rim size, rear axle, body drop, effecting gas mileage

I have a 95 Isuzu. It get crappy gas mileage. I was told that because I have 17's when the truck came with 14's that would cause the problem. I was also told because I have a disc brake rear end out of a rodeo and it is geared differently then the stock rear end that would cause my problem. Then I had one guys say because I have a traditional BD that my trucks aerodynamics are messed up and that is causing it. Is any of this true?

no,maybe, and definatley not

I think its all about how you drive it. The different gear ratio could play a big part in the gas milage though. I have irs in my s-10 and it changed my milage quite a bit.

your 17"s might even be lighter than a 14" wheel with a big tire so thats a big NO, and the body drop comment was about as cool as herpes. i'd say it has everything to do with that rear end you have.

yes, I had an isuzu with a rodeo disc brake rear and the next owner (I never got to drive it) was limited to like 75 mph because of the super high gear ratio.

THE REASON THE BAD GAS MILAGE IS THE DIA. OF THE 17" RIM AND TIRE COMBO COMPARED TO THE 14" COMBO AND THE RODEO REAR END HAS A DIFFERNT GEAR RATIO IT IS PUTTING YOU IN A DIFFERNT PART OF THE POWER BAND OF THE ENGINE AND IT HAS TO WORK HARDER THUS BAD GAS MILAGE YOU WILL MORE THAN LIKLY HAVE TO CHANGE THE GEAR RATIO IN THE TRUCK TO MATCH YOUE WHEEL AND TIRE COMBO.IT'S JUST LIKE THE GUYS THAT DO A MAJOR SUSPENSION LIFT AND PUT A HUGE RIM AND TIRE ON IT IT PUTS THE ENGINE IN THE WRONG POWER BAND AND THE ENGINE WORKS HARDER SO YOU HAVE TO CHANGE THE GEAR RATIO TO PUT IT BACK AS CLOSE AS POSSIBLE TO WHAT THE FACTORY RATIO WAS "IE" LETS SAY YOUR TRUCK CAME WITH A 3.55 RATIO AND 15"RIM AND YOU PUT SAY 22" ON IT YOU MAY HAVE TO CHANGE TO SOMETHING LIKE A 4.10 OR 4.56 RATIO TO GET IT BACK IN A DECENT POWER BAND OF THE ENGINE

If the overall diameter of the tires on your 17's is smaller than the stock size it will lower the gas milage a bit. If the Rodeo rearend has higher, numerically, gears than you'll have a lower top speed but quicker acceleration, and the engine will rev higher at the speed than your old rear end gearing which will burn gas quicker. And if anything, I would think a BD would help the aerodynamics a little bit, but definitely not enough to effect gas milage in any noticable way.

Originally posted by longnlow



THE REASON THE BAD GAS MILAGE IS THE DIA. OF THE 17" RIM AND TIRE COMBO COMPARED TO THE 14" COMBO AND THE RODEO REAR END HAS A DIFFERNT GEAR RATIO IT IS PUTTING YOU IN A DIFFERNT PART OF THE POWER BAND OF THE ENGINE AND IT HAS TO WORK HARDER THUS BAD GAS MILAGE YOU WILL MORE THAN LIKLY HAVE TO CHANGE THE GEAR RATIO IN THE TRUCK TO MATCH YOUE WHEEL AND TIRE COMBO.IT'S JUST LIKE THE GUYS THAT DO A MAJOR SUSPENSION LIFT AND PUT A HUGE RIM AND TIRE ON IT IT PUTS THE ENGINE IN THE WRONG POWER BAND AND THE ENGINE WORKS HARDER SO YOU HAVE TO CHANGE THE GEAR RATIO TO PUT IT BACK AS CLOSE AS POSSIBLE TO WHAT THE FACTORY RATIO WAS "IE" LETS SAY YOUR TRUCK CAME WITH A 3.55 RATIO AND 15"RIM AND YOU PUT SAY 22" ON IT YOU MAY HAVE TO CHANGE TO SOMETHING LIKE A 4.10 OR 4.56 RATIO TO GET IT BACK IN A DECENT POWER BAND OF THE ENGINE

all caps and no periods. this guy is serious!

(just screwing around)

the size of the wheel really has nothing to do with anything. its the overall height oh the wheel and tire and the gearing in the rearend that matters.

with my truck i had a stock 342 geared rearned in it with 24inch tall tires and in 4th gear i could do 55mph at 2500rpms. when i changed my rearend to a 410 ratio and put 22inch tires on it, i have to turn 3200prms to do 55.

wow bodydrops give people bad gas mileage.. that guy that told u that was a genious!