I have tried quite a number of knee/shin pads. in order of best to worst. I will only wear a slip on pad with straps as well or they just wont play in place in a crash.
1. Race Face Flank
2. THE Storm ( pain in the *** to get on and off and wore out quickly, but super light and stay in place )
3. Thor Force ( bit bulky, lots of chafing from the velcro if worn right next to skin )
4. 661 EVO ( fall apart quickly but they are comfortable and stay in place, no shin protection )
worthless...
5. EVS Pastrana ( Super light, but don't stay in place, velcro chafes )
6. Anything resembling those Fox ones above where the knee cap is just floating...doesn't work at all.
I don't snowmobile yet. but I ride XC Moto, and do mountain biking.
The only pads that have ever stayed in place for me in a crash are the full wrap ones with straps... all others just get knocked out of place when you wreck and are worthless.
I use these for Moto and Mountain biking, Race Face Flank's with d30 ( that soft stuff that hardens instantly on impact ).
Mine are an older version of these that fully wrap around my leg like a neoprene sock.. Im not sure it sounds like their new ones don't do that though which sucks!..
http://www.raceface.com/guards/legs/flank-leg/
These are the older full wrap ones I have
http://www.chainreactioncycles.com/us/en/raceface-flank-lw-leg-guards-2012/rp-prod67500