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Look KG381i questions(13 posts)

Look KG381i questionsmy327vette
May 15, 2003 6:35 PM
Hi, I am looking to purchase a new frame to replace my size 54 Trek 5200. I am 5'9" and am weighing in around 205 pounds these days (although i hope to get down to 190 pounds). The frame that I am most interested in right now is the Look kg381i, but I have a few questions about it. First, will this frame be well suited to a heavier rider like myself? I don't want a frame that is going to be flexing like crazy every time I hammer on the pedals.

I also have a couple fit questions. I am confused by effective top tube lengths. How would the top tube of a size 53 Look (54.8) compare to the 54.5 effective top tube length of my size 54 Trek. I have been told that although these measurments are very close, due to the different seat tube angles of the different frames the EFFECTIVE top tube lengths are quite different. I use a 100mm stem on the Trek. Can I correct the difference on the Look by using a longer or shorter stem?

Also, will I be able to achieve the proper seat position on the Look? I have heard that due to the different seat tube angle of the Look, it might be hard to get the same saddle position as my Trek. I have the saddle set around the middle of the seat rails or even set slightly back on the Trek.

And lastly, how much clearance do I need over the top tube. The standover of the Look is equivelant to a size 56 Trek. I checked the standover with my riding shoes on over my friend's size 56 Trek and I only had about 1 cm of clearance. Will this be OK?

Thank you in advance for any advice you can offer me.
Fit ballparkfiltersweep
May 16, 2003 3:34 AM
I don't think the frame will be too flexy-

I found that a 57 Look was actually larger than a 58 Trek (that I had been riding). Also, despite the fact that I THOUGHT Trek geometry worked for me, the Look works much better. You are correct in that with the more relaxed seat tube angle, the higher the saddle, the further the effective TT length. Someone posted a magical chart a few days ago that described all this geometry in great detail. My point is that while you might not end up with the SAME saddle position as the Trek, you might end up with a BETTER position.

The trouble with buying a 381 Look is that most LBSes don't have them built up to test ride. Mine started out as a bare frame hanging over the cash register, but I was able to test ride a sales rep's personal ride.

I'd be concerned that the 53 might be a bit too large. In my case, the Trek was a bit cramped, so I welcomed that longer top tube. 1 cm standover in your case is not much. I believe Look still makes these in 1 cm increments?
re: Look KG381i questionsHorace Greeley
May 16, 2003 5:18 AM
Not sure how Treks compare, but the general rule explained to me is 1 degree difference in seat tube angle equals 1.2 cm. So a few degrees difference in seat tube angle between the Look and the Trek will effectively shorten the top tube. IFor what it's worth, I'm 5'8'' with a 32.5 (slightly longer) cycling inseam, and a 54 Look KG 381 fits me well. I have no issue with standover, although it's on the shorter side of acceptable. I could have fit into a 53 cm, but I did not want an extreme drop or have to use spacers or a riser stem. I came from a 54 cm C'dale (which is about 53 cm sinc its C-T), and the Look was a much better fit due to my longish legs vs. my torso. I don't think Looks fit any different (their not large or small). Best advice is to match up measurements of your current ride to the Look, and adjust your likes and dislikes. Excel Sports was very helpful at providing measurements you could not get from the geometry chart. As far as flex, I really can't help you since I'm 155-60 lbs. and don't flex anything since I'm a spinner. Good luck. It's a great frame.
re: Look KG381i questionsjaybird
May 16, 2003 5:36 AM
I also made the switch from a steel Trek to a Look KG381i and I am a pretty big guy. At 6'3", 225ish I don't notice much flex at all on my 59cm. I also chose mine because of the ride compared to an OCLV. I didn't think the OCLV felt as dead as some people say but the Look just felt a little more lively. I also never saw a fat guy riding a Look, so I figured I start the trend.

If you go to a shop that sells Lemond or Merckx you can get the feel of Look geometry and since the 381 is available in 1 cm increments you should be able to get a perfect fit.

Could someone post that nice little diagram explaining effective tt length...
re: Jaybird Can I Ask You, Your Inseam Length ?268generation
May 16, 2003 8:43 AM
Im trying to figure out my size also im 6'2".

Im on a old 62 cm (way to big for me).

34ish in.jaybird
May 16, 2003 9:21 AM
I could have gone with a 60cm frame but the 59 just felt better... I have a little more than an inch of standover.
Haven't you decided yet?KG 361
May 16, 2003 6:19 AM
Sheesh. This was rehashed at least 2X before. Go to a Look dealer and have him fit you if you haven't figured this out yet. (Bikesbycyle). I would have thought you'd have been posting pics of your bike by now. If you continue at this rate, the summer will be over and you still won't have the bike.
re: Look KG381i questionsmainframe
May 16, 2003 6:21 AM
The Look will have a shorter effective TT length by an amount equal to 1.2cm for each degree of STA change, the Look being more slack than the Trek. Your saddle will move forward by the amount determined above to achieve the same KOPS as the Trek thus shortening the effective TT length.
re: Look KG381i questionsfiltersweep
May 16, 2003 7:22 AM
Am I missing something? The effective TT becomes shorter as the angle approaches vertical (ie. steeper) rather than slacker.
No. It's the opposite.Horace Greeley
May 16, 2003 9:14 AM
You can do a search on this topic. I had the same reaction at first, but it is the opposite. The slacker the seat tube angle, the shorter the effective top tube length relative to a bike with a steeper angle. C-40 and others explain it best using math formula. I can tell you that although my C'dale on paper has a longer top tube, the relaxed seat tube effectively shortened my reach because to keep KOPs neutral to slightly behind the pedal spindle, I had to use a seatpost with setback and push the saddle back on the rails. Keep in mind that if you keep KOPs the same, you are effectively shortening the top tube by moving the saddle forward (but keeping KOPs the same). For me, I went from a seatpost on the C'dale with a fair amount of setback to a U.S.E. Alien with virtually no setback. I also moved my saddle forward to retain KOPs virtually the same. The net effect, per the more scientific math formulas, is that my tt length was shortened (I did the measurements on both bikes).
Sure, throw KOPs into the fray ;)filtersweep
May 16, 2003 9:34 AM
OK- so let's say you have a compact frame with a very relaxed tube- you'd need to install a reverse way-back seat tube to maintain KOPs... but that doesn't discount the issue that KOPs is a non-issue to those endowed with long femurs ;)
A very crude drawing explaining KNOP and Eff TTDave Hickey
May 16, 2003 9:47 AM
Both frames have the same TT length(c). The frame on the bottom has slack angles but in order to maintain the proper KNOP, the effective TT is shorter(a).
re: Look KG381i questionsorange_julius
May 18, 2003 5:19 AM
In addition to the points made by other posters, LOOK measures their seat tube C-C (center to center) while Trek measures C-T (center to top). So my 55cm LOOK is indeed a little bigger than my 56 cm Trek. If you live in the Northeast, CycleLoft in Woburn, MA (north of Boston) has a deal where you can test ride one of the built up LOOKs for a few days for a fee. Or you can visit Bethel Cycle in Bethel, CT, which usually has a few LOOKs in the store. I never bought a bike from CycleLoft but I heard that they are good, and I can say from experience that the Bethel Cycle folks are good. Both stores should fit your new bike to your measurements.

Moreover, if you're concerned with flex you should look into the LOOK KX (Look! It's a LOOK!) or KX Light since they are specifically designed to give a stiffer ride, for example for sprinters. I have tried a few KG's and own one myself, but never tried the KX's.

Hope that helps. I really love my LOOK and I'm sure you'll love yours, too!