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Old 09-24-11, 07:48 AM   #1
SHIM_105
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Are my cranks too long?

I have a Specialized Hard Rock Comp mtn bike with the factory Suntour cranks. I'm 6'1 and have the seat height set so that my legs are dead straight and pretty much locked with my heel on the pedal at the six O'clock position. I have SPD pedals so my knee has a slight bend when I'm actually riding it.

I'm finding that on the up stroke my leg appears to come up to high, and is rather fatigueing. If I set the seat even higher to try and avoid this, then my hips start rocking on the seat. This is the first bike I've ever noticed this on. It's a 21" frame so it's obviously for taller people. You'd think the cranks would be shorter. Is this a normal occurence?
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Old 09-24-11, 08:43 AM   #2
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That's a big frame, I go a size smaller than the charts on a 26er ... I'm 6ft and I'd be on a much smaller frame.

But to your question: look at the inside of the crank arms, the length will be stamped in the crank, probably 175. A smaller guys MTB would probably be 170mm, that's a difference of only 1/5th an inch. Normally if the crank length is wrong you feel it as lack of power at the small end, difficulty spinning at the high end. I suppose it's possible you have custom 180mm crank on that bke, but I doubt it. But the wrong crank length is not a dramatic problem unless you are frequent rider and wired to a certain length.

I suspect you have a general fit problem, like you are way too far forward.
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Old 09-24-11, 09:01 AM   #3
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I was fitted for a road bike and that's a 57cm frame which translated to 22 inches although I don't know if that's a direct translation to a mountain frame. The only issue I know I have is stem length. It's a bit too long, but I knew that from the start. I'll be changing that out. The crank is a 175mm.
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Old 09-24-11, 10:26 AM   #4
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I suspect you have a general fit problem, like you are way too far forward.
+1
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Old 09-24-11, 05:42 PM   #5
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I'm 6'0" and ride a 58cm road bike and a 19" mountain bike. My mountain bikes have 175mm and 180mm crank lengths and I have no issues. Make sure you seat is in the correct forward/back position....a plumb line from the knee cap should line up with the pedal spindle of the forward foot with the pedals level.

The frame size sounds large for your height. Your local bike shop may have some shorter cranks you can try.
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Old 09-25-11, 05:47 AM   #6
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I think my frame is indeed a little to big, and that's my own fault for buying uninformed At the time. However I have made it into a commuter bike, so I'm not doing any real technical riding through trails. The bike is too expensive to lose and I'm not prepared to take a loss selling it. Is there something adjustment wise you think I may be able to do that will compensate for the frame? I.e changing my stem for starters.
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Old 09-25-11, 06:55 AM   #7
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I'm not so sure the frame is too big for you. I am also 6'1", one of my bikes is a 21" frame and fits me quite well, I even once had a 23" GT that I got rid of only because of the lack of standover clearance.
The only thing a smaller frame will do is give you a more cramped cockpit, which seems to me will make your problem worse, not better.
The KOPS (knee over pedal spindle) method mentioned by helifitz isn't absolute but it's a good starting point. A shorter and possibly higher rise stem may be in order. I still believe FrenchFit had it right, your saddle is too far forward. If you run out of adjustment on that then you can get a setback seatpost if necessary.

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Old 09-25-11, 08:06 AM   #8
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I took frenchfits advice and moved the seat back. I'm actually a bit further back than plumb and it feels much, much better. Now for sure I need a shorter stem. I believe I have an 80 or 90 mm fairly shallow rise on there now. Do you think I should go with a 40 or 50 something, with a steep angle? I do want the bars higher and closer.
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Old 09-25-11, 08:26 AM   #9
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Yes, you can do this. Remember, you are talking about fitting to a frame that's too big, so the geometry of the bike is all screwed up for you no matter what. Your CoG (center of gravity) will always be too far back. That said:

You can go with a riser bar and stubby stem, (say 50mm). Titec makes (made) cool blockhead stubby stems in different sizes, some with an aggressive rise. Very strong. Search eBay, they're cheap. Same with eXotic riser bars. And, you can add spacers under the stem.

Oh, and as far as KOPS position, lots of MTBers are behind the spindle. It's a mashing position, if you knees aren't complaining you're fine. Spinning up grades and sprinting isn't going to be your thing, you'll be standing.

Last edited by FrenchFit; 09-25-11 at 08:32 AM.
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Old 09-25-11, 09:59 AM   #10
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Remember, you are talking about fitting to a frame that's too big, so the geometry of the bike is all screwed up for you no matter what. Your CoG (center of gravity) will always be too far back.

Oh, and as far as KOPS position, lots of MTBers are behind the spindle. It's a mashing position, if you knees aren't complaining you're fine. Spinning up grades and sprinting isn't going to be your thing, you'll be standing.
OP said it's (now) a commuter bike, so most of that probably won't matter much.
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Old 09-26-11, 12:47 PM   #11
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Went for a fairly long ride today with the new Nimbus road tires and the new seat adjustment. Bike was perfect. Felt awesome. No fatigue at all. I just need to sort the stem out and it will be bang on. Frame size now feels great, and quite comfortable. I'm not jammed up on it at all. Cant belieave a 1/2 seat adjustment can make that much difference
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Old 09-30-11, 04:50 PM   #12
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Ya baby!

After you pull the cockpit backward just remember.. if you tackle a gnarly dirt hill that front end is likely to jump up into your face .. Hi-yo Silver!

Happy trails.
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Old 10-03-11, 07:50 AM   #13
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Glad to hear it's all worked out!
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