MTB--Larger Crank Ring?- Mtbr.com
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  1. #1
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    MTB--Larger Crank Ring?

    While leaving the rear cogs alone, and opting to have a single, but large 52-tooth, crank ring on the front? Does anyone think this will be worth the effort? Has anyone tried this with their bike yet?

    V/R,
    Phil

  2. #2
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    I guess it depends a lot on the stock setup in terms of final drive ratio and overall spread for the gears. My bike with a good cadence could move me at over 25mph in top gear which is more than fast enough imo. I may have different gearing or more hilly roads than you though so you might have no use for your low gears.

    It's worth a shot if you think it will help, but if you haven't already tried commuting with the bike then I would try it first with stock gearing and then possibly upgrade whatever you see fit after a few rides.

    Is there any reason why you want just one crank ring? Simplicity? Less maintenance? Cleaner look? I don't think I could trade in my three rings for one...I use them all far too much....

  3. #3
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    Well, you could if you have enough chainstay clearance. That's the first thing to check. The ring will be in about the same spot as your middle ring is currently. If you run 8spd in the rear you'll be fine, but if you do 9spd you may have problems with the chain coming off and will need a chainguide. So measure out from the center of the crank a radius of about 4.25" and see if that will contact your chainstay in the middle ring position.
    Maybe you'd be happier switching to a road cassette in the rear and a smaller ring if the 52 won't fit.

  4. #4
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    I don't use my front-cranks a lot, as the majority of my riding is on paved roads that are somewhat subtle. I like the idea of one crank in the front for the simplicity and the fact that I just don't think I'd need more than that for my 5-day/week rides. I ride 10-miles one way to work. Right now it takes approximately 40-minutes since a small portion of the ride is through the city. I'd like to shave 10-minutes off my trip by changing the gear ratios around.

    When I do get a chance to take the bike out for some trail rides, I would simply replace the crank rings that came with the bike.

    I didn't consider a road cassette for the rear wheel? I have a lot of experimenting to do this Spring.

    More input is greatly appreciated though!
    Last edited by SpartyBiker; 04-03-2008 at 04:59 AM.

  5. #5
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    I've got some gradual hills and with tail winds it's pretty easy to spin out with 44/11 gearing. For commuting, something taller would be definitely helpful. Has anyone tried a 'cross compact crankset on a commuter mtb yet?

    BM
    "I've come to believe that common sense is not that common" - Matt Timmerman

  6. #6
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    Unless you can max out your 44, there's no reason to switch. But if you want to gradually step up, try a 48 compact. That's what came stock on my cross bike and I comfortable cruise my 15 mile commute in a 14/15 rear.
    The wood is being bent! Let me know what you need!

  7. #7
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    If you go for one chainring and ditch the front derailer, you might need some sort of chain retention device. If it's a ramped ring (as opposed to a track or singlespeed ring) it will be more prone to throwing the chain. I had this problem with my old commuter that had no cable guides for a front derailer and I found plenty of different devices to solve this problem but eventually switched frames and never solved the problem. You can take my word for it, this is a very annoying problem to have.
    Other than that I think you are very brave to go with 32:52 as your lowest gear, but it's probably fine if you have a flat commute and little wind. I know I definitely need the 32 in front, even the 22 gets occasional use in winter. Mind the chainstay clearance, often less on mountain bikes (to fit wider tires).

  8. #8
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    Thanks again for the input, it is all great to read over while I ponder my decision making process.

    I think I'm going to adopt a new setup, which will replace the MTB's stock 44/32/22T crankset while I'm commuting, with two rings that are road-oriented.

    I'm looking at three manufacturers right now: Bontragers "Race X Lite GXP Compact" 50/34T road crankset, SRAM's "Force" 50/34T road crankset, and TruVativ's Rouleur 2.2Team 50/34T compact crankset. They all seem to accomplish the same end-result; speed, while keeping the price on par with my budget. Ultimately I just have to research their compatibility with my existing components.

