RPM Calculator

[Drake2]

Hi all, I've been looking at what I can expect from an RPM on the highway with 35" tires with a TH400 (no overdrive) and the 2 different sets of LC gears (3.73/4.11). Even the 3.73 RPM seems high for 65 MPH. What do you all think?

Spicer Engine RPM Calculator

Measure your engine’s RPM based on the ring gear and pinion gear ratio, speed, and tire height, with the Spicer Engine RPM Calculator.

spicerparts.com

 

[bikersmurf]

You're not factoring in the rubber overdrive factor. Factoring in 35" vs the stock 29" would likely be more like 2100 rpm.

 

[Drake2]

You're not factoring in the rubber overdrive factor. Factoring in 35" vs the stock 29" would likely be more like 2100 rpm.

Bikersmurf.......not sure how that would apply. Nothing in the calculator is asking for an original tire size to compare. Just like it is not asking for what engine is driving it all. Can you clarify a bit more of what you are thinking? Thanks

 

[bikersmurf]

I was mixed up. I was overthinking it... thinking of Speedometer error.

 

[1911]

Hi all, I've been looking at what I can expect from an RPM on the highway with 35" tires with a TH400 (no overdrive) and the 2 different sets of LC gears (3.73/4.11). Even the 3.73 RPM seems high for 65 MPH. What do you all think?

That looks about right to me. I am running (stock for my year) 3.70 diffs and 33" tires, and I turn 2450 rpm to go 65 mph in 4th gear.

 

[71FFJ40]

That calculator seems about right.
I'm churning approximately 2500-2600 rpm @ 63-65 mph.Stock F,3rd gear,4:11,35" tires

 

[jim land]

Dont forget reel tire size vs advertised size , most 35" tire are 33.5" or 34"

 

[middlecalf]

I’ll let you know once I reach 65. Almost there... get ‘em up scout. Putt, putt, putt...

 

[pb4ugo]

The numbers look close to correct to me. There are different rpm calculators out there that allows you to enter tranny final drive and overdrive ratios.

 

[JohnnyC]

looks like a rip off from here:

Engine RPM Calculator

I go to the automotive converters page here for all that conversion stuff:

AutomotiveCalculators and Converters

This thread has many useful links for converters:
This is a link... click it>>> Speed calculation