Bicycle Mechanics - can someone explain the physics of stem face plates?

i'm some what paranoid at how such a thin piece of aluminum holds so much weight. this is what supports the handlebar which you rest your upper body weight when descending and when you pull on the handlebars when climbing. it's hard to believe but true. is my understanding of the physics incorrect? doesn't the faceplate take a lot of the weight? by the way, does my faceplate look safe enough?

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well, I think it's quite rare that you'll be on the bars in a way to load up the faceplate only.

well, I think it's quite rare that you'll be on the bars in a way to load up the faceplate only.

true, that's why i pedal a little harder when going up the hill to put more weight on seat and pedals rather than the bars.

Why are your screws not the same?
Stem screws are a good place to use a 1/4 inch drive torque wrench. But don't exceed the torque specs for the handlebar or steer tube, as well as the stem.

[QUOTE=Al1943;10908537]Why are your screws not the same? QUOTE]

good question. and why does it look all chewed up by the screw holes?

my guess is that the replacement bolts did not have washers.

That little piece of Aluminum is a lot stronger than you think and is capable of supporting any reasonable stress you can put on it. In an accident, you will tear out the bolts before the faceplate itself breaks.

Not to mention that you're WAY overthinking the issue and making a lot of incorrect assumptions along the way.

For example the clamping plate sees only a small fraction of your weight that you put on the bars. And it's seeing it at an angle that is mostly focusing the load down into the main part of the stem. Unless you're in the habit of doing bicycle trials nose bounces while standing on the bars with your feet the faceplace and bolts will only see MAYBE an 1/8 of your overall weight even during an aggresive downhill braking maneuver.

Besides, there is more than enough clamping action from just the four bolts and the corners of the faceplate that form locking tabs to wedge the bars into place to take even your whole weight.

If you really do need something to worry about stop and consider the massive wedging loads put on the corners of a typical square taper BB and what it is trying to do to the crank arms. THAT will keep you up in a cold sweat at nights thinking about it and make you forget this frivilous concern over the stem's faceplate :D

salesman sold me my first bike with an adjustable stem that was set at a 40 degree rise on the floor. when i adjusted the stem later, i had to rotate the bar so the brake levers would be properly angled. i didn't know anything about bike mechanics so i overtightened the aluminum bolt and it broke off. i took it to the lbs and they replaced it with a steel bolt without washers.

now i know better. i will go to another lbs and have them replace all the bolts with new bolts + washers with proper torque & make sure my face plate is not compromised from the prior over-torquing. then i'll never ever mess with a wrench again. i just need this bike to last me until last week of august when the 2011 trek 6000 comes out (hopefully with shimano drive train + better paint job than 2010 model).


That little piece of Aluminum is a lot stronger than you think and is capable of supporting any reasonable stress you can put on it. In an accident, you will tear out the bolts before the faceplate itself breaks.

wow - that's pretty impressive. good to know.

Not to mention that you're WAY overthinking the issue and making a lot of incorrect assumptions along the way.

For example the clamping plate sees only a small fraction of your weight that you put on the bars. And it's seeing it at an angle that is mostly focusing the load down into the main part of the stem. Unless you're in the habit of doing bicycle trials nose bounces while standing on the bars with your feet the faceplace and bolts will only see MAYBE an 1/8 of your overall weight even during an aggresive downhill braking maneuver.

Besides, there is more than enough clamping action from just the four bolts and the corners of the faceplate that form locking tabs to wedge the bars into place to take even your whole weight.

If you really do need something to worry about stop and consider the massive wedging loads put on the corners of a typical square taper BB and what it is trying to do to the crank arms. THAT will keep you up in a cold sweat at nights thinking about it and make you forget this frivilous concern over the stem's faceplate :D

i'm sure you're right that i'm overthinking. i was (am) a newbie and i wish i hadn't overtightened the stem bolts (which was corrected by lbs). that's what got me worried. i won't make the same mistake again. this is a hybrid that i ride just for fitness up hills. next bike will be a trek and once its set up i'll never ever tinker with it again. i was even tempted to entirely replace the stem but that would require me to change handlebar too (because i'd want 31.8 instead of current 25.4). i don't want to overdo it especially when i'll get a new bike later this summer. although of course, i don't want to try to save money and then end up with an injury. i think i should just relax :P

Nah - minimal stress I believe. I know I don't worry about it.

