If you don't run the shim you may damage the sole of the shoe, thus voiding any warranty. You probably won't notice a difference in engagement, but twisting out of the pedal is were you'll meet resistance with the pedal body. I have Lake shoes that also recommend a shim. I used Lake's guide to determine if I needed the shims, which they say you do. I mounted the cleats to my desired position, and then measured the clearance. I had 2mm between the cleat and ground, so not ideal. The lugs on my Lake shoes aren't stiff though, so I gave it a shot as I didn't want to wait for or hunt down shims. XTR Trail pedals BTW, and although I did notice the interference on disengagement, it wasn't to the point were I was concerned, only 1mm difference but some interference with the pedal body. If your Ride Concept shoes are flat sole, I recommend the shims. If they are a more XC lug type sole you may be able to get by without. If your pedal isn't platform or caged, less pedal body interference too.

For Reference - Lake Cleat Guide

One final note. In order for proper cleat engagement adjustability to the pedal, you don't want interference with the pedal.

 

Thank you very much . It cleared things up. What spacer did you use? I saw crank brothers have a 2 hole spacer usuable with the SH 51/56 pedals and shimano has a 1 mm elongated ronded edged rectangle . I have the latter at home . Do you have any other suggestions?

 

I've used the Shimano type with success, and one underneath the cleat is all I've ever needed. I'm not sure the cleat bolt is adequate length to stack two, but the spacers are stackable in any case. I prefer the rear point of the cleat aligned with the slot cut-out for my rides, if you're riding mostly flow you can slam them to the rear for best support. I add silicon seal to keep the debris out of the slots and spike holes if my shoes came without spikes, the screws in the spike holes don't help on the rocks. I prefer no spikes these days as they wear fast in the granite, although on some soil they do add traction if you have to hike-a-bike. I saw a hack for filling in the hex hole with candle wax to keep muck out too, kind of overkill to me, but hey! I've been wearing the lugged XC type shoes for years now, and I'm finding flat soles are more comfortable on and off the bike. My pedals have been Shimano SPD's for many years, all models. I usually turn the cleat adjustment on the pedals all the way out and then two turns in on initial use and adjust in from there. I'm currently riding flats with Ride Concept Talluc and my casual shoes are Vice. I'm considering Talluc flats with clips next. I wear medium volumn with a half size up, because frog feet!