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Old 07-18-2007, 09:09 AM   #1
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Tire Size vs Fuel Mileage

I really want to lift my Wrangler 4" and then maybe 33" tires but I remember how bad big tires killed the fuel mileage in my full size Bronco.

I would just like input as to what fuel mileage they get on what size tires. I wann aknow that I wont drop to like 10 mpg just by gettin bigger tires.

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Old 07-18-2007, 10:10 AM   #2
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31 mtrs, 4.11 gears, 65mph=2600rpms=16mpg 90% "highway"

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Old 07-18-2007, 10:15 AM   #3
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I guess a little background on mine would be good. 4.0 Automatic (3 spd) 3.07 factory rear gear. 3.07 might not turn 33's???
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Old 07-18-2007, 11:29 AM   #4
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3.07 gears are going to take away a lot of your engines power. You won't have any low end take off power to speak of. I run a 4" lift and 33s with 4.56 gears and running 60-70 mph I still get around 14-16 mpg. I haven't checked it in a while, though. If you go with the lift and 33s I would strongly recommend changing your gears as well. Just my thoughts.
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Old 07-18-2007, 11:51 AM   #5
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3.07 gears are going to take away a lot of your engines power. You won't have any low end take off power to speak of. I run a 4" lift and 33s with 4.56 gears and running 60-70 mph I still get around 14-16 mpg. I haven't checked it in a while, though. If you go with the lift and 33s I would strongly recommend changing your gears as well. Just my thoughts.
Right now I turn 2500RPM at 65 on 215/75R15's. How much higher will my rpms run if i went to say a 3.73 or a 4.10?

If I did the math right i think 4.10s on stock tires at 65mph is like 3340 RPM.
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Old 07-18-2007, 12:12 PM   #6
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right now im running 33s on my wrangler and i get about 8mpg in the city
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Old 07-18-2007, 06:40 PM   #7
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I have 3.07's and 33's, not great gas miliage, but I have good low end take off, and can run down the highway well, still trying to figure out exactly what my mileage is. Also, remember with bigger tires, unless you recalibrate your speedometer ( or change speedo gear ) your odometer will be reading less miles than you are actually driving, therefore skewing your gas mileage calculations.
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Old 07-18-2007, 11:25 PM   #8
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With the bigger tires, your speedo will run slow, so if you tried to do the math at the pump, you'll have terrible mileage when in fact it might not be so bad. With 33"s get 4:56 gears and the speedo gear to go along with it. Then from what I've come to understand, you can "flash" the computer to recalibrate for the tire size. That will give you an accurate reading, and keep you from getting speeding tickets too.
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Old 07-19-2007, 06:46 AM   #9
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I have 3.07's and 33's, not great gas miliage, but I have good low end take off, and can run down the highway well, still trying to figure out exactly what my mileage is. Also, remember with bigger tires, unless you recalibrate your speedometer ( or change speedo gear ) your odometer will be reading less miles than you are actually driving, therefore skewing your gas mileage calculations.
My speedo is off like 3mph on stock tires... I actually use a GPS to determine gas mileage. I used it once to determine fuel mileage on my outboard motor... 2.4 mpg baby.... oh yeah
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Old 07-19-2007, 06:47 AM   #10
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With the bigger tires, your speedo will run slow, so if you tried to do the math at the pump, you'll have terrible mileage when in fact it might not be so bad. With 33"s get 4:56 gears and the speedo gear to go along with it. Then from what I've come to understand, you can "flash" the computer to recalibrate for the tire size. That will give you an accurate reading, and keep you from getting speeding tickets too.
When i had 33's on my Bronco, I got a ticket for 87 in a 55 and when he clocked me my speedo was only showing 75... so when i thought i was doing 20 over i go nailed for 32 over... good thing my sister works at a law firm or i woulda been screwed.
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Old 07-19-2007, 09:33 AM   #11
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When i had 33's on my Bronco, I got a ticket for 87 in a 55 and when he clocked me my speedo was only showing 75... so when i thought i was doing 20 over i go nailed for 32 over... good thing my sister works at a law firm or i woulda been screwed.
Don't be so sure your speed was that far off...cops seems to up the mileage to put you in the next highest ticket/point range. For example, I've noticed if you're doing 10-12mph over, they will ticket you at 16mph over which is 4 points, not 2.
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Old 07-19-2007, 09:45 AM   #12
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yeah, regearing is great thing, but not entirely neccasary with 33's. And it is my understanding that you can "flash" or reprogram the comp. on a late model jeep without changing speedo gear ( I don't think 05 - 07's even rely on speedo gears but rather on the comp. ) or gears... correct me if I am wrong.
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Old 07-19-2007, 06:25 PM   #13
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Don't be so sure your speed was that far off...cops seems to up the mileage to put you in the next highest ticket/point range. For example, I've noticed if you're doing 10-12mph over, they will ticket you at 16mph over which is 4 points, not 2.
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Old 07-19-2007, 07:15 PM   #14
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I have a 4" lift and 33" tires on my jeep.The gas mileage does go down a good bit,I would say I am getting probably 15-17 mpg after the lift and tires. It's fine though if you don't mind the gas mileage,lift it up.
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Old 07-19-2007, 07:29 PM   #15
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I have a 4" lift and 33" tires on my jeep.The gas mileage does go down a good bit,I would say I am getting probably 15-17 mpg after the lift and tires. It's fine though if you don't mind the gas mileage,lift it up.
5-speed? and what rear end gear?
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Old 07-19-2007, 07:48 PM   #16
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Yea,it is a 5 speed.Stock 3.73 gear. I'll regear one day though.
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Old 07-19-2007, 09:36 PM   #17
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Dont forget either that you can do a few performace mods that will bring you right back to about stock gas mileage. For example you can throw an intake or exhaust on there. It will boost power as well.
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Old 07-19-2007, 09:42 PM   #18
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Quote:
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Dont forget either that you can do a few performace mods that will bring you right back to about stock gas mileage. For example you can throw an intake or exhaust on there. It will boost power as well.
hes right.. or it will lower it a lot if you drive like me ... darn heavy foot man i'm telling ya
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Old 07-19-2007, 10:01 PM   #19
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Quote:
Originally Posted by lap49X View Post
Don't be so sure your speed was that far off...cops seems to up the mileage to put you in the next highest ticket/point range. For example, I've noticed if you're doing 10-12mph over, they will ticket you at 16mph over which is 4 points, not 2.
Maybe in your state, but I'm in law enforcement and don't, nor have we ever, done stuff like that.
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Old 07-19-2007, 10:30 PM   #20
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Quote:
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Don't be so sure your speed was that far off...cops seems to up the mileage to put you in the next highest ticket/point range. For example, I've noticed if you're doing 10-12mph over, they will ticket you at 16mph over which is 4 points, not 2.
ive had a cop lower my ticket to get me into the lower point range.. but he also tried to say i ran a stop sign..

