What is the "ideal" stem length for a road bike?
 

Maybe this is a dumb question-- but it seems to me that that the most important measurement of the bike is overall length from seat to handlebars.

I guess that it could be measured several different ways, but lets just use top tube length plus stem length as a simple approximation.

And lets say that my "ideal length" using these combined measurements is 68cm.

And lets suppose that I could get any frame size I want, and any stem length I want.

If that was all true, would I be better off with:

1) a 56cm top tube, and a 12cm stem
2) a 58cm top tube, and a 10cm stem
3) a 60cm top tube, and a 8cm stem

It seems to me that each of those three layouts would feel the same for length, but they would probably handle differently in some way that I don't understand.

So which is best, and why?

They handle differently cause the weight balance thats on/over the front wheel changes a bit, its something you may notice when you initially do the switch, but after a little bit of time its something that you aren't even going to notice anymore. Whatever is ideal I suppose depends on what sort of characteristics a rider likes in a ride. I myself have longer legs compared to torso making fit a challenge, bikes with short top tubes typically have short seat tubes so I can't reallly ride them cause I cant get the bars high enough where the bike could become safe, same thing with the seat post. So I go for the longer seat tube, 56cm is ideal for me, and that means the TT is typically 56cm as well, so I use a 60cm stem. I happen to like a twitchy lively feeling ride so It works out good for me.

For whatever reason Ive found a lot of bikes in the past and present in shops/stores come with a 10cm stem.

Stems become proportionatly longer as frame sizes increase because top tube lengths tend be shorter in relation to top tubes as bikes become bigger and vice versa. Body proportions increase as well, tall people have longer torso and longer arms. TT's are generaly a torso fit while stem lengths are generaly an arm length fit

As an example, 54 to 58 cm may be 'square' meaning that both the ST and TT are the same lengths: 54/54, 56/56 etc. Smaller frames are over sqaure, the ST are shorter than the TT: 48/50, 50/52. Bigger frames are under square meaning the ST is longer than the TT: 60/58, 62/60 etc. Because of this small frames need stems in the 60-90 range, mid size frames in the 90-110 range and big frames need stems in the 110-130 range.

Smaller frames: little seat post showing with short stems
Average frames: normal post showing (6 inches or so) with 90-110 stems
Big frames: alot of post showing with long stems

If I may distill the OP's original question, I think it is: provided that the TT/stem “fit” is appropriate to the rider, what's the difference in ride/handling between a long extension stem and a short one?

To many variables to say. This can come down to the rake of the fork, the head tube angle and your personal comfort or taste.
One of my touring bikes has a 60 stem another has a 100 and my oldest has a 90. All have the same size frame.

The one that gets you the proper fit. Adjust your saddle so youre properly over the pedals and find a stem that matchs your reach. I find the one that gets me in a good position without compromising lung capacity feels abit too long at first, like I'm reaching. If the stem is too short, you end up in a more upright position. Maybe you LBS has a few used used stems you can experiment with to get a good fit?

Typically, I like to have the view of the front axle blocked by the handlebar while on the drops for my own likes.

Assuming that your seat is the proper height:1.09 x leg length, when you sit on your bike with your hands on the drops,look down at the front hub. Your handlebar should be in the same line as the hub axle, and obscure sight of it. Or, as a starting point: if your saddle is properly adjusted for height, and is clamped in the correct position, place your elbow on the tip of the seat, and your finger tips should just touch the handlebar.
Many racers, and long time fast sport riders will often say that the stem would be too short using these recommendations, but most people would find these to be excellent starting points.

That's how I interpret it, Charles. All three scenarios presented would feature the same seat-to-bars reach and "fit," but the steering feel would differ somewhat. I have experienced all three scenarios -- 1980 Peugeot PKN-10 with long top tube aftermarket very short-reach stem, most of my other bikes with mid-reach stems, and 1970 Nishiki with short top tube and aftermarket long-reach stem. They did feel different, but all three worked well enough that I would still buy a frame based on height, rather than length, then compensate with the stem reach.

Just offering an opinion here - I have bikes with varying stem lengths and top tubes - I've substituted longer for shorter on several of those with shorter TTs, to avoid riding like a scared cat :
http://i254.photobucket.com/albums/h.../archedcat.jpg

(That gets very uncomfortable on long rides)

My sense of the before and after condition is that while I can stretch out a little more, the ride handling/stability is unaffected. (-Which would make sense, considering that the caster and the trail is established by the angle of the steerer tube, and the distance to the tire's contact patch with the pavement respectively.)

For me: 100mm on road, touring, hybrid, and XC mountain bikes. Don't ask me why, but my best fitting bikes have 100mm stems on 'em. I never actually realized until now that they're the same length, even with different length top tubes and different style bars. Hunh.


Freeride, jump, pump track etc. bikes: 40-60mm, better handling and more rearward position.

I read somewhere that Eddy Merckx insisted that all the bikes under his name be designed to be ridden with 110mm stems. He felt it provided the perfect fit.

This is exactly the question I was trying to ask.

It seems like you can make an argument for starting with the desired handlebars/stem combination when designing a custom frame. If you thought a 110mm was ideal you would spec a shorter top tube than if you wanted a 130mm stem.

Again, that was the crux of my question

from an aesthetic point of view I like the looks of a 100-110mm stem best.

I'm pretty sure a long stem puts your weight balance more towards the front wheel for what thats worth. I'd expect that the frame geometry has a lot to do with whether or not that shift in balance affects the ride.

The question is more complicated than it seems. Seat tube angles and bottom bracket height and Q factor are all going to contribute to the feel and fit of a ride in addition to the magic tt/stem number. In the end the answer can be different for each unique rider.

Not only that, but also call out your desired saddle and the desired knee position relative to the pedal axis. Based on those you can set the seat tube angle (letting the designer/builder select the seatpost), and hence know how far behind the BB the top tube must start.

Aesthetically, I like the looks of a 120mm stem. It just looks 'right' on my bike.

I suppose, over the years through trial and error, buying bikes and swapping parts, I have found a 58 or 59 cm c to c frame with a 120mm stem fits me best and I do like the overall balance a 120cm stem gives a bike of my size. I am 6' 1" and my stem length opinion suits me and the way I feel on my bike.

I have also come to realise that everyone that has a bike has an opinion as to how to determine the stem length. For some, it is purely a mechanical measurement; some rely on feel (perhaps medical condition); for others aesthetics do play a part in the choice of stem length. Perhaps it's a combination of all considerations.

I feel it's important to formulate your own personal requirements re stem length.

Best of luck,

Gary.

Dave Moulton's blog has him mentioning this as well. For all his customers' bikes, he discovered 100mm stem extension worked best. :-\

100-120mm, anything else and the bike does not really fit you.

I ride a 56cm frame and most bikes in this size range that I have owned came with a 110 stem.

It's interesting you say that because I have heard from a reliable source, (by a Colnago fitter, in reference to my 78 Colnago Super), that Colnago designed their bikes to be used with a 120mm stem for optimal fit and handling.