If one has several road frames to choose from with differing stacks and reaches, what is considered to be the ideal stem length and angle? I am asking from the perspective of the best road bike handling, not the best aerodynamics or lightest weight. I imagine this would vary with the size of the frame overall such that a "small" frame would have a different best stem length than an "Xlarge" frame. Are the stems that come OE considered the ideal or are they merely the company's attempt to fit the greatest number of customers? Thanks.
Joe
I think "ideal" is going to depend on a combination of the bike and the rider.

All bike geometries aren't created equal. If a bike is particularly quick handling -- maybe too much so -- some will favor a longer stem to slow that steering arc down a bit. The reverse also applies.

There is also the added wrinkle that a bike will handle differently for two different people. Lets assume you have two people that are 5'8" and they both fit a particular 54cm bike reasonably well, but rider A has a longer inseam and longer arms -- her weight distribution on the bike will be different and the bike will handle different than for rider B.

So is there a "safe" stem length that will work for most? I don't know the answer to that, but if I was forced to guess, I would bet that 105mm or so won't cause too many problems for most people. I'll stipulate, though that "not causing too many problems..." is a far cry from "ideal". ;-)
i think there's pretty good agreement on pitch. -17° (parallel to the ground) would be the flattest, maybe -6° might be the steepest, somewhere in between for *ideal*. you could make an argument for 0° (perpendicular to the steerer) but in order to get enough length in the x axis you'd have to have a pretty long stem.

length, i would just err on the side of conventionality. if you're 5'0" tall you're riding a 70mm stem. if you're 6'4" you're riding a 130mm stem. on average. as people scale in between, the stem length scales in between. yes, there's a lot more to the story. but you don't have the capacity to test everything. so, i think the above guide plays the averages.

Dan Empfield
aka Slowman
It's not just stem length you need to consider. This is a chart of steering lever length for a particular stem angle and bar reach.

When you're talking about changes in stem length - a 30mm change gives ~20mm change in steering lever so much less than 10% (7% for me) which gives context on how (in)significant small differences in stem length will be for handling.

Speedtheory
Thanks Dan that helps. That is an interesting chart regarding steering lever length. I have not seen it before. It looks to be simple geometry using the Pythagorean Theorem to calculate the hypotenuse of the right triangle from the center of the headset topcap to the forward most point of the HB. It does not appear to account for the hood length but I think I see your reasoning. Say for a 42 cm HB one goes from a stem length of 100mm to 130 mm. The increase in lever length is 20 mm which represents a 7% increase from baseline. This was what I was trying to get at with my question on handling. What you correctly point out is that fairly large changes in stem length, 30 mm in my example, have a small impact on handling from a lever standpoint. Thank you for the chart. Where did this come from?
anotherjoe wrote:
Where did this come from?

Me. You're correct that it doesn't include the hoods - it's an old chart that I quickly linked to.
This one does and calculates the steering lever orthogonal to the steering axis (ie to a point inside the HT)

I don't recall why I did that highlighted band

Speedtheory
Last edited by: cyclenutnz: Nov 4, 13 17:36
the chart is interesting but in a much simpler point of view the shorter the stem the more quick the steering will be. I call it twitchy, and clients relate to that. The longer the stem the more you can move the handle bars at the hoods to affect a small change in the wheel direction(this is very simple geometry, the arc of a circle gets bigger the larger the radius). If you are in a TT or Tri situation that is probably not that terrible since you tend to not be going downhill fast and turning sharp. The faster the bike moves the more important a longer stem is for stability at speed in my opinion. That is why pro riders use long stems and ride a frame size smaller than one would typically assume for them (of course the frame weighs less as well). So to answer the question I am reticent to use anything shorter than 90 and in reality I am dealing with something that suggests the reach dimension on that frame is too long for that person and their current functional stability and flexibility. If I could I would use nothing shorter than 110 but that is not always the case, and many people are not ready to buy a new frame because of this problem. They may however work on their physical issues and come back in a few months able to reach further and still be balanced, at which time they can get a longer stem fitted.
ok, it's taken me three weeks of reading and re-reading everything I have at home and on the internet about rake, trail, caster and steering angles. This thread has kept me awake at night dammit! Just as Dan says on his Steering geometry page, "the sum of facts I know is greater than the degree of understanding I possess..." This may explain why Dan and I disagree on 'ideal stem length for road'.

Stem length does not affect handling of a bike.

Nowhere in the study of bicycle dynamics or frame design is the stem length discussed.

Stem length affects the level of comfort for the rider. Given the same frame, changing from a 70mm stem to a 120mm stem only changes the riders' reach, some weight distribution and SOME relationship on how that rider behaves moving thru space suspended between the two hubs. The steering axis of the frame, rake and trail remain the same. Unless you are doing loaded touring, and must consider 15-20lbs of load on the front end. But that is a secret password-protected section of Slowtwitch. Cyclenutz' chart is cool, yes, but his shaded band is showing how negligible the change is when playing with spacers, pitch and stem length. Which is a better solution, the 100mm stem at -17/20 spacers at 305 or or 100mm stem at -6/20mm spacers with 308 score? Determining which solutions 'handles better' there madness lays. But a shorter or longer stem for the rider may reduce neck/shoulder tension, reduce hand fatigue or cause other tangible (and squishy) results. Plus we're not even talking bar reach either.

