[Z06] Relationship: RPMs and MPH
Thread Starter
Race Director
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From: Texas Hill Country
Relationship: RPMs and MPH
This is born from another thread.
The debate is whether aerodynamics, friction, or engine load can affect the engine RPMs at the same MPH when no other variables (tire size or gearing) are changed.
Example: Tailwind - 100 MPH at 5000 RPMs
Headwind - 100 MPH at 5500 RPMs
Go!
The debate is whether aerodynamics, friction, or engine load can affect the engine RPMs at the same MPH when no other variables (tire size or gearing) are changed.
Example: Tailwind - 100 MPH at 5000 RPMs
Headwind - 100 MPH at 5500 RPMs
Go!
Le Mans Master
Joined: Sep 2003
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From: Longview Texas
Seems like RPM would have nothing to do with aerodynamics. At a specified speed, the wheels are turning a certain speed. The engine speed is directly related to the wheel speed, so it would not change unless you are getting more slippage between the tire and the road surface.
Tailwinds and headwinds only work on airplanes.
Tailwinds and headwinds only work on airplanes.
Last edited by TEXHAWK0; Jan 8, 2008 at 06:37 PM.
Thread Starter
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From: Texas Hill Country
Seems like RPM would have nothing to do with aerodynamics. At a specified speed, the wheels are turning a certain speed. The engine speed is directly related to the wheel speed, so it would not change unless you are getting more slippage between the tire and the road surface.
Tailwinds and headwinds only work on airplanes.
Tailwinds and headwinds only work on airplanes.
Tailwinds and headwinds work on cars, but the RPMs increase with the MPH... You can easily see this in 1/4 mile times/MPH....
Instructor
Joined: Nov 2006
Posts: 211
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From: Alamogordo New Mexico
As long as the payment stays fixed to planet earth, and the drive train has no major slop or slipage (thats important as most drive trains do have some slop), then a certain RPM equals a certain MPH.
I am not sure of drivetrain compression factors with 100 mph winds and high driving speeds. I really don't think races would be held with such high winds. Normal racing, maybe 20-30 max winds, drive train compression could be a factor. But thats slop, at least its what I call it. How much, I will let that be for others to figure out.
Noise levels will change, drag becomes less downwind, and since the tires are not spinning, the factor of sliding friction doesn't even enter the picture. Tire compression for street tires, would be small, maybe for drag tires with low pressure, a very small difference. Like .01 or so something.
With drive train wear and possible clutch slipage into such a strong headwind, you could see a different mph for that given rpm, but you also might start smelling smoke.....or go deaf from all the wind noise........
I am not sure of drivetrain compression factors with 100 mph winds and high driving speeds. I really don't think races would be held with such high winds. Normal racing, maybe 20-30 max winds, drive train compression could be a factor. But thats slop, at least its what I call it. How much, I will let that be for others to figure out.
Noise levels will change, drag becomes less downwind, and since the tires are not spinning, the factor of sliding friction doesn't even enter the picture. Tire compression for street tires, would be small, maybe for drag tires with low pressure, a very small difference. Like .01 or so something.
With drive train wear and possible clutch slipage into such a strong headwind, you could see a different mph for that given rpm, but you also might start smelling smoke.....or go deaf from all the wind noise........
Last edited by Skypilot797; Jan 8, 2008 at 07:38 PM.
Le Mans Master
Joined: Mar 2002
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From: PNW
This is born from another thread.
The debate is whether aerodynamics, friction, or engine load can affect the engine RPMs at the same MPH when no other variables (tire size or gearing) are changed.
Example: Tailwind - 100 MPH at 5000 RPMs
Headwind - 100 MPH at 5500 RPMs
Go!
The debate is whether aerodynamics, friction, or engine load can affect the engine RPMs at the same MPH when no other variables (tire size or gearing) are changed.
Example: Tailwind - 100 MPH at 5000 RPMs
Headwind - 100 MPH at 5500 RPMs
Go!
If you go 100 MPH in 5th @ 5500 RPM with a 100 MPH tail wind ... or a 100 MPH head wind ... then you are still going 100 MPH in 5th gear @ 5500 RPM as long as the tires or clutch aren't slipping.
Of course it will take MUCH more HP (i.e., throttle opening) in 5th gear to go 100 MPH with a head wind than it does to go 100 MHP in 5th gear with a tailwind.
Last edited by ZeeOSix; Jan 8, 2008 at 07:22 PM.
Safety Car
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From: Bartlett, IL
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St. Jude Donor '06-'07-'08-'09-'10-'11-'12
No change in engine RPM vs. vehicle speed for either scenario providing we are talking about a manual trans car not some auto with a huge stall or something like that.
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Thread Starter
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From: Texas Hill Country
A converter (especially an aftermarket one) will be locked by the time aero plays a part. Even that wouldn't be a factor.
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From: Texas Hill Country
http://forums.corvetteforum.com/show....php?t=1905641
It must be a trick question to some.... I wondered how many people were confused about it.
I have seriously had people tell me their intake made their vehicle run 500 RPMs less down the highway. I'm not certain most people realize the gearing/MPH relationship.
Le Mans Master
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From: PNW
Besides Z06s don't have auto trannys.
Safety Car
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From: San Bruno ca
Le Mans Master
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From: Winchester TN
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St. Jude Donor '03-'04-'05-'06-'07-'11
Perhaps, but....
Automatic, on a hill, holding the car from rolling backwards by modulating the throttle to hold the car steady. Capture the RPM's necessary to hold the car steady.
Now, repeat that same rpm on flat level ground.
Did the rpm/mph ratio change?
On a viscous-coupled drivetrain, possible.
Not on a hard-coupled drivetrain IMO.
best regards -
mqqn
Melting Slicks
Joined: Nov 2007
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From: Indianapolis IN
I have noticed that if I raise the rear ride height, the car does go faster. I think it is because the center of mass of the car is going more downhill when I raise the rear ride height, and that allows gravity to provide more of a "forward pull" on the car, instead of just straight down. This weekend, I will try lowering the rear ride height and raising the front ride height and see if that slows the car down. (Center of mass would be going more uphill in this case).
Mr. Wizard is turning over in his grave seeing this thread; didnt anybody other than me actually watch the show?!?!?!?!?!?!?!
Mr. Wizard is turning over in his grave seeing this thread; didnt anybody other than me actually watch the show?!?!?!?!?!?!?!