Speedometer change when changing gears?
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Freshman User
Joined: Feb 2006
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Speedometer change when changing gears?
I've got a 1991 f150 4.9L 5spd with 2.73 gears. Am swapping to a Limited Slip TrakLok differential and 3.55 gears. The speedometer cable hooks into the tranny on this one - what's it going to do to my speedometer reading?
Senior User
Joined: Jun 2005
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It will make your speedometer read faster than your actual speed if you do not change your tires size.
if you drive between two mile markers at a constant speed, count how many seconds it takes to go that one mile. Divide the seconds it takes you by 3600, then do 1/(Whatever your seconds divided by 3600 is) and this will give you your speed, based off the old high school D=RT (Distance = rate x time). The 3600 is there because you need to convert the seconds into hours, so you get MPH as a result. This will tell you how much your speedo is off.
Ex: 45 seconds to go one mile: 45/3600 = .0125
1/.0125 = 80MPH. Quick check and this is right, since if you took 60 seconds, you would be going 60MPH. And 30 seconds would be 120MPH.
Or, just take it to a speedo shop and have it recalibrated for aprox $100.00
if you drive between two mile markers at a constant speed, count how many seconds it takes to go that one mile. Divide the seconds it takes you by 3600, then do 1/(Whatever your seconds divided by 3600 is) and this will give you your speed, based off the old high school D=RT (Distance = rate x time). The 3600 is there because you need to convert the seconds into hours, so you get MPH as a result. This will tell you how much your speedo is off.
Ex: 45 seconds to go one mile: 45/3600 = .0125
1/.0125 = 80MPH. Quick check and this is right, since if you took 60 seconds, you would be going 60MPH. And 30 seconds would be 120MPH.
Or, just take it to a speedo shop and have it recalibrated for aprox $100.00