If you think that is alot of stress - think about a motocross bike! Jumping 100+' and 20+' high and landing a 235 pound machine! Held together also by little bolts only.

I'm surprised that it had aluminium bolts. That's just NUTZ! By all means replace the whole lot.

If the bike is any good then it's still got a mission in life as a local area errand bike for runs to the grocery store, video store and other such "menial" tasks. As such it's worth sorting out and setting it up as a cargo bike with racks and bags. Don't diss it just because it's not a sports car. We need pickup trucks as well! ! ! :D

If your bike never leaves the ground while you ride and you aren't a super buff sprinter, I wouldn't worry about it.

BUT, if you even so much as jump off the occasional curb, I'd go ahead and replace the stem and bar (since its finish looks all chewed up to the right of the stem.)

Even the cheapo $20 bar/stem combo deals from pricepoint would garner more trust in a landing than your current set-up.

What's that gewgaw hanging under your bar there? Bell? Light?

Man, I can't imagine aluminum screws in there either! That's CRAZY!

I wouldn't hesitate to jump that bike off curbs or even a two foot drop, given that it's a hybrid. The so called "damage" looks far worse than it is due to the close up nature of the pictures. But I wouldn't be jumping or even riding far with only aluminium screws holding it together. THOSE gotta go!!!

Even with fresh screws I'd be worried about trusting any adjustable stems to many curb drops. I'm pretty wary of worn aluminum bars also, since I've seen someone snap 'em and I've bent a pair. Although you're right, that does look like superficial surface wear on the bar, I gotta wonder how it got there. doesn't look like it was from an accessory mounting, since it seems to go right up to the clamping area, almost like it was clamped off center for a while, or???

The hybrid nature of the bike doesn't bother me at all, however. I ride off 1 ft curbs on road bikes all the time.

Regardless if I bought a used bike with stem and bars in that condition, I'd replace both immediately. If I'd bought the bike new, I'd replace the stem with a solid one the instant I found out what angle I liked it at, and I'd figure I might as well go for the bar replacement too, since it's only maybe $5-10 more than getting just a stem shipped out to me.

lol thanks for your advice guys. i'm thinking a bontrager ssr mtb stem ($30) (http://store.trekbikes.com/jump.jsp?itemID=1998&itemType=PRODUCT&path=1,2,461,472&iProductID=1998&bShopOnline=1) + bontrager earl riser 710 mm wide with a 50 mm rise ($50) (http://bontrager.com/model/04477). i know risers look ugly but i need it because my current handlebars are too low and hurt my back. i want the handlebar to be level with my saddle. i like sluggish steering so i don't want the earl stems (70 mm max length) which anyway may not be compatible with my hybrid.

i tested a $10 bontrager chromoly 80mm rise handlebar as an experiment before considering more expensive stuff (a compatible bontrager b-dot, 2 bolt stem for this riser is only $15 (http://store.trekbikes.com/jump.jsp?itemID=1659&itemType=PRODUCT&iProductID=1659&path=1%2C2%2C4%2C461%2C472)). the riser was very ugly but it was much more comfortable. all trek hybrids & mtbs come stock with bars that rise 25.4 mm. i don't do jumps or drops but climb big hills and sometimes ride jittery gravel roads.

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if you look at this side view, there may be torque due to the rise radius that will want to rotate the handlebar around the stem, especially when climbing a steep hill. this was just a test so i didn't *perfectly* align the handlebar 90 degree to stem. i'll get the lbs' assurance that the earl & ssr stem are a good match and that this set up is reliable.

50 mm rise or 80 mm rise are both fine. i'm only opting for the more expensive earl + ssr set up because i'm thinking its more dependable and may give me the freedom to bike on jittery, gravel roads. besides, 50 mm rise will have 37% less torque than 80 mm rise.

this is how my bike is currently configured. a 120 mm 10 degree stem will increase the reach which i want. the riser handlebar will avoid the need for a steep stem angle. everything will be done by the reputable lbs (bikeline in pennsylvania) and NOT by me. once it's set up i'll never ever tinker.

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^^Those first couple pictures make it look like your handlebars are backwards.

