Wheelspin Posted March 1, 2012 Share I'm fairly new to MTB'ing and have just got onto a 2010 Giant Trance X3 after fiddling around for few years on an old Giant hardtail. I love the bike but suddenly I seem to be hitting rocks and the ridges of grooved paths with the pedals with shocking regularity. I'm not sure what the crank lengths are now but would shorter cranks solve the problem and what would be the consequences ? I've got the 120mm travel suspension front and rear set at 25% sag. Any advice appreciated. Link to comment Share on other sites More sharing options...
MrJacques Posted March 1, 2012 Share How tall are you? Crank length is usually matched to length, specifically inseam length. Link to comment Share on other sites More sharing options...
Pappa Bear Posted March 1, 2012 Share You are hitting the rocks because you are now riding a full suspension bike. Remember that when your suspension works your BB actual drops...... You just need to pay a bit more attention to the trail :-) After a couple of rides you would be used to the BB dropping and "anticipating" the BB drop will be second nature. Dubber88 1 Link to comment Share on other sites More sharing options...
Wheelspin Posted March 1, 2012 Share Thanks for advice, much appreciated. Yup the suspension is playing a big part but I still think I'm going to check out shorter cranks. The amount of hits I had was ridiculous. I had a look on the web at what cranks I should be using according to my leg inseam measurement and came up with 166 mm. Tonight I'm going to see what length the existing cranks are - should be in the region of 175 mm ??? so by going to 165mm cranks I could raise my pedal height by 1 cm. Then if I set my sag to 20% instead of 25% I could raise the pedal height by another 5 mm giving a total pedal raise of 1.5 cm. The pedals I'm using are also quite thick so maybe a could save another 5 mm there. What do you guys think ? Will 2 cm make a difference ? Link to comment Share on other sites More sharing options...
Caerus Posted March 1, 2012 Share I think maybe look at the way you are riding first before getting a new crankset or arms. Especially choosing the right lines, a full suspension bike makes you a bit lazier on the trails in my opinion, cause you just think the suspension will take it. I also ride a Trance and it does happen from time to time. I'm 1.8m and have 175mm cranks on my Trance. Don't forget momentum is your friend, so instead of pedalling, rather roll over the obstacles with your cranks parallel to the ground. Link to comment Share on other sites More sharing options...
The Drongo Posted March 1, 2012 Share I'm fairly new to MTB'ing and have just got onto a 2010 Giant Trance X3 after fiddling around for few years on an old Giant hardtail. I love the bike but suddenly I seem to be hitting rocks and the ridges of grooved paths with the pedals with shocking regularity. I'm not sure what the crank lengths are now but would shorter cranks solve the problem and what would be the consequences ? I've got the 120mm travel suspension front and rear set at 25% sag. Any advice appreciated. Crankspin... What shock you got on that Buysickle? Link to comment Share on other sites More sharing options...
andydude Posted March 1, 2012 Share As far as I understand, your crank length shouldn't only be based on your length/inseam, but also on the build of your legs/your strength. Generally, bigger legs could mean a longer crank would be better for you. You say according to your inseam that your crank must be 166mm, but the muscle structure of your legs might indicate a crank length of 180mm! Link to comment Share on other sites More sharing options...
Bike Mob Posted March 1, 2012 Share What size bike, how tall are you? The BB drop is the issue and not your crank arms 99% of the time. You need to anticipate the bb drop and crank rotation when riding the trail, you cant just steam roll willy nilly and expect nothing to get in your way. It's a mountain after all and that's why we ride on it. Your bike was specced with those cranks for a reason from the manufacturer. Unless you are riding an XXS I doubt you need 165mm cranks. Edited March 1, 2012 by Tarmac's Revenge Link to comment Share on other sites More sharing options...
Azonic Posted March 1, 2012 Share If your crank arms are hitting you should try work on knowing when you should pedal or when to freewheel. I'm not sure how long you have been riding, but after a couple of years on the bike you can tell instinctively whether your pedal will clear an object many pedal strokes before you get to the obstacle. My XC bike has 100m travel and I use 180mm cranks and rarely hit rocks. Link to comment Share on other sites More sharing options...
Caerus Posted March 1, 2012 Share As far as I understand, your crank length shouldn't only be based on your length/inseam, but also on the build of your legs/your strength. Generally, bigger legs could mean a longer crank would be better for you. You say according to your inseam that your crank must be 166mm, but the muscle structure of your legs might indicate a crank length of 180mm! The funny thing about this, after doing much reading and research is that most people won't even know the difference. Link to comment Share on other sites More sharing options...
MoreTrails Posted March 1, 2012 Share Trance is more of a trail bike, so its all about getting to the top so you can actually come down. Hitting the rocks will be cause you are new to a full sus and it takes a couple runs to get used to the bb height dropping. Now changing cranks for a trail bike is not a bad idea...175mm cranks are so called standard and give good pedal efficiency, but one does tend to clip them on stuff. Changing to a 170mm crank will make a world of difference but will not be the "be all and end all" to the problem. 5mm, I know, unbelievable. But it works.... Changing to 165mm cranks will be great for going down but murder going up...yes it makes that much difference. You can't generate as much leverage on the pedal stroke and pedaling will become uncomfortable on the ups or when you need to put in big effort. My 2c... Link to comment Share on other sites More sharing options...
MrJacques Posted March 1, 2012 Share Raising the bb height will also have an effect on the handling. From what I've heard a lower bb height should be more stable. Link to comment Share on other sites More sharing options...
Caerus Posted March 1, 2012 Share I came across this article. Link to comment Share on other sites More sharing options...
JA-Q001 Posted March 1, 2012 Share Okei whaoh! before you start thinking of something like changing crank length to stop it from hitting rocks, you should start thinking beyond only the length! Remember, longer cranks gives better leverage, something you need to get over small bumps and climbs. Going drastically shorter could drop your efficiency on the bike. There are numerous things to look at to stop this problem, cheapest is fitting a size bigger tyre, this could also give you a 10mm lift easily. setting your sag to maybe 18%, also a quick fix. Mainly, check your riding style, maybe riding lighter rather that heavier on these parts of the route? Edited March 1, 2012 by JA-Q001 Link to comment Share on other sites More sharing options...
andydude Posted March 2, 2012 Share I came across this article. Very interesting website! Now who to believe and who not?! According to his formula I need a crank length of approximately 190mm compared to my current 175mm Link to comment Share on other sites More sharing options...
Wheelspin Posted March 5, 2012 Share Thank you all for all the great input. As most of you advise, I'm going to hang in a while and see how things how things develop. This weekend I changed the sag from 25% to 20% and had and awesome ride from Van Galens up to the Greek Church. Didn't have nearly as much of pedal grounding problem as I had up and down Braamfoentien Spruit the week before. Link to comment Share on other sites More sharing options...
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