speedo gears

[123abc]

can anyone calculate the speedo cable drive gear needed for this application
1970 mustang
t5 5speed from a 87 gt mustang with the most common gear ratios
7 tooth gearbox drive gear with 3.25 rear gears lsd 9"
rear tyres are 255x60x15 and are about 680 mm in diam

[hybrid]

http://www.fordspeedo.com/Calculator.html

[123abc]

thankyou

[123abc]

thankyou

[hybrid]

Forgot I put a calculator on this site too

https://www.mustangtech.com.au/Calculators.html

[123abc]

it wont open I got a 17 tooth on the other site suggested would be good to compare

[hybrid]

What do you mean it won't open? Do you get an error?

[123abc]

opened this time

[Shaunp]

17, Mustang auto parts have if they are the same a TL