The Ford Barn

springerpete · 09-15-2023, 12:00 PM

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

nkaminar · 09-15-2023, 04:28 PM

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.

nkaminar · 09-15-2023, 04:36 PM

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?

Big hammer · 09-15-2023, 04:43 PM

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!!!!

johnneilson · 09-15-2023, 05:38 PM

Quote:

Originally Posted by nkaminar

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?

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

09-15-2023, 12:00 PM	#21
springerpete Senior Member Join Date: Jul 2012 Location: Central Maine Posts: 644	Re: 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

09-15-2023, 04:28 PM	#22
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,900	Re: maximum rpm, personal choice... 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. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

09-15-2023, 04:36 PM	#23
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,900	Re: maximum rpm, personal choice... 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? __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

09-15-2023, 04:43 PM	#24
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,131	Re: maximum rpm, personal choice... 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!!!! __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done