I was not impressed with the tires supplied with 42099 4x4 Extreme. I found references on another website about different tires for Lego. The rims for the 42099 take 1.9" tires. When I started my build I ordered R/C rock crawler tires from Amazon "4.7 Inch Outer Diameter RC Crawler Tires,1.9 Inch". I'm not posting the Amazon link as I'm not pushing the product, just showing personal results. The tires are Pro-line knock offs, they have multiple, really wicked cool tread patterns available. The tires are very soft, real rubber with foam insert. I have not taken it outside, but I am 100% confident they will perform substantially better than fairly hard, slippery stock tires.
This was my first Technic kit, built on 2/18/19. I am already going to disassemble, build efferman's ultimate MOC, then tear down and build the "Rocky" MOC. This is more a learning process before I actually take it outside to play.
I'm off work for shoulder injuries (torn ligaments), first surgery 2/21/20. Up to 6 months recovery, then 2nd surgery. I was going stir crazy around the house coz I had nothing to do, that wouldn't affect my shoulders. Walking by the Lego isle in Walmart triggered the proverbial light bulb (DING!) Building LEGO would be a FUN zero impact activity I can do! Browsing the Lego website I saw the Technic kits and all the other Lego themes. WOW lego has come a LOOOONG way since my childhood Lego days of the 70's! Between the other Technic kits I've ordered (current / retired), and the Creator 3in1 sets, I will not be bored during recovery, and beyond!
I also have the Briksmax light kit that I will install on build I will run.
A huge kudos to all the MOC creators for sharing builds! A huge kudos to Rebrickable for making a place to share! The greatest thing about Lego is being able to build something, take it apart an make something else with the same parts.