Analysis: Handlebar and stem length
The following is from a reply I had posted to a near-6-year-old thread in the AM forum. After I replied the thread started to get replies from others who didn't realize how old that thread was so I'm starting a new one here for discussion. I'm leaving the quote and my reply exactly as it was typed in the AM forum.
I know this thread is going on 6 years old but I thought this particular post was very interesting. I use a 660mm bar on 100mm stem so my effective lever length (that's what I'm calling it for now until someone gives me an official name for it) is 430mm. Of course, stem rise can shorten the effective stem length, and I think handlebar sweep MIGHT reduce the effective bar length but I'm not sure how to calculate effective bar length from sweep and length if it even makes sense to do so.
Originally Posted by All Mountain
I have used 710mm/75mm, 680mm/90mm bar and stem combinations and noticed the steering speed is roughly the same. Looking at how others setup their cockpits I have noticed that a lot of people prefer ~430mm ELL. For example, a 760mm bar coupled with 50mm stem has an ELL of 430mm. That is a pretty typical AM/DH/FR cockpit configuration I have seen throughout the web. Not everyone will be comfortable with the same ELL no doubt, but anyone preferring an ELL of ~500 seems unlikely as that would just be WAY too slow steering for any type of MTBing I can fathom. Maybe on the road at very high speeds does ELL that high make sense but you are still talking about a very large turning circle.
So if a rider, like myself, determines their ELL for a particular type of bike geometry and riding style then perhaps they can apply that ELL to other types of bike geometry and riding style. I mainly ride XC on a bike with a 71 degree HTA, 660mm bar and 100mm stem. So if I were to configure a bike for AM with a 68 degree head angle then I should get roughly the same "feeling of control" with a 740mm bar and 60mm stem, more or less depending on how much the HTA changes my "feeling of control".
Ergonomically there are trade offs since our bodies have a limited range of motion. I can't turn an AM bike in the same circle as an XC bike, just like I can't ride an XC bike down a steep, gnarly downhill with the stability of an AM bike. The cliche bar width determinant is to get into your natural push-up position. In this position, the body is quite stable and difficult to topple. At the same time, maneuverability has decreased. If you imagine turning a handlebar 90 degrees in your push-up position, you might need to bring your outer shoulder to your ear and inner elbow to your hip, and you may need to arch your back to the side. If you were on tight, twisty single track then this could tire you out very quickly as you need to use a very large range of motion to negotiate the corners in the trail. I realized this as I tried many different lengths of handlebars since I started riding almost 2 years ago. If the trail is fairly wide and flowy then I can take the widest line through a corner and use a smaller range of motion with a wide bar and short stem. As the trail gets tighter, I want to get the most turn per amount of body movement, so I would opt for a narrower bar on a longer stem to keep my range of motion within comfortable limits. In either case I keep ELL the same.
My questions: How much does 1 degree of HTA resolve to in stem length or bar width? How much does 1 degree affect the "feeling of control" when the bar and stem stay the same? As when a suspension fork gets swapped out for one with more or less travel? Does anything I mentioned above make any sense at all? lol
Maybe I should have started a new thread...
I guess Iíll take a shot at answering your question. Didnít know where you were going with your narrative for a while, but as you can probably guess, the answer is ďit dependsĒ. The other answer is it will quickly become so complicated that itís not worth losing sleep over. Just go out and ride. But for the sake of a mental exerciseÖ
Assuming that everything remains constant while only the head angle slackens, then the handlebars will only tip back towards the rider. How much will they move back? If we keep the handlebar the same, this now depends on how long the stem is.
Iím imagining this in my mind, and I hope Iím describing it clearly. Pretend there is an imaginary line pointing straight out the front of the stem. Since the stem is clamped to the fork, the stem will tip proportionally to the head angle tipping back. As this happens, you can picture that imaginary line out of the stem sweeping upwards and backwards. Your intuition should tell you that for the same degree of tipping, things further away from the tipping point will travel a larger arc than things closer to the tipping point. This is the difference stem length would make, all other things being equal. The longer the stem, the more your controls will move back towards you.
Where this all falls apart is when you bring different handlebars into the equation. Like youíve already stated, the general way of counteracting the twitchiness of a short stem is to increase the range of motion for your arms to control (eg longer handlebars). Now throw in bars with all kinds of upsweeps and angles, and objective calculations go out the window. And letís not forget that your head angle is always changing on the trail if you run a suspension fork. Furthermore, If you subscribe to the rule of thumb that 20mm of fork difference roughly equals 1 degree of head angle, then your sag setting alone messes with the head angle depending on how youíre sitting on the bike.
