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[paddy granger]

With 195/45-15 one may have problems with the speedo? Or can you calibrate it?

These are the differences:

185/60-14

Sidewall: 4.4in
Radius: 11.4in
Diameter: 22.7in
Circumference: 71.4in
Revs/Mile: 887

195/50-15

Sidewall: 3.8in
Radius: 11.3in
Diameter: 22.7in
Circumference: 71.2in
Revs/Mile: 889

195/45-15

Sidewall: 3.5in
Radius: 11.0in
Diameter: 21.9in
Circumference: 68.8in
Revs/Mile: 921

Speedometer difference with 205/45-15: -3.7%, ie. when you are travelling 60mph, it reads 57.8, assuming the speedo is perfect.

With 195/50-15, the difference is only 0.3%

[Matt Stolton]

33 speedos are never too accurate any way, and are always more of a guide to your speed, rather than anything deffinite.

AFAIK there is no way of adjusting them.

Overall, A539 195/45 R15 help the handling, without compromising ride, but with a theoretical lower top speed, but you accelerate to it quicker. However, in my expereince, with more mechanical advantage back to the engine, the engine will rev to a higher terminal velocity, meaning you top out at much the same actual ground speed, just at higher revs on the engine. Depending where your peak power is, the engine can actually pull round a little bit more too, giving a little more top speed.

It is the same as changing the diff to something with less teeth. You will have heard of racers using the 1.3 Diffs, and having engines that will scream past 8K RPM, so top speed is not reduced too much, but acceleration is increased. Using 195/45 R15 is just a little bit more subtle, and less oily.
_________________
Regards

Matt

Ex Alfa 33 'GTA' (P4 with Knobs On)
Now cruising in a 166 3.2 Ti!!