Speedometer/Odometer Calibration??

I have searched the forum and found where guys have "recalibrated" their speedo needles after doing dash mods....but nothing related to my dilemma....here it is:

I just bought this lovely 97 model that has 16 inch Toyota wheels mounted instead of the original 15 inch. I am still studying and learning all about it (hence I found this great forum!)

So I got some new tires for it and started thinking about the size difference and affects on speedometer readings. I plugged in the GPS and sure enough....my speedo and odo are about 10% pessimistic....

That is to say, When the speedo says 50 mph I am doing 55!!! At 70 indicated I am going closer to 77.

Now I can do the math easy enough to keep from getting tickets, but my mileage on the odometer is not going to reflect reality and how will I ever figure my fuel mileage with any accuracy??

Now I know of companies that sell speedo calibration devices for motorcycles that use a electrical pulse generator speed sensor to drive the speedometer and sure enough, they sell them for cars and trucks too. But I get the funny feeling my Taco has a cable drive....I've sent an inquiry to one of those companies to see if they have a "box" for me, but no answer yet.

Anyone have any advice for me???

 

Well if you know it's showing you are doing 10% faster than the speedometer says, the same will apply for your mileage. Just add 10%. Or you could get an ultra gauge or scan gauge and adjust it on there.

 

http://www.taeservice.com/speedo.html

 

Thanks...that looks like what I might need. Wonder what that will cost???

I also got a response from Yellow Box last night (they are one of the companies I am familiar with that make calibrators for bikes)

http://www.yellr.com/index.htm

saying their product will work and they might even have a plug-n-play wire harness adapter so no wire splicing.
Therefore I think perhaps it is NOT a cable driven speedo????

I still haven't dived under the car and hood to look for the cable or sending unit. Anyone know for certain, or shall i go out and crawl under to look?

 

The guys at Yellr are awesome.
I've had great customer service from them.
Jennifer is a really nice lady!

Aside from that, I'm 99% certain you do have a cable driven speedo.
Obviously the easiest way for you to be sure is by taking a look under the truck. The VSS or speedo cable will be sticking out of the back passenger side of the transfer case right behind the rear drive flange.

 

Yep, crawled under her at lunch break....Cable coming from the drivers side just ahead of the U-Joint and heading up to the firewall center of the dash area.

Guess I'll go for a highway ride and record some mileage and find out what that Toledo Auto Electric device is going to set me back. Thanks again for the link.

Update...TAE only has SAE fasteners, so their device has to be spliced in-line on my speedo cable....meaning I have to yank out the cable, send it to them and then reinstall....still no word on cost, though.

 

Use GPS or milemarkers at the side of the highway over a nice long run (100 miles or so is great if you have a 100-mile highway trip you need to do) to get "odometer mileage" and real milage to some reasonable degree of precision.

Put those in a spreadsheet. Put your odometer mileage and gas use in the spreadsheet. Access your actual miles and gas milage from the spreadsheet. Tape a reminder to the speedometer so you don't have to do the math to avoid the tickets. No expensive boxes required...

An ultragauge can (if you bother to calibrate it) also do the job somewhat easily and for only $70 or so (but I'm starting to think they will never come up with the $9 rebate they claimed...)

Say you drive 100 miles and your odometer shows 93.7: Every 0.937 miles indicated is a mile driven; which is the same as every 1.0 mile indicated is 1.0672 miles driven. However much is indicated, multiply that by 1.0672 (if that is the right number for your tires/odometer) and you have the actual miles driven. Not difficult. Just take reasonable care getting good numbers from the odometer .vs. the reference, and don't try to do it in a single mile, where 10% error is just about guaranteed since the odometer only reads to tenths. I've used a spreadsheet to do the gas mileage for years, so correcting the tire-size differential was simply a matter of finding what the difference was and entering it once. If you change tires/wheels, do it again. If you want to be fussy you can readjust as your tires wear down...

 

I used the Dakota Digital
never messed with the speedo drive gear.

 

15" or 16" rim doesn't matter. The outer diameter of the tire is what matters since that determines circumference.

C = pi*dia.

The larger the diameter, the larger the circumference and so the farther you travel per revolution of the wheel.

 

Damn i need to do this

 

Now that looks easy enough.....I'll check that out.

TAE got back to me. I do the mileage calculation, remove the cable and mark the area for the device to splice in (so it will go back on without interfering with anything on the chassis) and ship it to them. $71.02 plus shipping. Sounds reasonable, but a lot of work to R&R the cable.

The reason I want the OEM odometer to be accurate is so that, should I ever decide to sell her, I won't have to check that dreaded box on the title that says the odometer reading is not true. hat can be a red flag for some buyers and drop the value of the car.

Thanks for all the help guys!! I'll post up results when/if I do something.

 

Well....the specs for the tire/wheel size for my '97 show that I have installed the tire/wheel size for the 4WD model...

That is: the 2wd came with 215/70-14 and 4wd came with 225/75-15.....which is about what I have on my 2wd now.

I was looking at the speedo gear drive swap as shown at (thanks jberry813)....

but the 2wd transmission speedo drive shows 17 tooth gear and 17:6 ratio and the 4wd is 33 teeth and 33:11. So I don't think that's going to work.

Any Toyota parts guys or technicians out there that know of another model with a speedo drive that may work? I would guess I need a 15 tooth or maybe a 14.....My actual error is 11.7%.

 

I have decided to buy some new wheels and tires in the proper size. Should help the acceleration off the line, too.

Anyone interested in the 15" OEM wheels with nearly new Goodyear tires (about $700 worth).