15 to 16 inch wheels, how can we change speedo?

Hi

Have a 1998 Tacoma SR5, 4x4, ext cab. with 15 inch wheels.
Was thinking of putting my 4Runner 16inch wheels on it.
I still want the speedo to work. What can I do to correct?
DO I need to buy a new speedo transducer and display?

So, I just went out and measured the height of my 16" 4 Runner tires
and the 15" Tacoma tires.

They are essentially the same! Well golly gee!

Yet the Tacoma tires look much larger.

15" 31x10.50R15LT measures to 28" height
16" P265/70R16 measures to 28" height


Really, thinking about it now, what I was looking for is would I have to get a new Speedo transmitter for the tyranny and a new display?

Way back in 1996 I bought a 1996 Tacoma 4x4 SR5 short cab.
Best truck I ever owned. Should have never let it go.
The tires on that were 16" as I remember, and look big, but not too big.
Am I wrong, suffering early dementia?



Thanks!

b

 

The wheel size will not affect the speedo reading. A change in tire diameter will. Figure out any difference in tire size and go from there.

 

Hobbs, I got that, expected 16" to be bigger, but as I added above, they are, SHOCK!, the same. So why did my shorty Tacoma 4x4 look so cool, young optimistic eyes, not beat down by life yet?

 

Whats the tire say on the side? The tacoma Proably says something like 225x75x15 or 31x10.5 if they are stock size.
Then Look at the 4 runner and get the number off that, after put them both in a tire size calculator and see how close they are

 

Wait nvm i just read you already measured. How do you get 28” out of a 31” tire????
And the 4 runner tire is 30.6x10.4

 

Use a Dakota Digital speedometer recalibrator. $80 on Amazon

 

I ran my 86 4Runner with 32's for years. iirc, it was about 12% off. As long as I was indicating slightly below the posted speed limit, I was fine.

 

@JellyBeans wheel diameter (size) does not matter, its the tire diameter that does. 265/70-16 is essentially a 31x10.5x16 (same dimensions as your stock)

 

Use this sites tire calculator to compare and contrast.

Not familiar with the Digital Dakota calibrator that @BartMaster1234 mentions (but will be checking into) but HyperTech makes one as well.

Assuming you did something sometime that ended up needing correction to be accurate.

 

Beauty is in the eye of the beholder!

 

Will get you some today

 

Dakota Digital SGI-5E *Latest Design* - Universal Speedometer Signal Interface Controller

Dakota Digital SGI-5ELatest Design - Universal Speedometer Signal Interface Controller

https://www.amazon.com/dp/B014N07F8W/ref=cm_sw_r_cp_api_i_67vhBbD0BJ0WX

 

These vehicles are stock. I simply want to put the larger 16' rims on my Tacoma. I expect that will throw off the speedo.

BTW anyone have experience with aluminum mag restoration? I am in Washington and the road salt has beat the Toyota wheels up a bit.

 

They are neither aluminum nor mags.

Depending on the wheel they are painted steel or alloy.

Put up some pics and i bet someone will give some guidance other than mine.

Which would be sand, prime, paint.

 

Oh, no. You might want to take a closer look at the frame, if you haven't done that in awhile.

I think one of the reasons that your older truck looked like it had bigger tires is because cars used to have smaller whells, tires and fender gaps. Now, cars come oem with 17's and smaller and smaller fender gaps. So your mind kind of gets used to seeing that.

 

As you have already figured out, and as much as we try to explain it to you... NO, you do not need to get a speedometer adjust if the outside TIRE diameter is the same. rims/wheels mean nothing if the overall tire diameter stays the same. Also these are technically 31" (30.5 -30.7") tires. you may want to put more air pressure if you're only seeing 28" (measure with tire/wheel off the vehicle, not loaded down on the vehicle)

 

I am certain many know this, however many may not--In the common (silly) mixed metric/Imperial tire size designations (www/aa-dd) the first number ("www") is the tread width in millimetres, the second ("aa") the aspect ratio(i.e. the sidewall height of the tire, from rim to tread, expressed as a percentage of the tread width, the last number ("dd") is the wheel diameter in inches.

So to calculate a tire's outside diameter you only need to determine the sidewall height of the tire which is the tread width times the aspect ratio--which remember is a percentage so place a decimal point in front of the number --e.g. www * .aa the result is the height of the sidewall in mm.

Next, to get the overall tire height, convert the sidewall height to inches, then multiply by 2 and add the wheel diameter.

Ex. for the 265/70-16 standard tire:

• sidewall height = 275*.70 = 185.5 mm ;
• sidewall is counted twice * 2 = 371 mm;
• converted to inches = 371 / 25.4 = 14.6063";
• plus the wheel diameter = 14.6063" + 16" = 30.063

Or just take the sidewall height in mm and divide it by 12.7; then add the wheel diameter:

265 *.7 / 12.7 + 16 = 30.6063"

 

I think we are not hearing the question here. I want to put bigger tires on my Tacoma. I repeat, I want to put bigger tires on my Tacoma. I was looking around and it seems that the "Dakota Digital SGI-5E *Latest Design* - Universal Speedometer Signal Interface Controller" will work for my vehicles.

WRT the alloy mags on my Tacomas and 4Runner, what is alloy? I say aluminum, but we are nit picking. There are some guys out there who recondition Aluminum/alloy rims and I was interested in other peoples experience. Thank you.

BTW, if you are angry, I am most likely the cause, so please, leave me out of the anger. I am just trying to get by like most of you probably are. Thanks again.

 

That Dakota Digital interface is the solution to your issue. You can recalibrate your digital speedometer based on the input you give it.

Alloy is a combination of metals. Wheels are not made of pure Aluminum because it’s an inherently soft metal. If you make an Aluminum Alloy, however it will result in a stronger wheel because of the stronger metals associated with the alloy.

 

That's a different question than you have asked throughout this thread. You also have to understand relational difference.

I will repeat, "rims/wheels" and "tires" are different. Changing from 15" rims to 16" rims only matters if the "tire" size is different. 31x10.5x15 is the same size tire as 265/70-16. Therefore if you just switch rims you are essentially maintaining all the same dimensions, no corrections needed.

If you step up to a larger size "tire" then yes the speedometer will be slightly off.