Speedometer Calibration

The new VDO speedo from SE/Beck is GPS driven. Think the set of 3 is $589 (?).  They are different size from other replica gauges so doing only 1 might look odd.  You could probably sell old gauges for $250?.  Why not just mount a Tom-Tom or other GPS and go by that.  Suspect there are GPS phone apps too (Free GPS for iphone).  Did you use a GPS and how far is speedo off.  I think every car I've owned reads 3 mph faster - which is probably a good thing.  

I like my refaced 914 gauges and don't want to replace them. Also, I don't like the look of the LCD odometer in a replica of a car from the 50s.

In my daily driver, I do use the GPS display on my phone instead of the speedometer. But, I don't always have my phone mounted in my Speedster. Some people may just want an accurate speedometer.

I haven't had a chance to check the speedometer against GPS because I need to replace my oil cooler. I have oil leaking out of the fan shroud.

I am thinking my speedometer may read low. The engine seems to be revving higher than it should for a given speed for a 3.88 R&P.

I'm not concerned with the accuracy of my speedometer since I am pretty much 10 over the limit at any given time anyway.  

Michael, the nut on the end on our speedo cable can come off and be replaced with the Ford or GM(can't remember which one). The square end on the cable drive is the same. Honestly I think it's the same nut as what holds a supply hose to a bathroom faucet. I think I found all that info on the Samba.

If you buy a Vanagon short cable from the speedo to the "idiot light 60,000 mile black box" it is short, and has two threaded ends. One end could go to your speedo and the other to that expensive adapter you speak of.

I'm considering a universal cruise control for our trip out West next year. So to get a VSS(vehicle speed sensor) they sell a universal model and I'll have to hook up the cable again.

My new gauges have a GPS speedo from Speedhut, so I don't have the cable anymore.

FOLKS:

I have restored original 356 VDO gauges..with a 3:88 R/P and 15x 4.5 in Vredistein tires.  When they were installed there was speculation that my speedometer may be off between 7-10 MPH,  BUT..  Thanks to the California Highway Patrol and a $264 ticket I now know that my speedometer is deadly accurate.   80 is 80!!!!  

Any po po will be happy to help figure that out if you ask them.  Don't do it the hard way like I did..

Thank you for your minute of attention, I hope this may be of some help.

Tebs

ps Robert has to go ten over so he can keep up with me..

@DannyP  Are your other two gauges from Speedhut?

I was looking at that site and I was wondering how they look. I'd probably go with the 4.5" size in a tach, speedo, and a quad gauge. They can be semi customized too. They've got to be better than the China gauges in the car already.

@DannyP, it is good to know about the short cable. I want to keep the VW nut on the speedometer end. It is the end that attaches to the expensive device that needs the GM nut. I don't see how I could replace the nut on that end without cutting the cable because of the flared end of the cable that fits inside the nut.

Michael, I have the Chinese gauges that came on my 2014 VS. I have a 4:12 (what I wanted) and at 3100 rpm, I'm going 62 mph if that helps.

You didn't give us specific rpm vs mph so it's impossible for us to guess which ring and pinion you have.

...or you could use Teby's calculations: every mile over the speed limit will cost you $10.56

...but his calculations only work here in California...and possibly only on the Central Coast, everything costs more here...

@Will Hesch, I used this method to determine that I probably have a 3.88:

Jack up the car so both rear wheels are off the ground with the emergency brake off and the trans in 2nd gear. Turn one tire so the valve stem is at the top. Turn the engine over by hand, counting the engine revolutions needed to get 1 complete revolution of the tire.-

9 revolutions- 4.375 r&p

8 1/2- 4.125

8- 3.88

This method was posted here in 2013.

Instead of putting a valve stem at the top I turned my crank pulley to TDC and then put a piece of masking tape at the top of the tire.

If you try this, be sure to release the emergency brake. I didn't at first and it made the engine harder to turn over and gave erratic results.

Michael, here's a free speedometer iPhone app that works great.

Large display, so you can just leave your phone on the passenger seat to check the accuracy of your car's speedo. The one in my VS reads about 10 percent high.

I have that iphone app - works the charm as everything I own has been fettled with. Tire size or gear changes having been done (its a madness).

If you have a mechanical speedo cable just go with the inline mechanical adapter.

No reason not to. Don't over think it! Its inexpensive and just works. We have one in our '78 Camaro which has been re-geared & tire size changed slightly... Muy bueno! Its spot on (within 1 mph).

Here in the NW we have Tacoma Speedometer. Great rep, quick and cost effective. I'm sure you could do it over the phone.

I did it over the phone and my speedo is spot on by GPS. Just tell 'em your gearing change, noted mph at 60 (or whatever speed they'd like to calibrate by), and gps speed.

Easy peasy.

Sorry to resurrect a zombie thread, but does anyone have a source for these inline mechanical speedo calibration units?

Those are kind-a common in the Hot Rod world, and they MUST exist for the vintage rally car set because they need super-accurate speedo drives for their TSD events (Time-Speed-Distance) so there MUST be Metric ratio adapters readily available.

You would have to figure out how you are off - high or low - versus desired speed, and compute that as a percentage.  Let's say your speedo is low, showing 35 when you're doing 40mph.  Then you would want an adapter that would be 40/35 or +1.14  All of the adapters are sold by ratio, so yours would be important to know.

Anyway, a quick look got me to "Mr. Speedometer" and this site:

https://mrspeedometer.com/products/ratio-adapter

Remember, you're looking for a Speedometer Ratio Adapter if you go to a different site for Metric versions.

Good hunting!

And it looks like someone already beat you to this:

https://www.speedsterowners.co...ometer-ratio-adapter

@Michael McKelvey Easiest way to determine if your Speedo is off is with a tachymeter. (Well, second easiest. I guess the easiest would be a GPS vs Speedo)  If you don’t have a chronograph, here’s a face to use.  

If you have VDO gauges, PAS can calibrate them. Their website has a worksheet to fill out with what you need.
http://paspeedo.com/ratio.htm

The Waze app has a built in speedo as well.

I don't have a problem with my speedometer.  Palo Alto calibrated it for me.

Woops. Lol. Zombie thread. Just in time for Halloween.