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Shimano 36T Freehub experience

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#42 ·
Ronnie said:
The only reason wheel size is even in this debate is that 29" wheels are becoming popular. That resulted in the likes of Shimano even making a 36T cassette. It is completely conceivable that a 36T cassette could and will be fitted onto a 26" wheel. The same rider would produce the same torque on the freehub, irrespective of the wheel size. Although he may be on a steeper incline with a 26" than a 29" as the final ratio is slightly lower. The ability of the freehub to survive maximum torque does not change.

Ronnie.
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To the OP,
Were they in the 36T cog when said freehubs failed?

All:
(please let me know if I'm horribly mis-informed - trying to get my head around this)
:confused: :confused: :confused:

For level or uphill travel,
The torque on the freehub is a resultant of the tangential force at the ground/tire interface multiplied by the radius of the wheel. That tangential force is defined by the acceleration of the rider's plus the bike's mass; the acceleration coming entirely from the maximum power that the rider can produce (which occurs in only a fraction of the total rotation of the cranks). The tire pushes against the ground tangentially to make the bike + rider go forward, or up an incline. As the incline steepens, a larger component of the acceleration is against gravity. You cannot generate more torque at the hub than whatever the available power and traction will allow.

I'm a little surprised that the 36T cog even requires a stronger freehub since the resulting forces (that is, the tire reacting with the ground) aren't any greater. A person cannot suddenly generate more power because he changed gears - he can't step any harder on the pedals - he doesn't suddenly weigh more - he doesn't have more traction. Maybe he can climb steeper, but he is going slower since he only has a certain max power output, hence, certain max acceleration against gravity --> resulting in the same torque on the hub as if he had a 32T (in which case he would be climbing less steep, or slower). The only advantage of the 36T is when your pedals are not in the optimum position to generate maximum torque. And even with infinite traction, and the rider riding straight up a wall (assuming they had enough power), he still can only generate a torque equal to the total mass x acceleration x wheel radius.

If there was a smaller wheel, or different cogs the intervening numbers would be different, but the rider power, and the reactive force at the tire/ground would be the same.

I'm trying to equate this to a dragster that has tons of power and traction - or maybe to a 4x4 that has tons of power but not as much traction... I'm running out of words...

I think Shimano needs to redraw this one. The failure seems to be in the engagement, not in the torque load (just like Noah said).

-F

PS - chain tension is another thing...
 
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#43 ·
Fleas said:
To the OP,
Were they in the 36T cog when said freehubs failed?

All:
(please let me know if I'm horribly mis-informed - trying to get my head around this)
:confused: :confused: :confused:
.
Click to expand...
in the nicest way possible, i have no idea what you are on about.

the torque at the freehub is simply, and exactly = gear ratio * input torque

input torque is that applied by the rider, and gear ratio = output gear teeth/input gear teeth. the torque is also influenced by crank length and wheel diameter, but those are fixed per given bike so are usually ignored.

torque at the hub / cog interface (ie. the freehub) has nothing at all to do with anything but the input power, and the gears in between
my question about all this is that the torque difference between a 36t and a 34t is less than 10%

10% should not be enough to exceed any specifications for the hubs. there must be another design flaw in there somewhere.
 
#44 ·
I love threads like this, always make me laugh in a slow arrogant fashion, for knowing the answer.
 
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#45 ·
Dibs said:
The people who told the 36T cassette creates more torque are idiots. With a shorter (easier) gear, there is less torque on the entire drivetrain.
You can prove this out with any cassette. Put the bike in an "easy" gear and climb a hill. You don't have to push/torque the pedals too hard. Now shift up to a "hard" gear and climb the same hill. That puts way more torque on the drivetrain.
The failure is because of the crappy Shimano hubs.
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You CAN generate more torque with a larger cog. Just like you CAN generate more torque with the granny.

I have learned that I cannot stand and mash in the granny. I'll pull the freehub right over the pawls. With a 36T, I would probably have to spin. And given my current riding style and limitation to 32T on 8 cog, that is exactly what I would do with a 36T cog.
 
#46 ·
It's all related.

First thing to keep in mind:
Crank arm length x Pedal load = Chainring radius x chain tension. This is a simple second class lever situation.
Second area of interest:
Chain tension x radius of cassette cog = Torque applied to the freehub mechanism. This is a simple torque situation.
Third area of interest:
Torque at the freehub / freehub mechanism radius = Force on the freehub pawls.
Fourth area of interest:
Torque at the freehub / radius of wheel = Driving force of the rear wheel.

By following these basic equations you can see fairly easily that a given driving force at the rear wheel has to entail the same force on the freehub pawls and is independent of gearing choice. By choosing a larger cassette cog you can achieve that torque at a lower chain tension which would allow for some combination of larger chainrings, shorter cranks or lower pedal load (for most riders the significant detail is the lower pedal load, i.e. pedalling less hard.) So no big deal right?

Well, drive force is almost never constant.

