losing fuel economy?

[dauphija#99]

I have a 2002 4cyl ranger and I am curious about getting bigger tires. not sure what size just yet but how much would a bigger tire effect my km/per liter.
PS 100th post

 

[doorgunner]

I would connect a vacuum gage to the engine & drive the vehicle on a level road--no stop signs/traffic lights/etc. for a couple miles.....write down the average reading...then go back the same way.....write down the average vacuum reading again....

Now borrow 2 wheels from some one the size you would like to buy....put them on the rear of your vehicle & test drive the vehicle on the same road as before......writing down the vacuum readings both ways.....

This sounds like a pain to do.......but it beats buying a set of tires that you don't like & you're stuck with until they wear out....

If the vacuum readings stays the same or gets higher you're O.K.

If the vacuum reading drops 1 0r 2 psi....you'll probably lose 1 or 2 mpg's....etc.

 

[dauphija#99]

what's a vacuum gauge? and how does it work? never heard of one before. I was just curious on other peoples experiences and wondering if anyone else lost mpg.

 

[92ranger2wd]

what's a vacuum gauge? and how does it work? never heard of one before. I was just curious on other peoples experiences and wondering if anyone else lost mpg.

Your engine is essentially a big air pump. A vacuum gauge measures how much air is being pulled into the engine at the intake manifold. You can buy a vacuum guage at any auto parts store. Hook it up to the vacuum port tree on the intake manifold and run it into the cab. Higher readings on the vacuum gauge(which is typically measured in inches of mercury) equate to more efficiency. I currently have one rigged up in my ranger.
FWIW I noticed a drop in vacuum when installing my sno tires this year. Stock summer tires are 215/70r14, the snow tires are 215/75r14, so only about an inch taller. With the taller snow tires, 3.73 gears, 5spd, and a 2.3L, I don't shift into 5th unless I'm going faster than 60mph. In addition to watching your fuel economy, a vacuum gauge is a priceless tool when used for troubleshooting a rough running engine. I use them also for setting the mixture adjustments on my carbed vehicles.
Typically installing larger tires means less mpg. Larger tires are more rotating mass that your engine has to turn. That's why people often need to re-gear when they put larger tires on factory gearing.