    Does anyone out there have first hand knowledge regarding these manufacturer's parts?

    V/R,
    Phil

  9. #9
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    reason for big rings

    The reason to run a big ring in front is because smaller rear cogs (11-12t) are not as efficient as bigger ones (16-22t). The bigger rear gears can put out 98% efficiency while 11t is down around 92%. It's more work to wrap the chain around smaller gears.
    44tX11t, 48tX12t, and 52tX13t are all 4:1 ratio top gears. If you are into the wind the 52t ring will get you into your most efficient range at a higher speed than 44t. Also the % difference between 11t-12t down shift is greater than the differnce between 13t-14t. About 9% vs 7%. If you need more than 4:1 top gear then bigger frt ring is the only choice. With narrow 26" road tires this will probably be true. Not so much with 700c. Almost all 11t cassettes have 11,12,14,16 top gears. Road cassettes typically have 12,13,14,15 top gears, again much closer gears.

  10. #10
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    The higher gear is good on flat and downhill roads, at 30-35mph I am pushing a pretty fast cadence with my stock 42-11 top gear. I'll be going to a 44t large ring at some point.

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    go for the compact idea. high five trekjeff!

  12. #12
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    I've decided that I'm going to go with the Bontragers "Race X Lite GXP Compact" 50/34T road crankset, while utilizing a 29" wheel set, with SRAM's PG990 11-32/9 speed at the rear. I should have the parts in a few weeks since I'm going to order them after the mid-month paycheck comes in.

  13. #13
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    Unless you've already dropped the money, I'd really suggest a graduall step up. Read the cyclocross forum. Front Chain rings 36-48. This will give you more range then you realize and will provide plenty of off road range as well. And if you are changing out the rear then opt for a road/cross cassette, (Cassette)Shimano Tiagra #HG-50 9-speed 12-13-14-15-17-19-21-23-25t...SRAM also makes a nice cassette, I just had the gearing for the Shimi handy. Regardless, it's always great to see riders wrenching and looking to make their rides fit the need, well done!
    The wood is being bent! Let me know what you need!

  14. #14
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    tried 48-36 didn't like it

    I tried 48-36-24 rings and didn't like the 36t middle ring. For trail riding I had to shift in & out of low range all the time, and this is with 26" wheels 29" should be even worse. I went back to 32t middle ring and kept the 48. 50-34 sounds good to me, and maybe even 50-32. I've had no shifting problems with 48-32, maybe 50-32 will work. I don't want to give up my XT cranks to find out. I'm running 48-11 with 700c wheels and top gear is plenty tall. 50-12 with 29" might be better. I suggest doing the cranks, and see how your existing top gear works. There are some nice XTR cassettes with 12t top (12,13,14,16,...28,or 32 low) sometimes you can get a deal on them. A lot of off road cassettes with 12t top are 12,14,16,18 so know what you're getting. If you don't already have wheels Cane Creek has their Strados 700c disc wheels on sale, they're kind of narrow- 40mm max tire width, but other than that pretty nice.

  15. #15
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    I can't wait to see how the bike performs. The worst case scenario, I don't like it, and it sells on Ebay for what I paid. The majority of my riding is on road, with 20-miles per day--Monday through Friday. My goal is to reduce my energy output to cover the same distance in a faster time. The weekends are typically dedicated to riding trails around upstate NY; however, lately I've been tied up with projects around the house. At any rate, I'll let everyone know how the bike rides. I'm sure there will be a lot of speed that I'm not used to. There's a 1/2-mile stretch of farm land that's down hill, with the bike being setup the way it's going to be, it's a good thing that I wear eye protection when I ride!

  16. #16
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    Just for future reference

    If you find you like the 11t top gear, its almost impossible to find a cassette with 11t that doesn't skip 13t. Universal Cycles has Miche cassettes with 11,12,13,14 or you can stack them any way you want.They sell all the gears seperately if needed. I have one but haven't installed it yet so I can't say how they actually work (it's for my brothers bike).

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