Looking at a set of wheels that comes with an 11-speed SRAM/Shimano compatible hub. Seller says that a spacer is included in case buyer wants to use with a 10-speed cassette. I've not done much research into 11-speed systems, so not familar with specs. Is it common/ok to use an "11-speed" hub with a 10-speed cassette? Assuming use of proper spacer, of course. Downsides?
Generally speaking 11s hubs build to weaker wheels than 10s hubs due to their flange offset, all else kept equal. There are exceptions though, so each case its best to be analyzed separately.
Would this "weakness" be perceptible to the rider?
It depends. It depends on the forces the wheel is subjected to (rider weight and riding style), it depends on the number and type of spokes, it depends on the rim selection and maybe to a considerably smaller degree on the lacing chosen(certain lacing patterns result to higher tension ratios).
Typically, the lesser the rider weight and the lesser the rider output, the less one has to worry about this. The higher the rider weight and the higher the rider output, the more hub, rim and spoke selection become paramount in safeguarding the integrity of the wheel.
