Speedo / Tach / Gauges: Inaccurate Speedometer

[57studechampion]

Does anyone know which speedometer gear I need in my transmission?

I have a 56 2dr Champion Sedan with overdrive.

I had someone following me and I thought I was going 60 MPH and I was informed that I was going 54 MPH.

Where would I get the correct one?

Thanks for the help.

[thunderations]

This will not fix your speedometer problem, but will let you know your correct speed. There are several different apps for a cell phone that use GPS to correctly tell you what speed you are traveling. I just plug my phone into the lighter, just to keep the charge up, and bring the speedo app on screen. From then on I drive by the speed registered on the phone. My 1966 Daytona is 5 MPH slow at 65, actually only doing 60.
There are several apps available, some are free and some cast a couple bucks.
Having several inaccurate speedometers in my Classics, this is a cool thing to have.

[Commander Eddie]

Actually, only 6 mph off isn't bad. I'd suggest just doing the math in your head although the difference may be less as you slow down. Try to get a correct speed for 35, 45, 55, and 65 as shown on your speedometer. Then you don't even have to do the math. These are speeds that are commonly posted on our roads.

[Greenstude]

One reason for speedometer error is a change in tire size. If your tires are the same circumference as those on the car when new, you may not have much speedo error. On my '47 Champion the error is well under 1 per cent on the odometer, and a maximum of 2 mph slow on the speedometer --- but that's just luck because of the tires that happen to be on it now.

I agree with having a GPS within sight while you're driving, so you know your real speed. I often do this with my 2014 VW Jetta, whose speedometer reads up to 10 km/h faster than actual at highway speeds, with the original size tires on it. On my 2004 VW Jetta, there was 0.0% odometer error in 100 km with Michelin tires of the correct size.

[Jeffry Cassel]

They aren't precise when new. Tires now often have a smaller diameter. Suspect they don't improve with age . I'd just take the error into account ; if you are OCD it can be sent away for a couple months and be recalibrated for a couple Benjamins. Or use the GPS for a speedo-- That is spot on.

[StudeRich]

What size Tires are you running?
I am guessing that one More or Less Tooth on a Pinion Gear, will change the speed MORE than your 6 MPH error!

[57studechampion]

I did change to a radial tire, so it is probably my fault that it is off.

I can use an app. Good suggestion.

Thanks

[62champ]

If you look at some of the car reviews written back in the day, a lot of time they would post the indicated speed on the speedo and what the actual speed was - so it must have been a pretty common occurrence.

[JoeHall]

Stude speedometers tend to be 10-20 percent optimistic. I usually use a pinion that gets the odometer as close as possible. I then remove the bezel and adjust the hair spring on the speedo, to make it accurate in the 50-70 MPH range. It is simple, once you have done it one time.

[jackb]

I just drive ~15 mph slower than the traffic I'm in at the time. Puts me right about the speed limit...

[Jerry Forrester]

I just drive ~15 mph slower than the traffic I'm in at the time. Puts me right about the speed limit...

And a danger to everyone on the road.

[TWChamp]

I just drive ~15 mph slower than the traffic I'm in at the time. Puts me right about the speed limit...

Boy, ain't that the truth!
That's why they shouldn't have jacked up the speed limits a couple years ago, where some places are even up to 80 MPH posted speed.

[pinehurstbob]

When I restored my 60 convert, I switched to a 331 rear end and our friends at Studebaker International looked up the correct gear for the trans. Net result was I was out by 6 to 8 mph. reading high. I did what Stude Rich suggested, that is change the gear in the trans to one with 1 more tooth and now its right on. I am also running radial tires (205/75R/15) and agree that this is why the "correct" gear did not give an accurate speed. Hope this helps correcting your problem.
Bob

[Jerry Forrester]

I have never understood why someone would say "My speedometer is out X mph".
I ask "At what speed?"
It makes a big difference if it's off 3 mph at 10 mph and it's off 3 mph at 100.

[r1lark]

It makes a big difference if it's off 3 mph at 10 mph and it's off 3 mph at 100.

That's for sure Jerry, good observation! I wouldn't worry about the 3 mph off if it's at 100 mph