Here is the one I used with the wheel on trainer - the thinner tyres sit right down to the bottom of the ‘groove’ and the bigger (mtb) tyres sit on the shoulder
Only ever used it with a 700c x23 tyre, so can’t comment on how effective it is for an mtb tyre, but that is the design intent
The existing Saris block is fine with the MTB tire but not the sew-up on my racer. The upright nature of the MTB handlebars put it at a comfortable height but the racer handlebars sit much lower.
Here is a picture of another model Saris block showing the height off the ground. This model offers three different heights
Ok I am an idiot… I forgot we where talking wheel on trainers here 
Should be universal other than rider preference.
But that’s more about bike configuration, meaning your bike should be set up how you like it to feel and that bike configuration wouldn’t change from indoor to outdoor. Now, if you happen to like an upright position indoor and less so outdoor, then this makes sense. Pretty sure you have reasonable wind aerodynamics indoors :), so being bent over is not such an advantage other than keeping your training position the same.
That’s just it, a wheel-on trainer will always elevate the rear wheel so should not the front also be elevated? If I modify the block with a filler or get a different block that fits the sew-up better I can keep a comfortable height.
I wonder if those that don’t use any block do so to keep stress off the front wheel and forks.
.
Yes, without blocks is mostly wheel off. You should have a block that gets it to a similar height. Whatever’s comfortable for you is what I would suggest. That could be a bigger block than higher than the back wheel if you want. Obviously, that can be anything. It can be some duct tape books.
Having both wheels the same height above the floor makes sense to me.
I haven’t put this through a proper long workout yet, but I set up a tennis ball style rocker plate design I picked up through Etsy. I can’t say with 100% confidence, but I think this is going to help with saddle discomfort during longer rides. I can say it has motion and is more compliant for sure, but whether that reduces discomfort on 2 hour rides is TBD.
This a Saris H3 and is set up is on (6) tennis balls.
My setup:
Etsy site rear view:
I had to put a taller front wheel support to get the bike back flat. I already had this on hand so there was no extra spending for it.
Dave
