[pixelninja]

I'm curious to read people's opinions on how stem length affects the handling of an xc bike. What is more stable for climbing, shorter or longer? What about descending? And what's better for tight twisty singletrack?

I've noticed that downhill stems tend to be shorter, i.e. Truvativ downhill stems only go up to 75mm, whereas their xc stems go up to 130mm. What's the reasoning behind this?

 

[Wumpus]

I'm curious to read people's opinions on how stem length affects the handling of an xc bike. What is more stable for climbing, shorter or longer? What about descending? And what's better for tight twisty singletrack?

Stem length is more of a fit issue. It could marginally affect the center of gravity.

I hear a lot of folks say it speeds and slows steering but you are going to have to have a pretty big change in length for that to happen. Changing handlebar length would be easier.

I've noticed that downhill stems tend to be shorter, i.e. Truvativ downhill stems only go up to 75mm, whereas their xc stems go up to 130mm. What's the reasoning behind this?

A shorter stem gives you a more upright/rearward riding position which would seem to help when downhilling.

 

[clancy98]

shorter stem puts you more over the haedtube instead of the front axle. If you think about it with maybe a 100mm stem or longer, you are closer to being right over the front axle. steering would be more twitchy. Picture if you headtube was 90 deg., straight up and down. The bike will steer fast as hell because as soon as you turn, the wheel goes right out from underneath you. it puts you at the "apex" (term used loosely or incorrectly?) of the turn, whereas if you are on a 30mm stem, you are slightly behind the "apex" of the turn, the axle.

at least that seems like it would logical to me. If thats wrong, please correct

 

[Darkreaper]

Shorter stem increases the snappiness of the turn, because for a shorter distance moved by the end of your handlebar the wheel has rotated more.

I think...?

 

[Wumpus]

Shorter stem increases the snappiness of the turn, because for a shorter distance moved by the end of your handlebar the wheel has rotated more.

I think...?

Going from a 100mm stem w/ a 660mm bar to a 130mm stem w/ the same bars only increases the diameter of the circle created by the bars 2 cm. I just don't think that that is going to be noticeable.

 

[Darkreaper]

Maybe not... but a head angle change of just one degree is pretty small too, and most people can notice that.

 

[sanjuro]

Firstly, shorter stems handle quicker than longer stems. Think of it this way: BMX freestyle bikes have stems no longer than 5.5cm, so you can do bar spins and other tricks which require the quickest handling possible. But stem length differs for the type of riding, road, XC, Trail, FR, or DH.

Road stem length is primarily a fit and position issue. The handling on a road bike will be moderate to high speed (15+mph), so the handling is usually a function of bike lean. I have put as short at 6.5cm and as long as 14cm with not much effect on handling.

Traditional thinking had XC stems relatively long (from 11 to 14cm depending on the person's height) for superior climbing position. The farther out in front of your bike, the more power you can drive into the rear wheel without the "wheelie" effect.

However, due to the influence of DH/FR, XC stems have gotten shorter as of late (9-12cm), which gives you better handling on the downhills and not much penalty on the climbs. Conversely, the top tubes have gotten a little longer, but it does vary from builder to builder. A quick survey of Salsa and Fisher hardtails have the Salsa's effective top tube at 23 inches for a 18" frame, with 23.9 for a 17.5 frame from Fisher.

Trail and FR bikes are starting to blur the line between an all around bike and a DH only bike. My Kona Dawg Primo with 4 inches of travel has a 9cm stem but DH bars. I have a Norco Torrent, a urban/dj bike, with a 5.5cm stem which I will also use for some trail riding.

Finally, DH bikes will have very short stems, between 5 and 7 cm. In this application, slow speed turning is definitely par for the course. Also putting your weight as far back as possible is critical for jumps and drops, which shorter allow you to do more easily.

 

[ioscope]

The shorter the stronger
the shorter the machoer
the longer the more leg-shavey

It's all about style

don't kid yourselves, you know it's about style.

 

[sanjuro]

The shorter the stronger
the shorter the machoer
the longer the more leg-shavey

It's all about style

don't kid yourselves, you know it's about style.

Should I convert my road, XC, DJ, SS, and FR bikes to a Serial Killa, the cooler stem ever made? Whoops my Norco already has a Serial Killa...

 

[clancy98]

Firstly, shorter stems handle quicker than longer stems.

Finally, DH bikes will have very short stems, between 5 and 7 cm. In this application, slow speed turning is definitely par for the course.

good post but now you are just confusing me! or maybe i am not getting the second part... I would really like to know the truth about this stuff, I have always wondered!

 

[Darkreaper]

Slow speed turning but you want the handling to be as swift as possible?

Or maybe it's just to enable the rider to get their weight further back

 

[Changleen]

Long stem to make up for short penis? j/k

 

[sanjuro]

Firstly, shorter stems handle quicker than longer stems.

Finally, DH bikes will have very short stems, between 5 and 7 cm. In this application, slow speed turning is definitely par for the course.

good post but now you are just confusing me! or maybe i am not getting the second part... I would really like to know the truth about this stuff, I have always wondered!

The confusion is when I describe handling as quick or slow, where my description of a slow speed turn is a turn done at slow speeds.

A slow speed turn as I describe it is when you have to turn your bars 5-25 degrees when going less than 12-15 mph. The typical example is you are rolling along on a flat, and you see a rock in the trail. You have to turn the bars to get around the rock, so the quicker the handling the better, i.e. a shorter stem.

On a road bike, a high speed turn is executed at 15mph and faster by leaning the bike. When your ride through a corner at 20mph, there is little turning of the bars. The reason for this is at higher speeds, a bicycle wants to travel in a straight line due to the gyroscopic effect of the wheels. A longer stem makes no difference here.

If you were to try turning your bars 25 degrees at high speeds, you would probably crash immediately. The only time I turn my road bars 25 degrees is when I track stand (which I do at the slowest speed, 0mph).

On a dh section, there might be a rock garden or a rooty section which a rider has to pick through. There a rider will turn his bars often to avoid obstacles, most likely at a slower speed.

Most riders, road or mountain, make high speed turns by leaning their bikes and not use much of their steering radius. However, the best mountain bike handlers can use a technique called drifting, where they actually turn the front wheel away from the direction they want to turn, and "drift" the bike through the apex of the turn. But this is a very advanced technique, which I just mention to be complete.

Frankly, if this is all Greek to you, I would just worry about getting the stem appropriate to your bike size and your proportions. You do not want to vary your stem length and cause a fit problem or a bad handling bike.

 

[clancy98]

good explanation!

 

[pixelninja]

None of you REALLY know what you're talking about, do you?

J/K

Thanks for all the good posts.

 

[AustinM]

A small difference in stem length can make a significant difference. Just like if you raise or lower your seatpost 2 cm, you definitely feel it. A shorter stem is better in the technical, as mentioned before you aren't leaned over the bike, stretched out. Think of trying to take a roadbike off road.

As for turning a short stem makes the bike more responsive. I like it, some people may not.

 

[Changleen]

None of you REALLY know what you're talking about, do you?

J/K

Thanks for all the good posts.

I know exactly how long my penis is, thank you. I rock a short stem. :evil: