mr.clean

unless you changed your speed sensor in your trans out when you changed your tires your odometer is off and you are going more miles than it shows. This will make show that you are getting worse MPGs than you really are and throw off your speedometer. Changing your gears out to make up for the tire change will give you back the power you lost and make it show up that you are getting better MPGs and get your speedometer back close to right. I would have my speedometer checked to see how far off it is. I would guess about 5 to 8 MPH slower than you are really going(speedometer shows 55, you are really going 63). With that info you then need to know what number your speed sensor has on it. Then go to the dealer ship and tale them what it is and how far off it is and they should be able to get you one that will get it back right again. Then, check your mileage out after that. That should make it look better and keep you from getting a speeding ticket also. I know on my Jeep with a change on my tires from a 215/75 to a 31, just from my parents house to my, my Jeep showed it was 3 miles less than my parents car that is stock with a speedometer that is right on. By using that if I drove 7 days to my parents house and used 18 gallons of gas. If my odometer was right it would show 17.1 MPG but, with it being off by 3 miles just one way (6 miles round trip) it would show that I am only getting 14.7 MPG. Most people do not think about how much the speedometer being off will change or through thing off.

dave1123

In my town, the police use a stationary radar unit to warn drivers if they are going too fast. According to that, I'm going 33 when my speedo says 35 and 48 when the radar says 45. ANY change in tire size or gearing will effect speed and odometer readings. If you want to get picky, even tire pressure will effect this. I have checked my speed with the measured mile markers on the highway and a stopwatch. At 60 mph, speedo reading, my time was 63 seconds. BTW, I almost got run over only doing 60!

Fuel mileage is NOT an exact science, no matter how hard you try. Driving habits have a lot to do with it and there are so many other variables it becomes mind boggling. Even intake air temperature and humidity gets involved. Ever notice how much better your engine runs on a cool damp night? On the highway at speed, the contact patch on the ground gets smaller because of centrifugal force, increasing tire diameter. Ever watch a dragster's tires during a burnout? the tires get a lot bigger when they spin at high speed. Radial tires with steel belts don't "grow" that way, but they do become round instead of flat on the bottom.

Check your speed over a measured mile. With larger tires, your time should be quicker. Then, with a lot of math, you can calculate your actual mileage. You'll know how much to add or subtract from your odometer reading.

mr.clean

I love pulling people over that have put larger tires on there trucks and do not know or think that it will make there speedometer be off. They all say "I was not speeding, I was only going 55mph." When they show up for court they have had it checked and it was off by 8mph. I don't give everyone a ticket for it unless they talk themselves into one. I look it how new the lift and tires look, talk to them about it, and tell them to have there speedometer checked.
Here is a site that will help you know how fast you are going at what speed using your old tire size to your new tire size. http://www.paspeedo.com/calculator.htm And to help you with your tire size when using it a 31x10.5-15 use a 265/75-15.

dave1123

LOL! I love it when people think they can talk their way out of a speeding ticket! My friend is a NY State Trooper and he cruises the Thruway. He says he'll give you 5 over, but 6 over, no way. I told him when I'm out there, people fly by me when I'm doing 70! I find it amusing the troopers have an unmarked Ford Mustang!

jonoZJ

Haha just like the highway guys over here in CA with their unmarked ford explorers... A family car! Haha surprisingly they have a lesser roll over rate than the crown vics. Good to see a LEO on the forums Mr. Clean!

dave1123

When are people going to realize LEOs are your friends? They keep the roads safe from idiots. The only problem is they can't be everywhere it once. I've seen the NY State Police park cars that were in for maintenance under the bridges on a holiday weekend just to keep people from pushing the limits. Cool idea, I thought.

jonoZJ

After they go on a ride along! Just joking. Most people enjoy their presents if their activities are not criminal in nature. If they stop you its because you are doing something stupid, not because they want to harass you and are trying to violate your right to not self incriminate yourself lol. I can go on all day but ill spare the forum from my lecture. back on topic: Yes... the zj gets bad mpg go buy a ex police cng crown vic off craigslist and you can drive around for pennies

dave1123

Yeah, sorry about that. We did get off track, didn't we.

About all you can hope for is about 16 mpg with a Jeep, and then you're doing good. It's the price you pay for best 4WD vehicle you can buy. I've driven my boss'es Rav 4 and it isn't near as good in snow as my Jeep.

MECRAM

1997 ZJ 95k miles 5.2 4X4 w/ 242J transfer case.

I was hoping in part that it would improve fuel economy in 2wd. It didn't.

It's been 2 days since installing 12 port injectors. This is the only mod. I'd highly recommend this to anyone with EV1 injectors.

Instant starts. .5 seconds

Smoother idle and consistent

Faster response in throttle w/ possibly more power. In jockeying thru traffic, after the mod it responded faster and accelerated than usual, causing me to back off the throttle.

Best average fuel economy is 14.2. No matter how it's driven. When I've reset this it always steadily dropped steadily to lock on 14.2

Now after reset it's fluctuating 16 to 17 mpg, which is never done b4. I'll try to update this in a month.