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  1. #1
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    Anyone else have this problem?

    I love my 2011 Mojo HD but I am *constantly* banging the pedals on rocks.

    Does this bike have exceptionally low clearance or something?

    Going up some technical rocky sections it is almost assured that I will hit a pedal.

    I am running the Rockshox Lyrik RC2 DH Solo Air 170mm and pedals are some old Shimano 747s.

    I even bumped up my shock pressure just a touch to lessen the sag.

    So annoying.

  2. #2
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    650b wheels raised the BB and cured that frequent pedal strike irritation and momentum killing problem for me.

    However, only the HD140 is sanctioned for use with 650b by Ibis, needing no mods. But the HD160 won't clear the seat tube with 650b without limiting bottom travel by (very easily) adding shock bottom-out shims, to leave a little more than 150mm or 155mm travel, Gen-1 or Gen-2 HD160 respectively.

    The 1/4 to 1/2 inch higher BB with 650b depending on tire height difference, allows deep sag as the HD likes for rough trail. And obviously the bigger 650b wheels roll the rocks easier than any 26 inch wheel, and the HD feels like it has 1 inch added bump travel without adding wallow.

  3. #3
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    I run in the 140 and don't seem to have that issue.

  4. #4
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    Nope and I ride a lot of rocky terrain.

  5. #5
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    No problem with pedal strikes here. Pushing a slightly harder gear for better momentum and timimg pedal stroke to avoid rocks goes along way.

  6. #6
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    Thanks for the input.

    Does anyone suggest switching to a 170mm crank? My last bike was a SC Nomad and I'm pretty sure I had 170mm cranks on there. I don't recall hitting my pedals/cranks on stuff during the three years I rode that bike.

    This Ibis has 175mm crank arms. I rode Tamarancho on Friday and must have hit the pedals/cranks on rocks 4 different times.

    Sort of frustrating to have spent $6K+ on a bike I am not completely happy with.

  7. #7
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    Try 170 cranks. You could also run a 650b up front.

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    Occaisionally, but its really down to two things IMO
    1. Technique which I suck at on tech climbs
    and
    2. RP23 which wallows. I have run a vivid coil and now a Marzocchi Roco air TST and the issue has all but disappeared.
    Others will no doubt disagree but I have always felt that to get the RP23 to feel ok on the descents you end up with lower pressure, more sag and pedal strikes

  9. #9
    Kaj
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    did you just get the bike? I find it takes some riders several months of riding to adjust their clearance eyeballs even a few mm's. The HD's BB is avg for it's category, but if you last bike was a bit higher it takes an adjustment period.

    Also going with 170's would make a huge diff, as 5mm is a lot of clearance to your "clearance eyeballs". but I wouldn't do that unless you are 5'8" or so or under.
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  10. #10
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    Quote Originally Posted by nzl62 View Post
    Occaisionally, but its really down to two things IMO
    1. Technique which I suck at on tech climbs
    and
    2. RP23 which wallows. I have run a vivid coil and now a Marzocchi Roco air TST and the issue has all but disappeared.
    Others will no doubt disagree but I have always felt that to get the RP23 to feel ok on the descents you end up with lower pressure, more sag and pedal strikes
    I have a DHX Air on my bike but maybe I should double-check the settings (groan) on it anyway.

    As to my climbing technique, not sure. I've definitely lost some of the skills I had when I lived in Austin, TX but certainly am no slouch.

  11. #11
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    Quote Originally Posted by Kaj View Post
    did you just get the bike? I find it takes some riders several months of riding to adjust their clearance eyeballs even a few mm's. The HD's BB is avg for it's category, but if you last bike was a bit higher it takes an adjustment period.

    Also going with 170's would make a huge diff, as 5mm is a lot of clearance to your "clearance eyeballs". but I wouldn't do that unless you are 5'8" or so or under.
    I got it last year. I probably have about 30-40 rides on her. Couple trips to Downieville, many weekend rides at Skeggs, China Camp, Joaquin Miller.

    I am trying to ride more technical trails though (bored out of my mind with Skeggs) so maybe I am just not used to technical riding.

    I am 5'11" with 31" inseam. I'll probably just try the shorter cranks.

