# Track crank/bb with outboard bearings



## roomservicetaco (Oct 14, 2008)

I've got a Lemond Filmore, 05 iirc, which came with an ISIS bb and Bontrager cranks. 06 and later models came with Race GXP Track crank with outboard bearings. The ISIS bb is shot and I need to replace it. Anyone know:

-what size ISIS bb fits that frame?

-can I replace the ISIS bb and cranks with the Bontrager Race GXP Track crank with outboard bearings? (http://store.trekbikes.com/jump.jsp...ath=1,2,442,453&iProductID=1702&bShopOnline=1)

-are there any other companies that sell cranks/bb for fixed gear bikes with outboard bearings? I'd like to keep the set to under, say, $200. The Bontrager retails for $160 but doesn't seem to be available anymore/out of stock.

Thanks.


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## asterisk (Oct 21, 2003)

The only dedicated track crank I can think of with outboard bearings is the Truvativ Omnium but it retails around $270ish. 

The Bontrager model is probably just what they had left over after installing them as OE on production bikes.

Pretty sure the Fillmore has just a regular 68mm shell, you can replace it with anything you want.


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## roomservicetaco (Oct 14, 2008)

Thanks. The Omnium looks like the one to go for...saw a site + a few vendors on ebay that have it for $150-$175.

I would have guessed 68mm, but there is some marking on the outside of the ISIS bb that says 73mm. Not sure why.


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## CleavesF (Dec 31, 2007)

Because your BB is 73mm that's why


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## 11.4 (Mar 2, 2008)

Why do you want an outboard bottom bracket? Shimano looked at it and built some for the world cup crowd. They didn't like them. It affected Q-factor (how far apart the feet are from each other), the bearings required for outboard bottom brackets weren't as smooth and low friction as what could be done inside the bottom bracket shell, and it wasn't as stiff. The Australian, British, and Italian teams all tried them and dumped them. There's more buzz about doing an outboard bottom bracket on a fixie but there's actually a reason why no good outboard cranksets have been released.

Note that the Omnium only comes with a 48 tooth ring. If you switch to pretty much anything else, the chainring bolts will bottom out before they tighten all the way. You can replace the bolts, but it tells you that the dimensions aren't quite the same. Do you really want to mess around with that?


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## roomservicetaco (Oct 14, 2008)

I'd like outboard bearings primarily to increase the stiffness around the bb area. I use the Filmore mainly for group training rides and there is some noticeable flex when I get out of the saddle, both compared to other fixed gears I've owned and to steel road bikes with square taper bb's. I recently bought a road bike with Dace crank/bb and the difference in stiffness when accelerating is noticeable compared w square taper.

The 06 and later Filmore models (including the 07 and 08 where Trek downgraded the frame) come stock with the Bontrager ob bearing setup, so I assumed they felt comfortable with Qfactor, friction, etc.

Re: Omnium, I def don't want to mess around with improper chain alignment, etc. But, are you saying that the Omnium brand ring is the only one that fits properly or only a 48T ring of any brand?


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## Balderick (Jul 11, 2006)

asterisk said:


> The only dedicated track crank I can think of with outboard bearings is the Truvativ Omnium but it retails around $270ish.
> 
> .


I have them on my track bike but now branded SRAM. Seem fine to me. Q factor is not a problem for me, but I think I have probably adjusted to the wider Q factor over the past year I have been riding 10sp Shimano on my roadie.


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## jabberwocky569 (Mar 16, 2006)

I had the Omnium on my 06 Fillmore before I broke it, and currently run it on my Orange One. Its noticeably stiffer than the stock Fillmore crank was. I like it, no reliability issues and very solid.


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## Dave Hickey (Jan 27, 2002)

This post is directed at nobody in particular but this subject is a hot button of mine...

I think the whole outboard bearing BB is a bunch of marketing hype...They encourage people to "upgrade" when it offers has little or no difference..

If these guys aren't concerned about flexing a traditional inboard BB, why does the weekend warrior think that he/she is? 

chainrings flexing? you bet.....BB flexing?, highly unlikely..

