nlowe

I have one consistent problem while biking, and that is broken crank arms. I ride a single speed with a 52t chainring and a 15t freewheel. I lift and weigh between 190 and 210 depending on the month, and the only way to climb long hills is to stand and mash. I've tried various brands of cranksets, but broken crank arms occur roughly twice a year. One unexpected break after a long ride caused me to veer into the road. I'm up to 7 broken crank arms over the past 4 years. All have been 110 BCD square taper cranksets. Every failure has been on the non-drive side, and metal fatigue is always the failure mode. Two failures have occurred due to cracks starting from the square taper corners, one has been a failure of the pedal stem eyelet, and four have been broken clean in half. I'm well aware that my gearing and riding style are the cause of the damages. I'm essentially looking for a bulletproof crankset. Whether it is aluminum or a solid hunk of steel. The goal is durability, weight be damned.

Does anyone have a suggestion for an "unbreakable" crankset? If I'm left with no other options, I'll have a local CNC machinist mill out something indestructible.

TMonk

Have you considered decreasing your gear? In doing so you would decrease the torque applied to the cranks. At this point after your history that seems like the best choice IMO. For reference I'm an "A" track racer locally and race a 51/15 in mass start events. But I like to spin high rpms.

A few questions:

Were the cranksets new, or used?
What are the makes/models of the cranks used? I've personally had bad experiences with FSA cranks.
What are the lengths of the crank arms?
Have you been using the same frame this whole time? There may be something wrong with the frame.

Cheers,
Tmonk, a forum moderator

TMonk

Also, welcome to bikeforums @nlowe

nlowe

Yeah, I know my gearing is essentially entirely to blame, but that's just how I like to ride. Hard as hell on hills, but impressively quick on flats and downhills.

-All cranksets were purchased new, with the exception of one unmarked and borrowed crankset from a Giant MTB. Not sure what brand that would have been. The mind at the time thought "MTB=stronger".
-The first three breaks were with generic junk brands. Two breaks were indeed with FSA cranksets (FSA Vero). One was a Sugino crankset (unknown model). The last was the borrowed Giant MTB crankset (make/model unknown).
-All crank arms were 170mm.
-I started with a no name aluminum bikesdirect frame, but it started cracking in just over a year. I've since been using an older aluminum Gary Fisher hardtail MTB frame that has been converted for road use. It is far sturdier, and I've verified that all dimensions still check out. This frame has basically zero flex however, and likely contributes to the issue.

I'm starting to think that something has to give somewhere. Perhaps a steel frame would be better suited, and I can try that out. If the problem remains, I can always get that unbreakable (but likely 5 lb) crankset machined. If that's what it takes, then so be it.

tyrion

Maybe get a downhill crank and have a custom chainring machined.

https://www.jensonusa.com/Shimano-M825-Saint-Crankset

You'd need a custom chainring because downhill ones are too small and designed for multi speed chains.

Or maybe something from the trials bike world. (Again, you'll need a custom chainring.)

JohnDThompson 

What specific cranks have you broken? Are they professional-grade forged cranks or lower end "melt-forged" (aka "cast") cranks?

N.B. all else equal, a crank CNC machined from billet will not be as strong as a forged crank.

IAmSam

Maybe...110BCD crankset is not really your best option?

phobus

Definitely upgrade your crankset to something "indestructible", so maybe you can snap chains or strip the threads on your hub instead. Definitely don't switch to a lower gear ratio, that's just dumb.

REDMASTA

seamuis

nlowe

I agree with pretty much all of the feedback. From the average cyclist's perspective, everything about how I ride is wrong. And they would be correct! I don't get any enjoyment out of gearing down and spinning my way up a hill though. What I do find very fun is standing and leg pressing my way up the hill.