Where this starts to become an issue isn't climbing at a constant speed up a smooth grade. Instead it lies in the constant accelerations that occur to compensate for changes in grade and terrain and the unavoidable pulse that our human drive mechanism imparts to every pedal rotation. As you start into your pedalling power stroke you are always accelerating to overcome the slowing that occurred in the dead spot, when the grade increases you have to apply more force at the rear wheel in order to maintain your forward velocity, and any time that you have to overcome a midtrail obstacle (rocks and roots seem the most common offenders here) you also have a pulse of extra torque to deal with getting your tire up and over.

Human muscle systems don't apply force in a smooth fashion and the 'jerk' (that's the term I was taught for the increase in acceleration) can be quite abrupt when trying to compensate for these situations. This abrupt change in acceleration is magnified by anything in the drivetrain that increases the effect of pedal load and is where most freehub failures occur.

But what about available traction? It is difficult for the driving force of the rear wheel to exceed available traction at the rear tire. However, tire traction has increased by leaps and bounds between softer compounds, better treads, larger casings, larger wheels and rear suspension many people are now climbing hills they would never have considered ten years ago. And all this while still overcoming obstacles and compensating for imperfect power application. It is this very increase in available traction that has driven the industry to progress from 28t through 32t and now up to 36t cassettes for bikes. People are riding up things now where the limit isn't traction, but the mechanical gain their drivetrain can provide. All of which provides for that much more stress at the freehub.
 
#48 ·
Any more feed back on this issue? This thread had turned into 'How much torque' rather than freehub damage/destruction.

So far I gathered Shimano 12-36T +

XT hubs = not strong enough, especially the newer ones

M529/M629 = While designed for the 36T, still not strong enough

King = No problem

DT Swiss = No Problem

What about Hope?

My project this summer is to build up a wheelset with Flows. I already have the Shimano HG61 12-36T cassette and am looking for a compatible hub that would be able to withstand the torque (whether theres more applied, less or equal per previous discussions) of the 36T.

Will be upgrading from Mavic A317's with Deore hubs and PG980 11-34 cassette
 
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#49 ·
Hope is quality stuff should be fine for 36T applications however if you are using one of the cheep boat anchor cassettes they may chew into aluminum freehubs. Hopefully someone Sram or Shimano will come out with a 9 speed cassette with an aluminum carrier and a 11-36T.

My LBS guy thinks the first round of inexpensive cassettes was a test run for Shimano if they sold out then they will come out with a upgrade version. Makes sense to me why put money into an unproven market, as for the faulty hubs that were supposed to be extra beefy well that sounds like a screw up.

I should think 36T cassettes will get better 29ers aren't going away and a lot of people will want the easier gear.
 
#50 ·
ferday said:
my question about all this is that the torque difference between a 36t and a 34t is less than 10%

10% should not be enough to exceed any specifications for the hubs. there must be another design flaw in there somewhere.
Click to expand...
This was my thought. A strong rider can certainly apply more pedal force, and therefore more torque at the hub on a 34T cog than I ever could on a 36T cog. If 34T cogs haven't been failing regularly under strong riders, it seems like the problem is not the size of the cog but some other design flaw.
 
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#51 ·
like I said before I think there are other factors that contribute to the failure, but I see I lot of blown shimano freehubs on 26" bikes too - especially those in the XT wheelset. I think it is possibly more of an issue on 29ers b/c of the longer chainstays which when coupled with a slight backpedal/ratchet move by the rider will cause the chain to slack out and then quickly taughten (tighten?) when the hub engages oh a downstroke (forward pedal). A bit of a whiplash effect.....but I'm no engineer, just bike shop dude who sees it all....all the time.
 
#52 · (Edited)
DFYFZX said:
This thread is fun:)

Side note: Has anyone had issues with the Hope Pro ll rear hub shredding or is it considered a "36t compatible" hub? I want 36t...as soon as they come out with a respectable weight version. 2011 XT maybe???
Click to expand...
If you weigh 200+ I would avoid them. I broke 3 aluminum freehubs, 1 steel and 2 hubshells on Hope Pro II. I weigh 230. This was on a 29er with 22x34 low gearing. The aluminum freehub lasts about 3-5 rides. The Steel Freehub is a bad choice because it allows the pawls to extert too much force on the hubshell which then ruptures. Hope's warranty is awesome and they replaced every broken piece.

On the bright side, the Hope Pro II are definitely stronger than the XT freehubs. The Shimano freehub lasts literally minutes under me on something like Slick Rock or Moore Fun. But if you lower the peak torque, they are fine. My Shimano XT hub on my cross bike (34 front / 28 rear low gear) has lasted 2 years and I'm sure it will last many more years.

I have 3 Chris King hubs with the first purchased way back in 2000 and I have never broken one. After the initial 2 or 3 months of them settling in I never even adjust bearings unless I'm repacking the grease.

