Re-calibrating Speedometer and Odometer

In order to do this does one actually have to buy a device that has to be installed in the dash?

I thought it could be done with just a computer programmer.

I'm going from OEM size tires (265/65/17) to 265/70/17 size tires and I'm wondering if that is a big enough difference to re-calibrate everything. I want everything to read as accurately as possible but I don't want to spend really like any money doing it. So I guess I just need to know if I should not buy the tires now.

I think the size change is over all 3% difference, but I really do want all my odo./speedo to be perfectly accurate. Same with mpg calculations.

 

https://www.tacomaworld.com/tirecalc?tires=265-65r17-265-70r17 Honestly I wouldnt worry about it in your situation. im running 285/70R17 and i think im off by 5mph, says 70 im doing 75.

 

So when you are doing your MPG calculations you would have to subtract your mileage by 5% correct?
Mine would be about 3.3%

 

You would add 3.3% to your miles. The computer counts revolutions of the wheel, so the larger diameter makes it believe it is traveling less than it actually is. A larger wheel rotates fewer times to travel the same linear distance.

 

Yes you need a special tool to do this.

By law all vehicle manufacturers have to have the speedo less then actual speed limits. It is often to find vehicles at 3% less. Much more than 3% and car companies start to face fines from DOT (or regulatory bodies). Most have found that by going +1 on the tire size you actually run true to speed limit.

***ONE important note**** if you do not re-calibrate your speedo please think in your head that you are traveling 3-5% faster than it is reading. You can use a GPS to figure out your actual speed but remember that if you get a ticket, GPS is not recognized in court yet as a speed traveling device. Meaning you will still get a ticket even if you can prove that your GPS says lower.

Most of us that have only gone +1 do not worry about getting re-calibrated but you can if you wish. Please use the tire calculator to figure out the differences. You can then make the decisions for yourself.

https://www.tacomaworld.com/tirecalc?tires=265-65r17-265-70r17

Of course cost is a big figure. If you can get someone to do it for $10 then go for it. Most around here start at $150 and go up from there.

Now if you were going up to 35" then you may want to, as the numbers start to be more noticeable. Also remember that if anyone else drives your vehicle and gets a ticket. You can be found liable and charged with 'failure to maintain equipment'. This is usually only a minor offence and does not carry demerit points. It is also often less then the cost of a speeding ticket.

Please take all the above with a grain of salt. I am not a lawyer nor a police person. I take no liability for any decision you make but am only providing you with information to make a decision.

 

I usually don't calculate my mpg. I should also state that I have an UltraGauge so that can also keep track of my new speed mpg and fuel left etc.

 

You should add the miles, not subtract, or just multiply miles by 1.033 and divide by gallons to fill tank.

 

yes I realized once I noticed your post been at work for almost 2hrs already maths iz hard haha but I edited it to not look stupid, guess ya caught me

 

Sorry, I asked you a question you already answered.

What specific part do I need to get for this?
Forgive my ignorance I've never run bigger tires before.

 

Honestly just get an UltraGauge. I love mine they are fairly cheap and you can get quite a bit of information off of them. Although I wouldn't believe the miles to empty on one they don't seem to get that one very accurate. You can get it to display your new speed after you calibrate it correctly. IDR if the taco uses software or a physical part for speed I know some vehicles use a speed cable/gear and others use some sort of calculation.

 

Everyone around here is able to just re-calibrate. I have not heard of a 'part' before. But it is possible. They may want to put something on your axle/tire or in your gear box. (see above)

Perhaps try another shop to see what they say. I find classic or custom mechanical shop rates might be a bit higher but they often know work arounds for problems. They may have an option or be able to explain what the part is and why it is needed.

As with everything, try to ask a few shops and narrow down the answer.

 

I did not do it for my +1 size. The difference is so minor and everyone already knows to stay away from my truck.

 

my Harley speedo reads dead on.im pretty sure theres no federal law for auto manufacturers.and yes I got an Ultra Gauge.after calibration it shows the true speed.

 

Here is the law
https://www.law.cornell.edu/cfr/text/49/393.82

There are lots of articles regarding speedometer and how they read. Feel free to look them up. I do not really want to start an argument on this. (I have been in transportation and have seen some of these issues first hand so I know a bit of them). Different vehicles run truer than others. I would think motorcycles are more accurate.

Bottom line. If a car company sells a car that the speedo reads slower than actual speed. They are liable for prosecution because you as the driver have taken it on good faith that what they sold was true or accurate. The speedo issue has a lot to do with tires getting worn over time and never truly being the same diameter.
please also keep in mind that most vehicles in our market have to meet regulations from other countries. The strictest will prevail. In USA & CDN we often get AU laws and some European laws.

Ultra gauges work great but they do not change your ODO. If the OP is OCD then he may want this corrected. I personally can do the calculation when I update my fuel log book. It is easy by hand or most phones can do it for you.

 

OP

Good luck with your decision and if it is found that a 'part' is required please let us know what it is.

 

Yes, you just have a device to do it. Hypertech makes a very easy to use device for our trucks for this, it installs inline at the back of the Guage cluster and the software is a complete no brainier to use just fill in the blanks. You can leave the USB cord plugged into the module and stash it in the change pocket by the fuse box for super easy future use.

Note - for actual super true readings you need to measure your tire height on the truck not the BS specs from the tire co's web site because tires are always much smaller than those specs. My 35's for example show 34.6" on the manufacturers specs but in reality they are barely 34" tall mounted on the truck.

 

Thanks everyone for your help.

I called a few more places and they are showing that yes you do need to install a re-calibrator into the dash in order to reprogram everything. The Tacomas aren't reprogrammable without them.

I didn't budget for needing such a thing so I'm not getting it. Especially since I don't plan on doing any other tire size than these or OEM. Just not worth the expense. Now I just need to figure out if I want the tires or not.

Has anyone run this size? Did it mess with MPGs?

 

You will loose depending on tread pattern. I lost a very small amount. It mostly was because of weight as my winters are heavier. Most will say it is minimal.

More important was the loss of acceleration and downshifting on some hills. Not a huge deal unless you just want to go fast.

 

I rarely drive over 60mph for fuel economy LOL. So no issues wanting to go fast here.

 

For most vehicles, most speedometers and odometers are off different amounts. My 2009 with new OEM tires read 2-3 miles per hour high at 60 actual mph (ie 62-63 mph shown). Odometer was almost perfect, off less than 1 mile for 100 miles travelled. Any error in either speedo or odo will change over time as the tire wears. My OEM tires lost a full inch in diameter when replaced at 37k miles.

Who knows what the government mandates on tire wear?? Speedometer accurate when tires are new ? When 1/2 worn?? Some manufacturers were successfully sued over speedometer error, and I would bet there have been lawsuits over odometer error/new car warranty miles.

Again, who knows?