In the olympics where a 100th of second can make a difference, teams weren't using outboard BB and there were teams that spent millions on technology

I'll get off my soapbox now


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## Pablo (Jul 7, 2004)

Dave Hickey said:


> This post is directed at nobody in particular but this subject is a hot button of mine...
> 
> I think the whole outboard bearing BB is a bunch of marketing hype...They encourage people to "upgrade" when it offers has little or no difference..
> 
> ...


I'm waaay stronger than Chris Hoy.


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## roomservicetaco (Oct 14, 2008)

Dave, thanks for comments. 

I can't fully comment on the gear that pro track riders use because I don't follow the sport as closely as road riding. Perhaps pro track frames are built for such a single purpose (no varied terrain, no bumps, no tight handling for high-speed descending, etc.), the frames can be made exceedingly stiff and don't require anything else???

I do ride on the track occasionally, but my primary use for fixed gear is road training.

On the other hand, all the road pros have gone to outboard - may, of course, be marketing hype there as well. But just from my experience riding the two configs, I can notice a difference and I'm not a big torque-generating monster.

From a physics standpoint also, it seems pretty logical that the closer the fulcrum (bearing) is to the end of the lever (crank), the less force you will have going into deflecting the frame.

Last, the Lemond in particular seems more flexy in the bb area than other fg bikes/steel road bikes I've ridden. 

I guess I won't know for sure til (if) I try it, but that's my $.02.


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## roomservicetaco (Oct 14, 2008)

Balderick and jabberwocky569, thanks for the feedback. Did either of you have any of the prev mentioned issues with chain alignment or chainring bolts bottoming out? Are you running the Omnium 1/8 48T ring? I typically run 3/32, so I'd need to change the ring.


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## roomservicetaco (Oct 14, 2008)

In case anyone is searching this thread for Filmore info, the word from Trek is that the ISIS bb is a 68 x 108.


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## asterisk (Oct 21, 2003)

roomservicetaco said:


> On the other hand, all the road pros have gone to outboard - may, of course, be marketing hype there as well. But just from my experience riding the two configs, I can notice a difference and I'm not a big torque-generating monster.


Road pros ride whatever is given to them. Track racers usually have more say over their equipment and there isn't the pressure from manufacturers to use the newest parts, not enough public attention.

I am fairly sure if you use a decent track crank, like a Sugino 75 with matching bottom bracket and an outboard crank side by side you wouldn't feel any difference.


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## jabberwocky569 (Mar 16, 2006)

roomservicetaco said:


> Balderick and jabberwocky569, thanks for the feedback. Did either of you have any of the prev mentioned issues with chain alignment or chainring bolts bottoming out? Are you running the Omnium 1/8 48T ring? I typically run 3/32, so I'd need to change the ring.


I run the Omnium ring, so I can't speak to the chainring bolt issue. I've had no problems with chain alignment (running a Phil hub and cog).


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## 11.4 (Mar 2, 2008)

There's no chain alignment problem with the Omnium. The only problem dimension-wise is that a different chainring will not tighten up properly with the existing chainring bolts. 

The larger issue is that the crankset doesn't do anything that a DA 7710 or Sugino 75 won't do for you. When Truvativ stops making this crankset in a couple years do you want something with no parts compatibility or interchangeability?


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## CleavesF (Dec 31, 2007)

Why would the chainrings on the Omnium be an issue? They're 144 BCD. you can run whatever ring you want. Not exactly proprietary.


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## Balderick (Jul 11, 2006)

roomservicetaco said:


> Balderick and jabberwocky569, thanks for the feedback. Did either of you have any of the prev mentioned issues with chain alignment or chainring bolts bottoming out? Are you running the Omnium 1/8 48T ring? I typically run 3/32, so I'd need to change the ring.


I have not experienced those issues, but I run the 48t.

I used to have a nice Ti road bike frame, and swapped over my 9sp Ultegra groupset from my old bike. Rode the Ti frame like that for about 2 months. I then upgraded the groupset to 10 speed Ultegra - same frame, same wheels, same everything bar the groupset. I noticed a difference. Perhaps it is in my head, but I don't think so.


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## wim (Feb 28, 2005)

roomservicetaco said:


> From a physics standpoint also, it seems pretty logical that the closer the fulcrum (bearing) is to the end of the lever (crank), the less force you will have going into deflecting the frame.


