Rpm vs Mph - Automatic transmission

[gvillayandre]

Hi All,

I would like to compare my car performance related to Rpm and Mph.

Mine in fourth gear at 4.000 Rpm gets 55 Mph in a flat ride. No up or down hill drive.

Have anybody make this comparison?
Is there any table that compiles this info at standard?

Thank you!!

[w113dude]

It should be closer to 3000 RPM at 55 MPH

[georgem]

Our 230 manual does 3000rpm for 60mph, 3500 for 70mph if that's any help. The speed I`ll vouch for as it was from a GPS, the revs were off the tach so no guarantee there

cheers

[gvillayandre]

Appreciated!!

I will record speed from 3.000 to 5.000 each 500 rpm and post.

[Cees Klumper]

You know it all depends on your differential gear ratio, which is stamped into a flat surface on the side of it. Lots of us have replaced original differentials with high ratios (4.08) with lower ones to reduce the RPMs at highway speeds. US automatics were typically sold with the 4.08 and I replaced mine with. 3.69 years ago. Reduces RPMs by about 10%.

[gvillayandre]

Thank you Cees.

I will check what is my car differential ratio.

Is this change expensive?

[bogeyman]

In top gear, you should be about 2700-2800 at 55mph. If you are actually turning 4,000, my guess is that you are actually in 3rd gear?
No final drive ratio in the 113s will give you 4,000 @ 55mph in top gear.

[Cees Klumper]

I changed my differential for, as I recall, around €500 including labor which was an ok deal because it took the mechanic most of a day. He kept the old differential.

[66andBlue]

I will record speed from 3.000 to 5.000 each 500 rpm and post.

You can compare your data with the ones in this graph:

[Peter van Es]

Good stuff for Tech Manual...

[jameshoward]

What a brilliant graph, Alfred. Thanks.

Can't wait to finish my car now.  Assuming we both don't disappear in a ball of fire and engine parts the potential looks great.

James

[kampala]

Alfred,

You guys never cease to amaze ... much appreciated ... this is very nice.

[71Beige280SL]

Very helpful. Was there a standard Gear Ratio for 71 280SLs? Based on the chart, I believe mine would be either 3.69 or 3.75.

[gvillayandre]

Perfect!!!

[Rolf-Dieter ✝︎]

This has to be the best car forum on the Internet ... Pad yourself's on the back fellow Members ... Well done ... I'm just blown away from the wealth of information on this site.

My 280 SL (1969) at 60 MPH is around 3,000 RMP at 70 MPH shows around 3,500 RPM (numbers are approx. ~ I will record more accurate numbers), I will keep an eye on it and make a comparison to the Graph ... Thanks Alfred 

EDIT ---> Correction found out that my speedometer is out by about 8 KMPH (when compared to my GPS readout) so 60 MPH on my car speedometer is actually 88 KMPH on my TomTom GPS. and at that point I am at or near 3000 RPM.

[Eminent]

Alfred, i hope you don't mind.
I took your graph and convert it to Km/h.
Perhaps handy for the members with a Km tacho, like me.
I have a 3.69 spare diff wating for a swap with the 4.08 thats stil under my 280SE(L)
Rini.