Is there a caculation formula for estimating the travel speed knowing the rpm in fifth gear. I was at 4500 rpm in fifth gear on a flat stretch of road. The speedometer had already topped out at 85 mph. Anyway to get an mph estimate? Driving a 1982 280ZX NA 2 seater. Wishing I had a Garmin!
Calculate it by how many seconds you pass an object.
do a control as an example you pass object X at 1 mile going 60mph in x.x seconds to figure the formula on distance covered X Time =speed.
Have a friend stand at Object at your mile with a stop watch and when you get to your top speed starting the mile "point A" you keep it constant speed and when you pass over the mile "Point B" is when you hit the stop on the stop watch.
If your time is doubled from lets say from 60mph X 1mile= 1 minute - 1 mile X .5 minutes=120mph
In order to calculate the speed from the RPM, you need to know three things about your car. The gear ratios of the transmission gears, the differential ratio and the circumference of the rear tires in feet.
RPM X tire circ. X 60 / Trans. gear ratio X Diff. ratio X 5280 = Speed in MPH
D=RT Distance equals rate x time. On the freeway, tell me you were not on some back road, they have the miles marked off. Have someone time it between markers, then it's simple math. Rate = Distance divided by time.
Orrrr...how fast are you going at 2000 rpm...2500 rpm...3000 rpm...get the hang of it? Now all it is, is a simple algebraic graph of a slope. "When will I use this?" Makes you wish you'd paid attention in algebra 1, doesn't it?
Enjoyed the reading the responses. JuanitoZcarito gave a great resource for charting mph and rpm. Thanks for the help guys. When I am traveling that fast I do not pay much attention to road markers to mark the distance. Yes, 115 mph it was.