Thinking About Gears...

[5.0Flareside]

65 would bring you down to what 2600 area?

yeah, and push the gears up to 4.56.. that'll put at least up above 2800 again...

 

[LEB Ben]

just realized this, but theres no way...

my flareside with stock height tires was turning 2800 at 70..... the overdrives are geared differently compared to the AOD... but NOT THAT DIFFERENT!!

According to the calculator it's legit:

Data Input-
Ring Gear and Pinion Ratio (3.08, 3.55, etc.)............4.56
Tire Height (24.5, 26, 27.5, etc.)...........................31
MPH.................................................................65


Calcualted transmission results-
AOD.................................................................2249

 

[5.0Flareside]

he doesnt have 31" tires and theres no way its correct...

i need to find the calculator i always use that i KNOW is correct.. it was bookmarked on my old computer... but that thing crashed...

 

[LEB Ben]

^^^I gotcha...I was just saying that's the info the calc spit out.

 

[RedLariat85]

just realized this, but theres no way...

my flareside with stock height tires was turning 2800 at 70..... the overdrives are geared differently compared to the AOD... but NOT THAT DIFFERENT!!

he doesnt have 31" tires and theres no way its correct...

i need to find the calculator i always use that i KNOW is correct.. it was bookmarked on my old computer... but that thing crashed...

Yeah... I thought that number seemed REALLY low for 4.56's.

Chris, If you could find that calculator I would appreciate it. I need to find out how many rpm's it would really be turning.

Btw Chris, was your truck turning 2800 rpm's at 70 with the 4.10's, or the stock gears?

 

[FordF-SuperDuty]

Calculator says I should be turning 1871, I about 2000-2100 actually.

 

[DNFXDLI]

Do the math yourselves...(mph x gear ratio x 336) / tire diameter....so (65 x 4.56 x 336) / 31 = 3212 rpm...x whatever your OD ratio is...I don't know what it is, but if it was .7 then that would drop it to 2248.

 

[primetime]

I`ve seen instances where the stock tach is off as much as 400 rpm. You should also measure the TRUE height of your tires. Per the math, with a 28 in tire (a 275/60/15, for example), in overdrive, you should be turning about 2489 rpm. For what it`s worth, tires may as well be called "bob". My 33`s are actually 31`s.

 

[DNFXDLI]

Really 24-2800 rpm isn't that high, my truck with 32's and 3.50's will be turning roughly 2600 at 70 mph.

 

[5.0Flareside]

my truck was turning 2800 at 70 with the 4.10's according to a aftermarket tach that was dead nuts accurate..

 

[nobodyspecial]

Accurate based off what?

 

[DNFXDLI]

Accurate based off what?

The Harbor Frieght tachometer tester...
















Just razzin' you Chris

 

[5.0Flareside]

against a few other gauges, that friends have that are known to be accurate.

 

[Truckin4life]

I turn right at 3k at 70 rpms.....

This is in the car, the truck was at like 2800?

 

[LEB Ben]

against a few other gauges, that friends have that are known to be accurate.

Again...

Accurate based off what?

I've seen cheapy tachs against name brand tachs right out of the box be as much as 15%, and as time wears on, tolerances and calibrations only get worse.


And for comparison sake...at 65mph:

Red is right on 2800rpm (rarely highway driven)- 4.88's and 37's
Bronco is right at 2400- 3.55's and 35's
Thunder...been a while since she was driven but IIRC was under 2k- 4.56's and 37's