I'm thinking about putting 31" tires on my 97 4door 4x4 with 3:42 ratio. How much will this affect my performance as I will be towing light like loads and i dont wanna totally kill my performance the most I will be towing is 2k lbs.plus how bad will it affect my mpg. I'm getting about 16-17.5 right now. thank you

 

You'll likely see a 1-2mpg hit with going to 31's and towing. It really depends a lot on your driving style too. If you do mostly highway miles and granny drive you probably won't see any difference. If you do a lot of city driving and have your foot hard on the skinny pedal all the time you will definitely see a drop in your mpg.

 

It will change the effective gearing to 3.08:1, the acceleration will take a hit as well.

 

How did you calulate that?
Wanna kill your perfornance....try 33" and 3:42

 

Tried it! It wasn't as bad as it sounds, just poor off-the-line performance.

 

Wallace Racing - Automotive Calculators

 

my first blazer had 273s and 38s talk about slow. crappy transfer case too with only a 2:1 low ratio. half the time i couldnt spin the tires if i got stuck.

also had a 2.8 s10 running on only 5 cylinders with 33s and 373s. man ive owned some junk

 

I had 31" Cooper Discoverer STT (mud terrains) with the 3.42s and i went from getting 15mpg to 12mpg. Acceleration will take a nasty hit. as for towing, my personal opionion would be not to, lol, jk. but maybe look into a transmission oil cooler, because the extra stress the 31's alone feel like they put on the drive train on acceleration i could only imagine the combination of 31's and extra load.

 

I already have a trans cooler to put on and I'm towing 1800-2000 lbs so not a real heavy load plus I'm not sure how often I will be towing this trailer. Its only to haul my turbocharged sand rail buggy now and then. I just gotta make sure it can pull it

 

Not sure how they did it, but there is a formula...

Engine RPM x 60/(Axle Ratio X Tire Revolutions Per Mile x Transmission Final Drive Ratio) = Vehicle speed at designated RPMs

To find your tire revolutions per mile...

Take your tire measurement (the actual measurement, not the manufacturer's stated measurement)...
Multiply it by 3.1415... this gives you your tire circumference.
Divide the number of inches in a mile (63,360) by your tire circumference and that gives you your revolutions per mile.
So, let's say we had a set of 31s which actually measured 31 on the nose.. we'd be looking at 650.6 revolutions per mile..knowing the 4L60E has a .7 overdrive ratio (actually, .696), and say we want to see where we're at at 2000 RPMs..

(2,000 x 60)/(3.42x 650.6 x .7) = 77.0447483603

Of course, you'd be bogging down the engine pretty badly this way, especially if towing something, although you wouldn't be towing in OD..
Third gear is direct drive, so...

(2,000 x 60)/3.42 x 650.6 x 1) = 53.931.......

A little more manageable.