  12. #12
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    The hd160 has a relatively average height bottom.bracket for a 6 inch bike. The hd140 however is pretty low. Sounds to.be like its user error. I ride tamarancho often and with good pedal timing I never get rock strikes, on my hd.

  13. #13
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    I've used both 170 and 175mm cranks on the same trail bike, decades ago. At 6'0, 195 to 200 lbs, with much climbing around my local rides, I found 175mm worked better.

    Longer cranks increase torque (climbing, acceleration) power in the same gear. The difference is most noticeable doing steep climbing. Longer cranks help climbing and rough trail momentum without downshifting.

    A 5mm shorter crank adds nearly 1/4 inch pedal clearance, but also raises the rider weight center the same 5mm if maintaining the same reach.

  14. #14
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    Quote Originally Posted by Yody View Post
    The hd160 has a relatively average height bottom.bracket for a 6 inch bike. The hd140 however is pretty low. Sounds to.be like its user error. I ride tamarancho often and with good pedal timing I never get rock strikes, on my hd.
    User error!? Them thar are fighting words! J/K

    I fail to see how someone could time their pedal strokes when one sees a short, rocky uphill in ahead and has to respond with picking the best line and giving it a burst of power. I'm not saying that timing your pedal strokes is not important. I am saying that I don't think that is the issue here.

    I've been riding about 20 years. I don't want to blow my own horn but I'm not bad. I am a geezer (44yo) yet I can do Downieville sub-50 minutes (no problems clearing the rock garden either). Many technical sections of the trail that give typical riders problems (for example, the big rocky section on Alchemist) are easy-peasy to me. Just sayin' I'm no slouch and I don't think this problem is about my riding skills.

    I'll try the putting some more air in the shock/forks and grab a pair of 170mm cranks and see if that makes a difference.

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    Sorry, didnt mean to be harsh. Its likely I just know the trails well but I do plenty of climbing at both annadel and tamarancho and with the bike at 160, I pretty much never strike rocks and run over 30% sag. when ran in the 140 mode, I strike all the time, which is my fault, but ive also hit rocks with pedals in corners, which isnt worth the tradeoff to me, too low.

  16. #16
    Kaj
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    Quote Originally Posted by derby View Post
    I've used both 170 and 175mm cranks on the same trail bike, decades ago. At 6'0, 195 to 200 lbs, with much climbing around my local rides, I found 175mm worked better.

    Longer cranks increase torque (climbing, acceleration) power in the same gear. The difference is most noticeable doing steep climbing. Longer cranks help climbing and rough trail momentum without downshifting.

    A 5mm shorter crank adds nearly 1/4 inch pedal clearance, but also raises the rider weight center the same 5mm if maintaining the same reach.
    Agree with you Derby, I wouldn't go below 175 unless you need it for your leg length. Most people over 5'8" will like 175's better, but not all. I personally like 180's on my mtb (saddle height of 83cm's) but I trade off and ride 175's to get fewer pedal strikes.

    but then again, crank length is like saddles there is no right solution for anyone
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  17. #17
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    Quote Originally Posted by camus View Post
    I have a DHX Air on my bike but maybe I should double-check the settings (groan) on it anyway.
    ....
    I haven't ridden the HD with the DHX Air. Although many other riders have reported the DHX Air easily compresses or "blows" through mid travel with deep wallow when riding rocky conditions. Some have reported improvement adding air can volume reduction shims inside the air can, for the shock to ramp up resistance sooner in mid travel and resist bottom travel more without loss of small bump smoothness. Fox sells a shim kit.

    Under 50 second Downieville is near record speed. Wow! Very few pro racers have recorded sub 50's there.

  18. #18
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    Quote Originally Posted by derby View Post
    I haven't ridden the HD with the DHX Air. Although many other riders have reported the DHX Air easily compresses or "blows" through mid travel with deep wallow when riding rocky conditions. Some have reported improvement adding air can volume reduction shims inside the air can, for the shock to ramp up resistance sooner in mid travel and resist bottom travel more without loss of small bump smoothness. Fox sells a shim kit.

