reroll

I searched online for advise about stem lengths and what I thought would be simple turned out to be complicated. I am a commuter, grocery getter and occasional tourist, but learned a lot about stem lengths by reading what serious uphill, downhill and trail MTB riders had to say about theirs, recommended reading.

The easiest way to find a stem's length would be criticized by 'experts' but it shows up in nearly every stem length discussion I have seen and goes with what riders have found works best for them, that there is a correlation between stem length and fork offset, that the center-to-center length of a stem should be approximately equal to the length of a fork's offset, which produces a neutral starting point, parallel to the fork's rotational axis, and can be modified from there, longer or shorter. The size and type of handlebar could call for lengthening or shortening the stem, but even then many riders still stay close to their fork's neutral starting point. YMMV

Edit: Another bit of advise about stems, a weak stem can suddenly become very dangerous and the advise is to stay away from cast alloy stems and to instead go with stronger and more reliable 2D and 3D forged alloy stems.

Iride01 

You are making it hard by trying to figure out what that perfect for you stem length and rise is before you get one. So instead just get one and try it. If you like what it does for you, then it matters not what any of us think. If you don't like the results then you can try something else.

Also understand that a lot of what you read are by and for people that ride their bikes in very demanding conditions. If you just ride your bike, then those things they are talking about probably won't amount to much for you.

I wouldn't get too concerned about cast or forged. Just try to get a stem from some manufacturer that is reputable and has made stems for a long time.

If you change your stem length to shorter, then it might make the bike seem more twitchy, but you'll get use to it after a few rides. I changed my stem length from 100 to 70 millimeters a while back and that twitchy feeling wasn't really anything more than just being different. If the bike had come with a 70 mm stem from the start, I wouldn't have known any different.

79pmooney

Stem length is all about fit. (At least for properly sized road bikes.) Yes, changing the length affects steering some but very rarely to anyplace unsafe.

I raced an 11 cm. Rode decades commuting on a 18 cm. I have long arms so I steer toward stems most would call very long. For me, stem length and wheight ((edit: oops!) are critical elements in making a bike that works well for me. (And I figured out years ago that I can trade height for length and keep the position I love.) But as far as fork offset goes? Who cares? If you stay ignorant, that will never, ever matter.

Just my views after a few miles of riding a few different bikes.

And edit: The great Eddy Merckx (and by default, also God) was said to ride 12 cm stems. So by the rule of stem length equalling fork offset, I should have had all three of my custom frames built with 120mm fork rake. I'm guessing that a head tube angle of around 45 degrees would be needed to get proper steering. That would push my bikes' front centers forward about 15". To keep proper weight center over the wheels, I'd have to push the rear wheel back about 10". New wheelbase? ~65". New total bike length? About 92" or nearly 8'. Time to modify my garage for bike storage.

Polaris OBark

Is there a question being posed, or is this more of an exposition?

I think a good starting point is to get the seat height and fore/aft position correct, so that you are balanced, and then adjust the stem's length so that your forearms are about 90° from a line drawn through your spine.

This implies that the stem length is going to be dependent to some extent on the reach of your bars, brake hood position, etc.

oldbobcat

According to an article in Bicycle World, from around 1974 by a writer who actually measured a bike, Eddy's DeRosas were 58.5 c-c (60 c-t) X 57, with 13 cm stems and 175 mm cranks. His height has been reported as 181, 182, 184, and 185 cm. He appeared to still be growing taller during his first pro season, 1967. His arms and legs are longer than average for his height. In my estimate the 13 cm stem would have been too long if he were under 6' tall. But I ride with 57 top tube with a 12 stem, so I know what they look like together.

PeteHski

I'll take your word for it about this correlation between stem length and fork offset, but I don't think it actually means very much. What does this idea of a "neutral" starting point actually mean in reality? Stem length simply affects your hand position on the bike (reach) and how relatively quick or slow the steering feels (which is also affected by many other parameters besides stem length). So a long stem will increase your reach and make the steering feel slower/less responsive. That's about it.

As for weak stems, yes definitely avoid those!

reroll

Not sure I could give myself credit for an exposition, and I have used a range of stems from fairly long to quite short, but I was curious to see if there could be any sort of a formula or established guideline for determining stem length, so I went online and searched and what I wrote was a brief summary of the information I discovered.

