My wife is riding a 50mm stem. Here is why she is riding it.

My son is a long body. So as he grew, we had a nice racing bike with too long a top tube for a normal fit for her, but, didn't want to waste it and some nostalgia there.

She also likes a low TT position from years of riding that way. So it has clip-on aero bar short extensions. The handling is slightly better on extensions with a shorter stem. So...we go with it.

It kinda looks bad, works well.

I think we would all be well advised to give up height as a measurement for frame size.

I'm not sure if you are talking about frame height or using people's heights to predict frame size, but the latter works much better than inseam or any other rule of thumb I've heard of.

I'm a believer that body dimensions, even knowing all of them, isn't a great predictor of frame fit. I have long legs and a short torso. So you would be thinking long seatpost, shortish top tube, medium stem. I ride bikes with healthy top tubes on steep seattubes and long to very long stems. I learned a long time ago that if I want to go anywhere upwind, I need my back very low and aero. I have no big muscles. Racing, I always looked in store windows to check that I was riding with my back horizontal. Now, I had to bend my arms 90 degrees to get there. That was fine as a 25 yo pure racer. I could do that for hours. As I got older, I started thinking "I want my bars where I can keep my arms relatively straight with that same back position. It's a lot easier". So my stems starting getting far longer. I started seeking out bikes that could get me there using production stems. Having custom bikes built. Writing computer programs and CAD drafting my bikes so I can quickly see what I need to make any bike I am interested in work, stem-wise.

I get thanked by my body and legs for this work on a regular basis.

Ben

Maybe I'm a traditionalist. Back in the day frame size was approximated by inseam. Per people like Greg LeMond and his coach Cyrille Guimard. And others. For example....I am (now) 5'9" with a 32.25" inseam. A friend is 6' with the same 32.25" inseam. We both ride a 54-55 cm frame. His upper body and reach are longer than mine so he has a longer stem. That is not to say that we can't ride a range of frame sizes. But, IMO, inseam is a better prediction of ideal frame size. Has worked well for me over the pat 40 or so years.

Lemond's recommendation works great - if you have average proportions. Your friends torso is 3" longer than yours, but I'm willing to bet that he isn't using a stem 7cm longer than you are. Most people with his proportions would be better off on a frame that has a little less standover but a reasonable amount of reach. And he has the reach of someone closer to 6'3". That's why the best compromise is to spread the problem between seat tube and top tube rather than take someone with a 6'3" person's torso and put them on a bike with a 5'8" persons reach.

Guess we will have to disagree. If as you say there are variables that affect the use of inseam as a determinant I'd guess those variables exist using height as well. So, I don't see height as being better than inseam.

I don't see how you'd come to that conclusion. Frame size is like dress size - it is an overall size that attempts to cover both seat height and reach. You're suggesting that it is better to size something like that by only paying attention to one isolated part of the anatomy rather than the larger picture. Women don't size dresses by only looking at leg length, and I don't see why you'd size a bike that way. The "traditional" sizing advice wouldn't be used if someone fails to have a "traditional" build.


It would be interesting to see a picture of your 6' tall friend with the long torso crammed onto his 54. Does he have a 170mm stem?

You lose the argument to Bruce, because frame reach can be changed relatively easily with stem size but frame height aka head tube height aka effective seat tube height which dictates saddle to bar drop has much less adjustability.

This is why for 50 years, it is seat post length or effective seat post length that is used for a single metric of frame size which only indirectly corresponds to a person's height.

Also, your reference of a person's height has no direct correlation of stand over which can rule out a given frame size relative to a person's height.

Truthfully, a person's height doesn't matter at all. What matters is a person's leg length and person's torso length and how aggressive a person rides.

More enlightened fitters however never use a single metric to choose a given frame and therefore the whole discussion is somewhat meaningless.

Fitters don't use any simple metrics, and if you asked a fitter they would tell you that only a fitter can help you pick a frame size.

But I worked for a fitter for a long time, and height predicted frame size more reliably than inseam when compared to the frame size the fitter selected. So I'm not speaking of some sort of theory - I'm speaking as someone with decades of professional experience.


People with short inseams only have have standover height issues if they are trying to ride bikes with level top tubes. But sloping top tube bikes have drastically decreased standover for equivalent sizes. So what was true in the '90s isn't true today - a person with short legs can get what they need from a larger frame.

And that isn't just my opinion - many manufacturers, like Trek, offer height ranges along with frame sizes.


