Need some advice...replace tires or regear?

How many RPMs are you running at various speeds?

 

What engine, and why are you running so fast? How fast do you actually want to run? 65?

Switching back to 11r24.5 will drop MPG, but gain a bit with engine RPM.

 

If you are serious about being profitable then here is what you need to do. Keep the LP22.5's, if they are a low rolling resistance. If not, keep that size anyways and buy a low RR set (could be difference of 1/2 mpg). Go to a truck wrecker n find a set of 3.55 gears, roll em in (you will pay about $3500 max all in) and drive at 57 MPH. You will see 7+ mpg out of your truck if you try it. Just for an experiment, try it now just the way your truck is, drive it for a week keeping close track of your fuel mileage at your normal speed (65-75 MPH) n then try a week of staying at 57-58 MPH n watch how much fuel you will save. It will be painful getting used to slowing down, but just try it. On 3000 miles a week I can promise you will save at least 500 in fuel...x 50 weeks of the year on the road....sure adds up dont it?

 

Well what kind of hauling do u do is it heavy loads long or short distance hills ir no hill i thunk this goes a long way if u are thinking of changing diff

 

There isn't enough difference in 3.70 and 3.55 to talk about. To get 400 Rpm out of a gear change you are gonna have to go tall enough to affect your the way it steps out with a load.

 

You need to look a little harder for wheels.Around me 24.5 rims are passe. Tire shop usually sell good used Alcoa style rims for $200. If yours are in good shape they'll give you money for your 22.5's because there is demand for them. if your's are Pete style their worth more than that easy. BTW 00 CAT's aren't that sensitive to rpm so running at 1500 or 1600 won't kill your mileage like later engines can.

 

I also have a '00 379, and a speedo that would not calibrate using the codes off the internet.

Go to Pete and tell them what color your speedo is (mine is white) it is a different brand they used a couple years.

Most parts guys are to new to remember, an old timer will say oh yeah it's this book.

I have a single sheet copy, and it shows 2 4 6 7 8 10 closed/off.

 

Wow, I think thats a lot of RPM's.

I have 3.55 on 22.5LP on mine and 65 puts me right at 1450 RPM.

I have a BXS ACERT C15 in mine and anything over 1500 RPM it guzzles fuel like a $2 hooker. I cruise no more than 65 mph and even then I barely manage 5.5 - 5.8 MPG. I cant imagine the fuel economy at 1800rpm,.. I doubt I'd be getting 4 mpg.

I thought a 13 or 18 with out the splitter was the 9 spd? I've never heard of an 8 spd.

Hurst:smt111

 

Those RPM's are about where I'm at with a. 71 OD, 4.17 rears, and 11R24.5 tires and I run the speed limit +/- 2 or 3 mph wherever I go. 5.75-6 mpg is normal for me...then again, Mack motors are built to operate efficiently at higher RPM's to accommodate the more aggressive gearing needed for the kind of places Mack trucks typically go...