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Thread: Crank Chaos

  1. #1
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    Crank Chaos

    im building a carbon commuter from scratch and after not riding since i was a kid, all the weird-ass sizing y'all have is doing my head in!! lol i bought a BB92 carbon mtb frame and the dream was to run a 53x39 2x10 but ive since learned thats not possible on a bb92, so i'll likely run a 42x30/28 but from what i can tell theres no unified measure for crank width??? i know BB92 only fit GXP but that tells me crank diameter, but the BB92 is WIDE, and nothing tells me this, or am i missing something?

  2. #2
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    You can get BB92 in Shimano or SRAM gxp types, it will take the respective 24mm Shimano hollowtech 2 or SRAM cranks. It is designed for mountain bike cranks not the slightly shorter spindle road cranks. You can get 48 36 26 touring mountain cranks Shimano definitly and i think SRAM truvativ also make them

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    Quote Originally Posted by CH4PZ View Post
    im building a carbon commuter from scratch and after not riding since i was a kid, all the weird-ass sizing y'all have is doing my head in!! lol i bought a BB92 carbon mtb frame and the dream was to run a 53x39 2x10 but ive since learned thats not possible on a bb92, so i'll likely run a 42x30/28 but from what i can tell theres no unified measure for crank width??? i know BB92 only fit GXP but that tells me crank diameter, but the BB92 is WIDE, and nothing tells me this, or am i missing something?
    You should stop trying to build a custom bike since you really have no clue what you're doing. At least until you learn what you're doing.... BB92 doesn't "only fit GXP", any outboard bearing bottom bracket mountain crank will work. Why would you dream up some random road crank on a mountain frame without even finding out if it will work before you start buying stuff? I hope you also have your fork and headset sorted.

  4. #4
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    Quote Originally Posted by CH4PZ View Post
    im building a carbon commuter from scratch and after not riding since i was a kid, all the weird-ass sizing y'all have is doing my head in!! lol i bought a BB92 carbon mtb frame and the dream was to run a 53x39 2x10 but ive since learned thats not possible on a bb92, so i'll likely run a 42x30/28 but from what i can tell theres no unified measure for crank width??? i know BB92 only fit GXP but that tells me crank diameter, but the BB92 is WIDE, and nothing tells me this, or am i missing something?

    Just a thought...

    but maybe buy a beater and start riding before you make a whole bunch of desicions based on ????? dreams.

    Probably need to talk to a bike mech....just to get straightened out.

  5. #5
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    Also, welcome to the forum People seem cranky today for some reason.

    I do agree that you need to really dig around the internet and do your research before buying parts to ensure compatability matches your expectations. Since you already bought a frame, you will have to make some compromises, but you will learn a lot along the way. If you don't have one already, I recommend forming a good relationship with your LBS. It's nice to have a place to go for reliable help and advice when you inevitably get to the point where you are just spinning your wheels.

    Good luck!

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    cheers simplejon, and couldnt more agree kleebs, and i do goto lbs, but i just like to educate myself you tend to learn better when u find the answers yourself nvm, got it sorted i just didnt realize bb92's sit flatter, hence are the similar size across.

  7. #7
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    53T is way to big for a commuter anyway unless you are a complete EPO beast or commuting on a road bike (as I do) - If you haven't cycled for a few years a 44 or 48T big ring is more than enough with an 11T smallest rear sprocket

  8. #8
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    53t is MONSTER gearing, for sure. of course you wouldn't know this not having ridden since you were a kid. My purpose-built steel commuter bike MAXES at 46x11 and even that is such a big gear that I don't ever use it. That's with 700x32 tires at 75ish PSI.

    Most road bikes don't even come with 53t big chainrings anymore. Most riders aren't strong/fit enough to push that big thing.

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    i defo have them cyclist legs lol im on a merida crossway 10 at the moment, which has 48, and 12-32 at the back and on the flat i can max it out, so just wanted a little more omph!! it also has 700c wheels vs 650b on the cf one (which i assume will spin easier/quicker increasing the ratio?) ...so i pulled the trigger on a truvativ sram xo 42/28 and got a ceramic bb, with 11-36 cass. i kno with motos dropping 1T at the small sprocket equals 3-4 at the large so hopefully it at least gets close to same as the merida

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    BS. How fast you going when you max your 48x12?

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    On some of the reasonably fast paced group road rides i do i am on the 52t ring around the middle to lower end of an 11/23 or 25 cassette most of the time on the flat. Solo commuting on the same bike I could live with the 39 ring only (39 11 is good for 45kmph on a 700c road wheel) I mix it up by using the big ring and a lower rear gear but thats only to preserve cassette and chain ring life, it isnt really needed

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    When I started cycling again, I got a cheap MTB- style bike and thought for the first two weeks that I needed much bigger gearing.

    My Bosanova tops out at 50 x12, and I top out well below that. In fact, I can't remember the last time I used the big ring (on the front). I like that it is there should I be chased by rabid dogs downhill, but I'm not sure that the bigger ring gains me as much as a higher cadence. And that is on a road/ touring bike with drop bars and high psi slicks.

    Why the crazy high ratios on a frame with an upright position?

