Speedo / Tach / Gauges: Speedometer/odometer off

[paul shuffleburg]

The speedo/odometer in my Champ reads about 8% slow. It has a T-85 W/OD and has a
17 tooth pinion. Would a 16 tooth get the job done?

[Steve L]

http://www.partshp.com/speedometer_gears.htm

The Co. above have ratio adapters that can get you right where you want to be.
Dropping one tooth from a 17 would be a correction of 5.9%. Below the 8% you are
looking for. Their adapters are not cheap, but they work well & are easy to install.

[tomlewis]

My experience has been that if you just change the little pinion gear and don't change the worm gear, the pinion gear will be destroyed in short order. Tom

[thunderations]

I like the speedo to read low. That way I can drive the speed I want and the wife thinks I'm driving sensable. It's a win-win.

The speedo/odometer in my Champ reads about 8% slow. It has a T-85 W/OD and has a
17 tooth pinion. Would a 16 tooth get the job done?

[JoeHall]

IMHO, at 2.1 percent off, the 16 tooth is close enough. I do not recall a single Stude that was exactly correct on speedo and odo. Two percent is unusually close, as most are optimistic by 5-6 percent, which makes the owner think he's getting better MPH and going faster. I think Studebaker Corp wanted it that way.

[paul shuffleburg]

Joe. My 51 Commander and 61 Hawk both read a little
faster than actual speed. It seems I read somewhere that
if your speedometer says you are going 120 that you are only
doing 107 MPH.

[JoeHall]

Joe. My 51 Commander and 61 Hawk both read a little
faster than actual speed. It seems I read somewhere that
if your speedometer says you are going 120 that you are only
doing 107 MPH.

Years ago, I used mile markers and stop watch to calculate speed and distance error. Thank goodness, we now have GPS and can nail it down easily. As for anything written as a one size fits all, like you read, I'd consider that as least accurate; little more than a WAG. However, 107 versus 120 is about 10-11 percent error.

[thunderations]

Tire size will have a lot to do with speedometer error too. Not many Studebakers on the road with the correct size tire.

[53k]

Tire size will have a lot to do with speedometer error too. Not many Studebakers on the road with the correct size tire.

Very true! With 215x75x15 radials (closest in size to 6.70x15 bias ply) on my '64 Avanti, my odometer is .1 miles off at the end of ten measured miles. I am running a 3.07 TT. I don't remember how many teeth the pinion has.

[JoeHall]

Very true! With 215x75x15 radials (closest in size to 6.70x15 bias ply) on my '64 Avanti, my odometer is .1 miles off at the end of ten measured miles. I am running a 3.07 TT. I don't remember how many teeth the pinion has.

That's a 10 percent error rate.

[53k]

That's a 10 percent error rate.

You might want to recheck your math. Off by one tenth of a mile at the end of ten miles is a one percent error.

[JoeHall]

You might want to recheck your math. Off by one tenth of a mile at the end of ten miles is a one percent error.

Oops, I overlooked the, "ten miles" and was thinking one mile. You are lucky, I have never had one that close. Tire size also affects. I recall a 2-3 percent change when I once put on a set of 205/70 tires, instead of the usual 205/75s. When those tires wore out, I never strayed from 205/75s again.

How about your speedo? Usually, the faster the speed the more optimistic the speedo becomes. The GT Hawks' speedos are close enough till around 70 MPH, then begin to read excessively high. The 56Js' 160MPH speedos are pretty good up to 90-100, surprisingly. I once drove one at an indicated 120 on a two lane desert road in California. Young & dumb, and lucky to be alive. Never again.

[53k]

...
How about your speedo? Usually, the faster the speed the more optimistic the speedo becomes. The GT Hawks' speedos are close enough till around 70 MPH, then begin to read excessively high. The 56Js' 160MPH speedos are pretty good up to 90-100, surprisingly. I once drove one at an indicated 120 on a two lane desert road in California. Young & dumb, and lucky to be alive. Never again.

Good question. I had never considered speedometers varying by speed. My reading was at about 65 mph. I'm almost embarrassed to say that I have never had the car over 70.