# RPM/speed

Discussion in 'General Tech and Maintenance' started by danjones, Jun 11, 2004.

1. ### danjonesJunior Member

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On a 2003 Acura RL, what should the engine RPM be at a 70 mph cruise?

2. ### swannySenior Member

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I would guess it would be around 2,700 RPM or so, I tried finding info and found the transmission gear ratios
Gear Ratios

1st 2.46:1
2nd 1.45:1
3rd 0.95:1
4th 0.65:1
Final drive 3.13:1

I think there might be a way to calculate the RPMs but I do not know the formula. If it is anything over 4k RPMs you either have your overdrive off or your transmission may have some issues.

3. ### MikeBergyBlah blah blah....

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Measure the outside diameter of your tire. now divide that by two. that is the tire's radius.

Now lets say your tach says 4500 rpms, and you are in 3rd gear.

4500 x 1/.95 x 1/3.13 = 1513.36 rpms at the tire.

V = r(w), where r is your tire radius, and w is your tire's angular velocity( needs to be in radians per unit time).

1513.36 x 360deg x pi/180deg = 9508.7 rad/min

V = 1ft x 9508.7 rad/ min = 9508.7 ft/min = around 108 mph. But I doubt your tires are 2ft in diameter, that seems a little big; just showing you how to do the math. There is probably a calculator in the ref section somewhere.

4. ### Citizen_InsaneSenior Member

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stfu blanco. there is this thing called "Math" and it is used by lots of us to do "problems". Your problem if you can't understand elementary level mathmatics.

5. ### Bl6CRXSenior Member

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woah woah cool down there hotshot...he was just making a joke...we need not turn this thread into another pointless argument, otherwise this would be looking like honda-tech

6. ### ahedauSenior Member

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The simple answer is 2000 RPM at 70MPH given a tire size of 225/50/15. I'm too lazy to look up the OEM tire size but here's a link to the tranny calculator that does all that math for you

tranny calculator

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