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MTB alloy handlebars and stem LOAD TOLERANCE?

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MTB alloy handlebars and stem LOAD TOLERANCE?

Old 02-28-20, 01:53 PM
  #1  
BMarino
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MTB alloy handlebars and stem LOAD TOLERANCE?

Hey what's up fellow cyclists!


Just ended a customer service chat session with Bontrager customer service but unfortunately there wasn't a clear answer for this. I hope someone here either with a similar situation as mine, or with materials engineering knowledge can shed some light on this:


A couple years back I bought a set of alloy Bontrager RL stem (100 mm) and handlebar for my hardtail mountain bike.






Now, as I also use my bike for commuting duties, I sometimes carry loads hanging from my bike's handlebar. The most I've carried is 10 kg (5 kg on each handlebar end). Most of the times I'm only carrying say 3 kg on only one side.


I've grown a bit concerned that by doing this I may be surpassing my handlebar's or stem's (or both) weight tolerance, and as I also ride my bike on trails, I want to make sure I haven't compromised those components' safety by carrying excessive loads on them when commuting. I don't want the handlebars or stem snapping on me during a fast descent.


I asked Bontrager customer service what weight carrying or load limit do the RL handlebar and RL stem have, but their only answer was:
"we rate them as able to handle all normal riding conditions of a rider up to 300lbs, as that is the max weight limit for our bikes. Unfortunately we do not have a specific weight limit for our stems, nor we do specifically test them for bike packing or hauling purposes"



So what is your opinion on this? I would suppose the load forces applied on a handlebar are pretty big during trail, big step descents, and they are manufactured to perfectly sustain without fatigue those forces, but then again I really don't know how does that compare to loading a CONSTANT weight of more than 5 kg on the bars' ends.



Thanks for reading!


EDIT: My body weight is 84 kg.
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Old 02-28-20, 02:38 PM
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Wilfred Laurier
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If you are adding loads to your bars that are anywhere close to the loads put on by a rider near the bike's rider weight limit, you will have more trouble just riding than with durability.

Yours is kind of like the oft-asked question 'does it damage a bike to hang it upside down' by the wheel - if the wheel cannot support the weight of the unladen bike, I wouldn't dare try to load my carcass and luggage around on it.
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Old 02-28-20, 02:40 PM
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PS. If the bike is a few years old and you have ridden it hard many times, it isn't a bad idea to swap out the bars (and maybe stem) just to be on the safe side. I don't think carrying a grocery bag on the bars is going to cause any problems, but your 64kg body pushing down on it thousands of times per season might eventually cause it to weaken.
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Old 02-28-20, 06:18 PM
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I wouldn't worry since they're not made of cracken fiber.
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Old 02-28-20, 10:43 PM
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BMarino To answer the OP question as simply as possible; Constant loads will cause the bar to bend (very, very slowly) Peak loads will cause it to break, suddenly.

298g, 7000-series aluminum. Seems like a decently strong handlebar. Not anything crazy like the old 140g Scott AT-1/LF, or the Answer HyperLite.

Changing your bars every couple of years as a preventative measure seems a little excessive.
If you're really concerned about it, get a 'Downhill' bar instead of a 'Trail / XC' bar, like I did here (link)
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Old 02-28-20, 11:04 PM
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Carrying things on those handlebars will definitely not break them.

The greatest force on the handlebars comes when riding the bike and running into a pot hole, or something else which results in a sudden stop. Your entire body weight pushes on the handlebars.

They should not break if a rider of 300 lbs or 136 kg runs into a pot hole.

So unless there is something to indicate something is wrong, I would not be concerned.

I have never bent or broken handlebars. I have never replaced handlebars, and I never would unless there was something to indicate a problem. I ride bikes make for Western riders. The handlebars have all been made of steel or aluminum.

I did say those handlebars. In S E Asia, most people ride ladies bikes, which are not designed to be as tough as mountain bikes. I have seen these bikes with bent or broken handlebars. Sometimes the rider may be a 40 kg schoolgirl.

Last edited by alo; 02-28-20 at 11:16 PM.
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Old 02-29-20, 09:07 PM
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Here's some of the stuff I've loaded onto my handlebars while riding (and we're talking vintage road quill stem and 25mm bars which are weaker than fat MTB stems/bars)
-people sitting on them.
-multiple grocery bags (about 20lb/10kg each side).
-40lb/20kg bag of cement ridden 5 miles.
-A 80lb/40kg Pioneer SX1980 receiver (the biggest baddest vintage receiver ever made and found on the sidewalk).

so yeah, stems and bars are pretty strong.
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Old 03-02-20, 11:47 AM
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Thanks for your replies everyone! It seems I was definitely overconcerned over this!
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