Speedometer Gear
March 2nd, 2010, 03:55 PM
#6
Registered User
Join Date: Jun 2009
Location: Palm Bay, FL
Posts: 4,249
According to what I found that's equivalent to an H78/14 so use that as a guide line.
Also you need to make sure you have both the correct drive and driven gears in the trans.
So that would be 18 & 43.
Also you need to make sure you have both the correct drive and driven gears in the trans.
So that would be 18 & 43.
October 12th, 2010, 01:47 PM
#8
Registered User
Join Date: Nov 2008
Location: Mass
Posts: 1,119
If your tires are different than the chart you could ratio your new tire circumference to the tire circumference on the chart. Say for example your actual circumference is 5% more. I kind of called this my "correction factor".
This is assuming gear ratio between what you have and what is on the chart is the same. If your gear ratio is also different the same idea would work but you have to ratio for gear too.
Than take the ratio of driven and drive gear per the intended tire size on the chart and bump that ratio by 5%. This was my "magic number"
Use the chart to find any combination of drive gear driven gear ratio that is close to your magic number.
The drive and driven gear you now select may not make any sense per the chart based on what is says for tire size and gear ratio , its all about picking the right ratio (magic number).
Thats how i did it for my 3:90s without using one of those adapters. For comparison i believe at 40 mph my speedo was off by 1 or 2 mph. I couldnt get it exact but it was close enough.
When i did mine i had this whole sheet of math calculations that i never saved. I wished i saved it because it would be easier to show the formulas than just try to describe it. I wish i just put it into an excel sheet so all i had to do was plug in a number.
This is assuming gear ratio between what you have and what is on the chart is the same. If your gear ratio is also different the same idea would work but you have to ratio for gear too.
Than take the ratio of driven and drive gear per the intended tire size on the chart and bump that ratio by 5%. This was my "magic number"
Use the chart to find any combination of drive gear driven gear ratio that is close to your magic number.
The drive and driven gear you now select may not make any sense per the chart based on what is says for tire size and gear ratio , its all about picking the right ratio (magic number).
Thats how i did it for my 3:90s without using one of those adapters. For comparison i believe at 40 mph my speedo was off by 1 or 2 mph. I couldnt get it exact but it was close enough.
When i did mine i had this whole sheet of math calculations that i never saved. I wished i saved it because it would be easier to show the formulas than just try to describe it. I wish i just put it into an excel sheet so all i had to do was plug in a number.
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