I'll probably take the plunge and give one of those recommended forged "race" cranksets a go. My only hesitation with them is that most racing components seem to favor lightness over all, which is irrelevant in my case. From what I've read, they use higher quality forgings primarily as a way to reduce the total mass of the component. A bike ridden correctly doesn't necessarily need to be insanely strong, so that's not exactly their primary goal.

I've spent enough on $100 cranksets over the years, that I'm quite willing to go ahead and spend $300-$400 on another if it will last. I'll start there for now. If this doesn't last, the plan was to actually have a crankset machined out of steel instead of billet aluminum. It would quite literally be 5-10 pounds, and a third of the weight of the entire bike, but it would not break.

I appreciate all the feedback. Thanks to all.

50voltphantom

Omniums? I dunno.

nlowe

I agree with pretty much all of the feedback. From the point of view of a bicycle component manufacturer, I am 100% riding the bike the wrong way. The parts just aren't designed for this. I don't get any enjoyment out of gearing down and spinning my way up a hill however. I'd much rather stand and leg press my way to the top.

I've spent enough on $100 cranksets up to this point that I'm quite willing to spend $300-$400 to potentially be done with the problem. I'll likely go that route and give the Shimano Dura Ace 7710 and matching bottom bracket a shot. I've been biased against "racing" components in the past, as I perceive them as favoring lightness over all. True or not, I see them as using more advanced materials primarily as a way to reduce component mass, as opposed to improving strength as a primary goal. I'll ignore this bias though and give the Shimano a go.

If this ends up failing, the plan was to have a crankset machined from steel rather than billet aluminum. The crankset would quite literally be 5-10 pounds, and a third of the weight of the bike, but it would outlast me for sure. That will be left as a last ditch effort for the future if needed.

And chain, chainring, and freewheel wear is already a very real issue. After several chain breaks, and rapid wear on various chainrings, I now replace the entire set yearly.

I appreciate all the feedback. Thanks to all.

Lemond1985

If you start breaking racing components, ones that exceptionally-powerful riders like Peter Sagan use daily without incident, maybe you should consider going professional. That kind of power would definitely win races.

nlowe

Heh, don't get me wrong. Any real cyclist would beat me in any race. I bike on days that I don't lift, and I'm 100% spent after my normal 21 mile circuit. The goal is total exhaustion in the given distance, while maintaining what speed I can.

TMonk

Peter Sagan also doesn't weight 200 lbs and push a 52/15t up hill routinely. The issue here is not power, it's torque.

base2 

It sounds to me like he just likes to stand & stomp. Anybody can do that at 50 rpm. Anybody doing that would likely break their components too. All the other leg muscles are irrelevent to him. Quads, just like pecs & bi's are show-y & easy to make big.

Dude needs to just isolate quads & glutes with leg-presses at the gym. Cycling is the wrong sport for him. Maxing out the stack with Ham-string curls & working all the other smaller, hard to gain muscles is just dumb. Why spin & make 30% more power when standing & stomping breaks components better? Why deprive his ego knowing he is so stong "regular bikes" just cant withstand his awesomeness?

Snarkiness aside, seriously go to the gym. Go to the hamstring curl machine and start doing 50-60 rep sets of the whole stack...if you can, that is. It'll smooth out your power delivery, be less stress on your bike, and you'll generate more power seated. A LOT more power...I quit going to the gym because lifting the stack and doing and doing 60 minutes of stairmaster (level 14, with out using the handrails) 4 days a week was just a waste of time after a while. I hope you get to that point some day.

For the record, to establish credibility here, I can not wear regular cut bblue jeans. The leg holes don't fit & I can't actually get them on. I don't break crank arms.

I feel sorry for your bike.

base2 

It's torque delivery.

seamuis

Lemond1985

I don't mean to derail the thread, but I'm not understanding the distinction between power and torque. Torque produces power, correct? I know that a car that produces a lot of torque can accelerate from a dead stop faster than a car that produces less torque.

So is the distinction between energy produced at low RPM's (torque) vs. energy produced at high RPM's (power)? They seem like two sides of the same coin.