funny thing is that i stopped at a gas station right next to the stop sign and he tried to say i ran it going down the highway.. and i turned onto the other road that crossed the highway when leaving the gas station.. which means there was no way i ran the sign like he indicated

but also.. ive had a cop raise my speed up once.. when i talked to the judge about it he said that i have the right to ask the cop to show me the radar gun to prove that i was going the speed that he said i was going.

the cop that tried to raise my speed, his son was caught steeling out of my house and my dad pulled a gun out on him.. the same cop has parked outside my house and pulled me over while walking up my driveway trying to say i was about to egg my own house..
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Old 07-19-2007, 10:35 PM   #21
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Originally Posted by ripbiker13 View Post
With the bigger tires, your speedo will run slow, so if you tried to do the math at the pump, you'll have terrible mileage when in fact it might not be so bad. With 33"s get 4:56 gears and the speedo gear to go along with it. Then from what I've come to understand, you can "flash" the computer to recalibrate for the tire size. That will give you an accurate reading, and keep you from getting speeding tickets too.
With the TJ there is no flash required.
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Old 07-19-2007, 10:48 PM   #22
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Well, since we hijacked the thread already...

Arkansas has a law that you must move over into the left lane while passing a police car who has lights on while on the shoulder at a traffic stop.
Some yahoo cops were parking behind each other on the shoulder with one having their lights on, and stopping anyone who didn't change into the left lane.
Judge threw that one out, and the cops were issued reprimands.
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Old 07-20-2007, 08:08 AM   #23
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Since its my thread i guess i will approve the highjacking since i have the best cop story ever..

I actually got qa DWW (Driving while white). I was in a bad part of Daytona Beach around 1 AM with the top off. I was sitting behind this cop at a red light. He went straight as I turned left to head home... I spotted him making a u-turn, and got nervous so I dropve text book. I broke no law.... He pulls me over.

His words... the only reason white guys come down here is to buy "stuff" at this time of night. then he said he didnt care why i was down there but that i should never go down there at night. He was afraid I would be car jacked and killed( apparently they carjacked a city cop once). So then I thought I was off the hook and he would let me go... Oh no... he had to come up with a legitimate reaosn to pull me over...

License plate light was not bright enough!!!! WTF... i explained to him that if that were the case then the left brake light wasnt bright enough but he didnt listen.

So anyways there is my addition the highjacking my own thread
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Old 07-20-2007, 09:30 AM   #24
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I've got another one, i was drving home with my dad in the next town over, it was probabaly the second week i had been driving, so there was an intersection and a huge snowbank. So i slowed down saw no one coming and then went through, next thing i knew the a policecar was pulling me over, i had no idea what i did, apparantly there was a stop sign that had been covered by the snow bank and a cop hiding behind the bank waiting for people from out of town who didnt know there was a stop sign there to pull over. We managed to talk out of it seeing as i only had a permit and was just starting driving, he gave me a lesson about how you should always stop no matter what and that a car was a more dangerous weapon than a gun
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Old 07-20-2007, 01:38 PM   #25
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Gettin back to my math from earlier i was all wrong. As tire size increases, RPM at a given speed will decrease as Revs per mile decrease.
At 60 mph w/3.07 gears and the automatic transmission in Drive(torque converter locked up)

215/75R15 - 2300RPM
235/75R15 - 2211RPM
31x10.50 - 2061RPM

The problem is that with more unslung mass, the throttle will have to be open more to make a little more power which means more gas being used.
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Old 07-20-2007, 04:35 PM   #26
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^ so pretty much let say you have 6 speed manual tranny.. isntead of driving on 6th speed with 50 mph.. you should drive on 5th where there is a little more power?
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Old 07-20-2007, 05:17 PM   #27
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Well no. At a higher RPM the motor is moving more air therefore moving more fuel. So your mileage might not change much at all, but the lifespan of your engine should improve in 6th. Its amazing what you learn about motors when you work on ricers with turbos for a while...

What I want to do is get a fuel computer that measures in Gallons per hour GPH like an airplane and do some experimenting on what works best for fuel mileage.
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Old 07-20-2007, 10:37 PM   #28
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Old 07-22-2007, 02:45 PM   #29
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to see how much ur speedo will be off try that.. http://www.miata.net/garage/tirecalcold.html
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Old 07-22-2007, 03:32 PM   #30
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or you could do the new tire diameter divided by the old tire diameter, and then multiply that # by the mph that your speedo says to ge the real #

for ex.
33/29=1.138
1.138*50=57, so when your speedo reads 50 your going 57

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