I'm proposing a completely new way of handling tyre changes:
Get rid of this tyre wear percentage thing and the hidden "do/do not want to have repairs done" and have it done by a popup... LfS already recognizes when you're crossing the pit entry line, so why not capitalize on that?
Here how I think it would work (screens attached, excuse my crude paintings):
1. You decide you have to pit, and so you cross the pit entry line... In the moment you do that, a menu box like the old F12 menu pops up where it graphically displays what you can change... In my view it should all be red (for do not change) everytime you drive into the pits - this would make it more memorable since it's more likely you'd only want one or two things and be outta there already and after a bit of adjusting, you'd manage the pitmenu by body memory rather than consciously looking... Plus, I'd tie the pit menu options to the numpad keys - a) they're not used thus far and b) it would only need one hand to change the options, keeping one still on the wheel...
2. You've decided you need new front tyres and a refill (will go into that later), but wouldn't bother with repairs... So that would be 7, 9 and 5... The part that should be changed now lights green instead of red (colours configurable in interface menu?)
3. You stop and your crew is doing exactly what you ordered when you crossed the pit entry line...
Now to the issue of refuelling: I propose two ways...
1. The amount of fuel that goes into the car is still managed by garage/F12-menu, or
2. 8 and 2 on the numpad would become an increase/decrease fuel amount button, with the exact amount shown over the fuel icon and the repair-option moved to 4 or 6...
Personally, I'd prefer how it's done now, since pitlanes can be quite short - too short to adjust the fuel greatly in time before the stop...