1950s RPM@MPH

[Bob Kielar]

I have a 1955 Cadillac Fleetwood 60S. It has a 336 rear end with 15" tires I was wondering if anyone knows what the rpm's are going 30mph before she shifts into fourth also 60 and 70mph? Thanks

Keep Cruzin,

Bob

[tcom2027]

Since you didn't post the overall diameter of your tire I calculated it in two ways 26.5 and 23.5", IIRC the 15" tire and wheel diameter is 23.5 plus or minus a bit for wear and brand of tire.

Bias and radials vary in overall diameter depending on brand and wear.

                 So here goes, estimating.

   26.5"  30mph/1259 rpm         23.5" 30mph/1419 rpm

          60mph/2518 rpm               60mph/2839 rpm             

          70mph/2937 rpm               70mph/3312 rpm
           

          100mph/4196 rpm              100mph/4732 rpm   

tony     

[Bob Kielar]

Oops I forgot to mention that my tires are 235/75/15 radials. Thanks for the calculations Tony.

Keep Cruzin,
Bob

[Clewisiii]

Are you asking wheel RPM or engine rpm.

["Cadillac Kid" Greg Surfas 15364]

closer to 33 inch diameter
Greg Surfas

[Bob Kielar]

I am looking for engine rpm.

Thanks,
Bob

[Bob Kielar]

The diameter of a 235 75 r15 is 28.88 so maybe the engine rpm would be around 2200?

Keep Cruzin,
Bob

[Suntuned]

Bob ,  Google Wallace Racing Calculators, Its a Pontiac Drag Racing site with good info you can use for calculating this type of info.  Using there RPM calculator. Your input info would be gear ratio, trans gear in high, tire diameter, MPH,  converter slip %  the info you supplied would be the following
3.36 gear, trans gear high 1.0, tire diameter 28.8 inch, 5% convert slip, 30 mph = 1235 rpm,  60 mph 2470 rpm, 70 mph 2882 rpm,              They have a gear cal, mph cal, tire size cal, & RPM calculator, hope this helps.

[Bob Kielar]

Thanks for the replies. I'll check out the Pontiac drag racing website.

Keep Cruzin,

Bob