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    dont have a speedo yet to kno, but i havent been training for a couple months so if im pedalling out now once im back in the gym, i'll have no head room. the 53T obv isnt a option now anyway. i think i'll live with the 42/28T, but wouldve preferred lower gears. havent used my 28T once on my current ride (guess i'll have good chainring life too lol)! ...i hurt my arm in a motorbike accident so cant put weight through the bars, i pedal from the legs, so i prefer the upright position

  14. #14
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    Quote Originally Posted by CH4PZ View Post
    dont have a speedo yet to kno, but i havent been training for a couple months so if im pedalling out now once im back in the gym, i'll have no head room. the 53T obv isnt a option now anyway. i think i'll live with the 42/28T, but wouldve preferred lower gears. havent used my 28T once on my current ride (guess i'll have good chainring life too lol)! ...i hurt my arm in a motorbike accident so cant put weight through the bars, i pedal from the legs, so i prefer the upright position
    650b? If this is for a commuter/road this is a waste. You want the bike to be easier to pedal and fast? Those are inversely related. You can't have both. If going fast was easy and a matter of getting smaller wheels or a lighter bike, everyone would be fast. Also, 53t was never an option with a 36t cassette on any bike. This bike is going to be terrible. You should really get someone who know what they're doing involved in this project before you start buying more parts.

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    I agree, 53t is massive for a commuting gear, especially if you plan to carry any gear with you. I liked a compact crank with a larger little ring so like a 36/50 instead of 34/50 as it shifted a little better and the jump between front and rear wasn't as drastic. I like a little crossover in the gear range from the front to rear.

    If you max out a 48x12, I would suggest learning to pedal faster instead of getting a bigger gear. You should be able to easily hit 30 mph with that combo, assuming a 700c or 29" wheel (faster if actually running a 29" tire). Even with a 26" wheel with a 1.5" tire, you're only up to about 105 rpms to hit 30 mph.

    Also, getting an 11t on the cassette is really going to add a lot of top speed over the 12t.

    Here's a good place to figure out gearing. I use it a lot for figuring out 1x gearing on race bikes or when converting to 1x. Probably actually use it just as much when trying to figure out gear combinations on the single speed.

    BikeCalc.com - Speed at all Cadences for any Gear and Wheel

    And I agree on the craziness of the BB's right now. There are too many darn standards... and wheel size and axle dimensions is just as bad or worse since at least most BB's take one of 2 types of cranks, BSA (24mm axle: gxp, mega-exo, any shimano, etc.) or BB30 (30mm axle).
    BikeCalc.com - Speed at all Cadences for any Gear and Wheel

  16. #16
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    Quote Originally Posted by GTR-33 View Post
    650b? If this is for a commuter/road this is a waste. You want the bike to be easier to pedal and fast? Those are inversely related. You can't have both. If going fast was easy and a matter of getting smaller wheels or a lighter bike, everyone would be fast. Also, 53t was never an option with a 36t cassette on any bike. This bike is going to be terrible. You should really get someone who know what they're doing involved in this project before you start buying more parts.
    just so were clear first post said i was considering a 53/39 initially but is not possible, as this was never going to work in a mtb frame, it was never an option and i dunno where u got that i want easy to pedal (or fast for that matter, its for general commuting), the fact i wanted lower gearing says the opposite, and i also originally stated i dont know what im doing, hence why im posting in a forum first, to learn, not be judged and ridiculed for not being as experienced as u !!

  17. #17
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    Quote Originally Posted by Bikerector View Post
    I agree, 53t is massive for a commuting gear, especially if you plan to carry any gear with you. I liked a compact crank with a larger little ring so like a 36/50 instead of 34/50 as it shifted a little better and the jump between front and rear wasn't as drastic. I like a little crossover in the gear range from the front to rear.

    If you max out a 48x12, I would suggest learning to pedal faster instead of getting a bigger gear. You should be able to easily hit 30 mph with that combo, assuming a 700c or 29" wheel (faster if actually running a 29" tire). Even with a 26" wheel with a 1.5" tire, you're only up to about 105 rpms to hit 30 mph.

    Also, getting an 11t on the cassette is really going to add a lot of top speed over the 12t.

    Here's a good place to figure out gearing. I use it a lot for figuring out 1x gearing on race bikes or when converting to 1x. Probably actually use it just as much when trying to figure out gear combinations on the single speed.

    BikeCalc.com - Speed at all Cadences for any Gear and Wheel

    And I agree on the craziness of the BB's right now. There are too many darn standards... and wheel size and axle dimensions is just as bad or worse since at least most BB's take one of 2 types of cranks, BSA (24mm axle: gxp, mega-exo, any shimano, etc.) or BB30 (30mm axle).
    BikeCalc.com - Speed at all Cadences for any Gear and Wheel
    cheers for the help bro !!

  18. #18
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    I run a 53 chain ring on my commuter with no problems. I usually find myself somewhere around 53x20 with a reasonable cadence. Cassette is 36-12, and the lower gears are great for when I'm doing a grocery haul with the trailer (I'm car free), but still gives me the gearing for group rides. Unless you're going SS, no matter what you choose, you should be okay. Spin when you need to spin, and mash when you need to mash.
    Bourbon: Because no good story ever started with "So, there we were eating salads".

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