Honda / Acura speedometer and odometer accuracy issues
11-21-2006, 05:21 PM
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Honda / Acura speedometer and odometer accuracy issues
I am posting this thread for those "junior" or "younger" folks who are new to Hondas and Acuras. This may even apply to the pros out there who may be unaware of this issue. If you are already aware of this then disregard. I've been meaning to write this for a long time, but just haven't yet..........till now.
I have owned my 1995 Civic EX coupe with manual tranny since it was new. I soon discovered that my speedo was off by 10%. At the time I had the original tire size of 185/60/14. I discovered this problem on a long road trip. I was going 70mph, but other cars including highway patrolmen were flying right by me. So I slowed down to 60mph and timed myself between mile markers........1 minute 8 seconds. With an accurate speedo, the time should only be 1 minute. That meant that the speedo was reading faster than the actual vehicle speed. So I took it to my Honda dealer and demanded a fix. Their solution was to replace the speedo cluster. That did nothing. Their explanation to me was that Hondas "allowable" tolerance is plus or minus 10%. I took the car to a speedo calibration shop with dynamometer. It was confirmed that my speedo was reading 10% faster than the actual speeds from 20mph all the way to 80mph. So I then concluded a few issues with an inaccurate speedo:
1) If the speedo and odometer run off the same sensor (which I much later came to understand the vehicle speed sensor system in the tranny), then maybe the odometer is also off by 10%.
2) If the odometer is racking up miles faster, then warranty periods will expire earlier
3) When auto publications post performance data, that the 0-60 acceleration times may not be accurate........if they are going off the cars speedo only, and not some other measuring device.
4) The only upside to this is that one will be much less likely to get a speeding ticket. For years I ended up mentally compensating for the inaccurate speedo while driving. I did this till I upgraded my tire size about 6 years ago.
So the moral of the story is that one should seriously consider having their speedo accuracy checked at any speedo calibration shop with dyno. It is very likely that all 92-00 Civics and 94-01 Integras will also have this inaccuracy, especially with the original tire sizes with 14 or 15 inch rims, which many of the die hard Honda and Acura gurus stick with. The vehicle speed sensors in all these cars are designed the very same. The only difference I can see that could change things is the final drive in the tranny. All the Civics/Del Sols with any D series motor and tranny and all non-GSR Integras came with the 4.266 final drive gear or less. All the DOHC B series VTEC motors in Civics and Integras came with the 4.4 final drive gear, except for the JDM cars with the 4.78 final drive gear. If you know anything about these trannies, then you know that the little gear attached to the vehicle speed sensor spins off of a small ring gear that is pressed onto the differential.
There are only three solutions to adjust for the speedo inaccuracy:
1) Change the differential speedo ring gear to one with a smaller ratio to spin the VSS gear faster. Chances are that there is no part out there that will accomplish this. If there was, most aren't willing to tear apart the tranny.
2) Change the VSS gear to a smaller one so it will spin faster. Again, chances are that there is no part out there that will accomplish this. If there was, then changing this would be much easier since the VSS will come off the tranny easily without having to pull the tranny.
3) The easiest solution, which many have done anyway, is to change your tire size. I am using Toyo Proxes 4 205/40/17 tires. The overall rolling diameter is 23.5 inches. I now have a GSR motor with a hybrid Type R/LS manual tranny. The 5th gear and 4.266 final drive gear is Integra LS, while 1st through 4th gears are Type R. With this combo, my speedo accuracy is DEAD ON.
I know nothing about earlier Preludes, earlier Accords, earlier other Honda/Acura cars, or the current 2002 and newer Hondas and Acuras. Again, I'm only talking about 92-00 Civics and 94-01 Integras, which comprise a huge chunk of the Honda/Acura market. But if you have one of these other Honda/Acura models, then it is worth $20-$30 to get your speedo checked.
Again, smaller tire diameters will cause the speedo to read faster than actual speed, and bigger tire diameters will cause the speedo to read slower than actual speed. Since most cars have fixed ratio speed sensors built into the trannies and fuel injection systems, that there is little chance to correct any inaccuracy with replacement parts. You can only do that with older cars using non-electric cable type speedo drive systems.
I have owned my 1995 Civic EX coupe with manual tranny since it was new. I soon discovered that my speedo was off by 10%. At the time I had the original tire size of 185/60/14. I discovered this problem on a long road trip. I was going 70mph, but other cars including highway patrolmen were flying right by me. So I slowed down to 60mph and timed myself between mile markers........1 minute 8 seconds. With an accurate speedo, the time should only be 1 minute. That meant that the speedo was reading faster than the actual vehicle speed. So I took it to my Honda dealer and demanded a fix. Their solution was to replace the speedo cluster. That did nothing. Their explanation to me was that Hondas "allowable" tolerance is plus or minus 10%. I took the car to a speedo calibration shop with dynamometer. It was confirmed that my speedo was reading 10% faster than the actual speeds from 20mph all the way to 80mph. So I then concluded a few issues with an inaccurate speedo:
1) If the speedo and odometer run off the same sensor (which I much later came to understand the vehicle speed sensor system in the tranny), then maybe the odometer is also off by 10%.
2) If the odometer is racking up miles faster, then warranty periods will expire earlier
3) When auto publications post performance data, that the 0-60 acceleration times may not be accurate........if they are going off the cars speedo only, and not some other measuring device.
4) The only upside to this is that one will be much less likely to get a speeding ticket. For years I ended up mentally compensating for the inaccurate speedo while driving. I did this till I upgraded my tire size about 6 years ago.
So the moral of the story is that one should seriously consider having their speedo accuracy checked at any speedo calibration shop with dyno. It is very likely that all 92-00 Civics and 94-01 Integras will also have this inaccuracy, especially with the original tire sizes with 14 or 15 inch rims, which many of the die hard Honda and Acura gurus stick with. The vehicle speed sensors in all these cars are designed the very same. The only difference I can see that could change things is the final drive in the tranny. All the Civics/Del Sols with any D series motor and tranny and all non-GSR Integras came with the 4.266 final drive gear or less. All the DOHC B series VTEC motors in Civics and Integras came with the 4.4 final drive gear, except for the JDM cars with the 4.78 final drive gear. If you know anything about these trannies, then you know that the little gear attached to the vehicle speed sensor spins off of a small ring gear that is pressed onto the differential.
There are only three solutions to adjust for the speedo inaccuracy:
1) Change the differential speedo ring gear to one with a smaller ratio to spin the VSS gear faster. Chances are that there is no part out there that will accomplish this. If there was, most aren't willing to tear apart the tranny.
2) Change the VSS gear to a smaller one so it will spin faster. Again, chances are that there is no part out there that will accomplish this. If there was, then changing this would be much easier since the VSS will come off the tranny easily without having to pull the tranny.
3) The easiest solution, which many have done anyway, is to change your tire size. I am using Toyo Proxes 4 205/40/17 tires. The overall rolling diameter is 23.5 inches. I now have a GSR motor with a hybrid Type R/LS manual tranny. The 5th gear and 4.266 final drive gear is Integra LS, while 1st through 4th gears are Type R. With this combo, my speedo accuracy is DEAD ON.
I know nothing about earlier Preludes, earlier Accords, earlier other Honda/Acura cars, or the current 2002 and newer Hondas and Acuras. Again, I'm only talking about 92-00 Civics and 94-01 Integras, which comprise a huge chunk of the Honda/Acura market. But if you have one of these other Honda/Acura models, then it is worth $20-$30 to get your speedo checked.
Again, smaller tire diameters will cause the speedo to read faster than actual speed, and bigger tire diameters will cause the speedo to read slower than actual speed. Since most cars have fixed ratio speed sensors built into the trannies and fuel injection systems, that there is little chance to correct any inaccuracy with replacement parts. You can only do that with older cars using non-electric cable type speedo drive systems.
