RPM at 70 MPH and 80 MPH

[thatguy]

Hi all,

 

Could you please post what RPMs ya'll are running on level ground (no discernible incline) at 70MPH and 80MPH. If you can obtain readings without heavy winds (head, tail, or cross), without having your vehicle heavily loaded, and in dry conditions that would be preferable. If you can't please include the conditions.

 

Trim: [sE, SEL, TITANIUM, SPORT]

Engine: [2.0L I4, 3.6L V6, 2.7L V6]

Wheel Size (inches):

AWD or FWD:

Elevation:

RPM @ 70MPH:

RPM @ 80MPH:

 

 

Thanks!

[TheWizard]

The conditions (uphill or downhill, elevation, wind speed or direction, vehicle load, driver's mother's maiden name, etc.) make no difference in engine RPM to speed. For any given transmission gear, with any given differential ratio and tire size, the engine speed will always be the same for a specified speed regardless of other conditions. That is unless you have something seriously wrong with your transmission and it's slipping.

 

If you have the transmission gear ratios, the differential ratio and the tire sizes, you can plug the numbers into a spreadsheet to calculate RPM to speed. I may have those ratios someplace. I'll see if I can't dig them up and post them for you.

[POWERSTROKE]

Yes, with today's lock-up torque converters, no slippage in the transmissions, just the overdrive ratio for the transmission gear, rear axle ratio, and tire circumference effects engine rpm.

 

I know I've seen all that info, may be in owners manual. Might have been in a post on this forum too.

[TheWizard]

Here is the formula to calculate RPM:

RPM = speed in MPH * overall gear ratio * 336 / tire diameter in inches

(overall gear ratio is calculated by multiplying differential ratio by transmission ratio for the selected gear)

 

2015 Edge Specifications

 

Transmission gear ratios

1st - 4.58

2nd - 2.96

3rd - 1.91

4th - 1.45

5th - 1.0

6th - 0.75

 

Differential (axle) ratios

Ecoboost I4 without start/stop - 3.36

Ecoboost I4 with start/stop - 3.21

3.5L V6 FWD - 3.16

3.5L V6 AWD - 3.39

Sport FWD - 2.77

Sport AWD - 3.16

 

Tires

SE/SEL - P245/60HR18 - 29.57" diameter

Titanium - P245/55HR19 - 29.61" diameter

Sport - P245/50WR20 - 29.65" diameter

 

Example

Edge SEL FWD 3.5L V6...

70 mph

3.16 axle ratio

0.75 6th gear ratio

29.57 tire diameter

=> 70 * 3.16 * 0.75 * 336 / 29.57 = ~1885 RPM

 

[thatguy]

The conditions (uphill or downhill, elevation, wind speed or direction, vehicle load, driver's mother's maiden name, etc.) make no difference in engine RPM to speed. For any given transmission gear, with any given differential ratio and tire size, the engine speed will always be the same for a specified speed regardless of other conditions. That is unless you have something seriously wrong with your transmission and it's slipping.

 

If you have the transmission gear ratios, the differential ratio and the tire sizes, you can plug the numbers into a spreadsheet to calculate RPM to speed. I may have those ratios someplace. I'll see if I can't dig them up and post them for you.

 

That's news to me. In order for my current vehicle to maintain 70 mph on when going uphill it must downshift which causes my engine RPM to increase. Same affect when there are heavy headwinds. Is the Edge's powerband such that it never requires downshifts?

[TheWizard]

That is not at all what I said. I thought I was quite clear...

 

"For any given transmission gear with any given differential ratio and tire size, the engine speed will always be the same for a specified speed regardless of other conditions."

 

If you are driving in such a way that it requires downshifting then of course the engine RPM will increase. This is an effect of the different gear ratio and can be calculated in exactly the same way using the new ratio. The external driving conditions have no direct correlation to engine RPM - only the gear ratios do. In other words, an X mph head wind does not correlate to a Y% change in engine speed. Only the downshifting of the transmission to a different gear affects the RPM (regardless of whether you manually shifted or the vehicle did it for you).

 

Basically, you asked for engine RPM at speed in 6th gear (the gear that would be in use at 70 and 80 mph). That's a value that can be calculated with certainty and does not require trial and observation by other members. Nor will it ever be different for any drivers as long as they are using the same gear ratios.

[omar302]

Doesn't the torque converter lockup also have an affect on engine RPM? usually when it locks up RPM goes down a little?

[TheWizard]

Doesn't the torque converter lockup also have an affect on engine RPM? usually when it locks up RPM goes down a little?

That is correct. The engine speed will be somewhat higher until the torque converter locks up because there is a slight amount of slippage involved. The torque converter is a fluid coupling that is designed to allow slippage until it locks - that's what allows you to remain in gear when you're stopped and what smooths the transition between gears. But at highway speeds it will have locked within a few seconds of reaching speed. The formula and ratios posted above assume no slippage... either a manual transmission with the clutch fully engaged or an automatic transmission after the torque converter has locked.