RPM's at 70mph with 6.0 Ford

[DUKCALN]

Hey guys I went from 39.5 tires and 4.88 gears to a 38 tire with the 4.88's. How bad will it hurt me on the freeway. I think @ 70mph I am around 2150 with the 39.5's. I know I will gain some in town low end but what about the freeway.

[Diesel 73]

I know that going to a smaller tire, 70 mph with the 39.5's is about the same as 67mph on the 38's, I think you are going to be up around 2200 maybe 2250 on the freeway, if you are actually doing 70mph. someone smarter will know more.

[2007 5.9]

Does a 6.no go 70mph?:confused:

Sorry Jason had too!!!:D

Going 70mph with 38's and 4.88's should net you 2114 rpm's...here is a link to the site I used.

http://www.csgnetwork.com/multirpmcalc.html

[DUKCALN]

Does a 6.no go 70mph?:confused:

Sorry Jason had too!!!:D

Going 70mph with 38's and 4.88's should net you 2114 rpm's...here is a link to the site I used.

http://www.csgnetwork.com/multirpmcalc.html

It will if a CUMMINS is towing it........ Man, no love lost I see...... :rolleyes:

[Diesel 73]

Going 70mph with 38's and 4.88's should net you 2114 rpm's...here is a link to the site I used.

http://www.csgnetwork.com/multirpmcalc.html

those numbers dont match up. I see what you did, but if you input the same numbers except the go back up in tire size it will net you 2034. he is starting at 2150.

I went down to the bottom of the page and manually input the final drive at 0.74 with that 4.88 pinion gears, and 39.5 gives you 2150 which was Duk's estimate. than back the tires down to 38's and that gives you the 2235.

I could be wrong, but when I went from 33's to 35's my RPM dropped and my speedo was slow.

just my thoughts.

[2007 5.9]

those numbers dont match up. I see what you did, but if you input the same numbers except the go back up in tire size it will net you 2034. he is starting at 2150.

I went down to the bottom of the page and manually input the final drive at 0.74 with that 4.88 pinion gears, and 39.5 gives you 2150 which was Duk's estimate. than back the tires down to 38's and that gives you the 2235.

I could be wrong, but when I went from 33's to 35's my RPM dropped and my speedo was slow.

just my thoughts.

Good catch, I didn't think about resetting the O/D ratio!

[231jasons]

nice work Les!

[DUKCALN]

So do you guys think 4.88's with 38's will be too much gear?

[Diesel 73]

I think at this point it is a matter of preferance. if you like it keep it, if not change it

[DUKCALN]

Got the new 38's on the truck, the swamper sts radial 38/15.5/16.5 and I am very pleased with how they look and ride. Quiet, smooth and good acceleration...LOL...Shoot I even got my first kill...a Duramax....white lifted with edge stickers.....I was surprised with the power my truck let out....first time I really got on it and it moved really well......Not well enough for you yet Les.......LOL  By the way, I lost a tad les than 100rmp.......

[Neel]

you can always have 3.73's on 40's like me:eek:

man i need some gears lol. 4.56's

[DUKCALN]

you can always have 3.73's on 40's like me:eek:

man i need some gears lol. 4.56's

Gears will do wonders for your set up........

[Diesel 73]

By the way, I lost a tad les than 100rmp.......

Lost as in you went from 2150 to 2050 or last as you wen:confused from 2150 to 2250?:confused:

[DUKCALN]

went up to 2100......@65

[Diesel 73]

so relativly no change.