A shorter sidewall tends to give better handling at the expense of some ride quality, and can throw your speedo off. A taller sidewall gives better ride quality, at the expense of adding some sidewall squirm and raising the vehicle CG ever so slightly, so you can lose a little handling. You can also use changes in tire pressure to "tune" the car to your driving habits.

Both my Benzes came to me with Bridgestone Potenza Re930i tires. Old Yeller has them in 195/70R15, and Whitey has 195/60R15. Speedo and odo on Old Yeller are dead on. Whitey's read about 10 percent high. Of late, I've been running manufacturer recommended pressure in the big tires, and 36 in the little ones. Handling with Old Yeller is good but not great. Whitey acts like he's on rails, but he's my commuter, and I drive a five mile stretch of dirt with washboard and embedded rock every day, so after weighing the car (1800 on the steer axle and 1560 on the drive axle, full fuel and no driver), and consulting the TRA Yearbook, I've found I can get away with as little as 26 psi at all four corners. I'll be working my way down in steps until I find the right compromise of handling, ride quality, and rolling resistance.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.