Solving the x/y position for hood fit to the hands is pretty much 'it' in regards to 'ideal stem length'. Dans' conventional wisdom of Rider Height/stem length works here: if your frame size calculated with Stack/Reach is requiring a 150mm or 40mm stem something is wrong in the fit or the frame choice.

Anecdotally, whenever I have fit a lady, and she walks in with a Lemond frame, I instantly know the frame is too big. Lemonds' steepest seat angle is 72deg (61cm!) and his average seat angle is 72.5. The smallest frame size (45cm) is a 75deg SA. So ya, I put a lot of stumpy small stems on ladies' bikes over the years, didn't affect their handling at all. The fit was certainly better, but you can only move the saddle forward so much.

There is some Ego involved in stem length too, I admit. Can't imagine myself riding anything shorter than a 90. :P

for Tri bike: I'm still struggling, but instead of hand position we're looking at elbow position as the weight bearing point of contact. As we have more experiences with pedestal-style tri bikes, we need to see what sort of handling issues come out of rider position.

Anne Barnes
ABBikefit, Ltd
FIST/SICI/FIST DOWN DEEP
X/Y Coordinator
abbikefit@gmail.com
Stem length does have an impact based upon the length of the stem on steering efficiency and speed of steering reaction, that is why mountain bikes and particularly downhillers use a very short stem, it has to do with the turn arc, similar to why on old cars without power steering and tractors have a large radius steering wheel and why Formula 1 cars have a small stubby steering wheel, it affects the input speed for steering. Therefore the faster you go the more sensitive the bike will be to minute changes in steering input and hence what I call twitchy. It does not affect stability of the bike that is a whole different thing that has to do with the way the frame s made and its geometry and for rake etc. What I am talking about is how quickly a small input to steering will cause a response in steering nothing more. When you are barreling down a mountain at 70+ kph with switch back turns you want to be able to manage your steering and for that the longer stem allows for a more gradual change for the same amount of push from your hands then a shorter stem.

I hope I have explained what I mean by twitchy and why I believe a longer stem leads to a more precise steering of the bike in certain situations. My clients tend to agree after they try a short or long stem in a real ride situation.
yes and no. I agree with the lovely lady fitter Ms. Barnes. :-) The specific length of the stem is generally unimportant to overall bike handling. I like to keep the range of stems to between 80 and 120. I think it also depends on what type of bike geometry are we discussing. In the 80's when I started fitting a 56 cm Italian frame would generally have a 120 stem at -17 with 42 or 40cm bars and a 170 crank. Shops would stock 100 to 130 and there you go. block the front hub and your out of here. As the geometries changed and now with styles and classes of bikes (racing, touring, sport, gravel, gran fondo, etc.) the geometries of a given style, size and price point will generate different stem lengths for a given size. One of the beauties of stack and reach is that you can take a known on your fit bike. 100mm stem as an example, generate all the fit data and then compare which style of bike makes the most sense. Should you be on a tarmac or a roubaix. And H1, H2 or H3 Trek Madone and so on. From here if you need to make the stem a 90 or 110 to fit the bike perfectly that will not negatively impact your bike handling. An improperly fit bike will but not the stem length, except on the extremes.

Downhill bikes with super wide bar width and stubby stems is a different situation that requires a different solution.

Retul Certified Master Fitter, FIST certified fitter, Owner of Hypercat Racing http://www.hypercat.com, and friend to the animals.
I agree in general with you, if the client has the right frame size they should not have to use less than a 90-100 mm. But less than 90 mm gets touchy with me, I prefer not to use less than 90 but on occasion the client is not going to be balanced on the frame they have and they can not change to a frame with the right amount of reach for their current ability (read, functional and core stability) then there may be no choice. I do however warn them that they MIGHT find that their bike steers differently in certain situations but overall the feedback has not been unpleasant in that the the larger problem of either being to stretched out and/or too much weight on their hands also affect their abilities and comfort so it is a trade off that is done only in the worst cases.

But back to the original question, I think that between 100-130 is best and should be possible under the situation of a properly sized frame. In special situations one can go to 80-90 but I would not go less than 80 the frame is just not the right one for the client and that is unfortunate news one has to give on occasion.
Bikes come only in so many sizes and there are hundreds of different body size combinations and then the preferences or special conditions (riding style, numbness, pain, ...pro like look :-)

I, for example, started on one frame with a 100mm frame at +6deg up. After a while I decided to reverse it and liked the lower position. Then I went for 110mm and removed a spacer from under the stem - lower yet. Then I went for a new frame and a bit more aggressive position yet.

Seat height and aft/forward should be more or less by the book. My upper body position is as I want and as I like.

----------------------------------------------
Racing and Training Cycling Tires
http://www.tiremaniacs.com
ideal stem lenght for road bikes makes little sense.
Getting the right stem for the right aplication on the right day makes sense.if im doing a bike for some onewanting to do crits i look for frames with top tubes on the longer side. A shorter stem has a quicker response. I do the inverse when doing a bike for long road stages. then tou still have to do a proper fit to find the positions you need to place the rider in . in cluding bar width and drop as well as levers.

Happy Freedman
Orthotic Consultant
Bike Fitting Specialist
Prosthetics and Orthotics/DME
Hospital for Special Surgery
510 East 73rd Street, Suite 201
New York, NY 10021

Happy