REAR END GEAR RATIO


http://209.208.111.198/Topic39975.aspx 		Print Topic | Close Window

By 57f100 - 15 Years Ago
hey guys so iv been doing some thinking lately about the rear end in my truck 57 f100 with a 272 and a 4 speed manual trans the gear ratio in the rear end is 3:70 i was wondering if i geared it up to maybe 4:11 gears what would you guys recommend i put in there for good street use and freeway use im hardly on the freeway im mainly on the streets but i still want something that would do good both street and freeway any info would be great thanks guys
By charliemccraney - 15 Years Ago
I think the 3.70 is the better compromise. With 225/70-15 tires, a 3.70, and in 4th gear, 1:1 ratio, my motor turns about 3000rpm at 60mph, and about 3500rpm at 70mph. My speedo accuracy is not verified but even keep up with slow traffic requires at least 3000rpm. A stock motor can probably do it but it'll be real inefficient.

Think 3spd overdrive, 4spd overdrive, or T5 to have both worlds. 1st gear on a T5 will make it like going a ratio or 2 higher on the R&P and 5th will give you the highway speed you want.
By Canadian Hot Rodder - 15 Years Ago
FYI, I run 3:55 gears in mine with 225 / 60 / 16's on the back and rev at exactly 3000 rpm at 70 mph. I find this isn't pushing it to hard and if I drop down to 65 mph, (about 2600 rpm)  I can actually hear the secondaries close and I get some decent gas mileage (18mpg)! BigGrin
By speedpro56 - 15 Years Ago
If your 4speed has a granny first then you might even consider a 3:25 for an even better cruise speed. Using a 3:70 is a bit steep on the highway without an overdrive behind it as the others have stated.
By 57f100 - 15 Years Ago
yeah my 4 speed has the granny 1st it only last like 2 sec and when i jump on the freeway that thing revs up high the truck gets super loud
By joey - 15 Years Ago
I think the 3:70 is the better bet for street driving. 4:11 would be pushing it.
By LON - 15 Years Ago
Try this for size.http://www.f-body.org/gears/

You can play with rear end ratios for hours and not even get your hands dirty . Add different tire sizes ,gear ratios and diff gears .Sure takes out all the guess work .

Lon