dwight

As measured by mile markers
http://www.flickr.com/photos/cyanocorax/5409523760/http://www.flickr.com/photos/cyanocorax/5409523760/ by http://www.flickr.com/people/cyanocorax/, on Flickr
http://www.americanstreetrodassociat...ation-960.html

Or you could compare to GPS or a friend using cruise control in another car.

xviper

It doesn't matter what size rims you got. It's the tire diameter that determines how it affects the speedo. IE, if the 16" rims has tires that are 30" in diameter and the 17" has tires that are 30" diameter, there's no difference as far as the speedo is concerned.
You can't time 60 seconds based on what your speedo says. It may be wrong and off by just a second or 2. Many speedos can be off by 5% normally. You must use mile markers or a good GPS device.
A difference of 1000 rpm at 60 is not due to tire differences. You've either got different gears in the diff in one car or you've got a speed compensator that's not set properly.
I've got 4.44 F.D. with an AP2 tranny in an AP1 and the rpm difference at 60 is about 400 rpm in 6th.

bdo

hes trying to say go to 60mph and then reset the trip and time a min. if you go a mile in a min then your gearing should be correct with the speedo
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I'm not sure if that's what he's trying to say, but that won't work! They both use the same signal, so they will be in sync with each other, regardless of how far off both are.

As dwight said, mile markers would work, since they are usually measured out by surveying equipment. GPS is fairly accurate too. Personally I'd find a free GPS speedo app for my phone and compare to that. They're surprisingly accurate, at least at a steady speed. I wouldn't trust another car though.

dwight

The OP claims to be off by 14%. Even if both cars naturally were +5 and -5% from each other, it would still be noticeable.

In all three Honda cars I've driven and compared their speeds to GPS or radar, it's always been within 1 mph at highway speeds.

henrryxd

ive checked it with ym gps, seems like my car is about 3-5 miles off on slow speeds..
and about 10 miles off when im at higher speeds..
my gps said i was gonig about 70mph when i saw 60mph.
does that mean its a sensor ? or something is wrong with my car.

xviper

In other words, both cars are doing 4000 rpm when they are actually doing 70 mph. That's about the right rpm for that speed given stock gearing. Look for a speed compensator device under the dash. A previous owner may have had different FD gears, then took them out before selling but didn't recalibrate the compensator. It could be a Modifry Yellow Jacket or a Blacks Robotics Yellow Box. If you can't find the compensator, then you may have a bad VSS. Swap it with the other car and see what it does.

henrryxd

whats a VSS? also where would the location of the yellow box be?

xviper

whats a VSS? also where would the location of the yellow box be?
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Vehicle Speed Sensor - it's on the left side of the tranny.
YJ or YB is installed by the owner and can be anywhere under the dash, near the car's ECU by the driver's left foot. Google it to see what a Yellow Box or Yellow Jacket looks like.

henrryxd

whats a VSS? also where would the location of the yellow box be?
[/quote]
Vehicle Speed Sensor - it's on the left side of the tranny.
YJ or YB is installed by the owner and can be anywhere under the dash, near the car's ECU by the driver's left foot. Google it to see what a Yellow Box or Yellow Jacket looks like.
[/quote]

can this VSS go bad when the clutch is changed? is there anyway to know the sensor is faulty ?

xviper

The tranny comes off when you do a clutch job, so it's possible the VSS could be damaged. The only way to tell is to try a known good one. I doubt it's the VSS. It either works or it doesn't. I still think there's a speed compensator in play. Go here to see where it's spliced in at the ECU. Then you can trace it from there. Look at the installation manuals.

http://modifry.com/products/index.htm