how off is my speedo?
Oct 11, 2005 | 04:04 AM
#1
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From: middleburg, VA
how off is my speedo?
i tried looking it up, but couldnt find it, and i dont remember how to calculate howw off the speedo is. its an 88 4runner with 36" tires. i think the stock size was like a 235/75-15. i remeber you come up with a percentage or somethin of the sort. i need to know how fast im going when the speedo says 50mph?
Oct 11, 2005 | 04:48 AM
#3
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From: Overland Park, KS
Oct 11, 2005 | 09:06 AM
#5
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From: 100 miles offshore as much as possible, & Springfield Oregon USA
It's very simple to find out, nothing special required.
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Oct 11, 2005 | 09:17 AM
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From: Socal
Originally Posted by Flamedx4
It's very simple to find out, nothing special required.
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Oct 11, 2005 | 09:54 AM
#7
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From: 100 miles offshore as much as possible, & Springfield Oregon USA
um, the 10% was just used for an example. I have no idea what gears are in runnerboys rig so I couldn't calculate the error.
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
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Oct 11, 2005 | 10:28 AM
#8
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From: Dubuque, IA
Originally Posted by Flamedx4
um, the 10% was just used for an example. I have no idea what gears are in runnerboys rig so I couldn't calculate the error.
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
Factory 225s with 4.10s. How far off with 33x1250s and 5.29s?
Oct 11, 2005 | 11:21 AM
#9
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From: Socal
Originally Posted by Flamedx4
um, the 10% was just used for an example. I have no idea what gears are in runnerboys rig so I couldn't calculate the error.
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
IF he came stock with 225s (235s were not standard) and 4.10s (manual trans) for example, and now has 36s and 4.10s, then his speedo would be off roughly 30%!!
Oct 11, 2005 | 11:28 AM
#10
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Originally Posted by bryanr
Pop quiz
Factory 225s with 4.10s. How far off with 33x1250s and 5.29s?
Factory 225s with 4.10s. How far off with 33x1250s and 5.29s?
(33-29)/29 = 0.13793 (calculates how much your tire difference throws it off)
(5.29-4.10)/4.10 = 0.29024 (calculates how much you corrected with gears)
0.29024 - 0.13793 = 0.15231 or about 15.2% OVERCORRECTED (calculates how much overcorrection you have)
Last edited by bamachem; Oct 11, 2005 at 12:10 PM.
Oct 11, 2005 | 11:53 AM
#11
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From: 100 miles offshore as much as possible, & Springfield Oregon USA
Originally Posted by bamachem
225/75-16's are 29" tires.
(33-29)/29 = 0.13793
(5.29-4.10)/4.10 = 0.29024
0.29024 - 0.13793 = 0.15231 or about 15.2% OVERCORRECTED
(33-29)/29 = 0.13793
(5.29-4.10)/4.10 = 0.29024
0.29024 - 0.13793 = 0.15231 or about 15.2% OVERCORRECTED
Oct 11, 2005 | 05:25 PM
#13
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From: middleburg, VA
i have still have the stock 4.10 gears. from what was said also i guess the stock tires were 225's. wow 30%. so that means when the speedo says about 50 im realy doing around 65. truck drives better than i thought it would on the highway.
Oct 11, 2005 | 05:37 PM
#14
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From: ELN
Originally Posted by Flamedx4
It's very simple to find out, nothing special required.
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Use a stopwatch (most of us have this feature on our wristwatches these days...) or at least a second hand, and go drive somewhere there are mile posts. Drive at a constant speed. Time some mileposts. Be precise. Be sure and time multiple mileposts as they are not particularly accurately placed.
At 65 seconds per mile, you are going 55 mph. Couldn't be simpler.
At 60 seconds per mile, you are going 60 mph.
At 55 seconds per mile, you are going 65 mph.
At 50 seconds per mile, you are going 70 mph.
etc
Remember that your speedo will be off as a percentage - so if (by way of example) you are reading 50 but are going 55, then when it reads 30 you will be going 33, when it reads 100 you will be going 110. 10% - get it?
(By the way - you would have to tell us what gears you have before we could have calculated it for you.)
Oct 12, 2005 | 08:17 AM
#15
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From: Portland, OR
John, how's that new runner workin out for you? Sounds like you got a pretty good set-up with the SAS and 36s. You ever gonna be comin back to tech for school? I'll be back next semester and we should get out for some trail runs. The taco's come a long way 
Oct 12, 2005 | 08:57 AM
#16
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From: middleburg, VA
hey man, actually i came back to tech this semester. the 4runner is a whole different ball game than my 97 to drive and wheel. its gonna take me a while to get used to it. lookin foreward to you gettin back to school.
Oct 12, 2005 | 09:42 AM
#18
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From: Fort Collins, CO
It is about this far off [ ]
Don't drive faster than the person in front of you.
How much is mine off:
33" MT/R's from stock 225/75/15
5.29 gears from stock 4.56
A340F tranny from A340H
3.4 from stock 3.0
Don't drive faster than the person in front of you.
How much is mine off:
33" MT/R's from stock 225/75/15
5.29 gears from stock 4.56
A340F tranny from A340H
3.4 from stock 3.0
Oct 12, 2005 | 09:47 AM
#19
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From: Socal
Originally Posted by runnerboy97
i have still have the stock 4.10 gears. from what was said also i guess the stock tires were 225's. wow 30%. so that means when the speedo says about 50 im realy doing around 65. truck drives better than i thought it would on the highway.
