Speedometer correction for larger tires - 2WD

[presslab]

The 2WD speedo is driven off the front hub, direct drive. The stock speedo is 805 revs per mile, but the tires I have are 754 revs per mile, for about a 7% error.

I know that a speedo shop can recalibrate the speedometer to be correct. I guess they do this by changing the strength of the magnets in the speedo head. However the odometer will still be off by 7%.

I have read that it's possible to insert a gearbox inline. The cable is modified with two new GM style ends, and a box inserted in the middle. A different gear for the odo (are these available?) and a recalibrated speedo will work too, I suppose. Even a whole different speedometer will work, like a Jetta or Passat, but the matching speedos I've seen are only good for Syncros which have a different revs per mile.

Anyone have a solution for this?
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1986 Vanagon Westfalia EJ25
1988 Subaru GL-10 EJ20G --- 2000 Honda XR650L
2010 Titus El Guapo --- 2011 On-One 456 Ti

[Jon_slider]

no,

my 3 vehicles each have non stock tire sizes, and innacurate speedometers and odometers

I use a GPS for my speedometer, regardless which vehicle Im in.

though I still rely on the vehicle trip odometer to guesstimate my remaining distance to empty.

for my OBDII motor, I use the Scangauge2, which will do miles to empty, gps corrected speed, fuel cost per day and all sorts of cool stuff like code reading and clearing...

but no, I dont know of any gizmos that plug in inline to correct the stock odometers, in my world none of them are accurate

great question though, wish someone had a solution..

[andk5591]

Do some digging on some street rod sites. They may have something there. I vaquely remember reading about something like this in Hot Rod or a similar magazine. to help you calculate the error, there are a number of tire conversion charts on line such as this one

http://www.discounttiredirect.com/direct/brochure/info/tmpInfoTireMath.jsp
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D-Dubya Manx clone 1914. Ex wifes car.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Ex-wifes car.
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[elwood91]

As most stock speedometers have at least 5% error even with stock tires, check your current setup with GPS or stopwatch and milemarkers before altering anything. My upgrade to 215/75/15 changed the error from almost 10% over to about 5% under.
Just because it was factory set doesn't mean it was accurate.

[presslab]

Speedo was dead on with the stock tires.

Found a shop in Washington that will crimp ends and put a gear box inline. He said they have over 300 different ratios and they can get it pretty close to what I need. All that for less than $100, so I'm going to give it a shot.
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1986 Vanagon Westfalia EJ25
1988 Subaru GL-10 EJ20G --- 2000 Honda XR650L
2010 Titus El Guapo --- 2011 On-One 456 Ti

[jackbombay]

[?Waldo?]

It seems that with a gas van you ought to be able to simply add the gearbox in place of the O2 sensor light box and never have the O2 sensor reminder come on again. No crimping necessary.

Andrew

[presslab]

[Jon_slider]

I called to ask the price

they said for a vanagon, parts and labor would be about $100, they want the cable mailed in so they can split it and insert an inline ratio adapter.

link to ratio adapter
http://tinyurl.com/be5sw8

thanks for the useful info presslab

[presslab]

Installed the box today. Nice work, fast turn around. All in all $101.46; they charged tax even though out of state.

Ratio 1.0733:1 part number MAS TA 666 RATIO ADAPTER.

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1986 Vanagon Westfalia EJ25
1988 Subaru GL-10 EJ20G --- 2000 Honda XR650L
2010 Titus El Guapo --- 2011 On-One 456 Ti

[presslab]

I did a test today with the GPS. My odometer is 0.55 % off, and the speedometer is about 0.3 MPH off. Hard to tell on the speedo.

Good enough for me.

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1986 Vanagon Westfalia EJ25
1988 Subaru GL-10 EJ20G --- 2000 Honda XR650L
2010 Titus El Guapo --- 2011 On-One 456 Ti

[1621]

If you're in or around the Portland area, Speedometer Service in NW does this while you wait. I think it cost about $80. They install the little converter box inline right behind the grill - doesn't require pulling the cable out at all.

Took mine for a test ride afterwards and it was still a bit off. Drove back in and they switched out the gearing in ten minutes and now it's spot on with the GPS.

And correct me if I'm wrong, but it should correct the odometer reading as well. Haven't actually bothered to check, but I figure since it won't spin without the speedo cable that the two were linked.

www.speedometerservice.net
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'85 Westy

[Perales]

Not related to oversize tires, but for the record (from Bentley):

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-- 1987 Westfalia automatic (Captain Vino)

[TroySmith80]

Interesting. My speedometer reads WAY high (reads about 95 at 70mph gps indicated). I'm about to go from stock size tires to 215/70R16 so that will help some, but not enough.

My speedo also wobbles a bit, especially at lower speeds.

Any idea why this would be happening? It's an 84 wolfsburg with factory tach.
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1984 Westfalia Wolfsburg - 2.5L Subaru - Sold - Preparing to move to the dark side (4x4 Ford van)

[Perales]