I simply don't understand why a person who's upper body goes with a 59cm TT and 11cm stem is going to ride a bike with a 54cm top tube without a ridiculously long 15cm stem. Tradition can't compete with basic math.

Your last sentence query as to why...portends to pros and better amateurs that deliberately size down for a shorter bike which results in a longer stem. You need not make your example so extreme to denigrate a smaller frame and longer stem commonly used in racing. A rider can size down 1 frame size to ride a bike that more matches their short inseam and use a longer stem to match their long torso. No need is the point to ride a bigger and heavier frame with short stem they may even struggle with to achieve an aggressive riding position with short inseam.

It isn't my example, it's Bruce's example. His 6' friend, who would normally ride a 58cm frame, is riding a 54 - which is two sizes smaller. And we know his friend's proportions, so we know that the 58cm frame's TT would be slightly short for his torso length, which means we can assume that even on the 58 he would be using a longer than stock stem.

So the comparison that Bruce proposed is two frame sizes + additional stem length. I'm not the extreme one - Bruce's friend is.

We talked it out and as you have written, I believe our common ground is...no single metric can be used reliably to put a given rider on a given frame. That and you and I can ride more than 1 frame size and still have the 3 pts of contact we like. So that is our agreement I believe and likely 'nuff said.

FWIW I heard a pro on GCN say that his torso was longer than his inseam would indicate so he rode a smaller frame than most people his height. I don't know how this works today but in the past the pros would ride the smallest frame they could because it would be lighter. I do agree that there are variables that would allow a decent fit on a range of frame sizes.

Your stem length is determined by more than your height. I am 6ft 1in and i am riding a 58cm Cannondale Synapse and I had to swap out the 110 for a 100 as I felt a bit too stretched out with the 110. The 110 would have been fine 20 years ago but at age 50, when I got the bike (now 56), my flexibility wasn't what it used to be. Even now there are days when feel like I would be more comfortable with a 90 stem. I ride with the stem flipped down and for 99% of the time, I feel best this way. I am assuming that, in a few years' time, I will have to flip my stem up.

If you feel stretched out and have moved your seat forward, a shorter stem may be the answer. Did you get a bike fitting when you bought it?

I went from 100 to 80 and could tell very little difference in both handling and reach.

How come nobody talks about arm length? it's just torso, inseam, height, repeat.

Because none of them understand bike fitting.

Without seeing the rider on the bike(and actually measuring the rider), making recommendations is pointless.

Because we've been talking about torso vs. legs given an assumed fixed height, back angle, arm length and the same model bike. That's really the only way to make such a comparison.

If you want to talk about arm length, that's a different topic.

No one is making any recommendations aside from rather dated suggestions that frames should be sized by inseam. The OP just wanted to know if it was bad to go shorter than 110, and I don't think anyone would say "no" to that.

If OP can’t reach the hoods on that bike with even a 120 stem, then he either has the shortest torso and arms ever on a 6-footer, or...he’s just sitting too upright.

I do, kind of, because "it won't hurt" isn't advice at all, it's merely reassurance, and suggesting that someone swap out parts rather than have someone who knows something about bike fit take a look first is poor advice.
Meanwhile, all this talk about how the OP should have a 58 because he's six feet tall.... I'm 6'-0" and my frames are at most 55.5, albeit with a 120 mm stem, typically. Yes, I often ride pretty upright, as you can see in the photo at left (showing off after cresting a little hill, sitting up to wave to make it look as effortless as possible - the full image showed guys behind struggling on their way up. ) but on my latest fitting on a 55, we got everything set up where even on the tops, unless I really stretch out my arms, I've rotated my hips for a lower, more "pro" positioning.

It doesn't always work. My wife and I both have a 30" inseam. I am 5'2", she is 5'8". There is no way in hell we are riding the same size bike, even if we swap out for longer/shorter stems.

A 55.5 frame is one size down from a 58, not two full sizes down.


The original question was whether it is acceptable to use a shorter stem than 110. The answer is yes, it is acceptable. Why turn a simple question into a complicated one?

Many people would benefit from a fit. But not everyone is going to get one, nor is everyone prepared to pay $200 for such a service when experimenting with a $15 stem is in line with their needs. It doesn't have to be either/or.

Do you really want to know? Because we're bored and like to answer rhetorical questions? As prompted, I was just saying that mere reassurance is a weak substitute for advice. Not implying anything contrary to the good points you make.