Hi,

I have a singlespeed/fixed gear bike, and need some help figuring out what the right stem length should be. It currently has a 130mm threadless stem, with a threaded to threadless adapter. Below is a link to 2 pictures, does this stem look too long?

https://www.flickr.com/photos/147844...57679488048856

Dave

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I run stems up to 14cm in extension.
Don't worry about the visual, only = does it make the fit better?

Try this link:

https://www.flickr.com/gp/147844774@N06/N6Z937

This is the stem i've had on the bike pretty much forever. It has over 7000 mi on it, but now i'm wondering if i'm too stretched out on it.. A few years ago, I built another road bike (a scattante), with a little bit more modern geometry, and a longer top tube. That bike has a 110mm stem, and feels pretty much perfect. Would it make sense to measure the top tube length on the scattante, add in the 110mm stem length, and try to create that same distance on this bike? The reason i'm fiddling around with the idea of changing the stem is that my back has been hurting after riding this bike, so i'm wondering if it's a bike fit issue (or maybe just an issue from moving to a much hillier area?).

Dave

Generally the first step is to set the saddle position followed by the stem length. If you really like the fit of the Scattante. I would check that saddle position compared to the bottom bracket. I find it easiest to measure, using a level or plumb bob, from the pedal spindle to some fixed point on the saddle. Get that measurement from the Scattante then measure from the saddle to the bar and duplicate that on the other bike. Record those measurements.

Thanks for the suggestion. Based on some measurements, i'm thinking 100 mm is the way to go. Another thing i'm thinking about doing is changing the angle of the stem. Currently the bike has a really shallow angle (maybe 6 degrees?) so i'm trying to figure out what angle to get. Would a 20 degree stem be enough of a change?

Dave

Twenty degrees is quite a lot in one jump. I'd go half that. It takes quite a bit of messing around with bike fit and the problem is compounded as your cycling physical fitness changes. Road Positioning Chart | Park Tool I have several of the Park Tool charts going back about 5 years with recorded measurements. I can see haw my position has changed over time.

You have two bikes. You feel stretched on one and good on another. Time to do a real analysis and it is not hard. Get a large sheet of graph paper. (Not required if you have drafting skills with straight edges and triangles or a drafting machine or even better, a CAD program and skills.)

On your graph paper mark the center of the bottom bracket near the bottom left corner. Now take accurate measurements from each bike:
Vertically from the BB center to the floor
Vertically from the handlebar tops center to the floor.

I like to place a piece of tape halfway from the seat nose to seat tail, then measure:
Vertically from the seat top at tape to the floor.

I then hang a string with weight from the top tube to the BB center, then measure:
Horizontally from the seat mark to the string. (Easy to stand above the bike and sight down the string.)
Horizontally from the handlebar tops center to the string.

Subtract the BB to the floor measurement from the other two vertical measurements. Place them on your graph paper. Do the same with your other bike. You now have all the important contact points with the two bikes compared. (Not quite true. Different crank lengths and cleat/shoe thicknesses will make some difference, but mostly in seat height which isn't our primary focus here.)

I have all my bikes drawn in this manner on one drawing (in a CAD program, but a base drawi9ng on graph paper and translucent overlays for each bike would accomplish thhe same thing). I have fleshed out the drawings with the tube angles and lengths. From this I can see what stem will be required to get "this" position. Also see why "that bike" isn't comfortable. I now measure up perspective bikes and place them on the drawing. When I go the next day to pick up the frame, I can pick up the right stem and seatpost.

Now different bars and brake lever setups will change things, but you will have a strong visual picture to balance that by. When you start adding in the frame tube dimensions you will start seeing that the single most important dimension on a bike is the location of the intersection of the top tube and head tube relative to the BB. If it is in the right area, getting a stem to make the bike comfortable is, as they say, easy peasy. If it is not, you may end up having a frame builder make you a custom 180 mm stem or seeking out Nitto long quill stems, very short reach handlebars or other hard to find or pay for items.

For you, this may simply be a matter of seeing "oh yeah, my fix gear HB tops are 1 1/2" further forward and a half inch lower relative to the BB, No wonder I feel stretched!" Get a shorter stem and save the one you like for a bike with a shorter top tube or more laid back angles. (Again, that drawing will be a huge help, now and with future bikes.)

Edit: I said put the BB near the left hand corner. If you use a large enough sheet of paper, having room for the rear hub is a real plus. You can then start tracking your weight over the wheels and play with the best chainstay length/front center length for good bike handling. Not required for what you are doing, but if you are considering a custom frame ...

Ben