According to the general consensus of Trials Riders and Clydesdales, the best hubs for torque are: Hadley, Chris King and DT-Swiss 240. No hub is unbreakable and different folks have had troubles with each but IMO you will be MUCH happier long-term with any of those than Mavic, Shimano, American Classic, WTB, Hope, Joytech, etc.

Hub History:
1999 Shimano LX -- Freehub lasted around 6 months with 22f 34r or 2 years with 22f 32r
2000 King -- Still going strong 3000+ miles
2002 Kore -- Broke in 15 minutes on Troy-Built in Fruita (22f 34r)
2002 King -- Still going strong 5000+ miles (22f 34r)
2006 Hope Pro II -- Lasted 1 season, spring of the following year I started breaking them seemingly every ride (22f 34r)
2006 Borrowed Mavic -- Made lots of weird popping sounds on first climb, so I walked all the steeps since it was a borrowed wheel, my buddy who is 160lbs still rides it on a DH bike with 38f 34r
2007 King -- Still going strong 4000+ miles 22f 34r
2007 Shimano XT Still going strong 2500+ miles 34f 28r (cyclocross)

PS: The failure mode for Shimano hubs is that the pawls bend over backwards and get jammed, eventually breaking the sockets. The failure mode for Hope Pro II is that the pawls deform the seats and then the freehub gets hung up in the socket and tears in half-ish. This can take out all the bearings on the drive side even if the hub doesn't break.

PPS: In case you are wondering, yes I seem to be a bit stronger and fatter than average. I have also broken an XT cassette while climbing (only the 4-arm carrier version 11-32, never the 5 arm though.)
 
#53 ·
I'm 170lbs and not near peak conditioning so I doubt I would have issues. I think I'm going to wait and see if any nicer versions get released this year. I bet someone makes a version that's nicer to hubs at some point. You never know though...
 
#54 ·
Ronnie said:
No sir it is you... (well I won't say it) but it is you that does not know what you are talking about.
Click to expand...
Can I get an Amen? If what the poster said was true, then the freehubs would be failing regardless of the number of teeth on the rear cassette, which is not the case. The problems became obvious with the advent of the 36 x 12 cassette.

That said, I've broken a few shimanos before the 36 x 12 came on the scene. My solution was to upgrade to Hadleys and DT Swiss/Hugi Freeride hubs, with the Stainless Steel carriers. Problem solved. You can get SS carriers from Hadley, they are worth it for us big Clydes.
 
#55 ·
For what its worth:

I've been riding on a Shimano XT M775 36 spoke centerloc with a SRAM PG-970 11-34T cassette since last summer with ZERO problems.

I am 6'3" and weigh 260 lbs. I ride HARD. I have a LOT of leg strength. I ride mostly XC, but some AM type riding thrown in... I'm not afraid to take my hardtail up or down anything, and I'm more likely to stand on the pedals and push than I am to shift to a lower gear when it comes to climbing.

In short, I am not worried about my M775 XT hubs in the least.
 
#56 ·
GpzGuy said:
For what its worth:

I've been riding on a Shimano XT M775 36 spoke centerloc with a SRAM PG-970 11-34T cassette since last summer with ZERO problems.

I am 6'3" and weigh 260 lbs. I ride HARD. I have a LOT of leg strength. I ride mostly XC, but some AM type riding thrown in... I'm not afraid to take my hardtail up or down anything, and I'm more likely to stand on the pedals and push than I am to shift to a lower gear when it comes to climbing.

In short, I am not worried about my M775 XT hubs in the least.
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I couldn't agree with you more.

I've been riding nothing but Shimano hubs since I started riding years ago. I've still got a set of wheels with XTR M960 hubs that I've had since 2004 and only replaced ball bearings one or twice in that time. Of the tens (maybe hundreds) of thousands of Shimano hubs, some are likely to fail and those seem to end up on MTBR. Most of Europe is mobile on bikes fitted with Shimano hubs that probably don't see much maintenance. They definitely are not using the likes of Chris King.

Shimano started making the 12/36T cassette to test the waters in a growing market. The only reason that they then produced the 36T specific hub was to comply with European laws requiring the hub to be capable of the higher torque that can be produced by a 36T cog. I would not hesitate using one on my XT hub if I needed it. When I built my 29" bike I bought one but have been happy with an 11/34T cassette thus far.

Ronnie.
 
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#58 ·
DFYFZX said:
This thread is fun:)

Side note: Has anyone had issues with the Hope Pro ll rear hub shredding or is it considered a "36t compatible" hub? I want 36t...as soon as they come out with a respectable weight version. 2011 XT maybe???
Click to expand...
Mine died today.... I ran 11-32 on a Hei-Hei forever.... no problems. 12-36 killed it in less than a month. Screw it, I'm going back to 11-32.
 
#60 ·
36T? No thanks, i'll just walk and get there before you. :rolleyes:

Might as well start figuring out how to mount chainrings back there. :p :D

Seriously, how slow do you need to go on a bike anyway?!?!?! :skep:
 
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