maximum rpm, personal choice...

I think it is interesting that no one mentions stopping. I read all sorts of speed numbers and stress predictions but no thoughts on stopping. At 50-55-60 mph the narrow tires of a model A are not at all like our modern car tire surface area. There is a a lot less friction to stop the car. I am concerned about the kids on bikes, people walking, pets in the road, etc. My outlook. Bill
 
Good brakes, properly adjusted, help with the stopping. Regarding tires, it is only the coefficient of friction that determines how well the tires grip, not the area. If you go back to your high school physics book, the horizontal force is equal to the normal force times the coefficient of friction, or F=N X f. Area does not enter into the formula. That said, modern tires have a better coefficient of friction due to the thread design and the rubber compound, and yes more area. Look at racing tires. The rubber compound is very soft so that you can dig your fingernail into it. They are so sticky that it seems the car would stick to the ceiling.
 
So, did anybody check my math? Is 18 m/s average piston speed equal to a little over 5,000 rpm with a 4.125 inch stroke?

One revolution is 8.25 inches and at 5,000 rpm that is 41,250 inches per minute or 687.5 inches per second or 17.46 meters/second. Correct?
 
Interesting about driving speeds of our model A’s , sometimes 20 mph is to fast and sometimes driving at 55-60 mph isn’t fast enough. I can idle at 3 mph or go 65 mph, it just depends on the road conditions, rain, snow, traffic, road conditions, after sunset…… We all need to drive defensively!!!!
 
nkaminar said:
So, did anybody check my math? Is 18 m/s average piston speed equal to a little over 5,000 rpm with a 4.125 inch stroke?

One revolution is 8.25 inches and at 5,000 rpm that is 41,250 inches per minute or 687.5 inches per second or 17.46 meters/second. Correct?
Click to expand...

It helps to start the calculations with the correct stroke.... 4.25

But, yes, 18 m/s equates to about 5000 rpm.

No one even questions the 60's specifications, those included a pressurized oiling system, inserted bearings and more journals.

The early 20's designs were modeled after steam engines

FWIW, the "B" race motors can spin 7000 rpm.

John
 
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