gear ratio for easier highway speed
- redstone65
- Posts: 139
- Joined: August 30, 2017, 9:14 pm
- Location: Birmingham, AL
gear ratio for easier highway speed
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.
Dave
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
- charliemccraney
- Posts: 1743
- Joined: July 9, 2008, 10:02 pm
- Location: Lawrenceville, GA
Re: gear ratio for easier highway speed
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.
Lawrenceville, Ga
1961 F100 Unibody
318 Y-block (292 +.070 bore, +.170 stroke), FMS T5-Z w/Mustang 10.5" diaphragm clutch.
1961 F100 Unibody
318 Y-block (292 +.070 bore, +.170 stroke), FMS T5-Z w/Mustang 10.5" diaphragm clutch.
- redstone65
- Posts: 139
- Joined: August 30, 2017, 9:14 pm
- Location: Birmingham, AL
Re: gear ratio for easier highway speed
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.
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.
Dave
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
Re: gear ratio for easier highway speed
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..redstone65 wrote: Was just wondering if anyone had a good example configuration in their truck that produced reasonably low RPM at those speeds.
Robert
- bobenhotep
- Posts: 911
- Joined: January 9, 2007, 4:15 am
- Location: Las Cruces, NM
- Contact:
Re: gear ratio for easier highway speed
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
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
For every person with a spark of genius, there are a hundred with ignition trouble
My '63 short wrongbed
"The Iron Rhino"
300 I6, 3 spd manual, DS II/ HEI ignition.
Stuff I added to Hints and tricks
-300-6 choke tube repair
-duraspark II/ HEI
-Horn ring contact tube repair
-turn signal indicator fix
Mikhail Kalashnikov and Nikola Tesla are the guys i think of when i build things.
My '63 short wrongbed
"The Iron Rhino"
300 I6, 3 spd manual, DS II/ HEI ignition.
Stuff I added to Hints and tricks
-300-6 choke tube repair
-duraspark II/ HEI
-Horn ring contact tube repair
-turn signal indicator fix
Mikhail Kalashnikov and Nikola Tesla are the guys i think of when i build things.
Re: gear ratio for easier highway speed
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.
Re: gear ratio for easier highway speed
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.
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
- Posts: 139
- Joined: August 30, 2017, 9:14 pm
- Location: Birmingham, AL
Re: gear ratio for easier highway speed
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.
Dave
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
1965 F-100 Flareside (240 6-cyl)
3 speed. Former military truck.
Re: gear ratio for easier highway speed
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
30" tire up to 32" is about a 7% faster speed at the same engine rpm
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[b]'' I think what scares me the most about you guys is that I understand you '' ..... KID
'' lookin good, a little paint adds at least 100hp!'' ....... COOTER
'' well an old guy can dream cant he? ''............ICEMAN
''I would donate organs before selling my slick''........ HOOFBEAT RACER
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[b]'' I think what scares me the most about you guys is that I understand you '' ..... KID
'' lookin good, a little paint adds at least 100hp!'' ....... COOTER
'' well an old guy can dream cant he? ''............ICEMAN
''I would donate organs before selling my slick''........ HOOFBEAT RACER
- DanSanDiego2000
- Posts: 275
- Joined: August 14, 2006, 8:59 pm
- Location: San Diego
Re: gear ratio for easier highway speed
redstone65 wrote: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
Re: gear ratio for easier highway speed
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.
But if I had a 240 motor I probably would not go that low unless I had an automatic.
Last edited by HydroDog on October 8, 2018, 2:09 am, edited 1 time in total.
1965 F100
1988 F600
1988 F600
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- Posts: 500
- Joined: July 25, 2006, 8:44 pm
- Location: Dayton Ohio
Re: gear ratio for easier highway speed
I like 3.00 gears for highway driving with no o/d.
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- Posts: 1021
- Joined: April 21, 2007, 9:58 am
- Location: Mandurriao, Iloilo City, Philippines
Re: gear ratio for easier highway speed
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
Fred