I am considering purchasing a Look 381i and am looking for some feedback on the best size to get. After some thought, it looks as if a 54 would serve me best. My height is 5'10 w/ inseam of 33 ". My current frame has a 54.5cm tt and 73.5 SA with seat all the way back and using a 12 cm stem. Fit is just about perfect and I'm very comfortable on it.
Given the slack seat angle of the Look, should I assume that moving the seat to my ideal setback should give me a similar reach? Or do most find that they simply end up pushing the seat back further and in effect increase their reach. If this is the case, then maybe the 53 would be better, but I'm conserned that the bar height may suffer.
Thanks in advance.
Paul

I think the 53 would be too small for you. I ride a 53 and am only 5'9. The laid back angles are going to help you in not having to shove the seat all the way back. You are going to start with the seatpost a little farther aft of the BB due to the angle of the seatpost. The 54cm 381 has ~1cm longer TT also, so that is something to consider when looking at this frame. If I were you, I would get the 54.

Thanks for the feedback. Thats kinda how I'm leaning, but just wanted some real world comparisons to consider. I'm happy with my cannondale fit but to get the seat to were I want it, I need to use the Look ergopost in the 3 slot. The turbomatic saddles rails just don't allow for much adjustment.

What size KG381i frame would you all recommend for someone 6 feet tall with an inseam of 35.5 inches?

In general I would not use inseam for calculating frame size. The TT is a better indicator, as you can change more easily seatpost than with stem. I've recently build a 481SL (Same geometry i think, almost identical to the 381i) using www.competitivecyclist.com for measuring frame size and it fits really nice, only things is that I need a little time to get the handlebars lowered.

Reg. 381i take note that it has (compared to some other brands...) a rather long TT.

LOOK tt (for the 381/481 geometry) are not long at all. The slacker the seat angle, the shorter the effective top tube. General ballpark (I'm no trigonometry master) is you effectively shorten the tt 1.2 cm for each degree of setback. This happens if you wish to keep your knee over pedal in the same position. I have a C'dale 54 cm (c-t) and a 54 381i (c-c) and they both fit. The 381i actually has a shorter effective top tube than the C'dale, which is effectively a 53cm c-c. The tt is only a bit shorter, which was my goal..together with taking away some of the saddle to bar drop. I could have easily went with a 53 with a longer stem, but I would have had more of a drop. FYI, I'm almost 5'9" and have a 32.5 in. cycling inseam.

LOOK tt (for the 381/481 geometry) are not long at all. The slacker the seat angle, the shorter the effective top tube. General ballpark (I'm no trigonometry master) is you effectively shorten the tt 1.2 cm for each degree of setback. This happens if you wish to keep your knee over pedal in the same position. I have a C'dale 54 cm (c-t) and a 54 381i (c-c) and they both fit. The 381i actually has a shorter effective top tube than the C'dale, which is effectively a 53cm c-c. The tt is only a bit shorter, which was my goal..together with taking away some of the saddle to bar drop. I could have easily went with a 53 with a longer stem, but I would have had more of a drop. FYI, I'm almost 5'9" and have a 32.5 in. cycling inseam.

I really am no Trigonometry expert, but intuitively it seems that a slack seat angle would make the Tob Tube seem longer not shorter. What am I missing?

I really am no Trigonometry expert, but intuitively it seems that a slack seat angle would make the Tob Tube seem longer not shorter. What am I missing?

Assuming you want to retain the same knee over pedal (KOP), with the slacker angle you will need to either move the saddle more forward and/or have less setback on your seatpost. Saddle position over pedals should not be adjusted to shorten or lengthen your reach, although the effect (depending on the slacker seat angle) will be to shorten your effective reach.

If you do a search others can probably explain it better than I, with examples using real numbers and trigonometry.

Assuming you want to retain the same knee over pedal (KOP), with the slacker angle you will need to either move the saddle more forward and/or have less setback on your seatpost. Saddle position over pedals should not be adjusted to shorten or lengthen your reach, although the effect (depending on the slacker seat angle) will be to shorten your effective reach.

If you do a search others can probably explain it better than I, with examples using real numbers and trigonometry.

Cool. Now I get it. Thanks. Makes sense.

MIke