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sizing for Look(13 posts)

sizing for Lookchriscpa
Jan 28, 2003 6:37 AM
I am thinking to get a Look KG 381. I am 5'9" with a 31 inseam. I am currently on a 55cm frame with a 55.5 TT. Now the seat is all the way forward. Do I have a relative short torso or what? Now I am thinking to get a 53 Look. What is your view on this size.
re: sizing for Looklook271
Jan 28, 2003 7:03 AM
The top tube for a 55 kg 381i is 55, so perhaps a 53 would be a little too small. A 54 might be good, since the tt is 54, especially since you say that the seat is all the way forward now.
Actually, the tt of a 55cm KG381 is...serbski
Jan 28, 2003 2:35 PM
...56.9cm as the 381's have longer top tubes/steeper HT angle than the 361's. For example, the 55cm KG361 has a tt of 55.6cm with a HT angle of 73 while the 55cm KG381 has a HT angle of 74 and longer tt as mentioned above. Check out the Excel Sports site as they list all the LOOK geomety.
head tube angle is irrelevant....C-40
Jan 28, 2003 3:56 PM
The angle of the head tube has no significant effect on top tube length (1mm or less). It's the seat tube angle than matters. Seat tube angles change the efffective TT length by 1-1.5cm per degree depending on the frame size.

Here's the site for all of the LOOK geometry:
Common problemNessism
Jan 28, 2003 7:19 AM
One should not adjust the reach to the bars by sliding the seat forward. The first thing to do is adjust the seat up and back to give the proper position relative to the bottom bracket. After this position is established, play around the stem and handlebar reach to give you the desired reach.

Regarding the 381 Look frame, it has a slack seat tube angle of 72.5 degrees. You should consider this fact when deciding what size frame you need.

Good luck.

why 72.5?chriscpa
Jan 28, 2003 7:52 AM
The saddlle position is now right on. And I have a 110 stem. I got a feeling the 55.5TT is a bit too long. I have no hope understanding why a 72.5 angle make a shorter effective TT. (It is against my limited math intuition) And yes I have seen THE drawing.

So far as I have seen, most 55 frame have a 73 angle. What is the advantage of a slack seat tube?
why 72.5?Nessism
Jan 28, 2003 8:05 AM
If you currently have a 73 degree seat angle and have to slide the seat all the way forward to get the position you like relative to the bottom bracket, going to a 72.5 degree frame will require you to slide the seat forward even more. To acheive the same position as before, you will need a seat post with no offset (assuming your current post has some offset).

Honestly, it sounds like you should look for a frame that has a steeper seat angle than the Look 381. From the information you have given, a 74 degree seat tube angle would be more appropriate than 72.5.

Jan 28, 2003 9:44 AM
I'm 5'9" and ride a 55cm 381i with a 10cm stem. bike fits good, I do have the seat slid forward a little bit. I just posted a picture of it and my other bike, a 56cm GT ZR 2.0 in the bike shots. should be up either today or tomorrow. Check out the pick and you will be able to see how it is set up. We are basically the same size.
Look Top Tubellbr22
Jan 28, 2003 10:46 AM
One big rule is to not adjust seat fore and aft to compentate for bar reach... now your messing with your pedal power.

I too am about 5'9" but with a 32 inseam (pants inseam), and a short torso... I'm actually planning on getting a 53 cm KX light (54 cm Top tube). Yes, I'm gonna have a lot of seatpost, and stem stacked to the limit, but it's the only thing i can do to get my weight distribution where I want it. Right now I've only got 39% of my weight on the front wheel, and I want at least 44% or so.

My current bike is a 56cm with a 57 cm TT, and a 90 mm stem. It understeers.

Since your looking at a 381, you can go for a 54 if your size problem is minimal. For me and a KX i don't have that choice.

more info...C-40
Jan 28, 2003 2:05 PM
It's a simple job to compare the LOOK geometry to your current ride, but you didn't provide enough info. To make a valid comparison and a good comments, I need the seat tube angle of your current frame, or at least the model of bike that you're riding. The standover height would also help.

What type of saddle and seatpost are you using? You mention that you have the saddle all the way forward. Was this necessary to get the knee directly over the pedal spindle?

What stem length are you using?

Measure and post the vertical height of your saddle above the top tube, near the nose (looking for 16-18cm).

With this info, the fit of a LOOK frame can be compared.
Let's start from the beginning. where is Kerry when you need hiHigh Gear
Jan 28, 2003 4:12 PM
First of all, is your position correct on the bike you have now? Is your knee anywhere near to being over the pedal spindle when your pedal is at 3 o'clock? If your are 1cm either way than you are fine. On to the next question. What frame is it that you now ride. That would be helpful to us so that we can look it up and determin the seat tube angle you now have. Please post back so that we have the critical info as to help you better.
Let's start from the beginning. where is Kerry when you need hichriscpa
Jan 28, 2003 5:30 PM
oh thanks,

Knee is right on the pedal spindle now. Now I am on a Litespeed catalyst 55cm. It was a custom frame for someone else when I got it. Not sure the seat angle, but seat tube is 55 c to c and TT is 55.5 c to c.

thanks again
Wow!High Gear
Jan 28, 2003 7:07 PM
That may be your problem right there. You could be riding a real slack seat tube angle frame. Maybe we can figure out the angle with a few measurements. With the bike on a level surface, drop a plumb line from the top tube so that it intercects with dead center of the bottom bracket, mark a line on the top side of the top tube when you find it. Now measure from that line to the center of the seat tube, on the same plane as the top of the top tube. I need that number. Now take a tape measure and run it along the center of the seat tube and get a measurement from the center of the crank to where in intersects with the top of the top tube. With those two measurements I or someone else on this forum can figure out what your riding and if the Look for you.