Tire Size Affecting Speedo?

[Weldo]

Howdy, I recently sized up my tires from 225 75 r15 to 31 x 10.50.  They're about 3 inches taller and I think my speedometer is misleading me.  According to the build tag sticker on the driver side door jamb, 225 was the stock tire size.  Any way to correct this difference?  I believe I'm actually going faster than my speedo indicates.  Thanks a lot!

[whiteman]

I thougth that there was a small gear you could buy to install in your transfercase that would recalibrate you speedo to your tire size, but I have not been able to find it.

[Weldo]

I thought maybe the same thing except changing the gears in the speedo gauge instead of the t case.

[whiteman]

In the T-case there is a small plastic gear where the speedo cable inserts, you can access the gear by droping the rear drive shaft and pulling the 1st section of the T-case apart from the housing and it sit in a small indent.  I remember seeing one for sale, but can not remember if Marlin had it or All-Pro

[Cheesemaker]

Superlift used to sell recaliberation units!  Get a GPS unit to find out your actual speed!

[Willy Mammoth]

That's what I thought too, there should be a small gearbox you can install in the cable that has different gears to calibrate the speedo.

If you can find one let me know where.

[eightyfive]

re gear your axles, that'll bring you close to stock....but if you do, you may as well go bigger.

[reklund5]

What year is your truck?  V6 or 4Cylinder?

IF its a 4cyl, manual trans, it's an easy fix.  The speedo drive gear on the tailshaft of the t-case is easily changed to accomodate your tire size. 

Toyota did offer 31's as a factory option, so you should be able to order a different speedo drive gear from your local Toyota dealership.  If you pull the gear out of the tcase housing, you'll be able to see a number that indicates how many teeth are on the nylon gear.  Simply order the gear with the correct number of teeth, and you should be able to get your speedo pretty close.  (Note...this only works up to about a 31" tire...beyond that it'll always be off a little)

Ryan

[Cheesemaker]

The calibration unit from Superlift is called "Superlift TRUspeed," just do a search and anybody sells them.  Ebay to JCWhitney.  As long as your rig is a 1992 or newer!  Alot of write ups on this item!

[Weldo]

My truck is a 91 4 cyl manual trans.  The electric recalibration thing prob won't work for me.  How do I get the gear out of the t case?  Do I have to remove the drive shaft and a portion of the housing like whiteman said?  Thanks a lot for the help guys!

[blackdiamond]

The difference is always a percentage, so it is usually fairly easy to figure out from the stock setup.

It is constant so once you figure it out, use an online calculator, you can go from memory.  If someone else gets a ticket, too bad for them.

[whiteman]

Considering your truck is a 92, you may need the Super lift Recalibration computer.

Here is a link to some info for ya http://www.marlincrawler.com/htm/transfercase/tcaseinfo.htm

This is what it say's about your T-case.

Type 6-B

Installed 1992-1995 pickup, 1992-1993 4Runner
Tall Case
Forward Shift, 4" Offset
10mm Flange Bolts
Quite Run Gears
Block Off Plate
No Flat Washers on Case Bolts
Electrical Speedo Cable Drive

This is what i have.  So you know where I am coming from.

Type 3  EFI 4Cyl
Installed 1985 - 1988 EFI Pickup
Installed 1985 - 1989 EFI 4Runner
Top Shift
Tall Style Case
10mm Flange Bolts
Quite Run Gears
With Bearing Retainer Clip
21 Spline Input

I would call Superlift and see if it will work, because then you can just re-program for you tire size instead of re-gear

[Weldo]

I got a new speedo gear today from the dealer but there's no way it's gonna fit in the T-case, the gear's too big to fit in the hole of the T-case.  Also, the shaft is longer.  Is there a different transfer case housing for trucks that came with 31s from the factory?

[skid]

Wouldn't you have to replace the drive gear also?  Which would require removing the back housing off the t-case.

[eightyfive]

calculate your speed and other things here....put in 4.56s...that should bring you back to stock speed. unless you have the auto, get 4.88s.

http://www.ring-pinion.com/content/calculators/default.asp

[Weldo]

Wouldn't you have to replace the drive gear also?  Which would require removing the back housing off the t-case.

Yeah, I thought about that after I ordered the new one from the dealer.  On the way home I was wondering, if the new gear has 32 teeth as opposed to the stock 18, it must be a bigger diameter.  So it would make sense that the drive gear would have to be smaller to mesh with the new speedo gear.