Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

SRAM Omnium crank problems

Old 11-07-09, 02:54 PM
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FixedFiend626
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SRAM Omnium crank problems

I just installed a new set of these on my pista concept and was amazed how much stiffer they are than my old 75's. I went from 170mm up to 175mm with these cranks and it's had a HUGE impact. Does the longer crank make for a drastically harder gear-inch? It feels like I went down a cog-size. Either that, or I didn't install them right. Everything seemed to slide into place well enough, but I didn't use a torque wrench. Is it absolutely necessary to install them with this tool? Is there a significant break-in period? Ughh.. any help appreciated.
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Old 11-07-09, 04:14 PM
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First question: no it doesn't change your gear inches. But it DOES change your gain ratio.

Second Question: I don't use a torque wrench with mine. Though I should.

Break in Period? Huh? For what? The bearings? No...
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Old 11-07-09, 06:30 PM
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Having longer crank arms will make your bike feel EASIER to pedal, not harder. Maybe you just haven't ridden in a while? Anything else diff. that would cause your bike to feel like it has a higher ratio?

Torque wrenches are generally unnecessary if you know what you're doing. Even at the best bike shops in Austin, they typically don't use torque wrenches. Most good mechanics have a feel for how tight something should be.

Also, there is def. no break in period.
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Old 11-07-09, 06:35 PM
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Uh, actually you're both wrong.

Gear ratio is not affected. Nor is gear inches. Only your gain ratio is.

Some people have claimed that the bearings on the BB have a short break-in period.

I used a torque wrench with one pair, but they're supposed to be set at 50lbs (double-check this, it's from memory). That was high enough to meet that I ended up wrenching them with a pretty great deal of force. Didn't bother a second time. I was more worried about the torque being set much lower to avoid crushing the bearings.

Edit: Also, as far as the BB types, since omniums use external bearings, they're extremely stiff because they bolt directly to the other arm. Square tapers are weak and whack (IMO)... people bone Sugino 75's because they say NJS on them. If you put a 225 lb guy on square taper cranks and have him stand on them horizontally, you can see the arms flex down.
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Old 11-07-09, 06:40 PM
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yeah, square taper is probably inferior in terms of stiffness, but there is a reason people like sugino 75 cranks and it's not just cause they say njs on them

They are really stiff. Omniums might be a tad stiffer, but 75s are plenty stiff for most riders/racers. Whenever I'm at the velodrome I see plenty of people riding 75s
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Old 11-07-09, 06:42 PM
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Originally Posted by PedallingATX View Post
"Square taper is probably inferior in terms of stiffness... there is a reason people like sugino 75 cranks... They are really stiff.
K
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Old 11-07-09, 06:47 PM
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what i'm saying is that the difference isn't enoguh to make a difference to most racers. I've seen plenty of the guys in the track forum recommend 75s. I've also witnessed tons of racers (IRL) using them.

Also, having a fat guy stand on some cranks isn't really a good test for stiffness differences in bottom bracket types.
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Old 11-07-09, 06:49 PM
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Originally Posted by PedallingATX View Post
Also, having a fat guy stand on some cranks isn't really a good test for stiffness differences in bottom bracket types.
Would you rather have your fat friend sprint on your omniums or on your 75s?
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Old 11-07-09, 06:53 PM
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well, having someone stand on cranks and observing the flex takes into account several different factors. It could be the actual crank arms flexing, in which case the BB type is irrelevant. Or it could be the BB. Or it could even be the frame/wheels if you're not looking closely.

I think my fat friend would be fine on either cranks, honestly. As he would on campys or dura ace. They're all stiff and nice.
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Old 11-07-09, 10:44 PM
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Edit: Also, as far as the BB types, since omniums use external bearings, they're extremely stiff because they bolt directly to the other arm. Square tapers are weak and whack (IMO)... people bone Sugino 75's because they say NJS on them. If you put a 225 lb guy on square taper cranks and have him stand on them horizontally, you can see the arms flex down.
What? This statement is absurd; square tapers have proven themselves time and time again in almost any cycling scenario from road/track to MTB. Tell me how a hardened steel square taper spindle is the cause of flex vs a splined crankset. Any flex your seeing is out of the crankarm and/or loose ball bearing deflection, not the spindle. NJS has nothing to do with this conversation.

As far as bearing break in, taken directly from phils wood's site:

"hubs have a break-in period, which can last up to 350 miles"
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Old 11-08-09, 06:27 AM
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Originally Posted by Yo! View Post
What? This statement is absurd; square tapers have proven themselves time and time again in almost any cycling scenario from road/track to MTB. Tell me how a hardened steel square taper spindle is the cause of flex vs a splined crankset. Any flex your seeing is out of the crankarm and/or loose ball bearing deflection, not the spindle. NJS has nothing to do with this conversation.

As far as bearing break in, taken directly from phils wood's site:

"hubs have a break-in period, which can last up to 350 miles"
K. This has been argued before. I'll say this this: Why did Octalink replace Square-taper? And why did external bearings replace octalink? And why did BB30 replace external bearings? If the said crank/bb system was so great and infallible, I'm baffled as to why they keep evolving. Surely not for stiffness. It must just be another cycling trend. Yeah. That's it.

I know what NJS means. I know what NJS does not mean. It does not mean superior performance. Which, as I said earlier, is why I think most people buy 75s for. They falsely believe NJS = superior performance.
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Old 11-08-09, 09:03 AM
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Originally Posted by idiq View Post
K. This has been argued before. I'll say this this: Why did Octalink replace Square-taper? And why did external bearings replace octalink? And why did BB30 replace external bearings? If the said crank/bb system was so great and infallible, I'm baffled as to why they keep evolving. Surely not for stiffness. It must just be another cycling trend. Yeah. That's it.

I know what NJS means. I know what NJS does not mean. It does not mean superior performance. Which, as I said earlier, is why I think most people buy 75s for. They falsely believe NJS = superior performance.
njs is the latest in technology, you fool.
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Old 11-08-09, 09:07 AM
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People by Sugino 75's because they look nice and are actually a good quality crank. Are they stiff?...yes. Are they the stiffest?...no because NJS technology is frozen, while other non-NJS parts are free to evolve. Is any of this likely to have any relevance to 99.9% of the people riding them?...absolutely not.
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Old 11-08-09, 09:12 AM
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i want a 100% beef bottom bracket shell.
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Old 11-08-09, 09:13 AM
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To the OP who didn't ask about the quality of 75's or njs stamped product, I would just say give it some time and if it doesn't change or you don't get used to it take it to a good mechanic.
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Old 11-08-09, 09:41 AM
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Just to throw my 2 cents in, I think the Sugino 75's are a pretty awesome crank. I rode them for three years without issue and the finish-work on them beats the Omniums, IMHO. I just needed a longer crank on my track bike (I'll probably throw them on another bike).

Is it possible to tighten the crank-bolt on the Omniums enough that the bearings develop drag?
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Old 11-08-09, 06:35 PM
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MY FAT FRIEND IS OFFENDED BY THIS THREAD. why not up the ante and get a sugino grand mighty crankset? they're stiffer than 75's.
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Old 11-08-09, 11:02 PM
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Since the Omniums are only designed around a 68mm shell without any spacers, you crank the arm down until it bottoms out, so you can't really mess up the bearing preload. It's when you start running 68/73mm external bb's with spacers that you have to be careful.
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