We are considering adding a few small strips of silicone or rtv to the outside of our exterior bumpers. Only in the front and only where the ball contacts the bumpers. This will give us a little more grip for our ball intake. Any one know whether or not this is legal?
Not looking to make rubber bumpers, but would like to prevent the ball from spinning/slipping on the bumpers during intake.
I think that would potentially violate R21B and violates R21D.
R21 BUMPERS must be constructed as follows
D. be covered with a rugged, smooth cloth.
It may also be considered not constructed per figure 4-8.
As an LRI I would deem it illegal.
If I was one of your inspectors, I wouldn’t even bother you with this. 
R21 doesn’t say anything about silicon; imo not legal.
I was supposed to be an inspector at the WPI District next week but I got scheduled to be at three places at once…
I would also call in a Q&A asking about this. There is one, I’m just too lazy to go hunt it up. (And yes, it does mesh with what Steve said.)
Here you go:
Q376 Q. Can we add grip tape or other material in addition to the fabric on our bumpers?
A. No, this would not be consistent with R21-D.
Thanks for all the great replies 
Sounds like we’ll keep it off the bumpers to be safe. I’ll tell ya though, sure would have been nice and cured our problem of spinning the ball on the bumper material during intake.
What about silicone-impregnated fabric? That’s worth a Q&A. Be sure to mention that the recommended Cordura fabric is polyurethane-impregnated Nylon.
The bumpers themselves may not have such a feature. However, you can “deploy” a mechanism over the bumper that has the grippy surface. A simple length of lexan or aluminum or even wood, hinged to flip down over the top of the bumper, should work fine. Use a servo to release it and/or nudge it down.