This may have been discussed somewhere, but I don't remember where.
My '74 Thing is running with 205 65 15's. As a result, I believe my speedo. is not giving me an accurate reading. Does anyone know what this combo. yields relative to the shown speed?
Thanks,
Rick
Speedo. calibration
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Bob Ingman
- Posts: 2869
- Joined: Mon Mar 19, 2001 12:01 am
try info@nhspeedometer.com Hartmut there is always willing to answer questions and share his knowlege of this subject. In case you did not recognize the address it is for North Hollywood Speedo the VDO guys. Also this is not a Thing specific question so it could be worthwhile posting it on the Transaxle or any of the T-1 forums in general. I know three guys on the transaxle forum that can do the math. Good luck. Bob Ingman
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germansupplyscott
- Posts: 887
- Joined: Fri Jul 20, 2001 12:01 am
i have recalibrated my thing speedo, almost by accident.
what happened is that i had a speedo that did not work. rather it was the odometer that had a broken gear, which is common. i also have big tires (27 x 8.5 x 14), so i knew i was going to have a problem with the speedo reading wrong.
i had a spare beetle speedo, which i took apart hoping i could steal the gear from it. turns out it could not be done, as the two speedos were different, one had a plastic gear (thing one), the other was brass. i also noticed a different drive ratio on the beetle speedo, but it looked like it was in the right direction for me.
i measured the speedo ratio of each speedo emprically. since the odo on the OG thing one was busted i had to use only the speedo measurement. (they function independentlly inside the unit) i drove each speedo with an electric drill at a fixed speed. i recorded the difference in indicated speed between the two. using the tire size charts on thetirreack.com other sources i found out the revs per mile of the stock tires versus the new ones and came up with a error factor for the new tires, something like 4% (i forget the actual number in fact, but it was close to that) this meant that the correcetd speedo needed to turn 4% fewer turns for the same indicated speed. it turned out (this is the accident part) that the beetle one i had was almost exactly the correct "error" for me and my new big tires.
i took the OG thing speedo apart and removed the front face of it. i did the same thing to the beetle speedo, then i created a new thing speedo with the beetle speedo/odo unit and the thing face and main rear housing. it looks completely original, and it is accurate with the big tires. it took me a few hours to do it. after the new speedo was done i tested it by driving it with an electric drill at 60 pmh indicated speed and made sure it took exactly 60 seconds to turn over 1 mile. this adjustment is more difficult if it not correct. mine was fine.
this is appoximately the same process that NH speedometer will go through to recalibrate your speedo, but they charge about 150-200 bucks to do it. they may or may not change only the drive and driven gears of the speedo, as opposed to using an whole new rear assembly as i did. since i changed the odo i had to reset the mileage to read the same as my original odo. again, this was not all that difficult, just abit fussy. if you are handy, can do the math and have good jeweler's skills, you can do it yourself. beetle speedos are a dime a dozen at swap meets. i can post the part number of the beetle one i used, if need be. i think i got lucky in terms of having a beetle speedo that had the right drive ratio to suit my needs.
what happened is that i had a speedo that did not work. rather it was the odometer that had a broken gear, which is common. i also have big tires (27 x 8.5 x 14), so i knew i was going to have a problem with the speedo reading wrong.
i had a spare beetle speedo, which i took apart hoping i could steal the gear from it. turns out it could not be done, as the two speedos were different, one had a plastic gear (thing one), the other was brass. i also noticed a different drive ratio on the beetle speedo, but it looked like it was in the right direction for me.
i measured the speedo ratio of each speedo emprically. since the odo on the OG thing one was busted i had to use only the speedo measurement. (they function independentlly inside the unit) i drove each speedo with an electric drill at a fixed speed. i recorded the difference in indicated speed between the two. using the tire size charts on thetirreack.com other sources i found out the revs per mile of the stock tires versus the new ones and came up with a error factor for the new tires, something like 4% (i forget the actual number in fact, but it was close to that) this meant that the correcetd speedo needed to turn 4% fewer turns for the same indicated speed. it turned out (this is the accident part) that the beetle one i had was almost exactly the correct "error" for me and my new big tires.
i took the OG thing speedo apart and removed the front face of it. i did the same thing to the beetle speedo, then i created a new thing speedo with the beetle speedo/odo unit and the thing face and main rear housing. it looks completely original, and it is accurate with the big tires. it took me a few hours to do it. after the new speedo was done i tested it by driving it with an electric drill at 60 pmh indicated speed and made sure it took exactly 60 seconds to turn over 1 mile. this adjustment is more difficult if it not correct. mine was fine.
this is appoximately the same process that NH speedometer will go through to recalibrate your speedo, but they charge about 150-200 bucks to do it. they may or may not change only the drive and driven gears of the speedo, as opposed to using an whole new rear assembly as i did. since i changed the odo i had to reset the mileage to read the same as my original odo. again, this was not all that difficult, just abit fussy. if you are handy, can do the math and have good jeweler's skills, you can do it yourself. beetle speedos are a dime a dozen at swap meets. i can post the part number of the beetle one i used, if need be. i think i got lucky in terms of having a beetle speedo that had the right drive ratio to suit my needs.