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For those who care about anonymous .come friends, I will let you know I ordered some kind of second level computer chip and a turbo charger for my 2006 Tundra double cab 4X4. I will wait for a couple weeks to see what my gas mileage and power is stock, although the previous owner replaced the stock tires and wheels with some 285, 70, 17's. In order to go 65 mph the speedometer actually has read 60. I checked it for several miles and timed it until it takes fifty-five seconds for a mile.

I think I'm like a seventy year old teenager.

Edited to add: The turbo is suppose to add fifty HP. I forgot what the chip is suppose to do.

A Toyota dealer should be able to correct your speedometer if you can find out how many revs per mile your tires make. The tire manufacturer should have the revs per mile on their website.

I found the gear ratio on the web. With just a little math I can calculate it. I used to do that in the old days before tachometers. Figure out the RPM's for certain speeds and shift for maximum power. AS I wrote this the first gear ratio from my old Fairlane came to my mind: 232:1. I switched from a 3.25:1 to a 4.33:1 and could hardly believe the lack of wheel spin the new rear end made.

GPS will tell you too.

That would have saved a bunch of time. Why didn't I think of that?!

That's how I found out why everyone was tailgating me in my Suzuki. The tires are stock but the speedo is off about 5mph

Here's a calculator for tires and includes revs per mile if it helps:

http://www.miata.net/garage/tirecalc.html

Ray's Speedometer Repair over on Rogue River Hwy can take care of that.. right on the same lot as the Union 76 station...

Ray is also a very strong Christian, so you and he would get along... fine gentleman...

Seafire,

Great info. Thanks.

Divide the circumference (in inches) of the tires into [5,280�12]. The circumference of the tire = the diameter of the tire x 3.1415926536 (round it off to suit yourself � most practical folks go for 3.1416. Even 3.1 or 3.14 is probably practical here.).

I've got an '07 Tacoma and the speedometer is off by about 5%. I've been to the dealer about correcting it, and they say they can't do anything about it...something about there's nothing in the computer or the software or something in there to adjust that...

Since I've got a little bit of a lift on it maybe I'll just go to taller tires next time.

Bulletbutt,

I think that's what the previous owner of this rig did. It sure looks good to me. If the photobucket hadn't change their software I would post a photo, but it no longer works for me.

I am thinking since you are gonna be putting a chip in it, Most chips allow for speedo calibration for different sized tires.

you can also check by watching the mile posts along the road.

I've put taller tires on my Tacoma, and am off about 5% or 2.5 miles per hour at 50 MPH.

I just try to drive at what "reads" the speed limit and figure I'm "cheating" by about 3 mph.

Virgil B.