Weight variations across frame sizes - considering stem etc.

Discuss light weight issues concerning road bikes & parts.
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573
Posts: 230
Joined: Wed Sep 05, 2012 2:38 pm
Location: West Sussex, UK.

by 573

I'm looking to move onto a new frame and wondered what experience people had of the following consideration...

I currently ride a 56cm Trek 1.7 and am looking at Cannondale Supersix Evos. I'm going to go and get my leg over one in a shop before actually buying, but from looking at the geometries and tube lengths, the 56 Cannondale will be v. similar to my 56cm Trek, but with a lower headtube (which is what I want). However, I think I could get myself easily onto a 54 if I used a longer stem and laid my seat back slightly more.

Has anyone weighed the difference of offsetting a smaller frame against a longer stem and more seatpost left un-cut? Calculations I've made make me think the smaller frame will always translate into a lighter overall bike..?

xjbaylor
Posts: 158
Joined: Mon Jul 18, 2011 4:37 pm

by xjbaylor

573 wrote:...but from looking at the geometries and tube lengths, the 56 Cannondale will be v. similar to my 56cm Trek, but with a lower headtube (which is what I want). However, I think I could get myself easily onto a 54 if I used a longer stem and laid my seat back slightly more...


I can't tell you if the 54cm Cannondale will fit you, but do not go moving your saddle around to correct your reach on the bike. As a general rule you need to set saddle height and setback first. These measurements should be based on your relationship to the bottom bracket. Then worry about where your hands fall. The difference between a 54 and 56 TT lengths can be made up with a 20mm stem increase, i.e. 100mm to 120mm. The stack height can be changed with spacers and stem angle. If a couple of CM's of spacers don't get your hands high enough you need to stick to the larger frame size.

The smaller frame will probably be slightly lighter, but discomfort affects your ride far more than a few extra grams ever will. Get the size right first, then try to save weight.

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573
Posts: 230
Joined: Wed Sep 05, 2012 2:38 pm
Location: West Sussex, UK.

by 573

Thanks. I appreciate the importance of comfort over weight and wouldn't compromise fit to save a few grams. Part of the change of frame is to get lower at the front and a 54 should give me more scope to do that.

budgetweenie
Posts: 47
Joined: Fri Feb 17, 2012 5:33 pm
Location: Louisiana USA

by budgetweenie

573 wrote: Part of the change of frame is to get lower at the front and a 54 should give me more scope to do that.


They still make -17 degree stems (you can flip a +20 degree also for more neg gain, you can find track and mtb stems light and bomb proof) and as xjbaylor mentioned, the relationship of your knee over the pedal should not be monkeyed with.
However I have a 57 cm EV3 and a 59 cm Dolomiti (both Bianchi). They are totally different setups, one is a straight up race bike and the other is my "Rivendell crowd" bike. I have carefully set them up to have the same geometry between the contact points, without a bit of trouble, because really there's a net difference of only 10 cm; they both have the same seat tube angle, but the Dolomiti has a 1 degree slacker head tube, which effectively shortens the top tube. The EV3 has a 120 with a 10 cm spacer and the Dolomiti has a 110 slammed (well I have a 2 cm washer in there to make it look right). I'm 6'0" 182 cm with an 84 cm inseam.

Hope this helps.

Valbrona
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Joined: Fri Oct 28, 2011 3:25 am
Location: United Kingdom of Great Britain and Northern Ireland

by Valbrona

573 wrote:I think I could get myself easily onto a 54 if I used a longer stem and laid my seat back slightly more.


In the case of 2cm incrament frames it is often the case that two sizes could fit the same person. A longer headtube, slammed stem type of fit. Or a fit with a higher saddle and a couple of headset spacers.

My point being ... Let 'fit' be your guide and not 'weight'.

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