ambient light for indoor shows is poor more often than not. but it depends on the venue. I use my 24-70 2.8 pretty much exclusively for shows on a FX body. something like a 17-35 would be the range you'd be in most on a DX body, but a little more in either direction wouldn't hurt, or you could go ultra wide like the 11-16 if that's what you're going for (and have access to get close enough to the cars you want to shoot, which isn't always the case). you'll want speed though, 2.8 if you can get it, or opt for a faster prime or something (although you may not have much room to move around, again depending on the venue and crowds), from my experience, shows are poorly lit for photography, so a fast lens will help for handholding. a speedlight is definitely also something you'll want to take.
outdoor shows in the day are usually sunlit well, but a speedlight for a fill flash is still something you'll want there too, interiors and engine bays will be heavily shadowed.