Along (or near) Tioga Road, only Crane Flat on the west end requires reservations for 100% of its campsites. On the east end, at Tuolumne Meadows, only 50% of the campsites are reserved. All other campsites along (or near) Tioga Road in Yosemite are first-come, first-served.
If you want easy access to Tioga Road (and avoid bad roads) then avoid Yosemite Creek and Tamarack Flat campgrounds. For all others, the access to Tioga Road is fine.
Again, most of these campsites cannot be reserved (with the exception of Crane Flat and 50% of Tuolumne Meadows), so your chances of landing a campsite increases greatly the earlier that you arrive at the campground. If you can get their by 10:00 AM on a weekday, you should have a good chance in getting a campsite. If you manage to get there by 8:00 AM, your chances are a whole lot better.
A strategy that some employ to be able to arrive at these first-come, first-served campgrounds early in the morning is to camp the night before just outside of the Yosemite in the surrounding National Forests, either at a National Forest campground or in an area where dispersed camping is permitted. With this strategy, it is easy to be less than a 90 minutes drive from a first-come, first-served campground within Yosemite. Often times, the rangers at the Yosemite National Park entrance booths will have information on which first-come, first-served campgrounds still have space available as you enter the park.