The claims made for increased stiffness through outboard bearings rest on two facts: (1) you can design a much larger-diameter crank axle with outboard bearings than you can with a standard inboard bottom bracket, and (2) the bearings support the crank axle closer to its ends than inboard bearings can, shortening the cantilever. Those two considerations, the claim goes, increase stiffness of the crank itself. 

But there's no way any crank design can increase stiffness of a frame component. The most effective way to eliminate bottom bracket flex is to eliminate so-called negative forces during pedaling—in simple terms, become a powerful *and* smooth pedaler as almost all successful track riders are.


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## roomservicetaco (Oct 14, 2008)

I hear you - thanks.


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## 11.4 (Mar 2, 2008)

CleavesF said:


> Why would the chainrings on the Omnium be an issue? They're 144 BCD. you can run whatever ring you want. Not exactly proprietary.


They are also thicker at the chainring bolting point than standard chainrings. As a result, when you switch to a different chainring you bottom out your chainring bolts before they tighten up on the chainrings.

The posts above were pretty clear about this. One wouldn't be talking about bottoming out the chainring bolts if the BCDs didn't match -- they'd never be able to get mounted.


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## powerdan5 (Apr 27, 2006)

11.4 said:


> There's no chain alignment problem with the Omnium. The only problem dimension-wise is that a different chainring will not tighten up properly with the existing chainring bolts.
> 
> The larger issue is that the crankset doesn't do anything that a DA 7710 or Sugino 75 won't do for you. When Truvativ stops making this crankset in a couple years do you want something with no parts compatibility or interchangeability?


I'm considering trying the Omnium cranks out just to see what its all about. I've heard some very good reviews, and some moderate reviews. Some people seem to have strong opinions about these. 

I've seen people at the track using the Omnium cranks and swapping out the rings. If you got an extra set of standard bolts, could you use regular rings on the Omniums?

As far as the compatibility, I'm guessing SRAM GXP BBs will be available for a while regardless of whether Truvativ continues to make the Omnium. As for the rest of the parts on the crank, as with any other crank part, I pray nothing goes wrong.


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## CleavesF (Dec 31, 2007)

Well GXP is GXP... it's gonna be around for a while, like JIS. 

As for the chainrings, how fast can you wear out such a thick ring anyways?

If you do need to replace it, I'm sure you could find a spare if you could not, find a way to get other bolts and rings to fit on. I dont' understand why Truvativ would go proprietary when all their other stuff isn't. 

I run FSA rings on my rouleur carbon, no problem! Should be the same for the omnium. Maybe the 144 BCD ring you tried to put on is proprietary, and it can't go on non-proprietary spiders. Ever thought of that?

I'd test it out on my Omnium... except for the fact that I don't have any other 144 BCD rings around, and I'm actually putting it up on Ebay tonight lol.


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## asterisk (Oct 21, 2003)

CleavesF said:


> As for the chainrings, how fast can you wear out such a thick ring anyways?


It's not about replacing them. Most track racers have multiple chainrings to adjust for different disciplines/races. If you can't swap out the ring with one you or anyone around you might have it makes things difficult. For years you could count on being able to swap between a Campangolo, Sugino, Shimano, or whatever random manufacturer without issue. Throwing in an exception is a pain for people who've invested in equipment.

It sounds like the rings and therefore the stack bolts are wider than average. 11.4, does using standard bolts from someone like Sugino allow you to use standard rings?

Still sounds like the designers at SRAM weren't paying attention when they designed the rings.


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## Dave Hickey (Jan 27, 2002)

asterisk said:


> It sounds like the rings and therefore the stack bolts are wider than average. 11.4, does using standard bolts from someone like Sugino allow you to use standard rings?
> 
> .


I have some short stack BMX bolts that are REAL short..I can't imagine that any ring/spider would so so thin as to make these bottom out..The standard Dura Ace track bolts are pretty short too...


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## 11.4 (Mar 2, 2008)

You can use Dura Ace bolts with the Omnium crank and non-Omnium rings. But you probably want to swap back to the Omnium chainring bolts when you use that one 48 tooth ring (or for ease of switching stuff, dump the ring and the bolts and just standardize on some other brand, though at that time you're running your costs up).

It still raises the basic question: This doesn't work any better than the Sugino or either Dura Ace 7600 or 7710. If ya gotta have outboard, then you can make it work. But why bother?


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