Rpm vs speed vs diff ratio

[Iloveboost]

I questioning myself . I have 325is with 3.73 lsd diff . (PO said it was 4.10 but when I turn the Input shaft , the output shaft turn close to 3.75turn ) What shoul be my rpm at 100kmh with the right tire size ? I took a pic today and some of my friend tell me that im reving high. In the pic I was in 5th gear.

[Vincenze]

https://e30goodies.com/gearing-calculator/

It should be 2750 rpm with 3.73 and 105 km/h.

[Iloveboost]

Thanks for the link .
but the Gear ration you entered are not the one that I find on the web and e30zone.

+ the diff ratio is 3.73 and not 3.71
+ tire are not 215-55-16.

even if I enter everything right on this chart .
my car is over rev .

what can explain this ?

rev’limiter look at the good place
my speed do said the right speed ( verified side by side with digital Honda Civic lol ..)

the only explanation is maybe my final gear in tranny was replace by another ??

[R3Z3N]

What is your tire size? Also the E30 speedo is quite inaccurate, which can be fixed mind you... Without knowing your tire size, this is all an exercise is nothing.

[Vincenze]

the only explanation is maybe my final gear in tranny was replace by another ??

With a 4.1 differential and 195/65/14 tires, the calculator shows 3250 rpm at 108 km/h.

That's close to your numbers.