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Speedo Adjustment
- Thread starter Tullamore
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SilentUnicorn
Yoda
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dklawson
Yoda
Offline
If you've changed your final drive and/or tire size you only have three real choices.
1) Get an instrument designed and calibrated for your new turns/mile.
2) Contact a quality, local speedometer repair shop and ask them about building you a ratio conversion box. (Goes inline with the speedo cable to change the cable RPM to be correct for your gauge).
3) Live with it.
OK, there are two other options but they aren't necessarily what you want to hear. Do download the PDF listed above, I keep a printed copy of it in my files. It's very helpful. Using it you can get your "needle" to read right but the odometer won't read right until you get a different speedo or the ratio box.
Lastly, leave your existing speedo in place and alone. Buy a $25 Sigma BC800 bicycle speedometer and wire it up to monitor driveshaft rotations. You'll be able to calibrate it to be MUCH more accurate than a standard Smiths gauge. The drawback is that the bicycle speedometer is not backlit for night driving. Still, at $25, being programmable and accurate, and being able to INPUT odometer values... it's a great investment.
1) Get an instrument designed and calibrated for your new turns/mile.
2) Contact a quality, local speedometer repair shop and ask them about building you a ratio conversion box. (Goes inline with the speedo cable to change the cable RPM to be correct for your gauge).
3) Live with it.
OK, there are two other options but they aren't necessarily what you want to hear. Do download the PDF listed above, I keep a printed copy of it in my files. It's very helpful. Using it you can get your "needle" to read right but the odometer won't read right until you get a different speedo or the ratio box.
Lastly, leave your existing speedo in place and alone. Buy a $25 Sigma BC800 bicycle speedometer and wire it up to monitor driveshaft rotations. You'll be able to calibrate it to be MUCH more accurate than a standard Smiths gauge. The drawback is that the bicycle speedometer is not backlit for night driving. Still, at $25, being programmable and accurate, and being able to INPUT odometer values... it's a great investment.
OP
Tullamore
Jedi Warrior
Offline
[ QUOTE ]
2) Contact a quality, local speedometer repair shop and ask them about building you a ratio conversion box. (Goes inline with the speedo cable to change the cable RPM to be correct for your gauge).
[/ QUOTE ]
Has anyone done this? This would be a great option if it actually works and is available.
2) Contact a quality, local speedometer repair shop and ask them about building you a ratio conversion box. (Goes inline with the speedo cable to change the cable RPM to be correct for your gauge).
[/ QUOTE ]
Has anyone done this? This would be a great option if it actually works and is available.
dklawson
Yoda
Offline
Yes, I've had the ratio box built.
I had it done ten years ago for my Triumph which had a different final drive than stock. You supply the speedo shop a brand new speedo cable (marked for where you want the ratio box to be located). You also provide them accurate measurements for what the gauge is set up for and the number of turns/mile you're actually getting with your wheel/tire/final drive combination. (Alternatively, you also send them your speedo along with tabulated data for what your odometer reads after you drive a measured mile). Ten years ago it cost me $50 plus the new cable. The ratio box is about the size of a pack of cigarettes. I'd expect the price to have doubled by now.
I had it done ten years ago for my Triumph which had a different final drive than stock. You supply the speedo shop a brand new speedo cable (marked for where you want the ratio box to be located). You also provide them accurate measurements for what the gauge is set up for and the number of turns/mile you're actually getting with your wheel/tire/final drive combination. (Alternatively, you also send them your speedo along with tabulated data for what your odometer reads after you drive a measured mile). Ten years ago it cost me $50 plus the new cable. The ratio box is about the size of a pack of cigarettes. I'd expect the price to have doubled by now.