Bigger Tires. What does It Do To Speedometer and Fuel Economy Calculations?

[beaglegun]

I put 33X12.5's on my 97, 4.0 Ranger 4X4. How much does this affect my speedometer/mph?

I calculated mpg. 11.9!!!! That sucks! How much does the change in tire size affect my calculations. (tripmeter)

 

[heptofite]

I put 33X12.5's on my 97, 4.0 Ranger 4X4. How much does this affect my speedometer/mph?

I calculated mpg. 11.9!!!! That sucks! How much does the change in tire size affect my calculations. (tripmeter)

bigger tires makes everything turn slower, so the speedometer will read lower than you're actually going, and you will travel more miles than you trip says you are.

short version: your milage isn't 11.9

also, have somebody clock you with their car, so you can figure out what your new speeds are.
for example, get a buddy with a car that is stock, have him follow you and be on your cell phone, get your truck up untill the speedo says 45mph, and then ask him what his says.

 

[triumphrider-1]

I put 33X12.5's on my 97, 4.0 Ranger 4X4. How much does this affect my speedometer/mph?

I calculated mpg. 11.9!!!! That sucks! How much does the change in tire size affect my calculations. (tripmeter)

Calculate the percent difference in tire height (assuming you never changed the speedo gearing from stock) and that percentage will carry to your speed and odometer(s).

Example:
Stock tire: 29"
New tire: 33"

Calc:
29"/33" = 0.878787
1-0.878787 = 0.121212 => 12.1212%

So with that, take whatever speed cruising at and add 12% to it.
70mph *0.121212 = 8.5mph => speed is 78.5mph

Also the same for the odometer(s)
350 miles *0.121212 = 42.4242 miles => miles are 392.42 miles

 

[GoodOld85BlueBalls]

Use one of the online calculators. I seem to remember one in the Tech section here.

Heres on I found on a quick search:

http://www.paspeedo.com/calculator.htm

I use one of those residential speed signs to see that mine is about 5 mph off with 33" and 4:56 gears.

 

[trail B2]

You need to change your numbers like they said and the same works for your speedo gear you want it smaller.So if you pull the gear out at the end of the cable in the tranny end and its 18 teeth you times that by .88 and that gives you the number of teeth you need on the gear to correct the problem.That being said you won't get the mileage with 33" tire that you got with stock tires rolling and wind resistance goes up.