMC RM02 in 51 cm with low cap position and a 11 cm stem with -12 degrees is really close to my C60 :thumbup:

Reach with stem: 483 (vs. 486)
Stack with stem: 570 (vs. 571)



So and now looking for a nice -12 degrees stem

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