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Tue Mar 27, 2007 7:29 am

With 215's on the front of my '67 the speedometer is 8.1% slow. 100 miles on the speedo means 108.1 miles actual travel.
I finally found a place in Atlanta that will insert a ratio adapter for $136.00 +or-. WWW.speedometerservice.com (770-569-8255 Steve)

They only need your cable and will splice in the adapter in a straight portion of your cable. You need to do the math for your particular percentage. If at a later time you change to a different size tire they will re-gear for around $55.00.

And no, I have no affiliation with them. This is just a public service anouncement. I have searched for 2 months and this is all I could find.
I even thought of re-surfacing the numbers accurately on the dial face but then my odometer would still be off.
Have a good day, Marvin

Tue Mar 27, 2007 7:34 am

I have not checked...but I am pretty sure you can get aftermarket Speedo's, as most people here do. I have never installed one....but I could not imagine not being able to calibrate them as they have no idea what your tire size is.

Tue Mar 27, 2007 7:46 am

wouldnt you be able to just move the needle backwards a bit?

Tue Mar 27, 2007 7:53 am

dirtydeedss wrote: wouldnt you be able to just move the needle backwards a bit?

No, because it is off by a percent, not a fixed number.

What he is looking for:
Code: actual speed = read speed + read speed * .081

What your describing:
Code: actual speed = read speed + 8.1

See the problem there? Work it out with a few speeds and you will see the difference. The variation is porportionate to speed, so if you go faster it will be off more.

Tue Mar 27, 2007 7:55 am

i thought that because the speedo cable was mounting in the middle of the wheel hub that it wouldnt matter what size tire you have on there.

Tue Mar 27, 2007 8:15 am

72BajaBen wrote: i thought that because the speedo cable was mounting in the middle of the wheel hub that it wouldnt matter what size tire you have on there.

No, think about it. The larger the tire, the larger the ouside radius. That means for every revolution more distance is covered. So if you spin a large tire 10 times, and small tire 10 times, which one will cover more ground? Speed is distance / time. Time stays the same, so what happens when you increase the distance?

Tue Mar 27, 2007 8:27 am

alright i see what your saying. so how do you figure out your off percentage?

Tue Mar 27, 2007 8:54 am

Get a handheld GPS and find a highway and travel at a variety of speeds (like 30mph, 60, and then faster if you can) and compare what the GPS says to your speedo.

X is your percent
Code: GPS Speed = x/100 * Read speed

If you don't have a GPS you can use mile markers. Travel at 60MPH (according to your speedo) and time the distance between mile markers. It's best if you use several, say do it over 5 miles. Maintain your speed!!! Then compare the time, it should take exactly 1 minute for every mile. This is not as accurate though.

Tue Mar 27, 2007 9:00 am

crane550 wrote: 72BajaBen wrote: i thought that because the speedo cable was mounting in the middle of the wheel hub that it wouldnt matter what size tire you have on there.

No, think about it. The larger the tire, the larger the ouside radius. That means for every revolution more distance is covered. So if you spin a large tire 10 times, and small tire 10 times, which one will cover more ground? Speed is distance / time. Time stays the same, so what happens when you increase the distance?

Here is a chart I have taped to my dash.
Reading Actual
10 10.81
15 16.22
20 21.62
25 27.03
30 32.43
35 37.84
40 43.24
45 48.65
50 54.05
55 59.46
60 64.86
65 70.27
70 75.67
75 81.08
80 86.48
85 91.89
90 97.29
Marvin
PS havent had it past 75 yet.

Tue Mar 27, 2007 9:14 am

72BajaBen wrote: alright i see what your saying. so how do you figure out your off percentage?
The way I figured mine was I towed the bug behind my van ( I know for a fact that the van odometer is accurate to a tenth of a mile in one hundred miles. I used MM's on the interstate to check.) for 1200 miles and subtracted the difference in odometer reading on the van and VW.

Marvin

Tue Mar 27, 2007 9:47 am

I have a new VDO speedo that claims that you can use the menu on it to calibrate your speedo. I have yet to install it, but I have read the paperwork. I was planning on just turning on my handheld GPS while someone else drove, and monkeying with the damn thing until the indicated speed on the speedo, and the speed indicated on the GPS were the same.

Like I said, I haven't tried it, but I can't imagine any aftermarket speedo manufacturer making something which couldn't fit a variety of applications.

I will have two completely different size tires for street and off-road, so being able to calibrate speed on the street and distance in the dirt will be aided by being able to recalibrate at will.

Tue Mar 27, 2007 9:53 am

wythac wrote: and monkeying with the damn thing until the indicated speed on the speedo, and the speed indicated on the GPS were the same.

Just make sure that the road you are driving on is straight. GPS don't read accurate speeds on a curve. Some are a little off, others can read quite a bit off depending on how often they update location. :D

Tue Mar 27, 2007 10:02 am

I have a much more practical reason for needing to do this on a straight road; straight would also be essential for me to be able to operate a GPS and a leetle tiny menu button on the dash at the same time. You'll notice that I plan to have someone else drive...that would surely result in disaster.

Tue Mar 27, 2007 10:06 am

The VDO speedometers I've used just need the tires circumference. Easily obtained with a bit of chalk.

Tue Mar 27, 2007 10:11 am

What is a VDO speedometer? (the VDO part)

Btw...does anyone have any good links for speedo's, tach's and guages?

Tue Mar 27, 2007 10:22 am

When I get home tonight I can get the part # for you. It is an inductive one that requires a rather expensive pickup to use the stock speedo cable. I bought mine from Chirco.com. I think it is 3 1/8" dia.

Tue Mar 27, 2007 11:07 am

Thanks, that would be great. I think I am going to run 2 speedo's on mine. Stock, and an aftermarket. Will mount the stock speedo in the center dash, and then the after market speedo, tach and guages closer to the drivers side.

Don't ask me why I have to have TWO, I just do.

Wed Mar 28, 2007 1:02 pm

OK, I have to speculate on the two speedos thing;

IT IS BECAUSE;

1.)You like things in stereo.

2.)Your double vision has gone away and you find it disconcerting to drive with only one instrument

3.) You have a significant other who feels a need to associate a number on how much faster than the speed limit you happen to be going.

4.) One of the speedos is manufactured by Lucas.

I don't even care if I was close. That was fun.

Wed Mar 28, 2007 1:12 pm

wythac wrote: OK, I have to speculate on the two speedos thing;

IT IS BECAUSE;

1.)You like things in stereo.

2.)Your double vision has gone away and you find it disconcerting to drive with only one instrument

3.) You have a significant other who feels a need to associate a number on how much faster than the speed limit you happen to be going.

4.) One of the speedos is manufactured by Lucas.

I don't even care if I was close. That was fun.

1. -True
2. -Very true
3. -Also true, however that gives me an AWESOME idea:....have the second speedo run slow!! Everyone is happy!
4. -No idea.

Wed Mar 28, 2007 1:49 pm

"VDO" manufactures lots of things, including gauges. I don't know what VDO stands for.