RPMs - Smart Car of America Forums : Smart Car Forum

Ron F · 03-21-2009, 12:12 PM

I would appreciate it if someone could give me the RPMs at the following speeds. Obviously I don't have a tach and sometimes worry about getting near or exceeding the 6400 RPM redline when entering an interstate or driving on open roads. Most all of my driving is done using manual shift:

40 MPH in 2nd
55 MPH in 3rd
65 MPH in 4th

**jwight** · 03-21-2009, 02:19 PM

I've seen these in another thread but not sure which one. However, not to worry because the computer will not let you over rev the car; it will either shift to a higher gear or hold the revs at redline if it's in 5th gear*. Same on downshifts - it won't let you over rev. I won't say it's foolproof but it's pretty close.

* actually not in 5th because I think you hit the speed limiter before getting to the redline.

mvaldes · 03-21-2009, 09:58 PM

Does this help?
Quote:
Originally Posted by theguywiththelongestname

i usually shift in the 3500rpm range...

1st>2nd about 3000- 3500 rpm
2nd>3rd about 3600-3800 rpm
3rd>4th about 3500-4500 rpm
4th>5th about 3500-4500 rpmQuote:
Originally Posted by theguywiththelongestname View Post
1>2 about 15-20 mph
2>3 about 25-30 mph
3>4 about 40-45 mph
4>5 about 55-60 mph

Ron F · 03-30-2009, 03:16 PM

I'd still appreciate it if someone could tell me the RPMs in 2nd, 3rd, and 4th gear at the speeds that I listed. Thanks.

NCC1701 · 03-30-2009, 04:12 PM

40 MPH, 2nd gear around 5,300
55 MPH, 3rd gear around 4,800
65 MPH, 4th gear around 4,300

2008 Cabrio, windows and roof closed. 40 & 55 A/C On, 65 A/C Off

andrewd · 03-30-2009, 04:36 PM

Quote:

Originally Posted by jwight

* actually not in 5th because I think you hit the speed limiter before getting to the redline.

you hit the limiter in 4th too,

dont ask how i know but 4th gear is good for just under 100mph

**jimvw57** · 03-30-2009, 04:49 PM

sounds like a good reason to pick up a Scangauge II. I have mine setup to show RPM, MPH, MPG, and FWT (temp) They are extremely helpful to have to educate yourself on getting better MPG. and can read & reset engine codes too.

Old smart · 03-30-2009, 05:49 PM

Moon,

Call or email me. We can take my tach-equipped vehicle out on Rt. 199 and collect data - me with MPH and you with the tach. Thence, we can retire to the Green Leafe for "Rope Yarn Wednesday."

CAPT Dave

geosynch · 03-30-2009, 07:47 PM

Quote:

Originally Posted by NCC1701

40 MPH, 2nd gear around 5,300
55 MPH, 3rd gear around 4,800
65 MPH, 4th gear around 4,300

2008 Cabrio, windows and roof closed. 40 & 55 A/C On, 65 A/C Off

FYI, unless something is slipping (clutch or tires) there is a direct correlation to engine speed (RPM) and the car's velocity (MPH). Stated another way, it doesn't matter if the top is up or down or the AC is on or off. 65 MPH in 4th gear will always be (about) 4,300 RPM (although these things will impact the gas consumption).

You can calculate the speed as a function of RPM by:

RPM x /60 / (gear ratio for gear in question x gear ratio of the differential).

This will get you the wheel's rotational velocity in rev/sec. Then simply multiple that number by the circumference of the driving (rear) wheel in inches. That will get you the car's velocity in inches/sec. To convert to MPH simply by 0.05682.

I had looked up the gear ratios and the differential ratio once. They are on the web somewhere, it just takes some digging to find it.

geosynch

NCC1701 · 03-30-2009, 08:03 PM

Quote:

Originally Posted by geosynch

I had looked up the gear ratios and the differential ratio once. They are on the web somewhere, it just takes some digging to find it.

Well, when you find it ... do the calculations and let us know how close my (admittedly unscientific) observations were.