gear ratio for easier highway speed

[redstone65]

I'm not sure what's currently in the rear end, but any suggestions for a better gear ratio would be welcome. I spend about half of my commute at 55-60mph. The no overdrive 3 speed makes it a bit of a challenge.

[charliemccraney]

Hard to suggest anything if you don't know what you have. It would also be helpful to know your current RPM at 55-60. A lot of people say their truck is "screaming" and what they really need is mufflers, not a different ratio. That might not be your case, but impossible to say without the info.

[redstone65]

I'm not sure how to tell what ratio is currently in it. So far, this truck has been bone stock in every respect.

I know I need to figure out the RPM's. I'll pick up a cheap tach and see what it's doing at speed and post back. Was just wondering if anyone had a good example configuration in their truck that produced reasonably low RPM at those speeds.

[Day 2]

Was just wondering if anyone had a good example configuration in their truck that produced reasonably low RPM at those speeds.

Well, mines not a good one, thats for sure. I have a 3.50 and at 55 I'm "screaming" along at 2500 rpm. So something in the 2.89/3.00 range might be a good start..

Robert

[bobenhotep]

on the rear end there is usually a tag with the ratio.

I have a 63 f100 with a 300 inline 6, 3 speed manual, and a 2.80 rear out of a t-bird. I run fairly short tires (215/75r15) so my final drive ratio is about the same as someone with a bigger tire like a 235/75r15 and a 3.00. It seems like a 3.25 would be pretty good for most as long as you don't live in hill country.

Dan

[ratrapp]

definitely need to find you current gear ratio out.my old 63f100 that I had as a teenager sounded like it was going to blow up on the interstate.itdidn't have the original engine/tranny or rear end.it had been crudely changed over to a 352/c-6 combo.i pulled the 3rd member out and was going to change it out with a spare 3.25 center section I had.come to find out I only had 3.00 in it to begin with.the loud cheap glass pack mufflers on it made it sound like that.a quick trip to the muffler shop fixed that.charliemccraney is right about that.

[Jerry D]

Jack the rear of your truck up with it in neutral, and count the number of driveshaft revolutions in one revolution of the tire. If you rotate the tire 1 turn and the driveshaft rotates 3-1/2 times, it's a 3.50.

I had the same issue back in the day, with the engine running at high rpms at highway speeds. I had a 3.73 rear end, and switched to a 3.25. Made about a 500 rpm difference if I recall.

[redstone65]

Haven't figured out the ratio yet (no tag that I can find, hope to jack and spin this weekend), but installed a tachometer. It's running 2500 rpm @ 55 mph, and 3000 rpm @ 65 mph. Will post back when I figure out what the ratio is.

[slick4x4]

Tire height is another way to change rpm/mph
30" tire up to 32" is about a 7% faster speed at the same engine rpm

[DanSanDiego2000]

Haven't figured out the ratio yet (no tag that I can find, hope to jack and spin this weekend), but installed a tachometer. It's running 2500 rpm @ 55 mph, and 3000 rpm @ 65 mph. Will post back when I figure out what the ratio is.

There is almost enough information here to get your answer to your ratio.

What is the diameter of your tires?

With that last piece of the puzzle, we can calculate the ratio.

Dan

[HydroDog]

In my 65, I had 3.70's with my 300 six and 3 speed manual. I found a reared from a 1980 that had a 3.00 ratio. I swapped the yoke and side gears and it has worked out great for what I do with the truck. 2200 rpm at 60 mph instead of 2800 rpm.
But if I had a 240 motor I probably would not go that low unless I had an automatic.

[66camperspecial]

I like 3.00 gears for highway driving with no o/d.

[fmartin_gila]

The 62 that I sold to Doug came with a 3.70 ratio. After I installed the T5 with OD, 5th gear made it comparable to a 2.70 ratio and made a nice cruiser out of it.

Fred