# RPM to MPH conversion

Does anyone know the RPM to MPH conversion for a Honda Civic DX 1992 manual gearbox?

No, we do not know that…Why would we care?? Why do YOU care??

To figure it out, you need to know three things…The final drive ratio of the transmission in top gear…The differential gear ratio (final drive ratio) and the circumference of the tires on the car… There are 12" in a foot and 5280 feet in a mile…Go for it…

Because his speedometer broke and he’s trying to determine speed from RPM

Why no, that has never happened to me. Ever. And I wouldn’t lie about a thing like that

You find one of those “Your Speed Is” radar display trailers the cops use here and there and make a RPM to speed conversion chart…

I believe its only going to give him a general idea as the rpm should change compared to mph per incline blah blah blah

I’m on vacation NOW…Two Martini’s, that’s the problem…

Thanks for the Laugh :-)…

For each gear the ratio would be different. Four thousand RPM in first gear might be around 30 MPH, in second gear around 40 MPH, in third gear around 55 MPH, in fourth gear around 65 MPH and in fifth gear around 75 MPH. If you have five manual gears.

You should drive in the highest gear possible at all times. If you can keep the tachometer below 3,000 RPM’s most of the time, you will have your car for a long time.

Otherwise, to avoid speeding tickets, just match the speed of traffic on highways and go slower than necessary on single lane roads.

I used to ride an inter-city bus to and from college that was probably built just after WW II. The tachometer served as the speedometer. It had a scale in MPH for each of the 5 forward gears in the transmission. This was a Flxible (yes, the spelling is correct) body on a GM chassis. I suppose you could do the same with a little calculation if you knew the ratio of each of these gears and calculted that against the final output to the wheels. You would have to take into account the diameter of the wheel.

If your speedometer is busted, get a GPS. It will give your speed and miles traveled.

Hold a steady rpm over several measured miles. Divide your time in seconds for each mile into 3600. The result will be your speed for that rpm. For example 60 seconds for a mile =60 mph, 50 seconds = 72mph.

Don’t try this in Ohio, they seem to plant the mile markers wherever the fall off the truck.

If you don’t have a GPS, but you have a Blackberry or other smartphone, you can use the GPS-based map or navigation application to do the same thing–it will at least give you an idea of what RPM corresponds to highway speeds in top gear.

Or you could just get the speedometer fixed…

Thank you for all your replies. I know all these suggestions but I wondered if anyone knew an official Honda conversion - they will know the drive ratios, etc. I have another ‘fix’ in mind which is to follow a car doing a known fixed speed on a clear road. Then I have the speed - to the accuracy of the other vehicle’s speedo - and can make a conversion chart for a given gear. Happy New Year all. Bye.

Why don’t you just replace the speedo cable?

Electronic - no cable. Replaced the speed sensor on the GB (\$180!!) and still nothing so it’s the speedo or the wiring harness. Knowing my luck it’s the harness - good luck finding that break. I’m only concerned because the check engine light comes on (code 17 - VSS speed sensor) and this could cause a smog check failure in CA.

“… I wondered if anyone knew an official Honda conversion”

Why would they have a conversion available? They sell speedometers to take care of this issue.

funny reply and the only real solution.

I had a 93 and my spedo went too, so you are in luck!
2nd-2000 to 2300-20mph for use in school zones
3rd-2000rpm-25mph
4th-just a hair below 2000-35mph
And I wanna say 5th-2700-65 to 70mph

those were the only speeds I ever seemed to need. When I noticed my speedo starting to go I began to keep track of the relative position of the tach for a given speed. That’s how I came up with these numbers. Hope it works for ya.

P.S. Use discretion it’s been two years since I got rid of this car, and my numbers may be a little off.