    Under 50 second Downieville is near record speed. Wow! Very few pro racers have recorded sub 50's there.
    Thanks. I'll have to look into the shim kit. It does seem to wallow at times.

    Yes, 50 seconds down the mountain would definitely be fast!

    In all seriousness, I did an official race time (geezer class) of 54 minutes several years ago on a first generation SC Bullit. Would have done a lot better but I took a wrong turn at the very last section of the trail, where you come through the fence and it you're at the fire road) and went down to the riverbank. (Still irritated that the race organizers did not put tape across that section). Took a few minutes to push my bike up to the trail and resume the race.

    I haven't timed myself officially and I could be wrong, but on a much better bike and knowing the trail much better than back then I assume I am doing better times. Looking forward to heading up there in a few weeks and hoping that Strava works.

    BTW, I thought the pros were doing DV runs in the mid-30 minute range these last few years. But I very well could be mistaken. The dementia is getting worse and the beer drinking doesn't seem to be helping it.

  19. #19
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    The 30 minute times last year were on the snow shortened course. They are still running in the 43's on the full course.

  20. #20
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    How much sag are you running? I'm running a 140mhd w/650b's 25% sag and have very few pedal strikes.. As said timing is your friend but you've been riding for a while so I would doubt that would be a issue... Too much sag or not enough compression dampening might having you blow through Tavel a bit to easy and lead to pedal strikes...I would be very surprised If your sc shipped with 170 cranks unless you ordered it like that..my guess is your sitting a bit far into the travel and just a catching those pedals..
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  21. #21
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    Quote Originally Posted by derby;9565045A
    5mm shorter crank adds nearly 1/4 inch pedal clearance, but also raises the rider weight center the same 5mm if maintaining the same reach.
    HUH? how does a shorter crank raise the riders weight center? I'm confused. This would only be true when one crank arm is at the lowest point.

    I'm 5'9" and went to a 170mm crank cause I ride in rocky terrain and spin more. Personally I like the shorter crank see more advantages with it. Use to bash my cranks all the time with 175mm, then got a bike that came with shorter cranks and haven't looked back since.

    IMO shorter cranks work better with bikes with a lower BB. When I was ordering my bike from Ibis I was a little surprised they didn't offer shorter cranks.

    The difference in length translates to about 3%
    Last edited by gunnirider; 08-06-2012 at 08:52 AM.

  22. #22
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    It raises the rider's center of gravity if you adjust the pedals to have the same leg extension (i.e. knee angle) when the pedal is at its lowest. The lowest point is now 170mm below the BB spindle vs. 175mm with the longer crank.
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  23. #23
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    Quote Originally Posted by slideways666 View Post
    How much sag are you running? I'm running a 140mhd w/650b's 25% sag and have very few pedal strikes.. As said timing is your friend but you've been riding for a while so I would doubt that would be a issue... Too much sag or not enough compression dampening might having you blow through Tavel a bit to easy and lead to pedal strikes...I would be very surprised If your sc shipped with 170 cranks unless you ordered it like that..my guess is your sitting a bit far into the travel and just a catching those pedals..
    I am running 30% sag.

    When I got my Nomad it had some RaceFace boat anchor cranks on it. I ordered some XT cranks off flea-bay and didn't even realize they were 170mm. Threw 'em on and rode for 3 years without issue.

    When I first got the bike I was running more PSI in the shock and fork but found I was really getting beat up on rough descents, especially compared to my old Nomad with coil suspension. Decreased the PSI and it descended much better.

    I've been riding more technical trails lately so it is only recently this issue has come up.

    I'll futz around with the pressure and settings a bit on the suspension and see if I can find a cheap set of used XT 170mm.

  24. #24
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    Nope...and I run my front at 140 when riding up......pick a better line when climbing.

  25. #25
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    Quote Originally Posted by DRSpalding View Post
    It raises the rider's center of gravity if you adjust the pedals to have the same leg extension (i.e. knee angle) when the pedal is at its lowest. The lowest point is now 170mm below the BB spindle vs. 175mm with the longer crank.
    The lowest point has moved up 5mm, but the highest point has also moved 5mm down. That should cancel it out, so that there is no change in CG.

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