Recalibrate tacho needs maths confirmation

Tweety · Post by **Tweety** » Sun Oct 16, 2011 11:56 pm

Re my trike VW to ea81 conversion nearly completed.
My tacho is adjustable by a small screw behind it. is easy to do. Tacho is dependant on electrical feed.

After engine was installed the tacho was cearly out eg 100kph indicated 2000 rpm. with the VW it would be about 3100 rpm.

So have done some calculations and I ask any of you to confirm them so I can adjust it to be accurate when I get it back form the exhaust place this week.

Tyres are 275/60/r15. according to tyres calculator site has a circumference of 2.233 metres.

Tyre circumference 2.233 metres
Final drive is 3.67:1
Top gear (VW 3 speed full auto) is 1:1

At 2750 rpm

2750rpm/3.67 FD x 60 (mins) x 2.233 circum =100kph.

If this is correct then the formula could extend to the other 2 gears eg

2nd is 1.6:1

2750/3.67x60x2.233 divided by 1.6 = 63kph

1st is 2.65:1

2750/3.67x60x2,233 divided by 2.65 = 37kph

if you can please confirm

Post by **TOONGA** » Mon Oct 17, 2011 9:15 am

Do you have a dwell meter that measures RPM? if not test your guage against another tacho and see how much difference there is.

as for speed a GPS is a good indicator as to truness of speedo guages.

and as for the math I have no idea but it looks impressive

TOONGA

Tweety · Post by **Tweety** » Mon Oct 17, 2011 10:55 am

dont have a dwell meter. I do have a GPS. but have to ensure the maths are correct. Speedo I had checked before and its accurate.

will look for a dwell with rpm. thanks Jules