Tire Size / Final Drive Ratio - Reality Check (More-fun-with-math!)

[Joe_Pool]

Assuming that you were in 6th gear (.73:1).

 

Axle ratio = [(engine rpm) (tire diameter in inches)] / [(mph) (336) (transmission gear ratio)]

 

 

? = [(1825 rpm) (33.4")] / [(70 mph) (336) (.73)]

answer = 3.55 rear axle gear ratio

 

 

If you pull the diff cover you will find that Dana gears are marked on the ring gear like this.  At the top you will see 43X13, that is 43 teeth on the ring gear and 13 teeth on the pinion.  43/13=3.5384 or 3.54 gear ratio.

 

 

 

Edited October 15, 2020 by Joe_Pool
To add information

[leety]

On 10/15/2020 at 9:04 AM, Joe_Pool said:

Assuming that you were in 6th gear (.73:1).

 

Axle ratio = [(engine rpm) (tire diameter in inches)] / [(mph) (336) (transmission gear ratio)]

 

 

? = [(1825 rpm) (33.4")] / [(70 mph) (336) (.73)]

answer = 3.55 rear axle gear ratio

 

 

If you pull the diff cover you will find that Dana gears are marked on the ring gear like this.  At the top you will see 43X13, that is 43 teeth on the ring gear and 13 teeth on the pinion.  43/13=3.5384 or 3.54 gear ratio.

 

 

 

Very cool thank you for the photograph.

 

I was thinking about that formula and wondering if you would want to put in the number for speed based on the speedometter, which will be innacurate with non-stock OD tires, or use the speed on a GPS (usually fairly precise) or manualy adjust the speed based on a different formula and the actual tires size if non-stock.

[Joe_Pool]

For speed adjustment:

 

(new tire diameter*/original tire diameter*) X speedometer reading = corrected speed

 

* can be mm/inch/feet... -- both must be the same units

 

235/85R16 = 31.7"            (235mm/25.4mm)" X (.85 X 2) + 16"  =  31.7"

245/70R19.5 = 33.0"         (245mm/25.4mm)" X (.70 X 2) + 19.5" = 33.0"

 

33.0/31.7 = 1.04        Multiply indicated speed by this number to get actual speed (+4%)

Edited October 16, 2020 by Joe_Pool
To add information

[leety]

2 minutes ago, Joe_Pool said:

For speed adjustment:

 

(new tire diameter*/original tire diameter*) X speedometer reading = corrected speed

 

* can be mm/inch/feet... -- both must be the same units

 

235/85R16 = 31.7"            (235/25.4)" X (.85 X 2) + 16"  =  31.7"

245/70R19.5 = 33.0"         (245/25.4)" X (.70 X 2) + 19.5" = 33.0"

 

33.0/31.7 = 1.04        Multiply indicated speed by this number to get actual speed (+4%)

This is exceelent!!!  More fun with formulas.  Thank you!!!

[Mopar1973Man]

As for stashing a Quadzilla that is so simple. Since there is no display in the cab no one would know it was there. Now for the module and hook up hook up the same just hide your wiring with factory stuff. Hide the module like inside the fender skins I'm pretty sure there is a enough reach. 

[leety]

2 minutes ago, Mopar1973Man said:

As for stashing a Quadzilla that is so simple. Since there is no display in the cab no one would know it was there. Now for the module and hook up hook up the same just hide your wiring with factory stuff. Hide the module like inside the fender skins I'm pretty sure there is a enough reach. 

What they can’t see won’t hurt me ;-)

[Mopar1973Man]

Being the display is your phone then just turn off your iQuad App. Nothing to see folks... Just a stock truck needing a smog check. Even @Me78569 master the Quadzilla enough to be able to run the Quadzilla and pass his smog check. You could like many just set a lower power limit for Valet Mode and that all the fuel they would get period. Hence all most look for is how dark if any smoke is produced. Same rule is Ada County, Idaho. 

[leety]

8 minutes ago, Mopar1973Man said:

Being the display is your phone then just turn off your iQuad App. Nothing to see folks... Just a stock truck needing a smog check. Even @Me78569 master the Quadzilla enough to be able to run the Quadzilla and pass his smog check. You could like many just set a lower power limit for Valet Mode and that all the fuel they would get period. Hence all most look for is how dark if any smoke is produced. Same rule is Ada County, Idaho. 

Some of the smog guys here will notice the box in the engine compartment so that’s the thing I will have to conceal somehow. The branding on the device will give it away. I could organize a 2nd cover for it over the fuse box to sweep it under the rug.

[Mopar1973Man]

Some have extended the wiring all inside under the dash so there is nothing to see. 

[leety]

6 minutes ago, Mopar1973Man said:

Some have extended the wiring all inside under the dash so there is nothing to see. 

Sounds like a hassle lol.

 

I should be able to put a little costume over it on the fuse box lid. I could probably build an enclosure out of a spare fuse cover lid and attach it to the actual fuse cover.  I’ll try that first.  There are other ways around it as well.

 

I know a guy lol