speedo calibration

Go electronic and put your old one away in the vault.

To calibrate it requires watchmaker skills in manipulating the hairspring.

Speedy Jim

Speedy Jim, My 65 came with 135's on the stock rims. Do you know how much that puts my speedo off by? Greater or less than the actual speed?

Thanks Eddie

| > Me again with yet another question. Here is my yet another "minor" | > problem. I have 165/45R15s tires on the front (droped from 195/50) and | > now my speedo is way off, by which I mean i am reading 70 while going | > around 50. And 80 while in the right lane on the freeway. Which looks | > totaly cool and all, but I would like to be able to tell my actual | > speed. Is there anyway to recalibrate stock speedo? Or the only way to | > remedy this problem is to replace it with an electronic unit? Car is | > 64 T1. | >

| > Thanks again, | > Anton | >

| > P.S. I had to go this small on the tires, because previous size was | > rubbing on the fenders and I want it low. (droped spindles, cb wide 5 | > disk breaks, 2" narrowed beam). | >

| | Go electronic and put your old one away in the vault. | | To calibrate it requires watchmaker skills in manipulating | the hairspring. | | Speedy Jim |

|

I'm not an expert on tires. Best way is to measure the tire radius (as it sits on the road). Compare that to a stock tire radius.

Here's a very handy calculator for gear ratios and tire dimension influence:

This site may help too: and Jim

Thanks, I just don't have any stock tires unless the back 165's are close to the stock size.

| > Thanks | > Eddie | >

| | I'm not an expert on tires. Best way is to measure | the tire radius (as it sits on the road). Compare that | to a stock tire radius. | | Here's a very handy calculator for gear ratios and | tire dimension influence: |

| | This site may help too: | | | and | | | Jim

Smaller outer diameter tires should cause the stock speedo to over-report the speed. Bigger tires would be under-report it. So smaller seems faster on the speedo, bigger seems slower on the speedo.

I usually just drive by one of those speed measuring traffic signs a few times to see what it says. (Although who knows how calibrated they are.) You can always use the mile markers on a 60mph freeway or something like that.

Hi Jim,

Well I do realize the intricacies of the speedo mechanics, floats and magnets etc. So I wouldn't dare going inside of it myself. I was thinking more along the lines of who can do it for me? I cannot find ccspeedometers and don't know if there is anybody else that is capable of doing this.

Thanks Anton

Speedy Jim wrote:

Many years ago I had a GM car (I won't go into the specific model because it is not important here). It was necessary to replace the transmission (it broke). The new tranny had a different speedometer gear and so the speedo read slower than actual vehicle speed.

One day I got stopped for speeding. I explained to the officer that the tranny had been replaced and I was sure the speedo wasn't reading correctly and so I really "...didn't know how fast I was going". To avoid the fine and the insurance points I took the car to a speedometer recalibration shop. This shop had a huge roller drum (similar to a dyno) where they could measure the true speed vs the speedometer reading. Based on the results, they built a "ratio adapter". Basically a geared box w/ male/female speedo connectors on each end. This geared up my speedo cable RPMs and resulted in my speedo reading the correct speed.

I did a quick Google search and found a company in CA that builds the same things. I'm sure there are others places out there. Maybe someone else can recommend one?

can't speak for their quality or if they even have the parts to buildan adapter for a VW, but if you have no choice but to run non-stocktire diameters, this is another alternative to replacing your speedo w/an electronic one, or giving your original speedo a "root canal". Such an adapter would connect behind the dash between the speedo and the cable, gearing down the RPMs. Total service cost to build a "ratio adapter" and test it in the car (many ago)... ~$250 !!!! Well, I didn't say it was a cheap solution :-)

AshMan

Could you not get a freind to drive with you and tell you your correct speed - at 10mph intervals (for example) . Then print yourself a new dial onto acetate ?

Rich

Try this site

Eric 62 Ghia 68 Bug

your 195/50's also made your speedometer read "fast"....assuming your speedometer was accurate with the stock sized tires, 195/50's are approximately 10.5% smaller than stock..therefor your speedometer will read

10.5% fast.... the 165/45's are tiny little fellows....according to an internet tire size calculator( ) they are 17.9% smaller....therefor your speedometer will read 17.9% faster than you are going....any shop that does certified speedometer checks(for verification of speed readings...ask any local police officer they can refer you to the closest one) can make a componet up that increases or decreases indicated speed based on the percentage it is off...it is an add on piece that is put inline between the speedometer and the cable....i have one on my chevy pickup after re-gearing and adding larger tires...was about 20 percent slow on indicated readings....that is a bad thing...well unless you like tickets....

Hi Joey,

Thanks for the numbers. I did a search, looks like there is wolfsberg speedometers shop in my area which might be able to build transmission box for my speedo. Good thing my speedo is reading fast, will keep me from speeding for a while :)

Cheers, Ant> > Hi All,

North Hollywood Speedometer can fix it for you:

'll cost though.

Hi Neil,

Thanks for the link, I am going to try local shop see how much they would charge. Another option is see measure error, calculate error ratio, and one of those adapters with right gears. Gears are around ~$6...

Thanks aga> North Hollywood Speedometer can fix it for you: