My car knows what speed it likes

mini
cooper

#1

Hello, I love your show and have been listening for many years.

I have been thinking about this question for at least a year, but been waiting until I had nothing better to do…here goes: I purchased a new Mini Clubman in 2009, and found when I first began to drive it on the highway that I was having trouble maintaining the speed limit, which at the time coincided with about 2600 rpm. On a hunch I decided to clear my mind of as much conscious pedal-pressure thought as possible and let the car do its thing, like a Ouija board, and the car seemed to increase on its own to 3000 rpm and hold there - it seems to like that engine speed. Is this my imagination or can an engine have a rpm “comfort zone”? By the way this is an automatic transmission; my ex-wife did not know how to drive a standard.


#2

3,000 rpm is YOUR comfort zone, not the car’s. The car doesn’t care. You like 3,000 rpm because the engine sounds and feels right to you at that speed. Nothing wrong with that.

How much over the speed limit are you going at 3,000 rpm?


#3

it’s more likely that this is your comfort zone. At whatever speed 3000rpm is for your car, you feel, consciously or not, that this speed is a good balance between unsafely fast and annoyingly slow.

(edit) Well, two posts saying the same thing within 21 seconds of each other. We must be on to something :wink:


#4

Engines have an optimal RPM value where they get the most torque, and an optimal RPM value where they get the most horsepower. Usually, these values are not equal.

These sweet spots vary by engine type and size, and depend heavily on the gears in use. 3,000 RPMs might be one of your engine’s “sweet spots,” but it might just be your driving style too. Since it has a manual transmission, when you are having trouble maintaining the speed limit, it just might be time to downshift until you encounter less resistance.


#5

The engine will have an optimum rotational speed based on the load being put upon it which is a combination of gearing, terrain, wind speed and direction, aerodynamics of the car and so on. As such it will vary based on those conditions. One day, on a particular stretch of road, it may seem to run effortlessly at 3000 rpm (not lugging, not over-revving). The next day, with a 30mph headwind for example, it may not be able to handle the extra load as well without changing gears and/or engine speed. These effects are amplified when the engine size is not well matched to the application (a dinky engine in a minivan for example).


#6

My BMW really likes 125 MPH, unfortunately.

Twotone


#7

And what is the tach showing at 125 mph?

Just curious.


#8

About 4,000 rpm


#9

All my cars are completely silent at rest. When forced to move, I agree with “Whitey”.
My wife’s 91 Accord was a little strange though; the chassis was a little unstable but the motor was exceptionally smooth at speeds 80 mph to 105 mph. That explanation didn’t seem to impress the traffic cop either.


#10

Does your BMW have an inline 6 or V6 or V8? My inline 6 cylinder Mercedes likes higher rpms, whereas V6’s and V8’s I’ve driven don’t sound like they like high rpms as much as that inline engine.


#11

540i sport – 4.4l V8, 6-speed manual transmission.


#12

BMW doesn’t believe in the V6, all their 6 cylinders are inlines.


#13

You cleared your mind of all your conscious pedal pressure…and your unconscios took over. Your unconscious apparently likes to go faster than your conscious does. Mine does too.

All cars have “sweet spots” where the engine is operating smoothly and in its “zone”, but that’s as much a result of tranny ratios, load, tires, air resistance, and terraine as it is the engine itself.