Increasing tire size is a common way to effectively get "overdrive" without going through the expense of a new transmission. You would drop your RPM from around 5000 to about 4675 @ 100 mph according to the info you gave.
Insignificant reduction, if jtr's calculation (how did you do that btw?) is correct. Depending on the vehicle (push rod, slow rpm old style Amer big V8's an such, this would make a difference, with overhead cam designed smaller engines that are not feeble econobox models, 5krpm is in the normal operating range, and in fact letting such a car idle for more than 5minutes at a time produces even more wear on the camshaft lobes, my mechanic scolded me and turned off my engine, the old 2.0 Alfa which he had installed high-lift, but short duration-meaning sharply shaped lobes- Autodelta race cams for the fuel injection, telling me that creates excessive wear),
IIRC it's an recent model Jetta with variable rate-rpm cams, dual overhead??? It will be fine @5k or 4.7k, you'd get lower overall wear if you dropped to 4k, but not a huge reduction. Total miles will get you more wear-that is far more significant as to wear (I know an Alfa owner told me he ran repeatedly in the 6krpm range, wear max is 6.8k IIRC and the engine purred to 60k miles, but you need to do timing chain changes and replacement of associated parts that DO wear, upon inspection of the engine by a qualified mechanic), in the long run; IIRC this Jetta has a lot of miles on it? Save the money to be spent on tires (~$400 incl. balancing & disposal +taxes, correct?) and be ready to buy another car with fewer miles on it.
IIRC, 85mph is the point where speeding tickets become a gross violation of excessive speed (do a search of the CA Vehicle code online), and the penalty can be suspension of license (repeat offenders) and an initial $300+ citation. Put a little oil from a leaking vehicle on the freeway, maybe some morning dew/mist from the ocean there, and yet another reason we could find ddrueding MIA from here...in intensive care a the hospital for extreme injuries suffered in auto accident (don't even have to be flirting either)
Calculations are fine, printed sizes on bicycle or auto tires are nice, but you're both incorrect. There are variances, sometimes significant for the same tire sizes (I don't know if there is an actual penalty for violation of listing standards). Ie. a 195/60 15in tire from one manufacturer could be as much a 1/2in different in true diameter, this I have seen myself measuring the tires side-by-side standing next to each other. Go into a performance, or experienced auto tire seller and ask. Also matters as the weight of the vehicle, tire inflation, and what width the wheel is that the tire is being mounted to...those all effect 'true' diameter of wheel on the car. The shops that do, plus 1, 2, 3 size wheel packages will all know these things for sure.
Damn, I just got me haircut yesterday at the usual place of young thang's hangout in SM, CA. I was simply devasted; my dreamy, super hottie taught, thin, late-teens/early 20's Korean babe, whom I haven't seen in over a year, went back to community college for a year or so, and put on her freshman 15, eeks! How could she change so quickly? *sniff* It’s a cure world (back to you later jtr).
Oops, Bozo beat me to it.
