Technical FAQ: Shoes and cleats

  • By Lennard Zinn
  • Published Aug. 5, 2014

This Specialized Body Geometry “-1.5mm valgus shim” goes in my left road shoe under the orthotic. Photo: Lennard Zinn |

The Body Geometry -1.5mm valgus shim is 2.5mm thick on its lateral (little-toe side) edge and 1mm thick on the medial side, to lift the lateral edge of my foot 1.5mm higher than the medial edge. Photo: Lennard Zinn |

I use a Body Geometry -1.5mm valgus shim in the left shoe of all of my mountain bike and road shoes. That is not a shim under my cleat; that is a Crank Brothers “Shoe Shield” to protect the carbon shoe sole from the pedal spring clips. Photo: Lennard Zinn |

Dear Lennard,
I have a slight leg-length difference (3/8″) and the LeMond wedge system has helped on my road shoes. But what can be done for mountain bike shoes?
— Jim

Dear Jim,
Good question. Wedges and shims like yours placed under the cleat work on road shoes because the pedal not only grabs the cleat, but it also supports the cleat. That is not the case with mountain bike shoes, because the pedal supports not the cleat but rather the shoe tread knobs.

This is especially true on Crank Brothers pedals, which I use, and I would think would be similar on Time pedals as well. With these pedals, the cleat needs to be at the proper height relative to the shoe tread for the pedal to work properly. If the Crank Brothers cleat is raised relative to the shoe sole, when you stomp down hard on the pedal, you’ll spring the pedal’s spring clips open further. Besides giving away some of your pedaling power in prying open the spring, it will give you a noisy, moving, less-secure shoe/pedal interface. So, if you raise the cleat off of the shoe sole with a shim, or if you cant the cleat at an angle with a cleat wedge, it will not lift your shoe or cant it unless you put a huge stack under there, but then you’d be teetering on the center of the pedal.

You can buy little two-hole MTB-shoe cleat wedges and shims, but, having tried them, I cannot recommend them for Crank Brothers (or probably for Time) pedals. Perhaps the shims work on Shimano SPD pedals, but the interface is so small that I can’t see the wedges having enough leverage to cant the foot. Shimming an SPD cleat higher would still result in a feeling of teetering on the pedal, I would think, unless you were to also build up the height of the shoe knobs at the same time, so the shoe could be supported on its medial and lateral edges and not just in the center.

To raise your foot higher off of a mountain bike pedal, I recommend using a shim under your insole or orthotic inside of your shoe. Obviously, you can’t raise it up much or you won’t be able to fit your foot inside the shoe. The same goes with wedges or cants — you can put a wedge under the forefoot of your insole or orthotic to tip your foot at an angle relative to the pedal — see the photos.

If you only need a small height or angular correction, using in-shoe shims or wedges is actually an advantage, I believe, because it makes it easier to set up and switch shoes. I use a Specialized Body Geometry “-1.5mm valgus shim” in my left shoe under my orthotic to lift the lateral (little-toe side) of my foot 1.5mm higher than the medial side. I can use this wedge shim (a.k.a. “cant”) in any pair of shoes, road or mountain, without having to put anything under the cleat when installing it.

Unfortunately, in your case, you don’t have a “slight” length difference at all; 3/8” is 9.5mm — almost a full centimeter! You can’t put something that thick under your insole. You could probably put another insole or two under your existing one, which might give you 4-5mm of additional height.

You may not have to lift your foot the full 9.5mm, however. If your leg-length discrepancy is entirely in the lower leg, then, yes, you want your foot 9.5mm higher off of the pedal on the short side. But if your leg-length discrepancy is instead entirely in the upper leg, then you would want to do a combination of shimming under the insole on the short side and putting the long-side foot deeper into the pedal (moving its cleat further back) and the opposite with the short-side foot (moving its cleat further forward). In that case, shimming inside of your shoe might be sufficient.

If indeed your leg-length discrepancy is entirely in the lower leg, then I suppose your best alternative is to stack up 9.5mm worth of BikeFit SPD shims and somehow build up your shoe treads by 9.5mm on either side of the cleat. If you have Crank Brothers Eggbeaters, you could wrap 9.5mm of duct tape around the pedal body on either side of the spring. You would be doing to do this very frequently with a layer of tape that thick. Crank Brothers does offer clip-on pedal shims to go on both ends of either Eggbeater or Candy pedals, but none of them are close to 9.5mm thick.
— Lennard

Dear Lennard,
My feet aren’t quite the same size (half-size difference) and I have difficulty mounting my Look cleats in such a way that my metatarsus are both correctly positioned.

My smaller right foot is too forward and my pedal stroke is compromised by this.

Do you know which brands produce cleats that allow for more longitudinal adjustment? Time, Mavic, Speedplay? I know that my S-Works shoes have cleat mounts that are quite ‘backward’ so that doesn’t help either.
— Marten

Dear Marten,
Speedplay offers the most longitudinal cleat adjustment. It offers a cleat extender base plate kit. I use these on all of my road shoes to move my cleat 14mm further back than I otherwise could get it.

I guess in your case, you’d need to mount your left foot further back with the extender plates, drop your saddle accordingly, and then mount the right cleat in a more standard position. In order to get the same spindle-to-sole distance on both shoes, you might need to put a shim from the “leg length shim kit” found on that same Speedplay web store under the right cleat.
— Lennard

Dear Lennard,
I’m shopping for a new mountain bike — a trail bike to replace my XC bike that has stripped me of all confidence after moving to Colorado from Michigan. I will never use a trail bike even close to its full potential (i.e., I prefer my tires on the ground at all times), but living in Colorado, I really want the stability of a trail bike.

My question: I’m looking at the SRAM XX1 on a Niner Rip 9 RDO that would allow a granny gear. Using a Wolf Tooth 26t chainring in front with the SRAM 42t cog in back, I would have a great granny gear for climbing. The problem I foresee is that I would do most of my climbing in the 42t cog in back, because the next gear is a fairly big jump to a 36t. Since the cassette is a one-piece deal, I’m concerned I’d wear out the 42t cog far earlier than the other cogs and then have the $400+ replacement cost on the cassette with most of the cogs like new. Some of my concern is based on use and some on my assumption that the sweet spot for optimal alignment with the chainring is somewhere in the middle of the cassette. Would you share my concern?
— Janice

Answer from SRAM:
I wouldn’t worry about the 42t tooth cog wearing, but she will see some wear on the ring. That’s a pretty low gear, and I don’t think she will spend as much time there as she thinks. As always, the single most important thing you can do is clean and lube your chain for optimum performance and durability of your drivetrain.
— Chris Hilton
SRAM mountain bike product manager

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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