Cross-posting from shorter crank thread

[sfscott]

I run 170s on road bikes.

My MTB has 175, which was kind of the default size available. I am having a lot of issues with pedal strikes, particularly on abrupt inclines after declines (rollers.)

I have added a fair bit of air to my rear shock, which should lift the BB up some, and a tech at the LBS suggested riding with the rear shock in "trail" setting.

Wondering if a move to 170s would help the pedal strikes--and what I reallywould be losing in leverage.

[stien]

My initial thought is that technique has a lot to do with avoiding strikes in the woods. You wouldn't be giving up much swapping to 170s. Swapping pedals might help too if you want to go down this route.

[ultraman6970]

How tall are you? that just to start... second issue IMO because I dont know you is... how is your pedaling technique? Some guys no matter what lenght of crank they use they wont pedal rounded ever.

If you can pedal round in a road bike the question is why you cant in the MTB bike? If you have the problem in both bikes using even different crankset lenghts then clearly is a technique problem.

If you use the cleats all the way to the middle (or back) then that could be part of your problem IMO. Foot is more stable but you cant round the pedaling too much specially with super light gearing because you cant spin. Middle foot or all the way back cleats gives you more power and stabilize the foot better but you lose agility and grace at the time of spin in other words you can't spin well, or in other words the pedaling is not too rounded. IME and IMO ok? other guys could think something else.

[sfscott]

I am sure that my pedal stroke could be improved. I could share with people the data that comes off of my Vector pedals, which I don't exactly know how to interpret. Or how to share for that matter.

I recently moved my cleats back vs. traditional road placement because when descending and standing out of the saddle with pedals level, having the cleat further back seems to provide me with better balance/control and is more comfortable/less fatiguing on long downhills. I tend to ride off of ski lifts primarily, but in some XC sections, I get into trouble.

Being a heavy dude, suspension adjustments and closing off some of the rear travel will help some, I think because I was probably compressing so much that the BB was getting too low.

And I am 5-7 riding a medium MTB frame with a DW-link rear (Ibis Mojo 3)

[ultraman6970]

Im a road ex tracker guy, and my experience in MTB is close to null...

The data could help if somebody can read what it means you know, personally im too old for those new things

As for the line about moving the cleats back to get more control in downhills, I'm not sure about that because is do not do mtb.... i imagine your legs get more extended, etc etc... IMO. if you put shorter cranks the further back cleat situation you have going on will change at some extent, how much no idea.

Sure some of the MTB guys can help you a lot more than me because my experience in MTB is pretty much zero, specially with the things that defy common sense

[fmradio516]

Are you bottoming out of travel on your shock? If so, check with the shock manufacturer if you can add a volume spacer, that should help. Also low profile pedals may help as well.

And im sure the bike shop would have mentioned it if it were possible, but some mtn bike frames have something built in usually called a "flip chip" which basically changes the geometry of the frame including raising the BB height for "trail mode" in order to help with pedal strikes.

[Moyboy]

if it's happening on rollers from declines to inclines your fork might be too plush as was mentioned above.... 170mm will help only a little.

[Gummee]

I had a carbon HT with a 'lower than I'm used to BB' and I'd still get pedal strikes using the same length cranks I've used since I could buy em: 170mm

Sometimes it's about the geometry and adjusting your pedaling

M

[benb]

This has 0 to do with any of your gear and 100% is your pedaling technique.

If you're hitting rocks with your pedals changing to 170mm cranks will only get you 5mm of extra clearance!

Your shock needs to be setup to work correctly, not to try and jack the bike up to get clearance.

My pedal strikes were horrible when I started riding MTB and I almost never pedal strike these days (we're talking 20 years). It's all about timing which pedal is down at a given time so you always have the pedal out of the way of the rocks on that side of the bike. Knowing the trail & not riding ahead of your limits is a big part of it too.

It's not road where you churn the pedals non-stop... you can back pedal and pedal a 1/4-1/2 stroke in strategic places, or just stop pedaling and hold the pedals horizontal, etc.. if you have the right momentum. Nailing a curve just right and hitting a transition just right you will distance yourself without even pedaling from someone behind you who is pedaling madly but not getting the technique right.

That said if you're striking the pedal on these rollers and you're striking it on the ground and not a rock it sounds like maybe you really might be running insufficient sag on the fork/shock. But if the change from decline to incline is that sharp you might be better served by BMX/Skateboard style "pumping" rather than sitting and trying to pedal through. Instead of sitting & pedaling get out of the saddle & put the pedals horizontal and then sink your weight into the transition and then spring back out as the bike starts to go up. This is the same thing you see BMX guys & skateboarders on the half pipe doing where they seem to defy the laws of physics and speed up in the half pipe without pedaling or pushing. A lot of the places you're talking about you get very little benefit from pedaling vs "pumping".

Great explanation here:

https://www.imbikemag.com/technique/skills/pumping/

I'm not sure how hard this stuff is to learn as an adult. I learned to bike when I was like 5 and probably knew how to pump by 6 without having any idea what I was doing.