My truck is running at 2100rpm at 65mph, is this normal for a 4.0 5spd? I put a set of 235-60-15 tires on my truck from my old mustang. Also would the tire size alter my speed limit? I am 5mph slow on the speedometer.

 

Should we all guess what the previous tire size was or what gearing you have? I would say it is normal.

 

Ya we should all guess. I do not know the original tire size, or the gear, but I am sure Ford made a trillion of these trucks and I figured someone out there has a stock ranger like mine. I bought this truck used, the rear tag has long rusted off, there was not one matching tire on my truck when I bought it. So I thought I would ask and maybe someone out there has a stock 4.0 5spd 4x2 ex cab truck that could give me an idea what the cruising rpm should be.

 

sounds about like mine

i had 225 tires with 3.45 gears stock

i'm now running 245 tires with the same gears....my rpm is about 2-2200 at 65
and my speedo is off by about 11%

 

Thanks for the info, so around 2000 rpm is normal for the smaller motors, my F150 cruises at 1600-1700 rpm 65 w\ 302.

 

sounds rite. thats about what my RPMs are in O/D at 65ish. i hate how low geared they made the 4.0s. good for towing though.

 

I'm running 3.73 gears and 33" tired and thats what i run at also.

 

I turn approx 21-2200 at 60, 285/75/16 and 4.10s.
Just food for thought.

 

Ok, thanks for the info.

 

Just curious, how is your truck with that gearing setup? I have stock 225-70-R14's with 4.10's (2900 rpm at 65 mph) and its still really poochy as is. I'm starting to think of things that could be causing it like spark plugs/wires, or if my truck is really supposed to be this slow with 4.10's.

 

how many miles are on your truck? when was the last time you did a tune up?
i've got 3:73s and i'm sitting at about the same 2000-2200.
as far as i know, 4:10s with that size tire should be relatively quicker then 3:73s off the line.

 

112k and bought it with 97k just over 2 years ago, in all honesty I haven't done much at all except changing the oil and replacing the starter. I'm guessing the spark plugs/wires are pretty overdue, are there any other big things to look at first like the injectors or pcv valve or whatnot?

Just realized Im threadjacking. If its easier/better to respond via PM's, fee free to do so.