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Discussion Starter · #1 ·
Oz spec 260Z 2+2 5sp L28EFI

Ive got a 17 tooth black speedo cog in my gearbox.

The speedo reads higher by about 10% (ie. it reads about 66kph when im actually doing 60kph).

I've got no idea what diff I've got (i think stock was 3.545), but Im running 215x65 14" tires (diameter 25.004", stock is 24.748" - but that should make the speedo read less, reight?)

So to correct this, i want to adjust the speedogears by 10% (1.7) but do I go up (to say 19) or down (to 15). The Z Garage only lists 16 - 21 toothed gears.

I know this has come up before - but I couldnt see it in the archives...

Jeremy
 

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more teeth will make speedo read lower. bigger tires should have made it read lower. i'm running 205/70/14's. i would hae gone to 215/60/14's, but the used tires they had in that size did'nt match, or i did'nt like the tread. i got 2-205/70/14 BFG exentia T/A's mounted and balanced, for $53. so i don't mind keeping the skinnier tire.
 

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Discussion Starter · #3 ·
So I should go to a 19 tooth then?

i didnt think the tyres would make much difference at all, maybe 1kph or something like that...

A mate has a stock car with a digital speedo and cruise control, so I'll get a 19t and do a couple of runs and see how it goes.

if the 19 tooth makes it accurate, that would mean I have a 3.90 diff right (81-83zx)? My car is a bit bastardised so its hard to know whats what!

What RPM would I get in 4th gear 1:1 ratio (cant be sure on any other ratio in my current 5sp - getting a new 280zx one next week) at say 50mph?

i cant use the transmission calculator because it doesnt work on my comp eith in Netscape 4.7 or IE 5.
 
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