^^ yeah i had realized that but figured i was just talking about the stem. it looks that way because the almost vertical stem angle. now that i started talking about handlebars i felt i'd have to clarify with other pictures :)


Although you're right, that does look like superficial surface wear on the bar, I gotta wonder how it got there. doesn't look like it was from an accessory mounting, since it seems to go right up to the clamping area, almost like it was clamped off center for a while, or???

that's not surface wear. i think there was sticker there that i tried to peel off and some of the paper & adhesives remained.

yes, i will definitely replace the aluminum bolts rofl...

There's a lot more metal in the stem's faceplate than in the cross-section of the handlebars. When was the last time you snapped a handlebar? Humans are amazingly weak compared to metals.

And it's actually the bolts that take the load... in single-shear no less... :(

That faceplate is in pretty bad shape, why? Once you put it in besides a few minor adjustments in the bolts there is nothing else to do, the holes are ovalized for example, grease everywhere, I would buy a new one if i was you.

Nice job on the pics, though....

yes, i will definitely replace the aluminum bolts rofl...

Put a magnet on those bolts when you remove them. I highly doubt they are aluminum. Steel can be finished in many different ways and can often look like aluminum especially with a matte finish.

^^^ :thumb: just use macro mode (flower symbol) on a simple point and shoot camera to get detailed close ups.


That faceplate is in pretty bad shape, why? Once you put it in besides a few minor adjustments in the bolts there is nothing else to do, the holes are ovalized for example, grease everywhere, I would buy a new one if i was you.

tomorrow i'm going to a reputed lbs to have them install bontrager ssr oversized stem + bontrager earl riser bar. the stuff you see pictured are going to the recycle bin. this will give me a peace of mind and insure safety. i'll check with them too that the 50 mm riser bar does not rotate around the stem clamp while i'm climbing hills since it is subject to a torque of the radius 50 mm. once the trek 2011 models come out in late august...i'm getting me a 6000 mtb bike :love:

I highly doubt they are aluminum.

it's aluminum. it's much lighter than the steel bolt and broke off very easily when i overtightened it the first time not realizing that i should have my lbs do it with a torque wrench (lesson learned). i'll check with the magnet though. i'm not taking chances with aluminum bolts but i assume that the bike manufacturer fuji (not as famous as trek or specialized but reputed nevertheless) considered the physics of it. i bet those bolts are just fine for tensile stress or whatever stress it takes to keep the faceplate together. of course, i'll make sure to have lbs use steel bolts tomorrow :P

Going back a step or three. The riser handlebars on that original setup WERE backwards. Very definetly backwards. No doubt about it. Your wrists must have felt like they were being subjected to the Spanish Inquisition.

When you get some new riser bars make them look the opposite...


.... waits patiently now for the first Monty Python fan to post.... :D

There's a few decent brand name stems that can be had with a 25 to 30 degree angle. That and some mid range riser bars would give you a level with the saddle or only very slightly below fit.

oh...i thought that the handlebar 9 degree bend was supposed to be like \ / because that's the natural position of wrists. that's why keyboards are designed like that. bikes and keyboards are chalk and cheese. thanks for pointing this out...my lbs will take care of it all.

http://www.pcguide.com/ref/kb/layout/z_011134ergo.jpg

thanks for the idea about midrange risers + 25 degree stem...that's definitely something to consider tomorrow when i go to lbs

That keyboard is all well and good. In fact I'm typing this on an ergo keyboard very similar to that one.

But I don't hold my arms and hands the same way when I ride a bike as when I type. The angles that the backwards bars produced would force the forearms and wrists into a very stressful position. To get the most out of your arms when required it's best if the arms can extend forward in a natural and inline manner and the fingers wrap around the grips without altering the natural line of the forearms and hands

thanks for all your help. lbs installed for me a new handlebar & stem with metal bolts. the old stem and handlebar are in the recycle bin. these risers are awesome. they look nice, are comfortable, and offer great control.

i have learned (1) bolts holding the faceplate are very strong (2) the faceplate looks light but is incredibly strong (3) let the lbs properly install & torque the stem, verify everything is safe and sound. now i never tinker. as a newbie i'd look at my new stem installation think about the gap between the faceplate. now i know better. tighter does not equal more secure. obvious to you guys new to me.



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No one has ever learned anything without making some mistakes. Don't let your early learning mistakes shut you down. We were all at your stage at one point but we forged on through and that's how we learned.

I may be one of the folks here that types the most but I still learn something new from the other guys here at least once a day. And I still make learning mistakes even after 50 years of shop time doing my different hobbies.