:laugh: When was the last time any of you guys have heard of a temp failing because someone was speeding on it?
The manufacturers put that rating on there because it's easier to say "Do not use over 50mph" than "Do not use over 50mph if spare is on one of the drive wheels and also don't take corners fast or brake hard". Everyone who is even a little bit car savvy would know this, but many people don't even know which ones the drive wheels are. And, even for people who do know their way around a car - someone who gets a flat in the rain at night for example, is usually not going to take the time to transfer a good wheel from the non-drive axle to the drive wheels, and put the spare on the non-drive axle.
Using wheels with different overall diameters will burn up differentials / wreck transmissions over a period of time, and do so much more quickly at high speeds - hence the "rating". Not to mention, the handling and braking of the car are negatively impacted with a temp spare on there - which again, becomes a much bigger problem at higher speeds. The manufacturers put that ultra conservative rating on their to cover their ass in the event of an accident being blamed on a temp spare, and also to save them millions of dollars worth of warranty transmission / diff repairs caused by mismatched wheels.
As long as you are mindful that you are on a temp spare and drive accordingly, you could probably double the 50mph speed rating of that tire without any issues.
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