Yes, seat height and adjustment is always the first thing I pay attention to, yet even when that gets done here in my living room it is usually not until after I have put some miles on a bike and have made some minor adjustment tweaks that the seat finally gets into the position it needs to be in.

Then after that comes getting the bars to where I want them. I rode with drop bars for more than a dozen years and eventually found myself spending nearly all of my time with my hands on the tops of the bars, so I switched over and experimented with a number of different styles of flat bars and my favorites became the 48mm Velo Orange Porteur bars which are somewhat like drop bars but without the drops.

Along with experimenting with bars came experimenting with stem lengths. Long story short, I found my bikes get along nicely and I get along nicely with shorter stems and 50 or 60mm is about right for the both of us. But I was curious as to whether there could be a 'best' stem length, which led to my searching online.

reroll

Yes, stem length determines how quickly or slowly a fork steers. Yet there is a 'neutral' length which is neither long or short and is realized by a stem having the same center-to-center distance as the fork's offset, or rake. Stems longer or shorter than neutral alter the needed rider input while a neutral length does not and represents the minimal input needed. In other words, using a neutral length stem allows a rider to 'feel' a front tire's traction more directly.

Forged metals are stronger and more durable than cast metals and are more expensive, but consider the value of your safety. 2D is traditional forging and heavier, but gets the job done. 3D is modern forging and lighter, but usually is more expensive.

PeteHski

This concept of "neutral" stem length is questionable as there are many other variables that contribute to steering feel and weight. Like for example simply how wide your bars are or what tyres you are running. There is also nothing magical about this "neutral" length allowing you to "feel" the front tyre's traction more directly. What does that last statement even mean? Factors like trail affect the steering "feel", not to mention the actual tyre characteristics. Stem length is really just a geometric gain factor in the equation i.e. shorter = faster. There is no such thing as a "netural" length other than some arbitrary number. There's nothing special about it. The main reason to change stem length is to adjust your reach. The affect it has on steering feel is very much a secondary consideration within reason. Obviously if you run a ridiculously long or short stem you might not like the affect it has on steering weight/travel.

Carbonfiberboy 

See: How can I fitting my bike
Essentially it has almost nothing to do with bike handling and everything to do with comfort on the bike. Stem length affect quickness of steering, but one adapts to that quite quickly. I use a 100mm stem, my wife has a 15mm stem. Both work fine and have the same fit vs. their rider's anatomy.

phughes

Stem length has everything to do with fit, and is variable based on the top tube length, bar reach, seat setback, length of the rider's arms, forearm length, drop, personal preference, etc. As for steering, any difference in steering is adapted to in a matter of minutes for most people and is insignificant, it also comes down to personal preference. It has nothing to do with fork offset. Figuring neutral steering using fork offset and stem length is an exercise in theory, and has no practical application in regards to fit. Fit is how the rider interfaces with the bike.

GhostRider62

For a variety of reasons, I sometimes use a 110mm stem on a particular bike but usually 150 mm. I notice the difference in handling.

Also, the closer the center of gravity is to the wheel axis, the more difficult it is to balance and steer a bike.

Sitting upright with Porter bars has your head in a normal position from a balance perspective (vestibular) and the higher position makes balance and steering easier

I suspect what I notice is a combination of the above factor and more. I really noticed these things when on an extremely far flung recumbent

Differences in frame geometry, materials, and layup are probably bigger factors in handling response than stem length. I have two bikes with about the same length. One of them is a handful on twisty, bumpy steep descents. I was on the other one going down a hill that always took my attention on the lousy bike (Cervelo). My first thought was, "This bike is slow downhill" and then I looked at the Garmin and the speed was the same (about 40 mph) but I could almost take a nap, that is how different. 140 vs 150 mm stem. Totally different geometry and material

phughes

And that goes under personal preference. No doubt there is a difference, but fork offset to stem length doesn't factor in a fit. Yes, you can feel a difference between stems that are very different in length, but still, you can get used to either. The point being though that fork offset isn't really a factor given the fact there are so many other measurements that come into play in a bike fit.