Those general guidelines for bar and stem combos that you mentioned are used in their respective disciplines based on what the rider, regardless of the bike they are on (within reason of course). Riders who value charging up climbs will find better control if their weight is forward on a long steep climb. You know this, as someone who uses a short bar with a long stem. Riders who rather charge down a steep hill value being able to keep a rearward weight bias, hence the short stem. Yes, there are exceptions to every rule, but this is just a description of how current bikes on the market are equipped.
In summary...go ride.
I wouldn't try to roll a degree of head angle into it.
Changes in head angle do change handling. The mechanism is pretty different, though - for a bike with the same reach, they change weight distribution. Something else that changes weight distribution is climbing or descending.
That feeling of a wandering front wheel, IMO, is all about not having enough weight on the front wheel. Combine a slack head angle and an uphill grade shifting a rider's center even more toward the back of the wheel, and you can see why XC race bikes - those that are supposed to climb like squirrels - have a steep head angle. It makes a good weight distribution on the way up.
That feeling of "uh-oh, I'm going to endo" is all about being pretty far forward in relation to where the braking wheel generates force against the ground, IMO. That moves back relative to the rider when the bike is already pointing down. Move it back far enough, and the rider doesn't even need to be braking. That's why it can feel disconcerting to ride a road bike off a curb - they're steep, the rider's forward, and so it doesn't take much to start having a ton of front bias. Since downhill bikes are all about pointing down a hill, one can see why it's desirable to give them slack head angles. If the expectation is that they'll get to the top on a ski lift or in the back of someone's pickup truck or be pushed up or something, it's pretty much a non-issue that they're harder to manage on a climb.
I wouldn't be too surprised if there's some nominal weight distribution that both bikes nail when they're on their preferred grade. But I also wouldn't be surprised if there's not, or if the idea doesn't really make sense - I'm just speculating at this point.
IME, quantitative approaches to bike setup have big problems. Not that I can't get some help by taking good measurements, but it seems to make more sense to compare to reference bikes that fit or handled in ways I liked.
"Don't buy upgrades; ride up grades." -Eddy Merckx
Good responses so far! I guess my goal with this thread was to show newer riders like myself that asking the forum what size bar and stem they should use without providing useful information, like bike geometry and riding style, will almost always generate the same answers. You will have those replies that simply state "760mm bar on 50mm stem is the way to go!" or "Ride what you like brah!" when that is not really the information the OP is looking for.
What have you calculated your optimal ELL to be?
I haven't calculated anything.
Since you asked and I'm procrastinating, my handlebars measure 21.25" between the bar ends. So my ELL works out to be 360. (90 mm stem.)
If I had it to do over, I wouldn't have cut as much before installing the bar ends. Oh well.
I think it's all about what you want to do with the bike. I like to go on long rides, when I have the time, and I do some racing, sometimes really long races. I find it tiring to ride a bike with really wide handle bars. Clearly I'm not doing '80s narrow, but I find I get more tense if I have to ride with wider grips.
"Don't buy upgrades; ride up grades." -Eddy Merckx
Your ELL calculation completely negates the affect of saddle position and top tube length in terms of overall reach. Good for calculating the differences that a handlebar and stem swap would have on the same bike but horrible for comparing between bikes. I like getting nerdy and comparing reference points on my bikes but I've never tried to look only at the front cockpit without looking at the bike as a whole.
When setting up a new bike, I normally just measure the direct line from the front tip of my saddle to the outer edge of the bar and try to keep that similar between bikes. My road bike is a good bit longer so I can get aero and climb better, my dirt jumper is shorter, my two trail bikes are within 10-15mm of one another despite a massive difference in ELL and top tube lengths. I try to measure bar height relative to the BB to get a more consistent measurement than from the front axle or ground (both will shorten with suspension travel).
FWIW, I'm running 787mm bars on a 50mm stem (ELL of 443.5) on my 29er but feel too cramped so I'm bumping it up to a 70mm stem (463.5mm ELL). I'm 6'9" on a good day so thats why I can get away with longer bars and a longer stem.
Using your calculation, my vintage Karakoram with 28" bars and a 140mm stem has an ELL of 495mm yet shreds and has about the same reach/posture as my 29er will with the longer stem.
I don't know how the overall reach affects the length of the lever though. I mean if I am trying to loosen a lug nut with a 2 foot breaker bar then it is still 2 feet long no matter what my reach to it is. On a mountain bike we change the reach the whole time we are riding by standing up, sitting down, getting back off the seat or putting our chin down to the stem.
I imagine the connection between the body and the handlebars as a hexagon composed of your shoulders, upper arms, forearms, and the handlebar. If you have wide shoulders or long arms then you can tolerate a longer ELL. So it makes sense that a taller person would prefer a longer ELL, and a shorter person would want a shorter ELL. I am 5'11" with a 430mm ELL so I would imagine someone of similar stature to me would prefer close to the same ELL.