TMonk

Power is work/time. Torque has the same units as work (force x distance), and in this case time can be thought of as the inverse of cadence. So high rpm = short time interval and vice-versa.

So, you can produce the same amount of power by producing less torque at a faster rate (higher cadence), or more torque at a lower rate (lower cadence). If the OP got up the hills in the same amount of time using a lower gear, his power would be the same, but torque would be lower, and cadence higher.

As @seamuis mentioned, he should be using a track crankset. Track sprinters produce the most amount of torque of all cycling athletes, especially in those first moments when they are launching full gas from a relatively low RPM.

nlowe

@base2
No ego issues here. I just enjoy doing something that bikes aren't designed for. The breakage isn't a result of me being "too strong" or any such crap. It's really just my weight and riding style. I'm enjoying an entirely different activity than most of the people here, I get that. I was just looking for a recommendation for components that might endure my intentional abuse a bit better.

The gym is great, but biking offers something that lifting and staring at a wall cannot. I'll continue doing both.


I appreciate the recommendations @seamuis. I looked into track racing, and it mirrors my riding style quite a lot. I wasn't aware of this particular cycling niche before. I've gone ahead and ordered the Sugino 75 DD crankset. It looks like it should serve me well.

TMonk

@nlowe if there is a velodrome in your area, I highly recommend checking it out! Track racing is a very diverse genre. A real track sprinter focuses on races that are under 1 km and sometimes as short as 3 laps, where the first half of that might be spent at 0 - 5 MPH in a tactical positioning battle with one other sprinter, followed by an incredible burst of speed and power (match sprint). Another cool sprinter event is the Kierin race, where 5-10 sprinters line up behind a motorized bike that spends a few laps getting everyone slowly up to speed (30+ MPH), prior to moving off the track and leaving the rest in a high-speed sprint for 3 laps.

On the flip side you have skinny endurance racers who focus on longer races with a highly aerobic component. Often times these guys are also road bike racers (like myself). A real track sprinter would smoke me in any one-up sprint, provided there wasn't 50+ laps of high speed racing preceding it . Watching some of these guys (sprinters) wind up for 1 km time trial (for example) is seriously impressive - so strong.

seamuis

base2 

Ok. No worries, I was being a bit snarky. When I was a gym rat, I used to see people with terrible form doing everything they could to lift the biggest plates they could. Often times it was with a few buddies just trying to 1-up eachother, show off, or just plain ignorance. Usually it was some combination of all 3. After a while the wrong muscle groups got disproportionatly strong & they progressed with higher weights until they injured themselves or lost interest. Core strength & a strong back lats/traps doesn't get the ladies & leg day is a lot of work to see gains.

I (rightly/wrongly) was reading a bit of that here. Your bike is suffering from your improper form. So I suggested strengthening the muscle group you are compensating for (hams) so that you can have proper form.

A strong stroke & all the groups participating/being activated for gains is what you want. Right?

Specifically your form is leaving out your adductor magnus, semitendonosis, bicep femoris, semimembraneous muscles & you are compensating.

Additionally, standing & stomping disengages all of your core muscles and places additional load on your heart/cardiovascular system resulting in further inefficiency.

The additional force on your knees, hips, achilles tendon, and ankles isn't gaining you any strength or doing you any favors either.

Runners do the same thing. It's a natural human tendency to be enthusiastic & over do it. Runners have bad knees from the different lobes of their quads getting strong at different rates & it pulls their patella off track causing inflamation & ultimatly injury. Then the inevitable claim: "Running is bad for your knees." No, it isn't. Running wrong is bad for your knees.

You are selling yourself short & readily admit that you can't keep up with a regular cyclist. The reason? A regular cyclist has proper form and is way stronger.

In anycase, I concure with the track crank recommendation. But I hope you consider your form as a vital & necessary component of your strength/fitness routine.

I followed this guy until he quit riding. He broke cranks too.
Aaron