Right Speedometer gear and drive gear

[timachone]

Hi folks,

I have a 3.50 gears ratio with a 4 speed manual trans and 275/60 R 15 tires at the back. The problem is, the speedometer reads a lot less than the real speed, so I assume I need a new speedometer gear. Which one should I use now - my maths (I am bad at that) results in a 20 teeth. Is that right? Which drive gears should I have - 7 teeth?

Thanks,

cheers,

Tim

 

[Don C]

You probably do have a 7-tooth drive gear in the transmission. However, for that diameter of tire (28-inches/710mm) my calculations show that you need an 18 tooth speedometer gear.

Attached is a spreadsheet with a calculator and information.

[attachment=21306]

 

[timachone]

Hi Don,

thank you very much, that is EXACTLY what I needed

Cheers,

Tim