The Ford Barn

1929 · 12-29-2018, 04:51 PM

Took the car out for its weekly winter exercise, speed was 58 mph at 2400 rpms, is that about normal for a 3:54 in the rear?

HDowse · 12-29-2018, 06:59 PM

Try this link on rpm, rear end ratio, tire diameter and speed. You can plug in your values and check the rpm or change any three values to get the fourth.
http://www.advanced-ev.com/Calculators/TireSize/

sphanna · 12-29-2018, 08:27 PM

That is correct

GRutter · 12-29-2018, 08:29 PM

It depends on wheel diameter. Assuming from your user name that it is a 1929 model.
If you have 21" wheels with a dia of approx 30" your speedometer should show close to 62 mph for a 3.54 rear.
If a 30-31 with 19" wheels, your speedometer would be closer to 60 mph with a 3.54 rear.

If you are reading 58 mph I would believe you have a standard 3.78 rear and not a 3.54. Why do you think you have a 3.54 rear? Did you rebuild and change ring & pinion?

Jim/GA · 12-29-2018, 08:32 PM

Quote:

Originally Posted by 1929

Took the car out for its weekly winter exercise, speed was 58 mph at 2400 rpms, is that about normal for a 3:54 in the rear?

Yes, that's about right.

1929 · 12-30-2018, 10:41 AM

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Quote:

Originally Posted by GRutter

It depends on wheel diameter. Assuming from your user name that it is a 1929 model.
If you have 21" wheels with a dia of approx 30" your speedometer should show close to 62 mph for a 3.54 rear.
If a 30-31 with 19" wheels, your speedometer would be closer to 60 mph with a 3.54 rear.

If you are reading 58 mph I would believe you have a standard 3.78 rear and not a 3.54. Why do you think you have a 3.54 rear? Did you rebuild and change ring & pinion?

I installed the 3:54, but, I have 16 inch wheels.

GRutter · 12-30-2018, 11:04 AM

That makes more sense.
My chart shows a rolling circumference for a "typical" 16" tire to be 89.10", which would put you at 57.1 MPH at 2400 RPM with a 3.54 rear. With the variation in tires, you could be spot on at 58

1929 · 12-30-2018, 12:17 PM

Quote:

Originally Posted by GRutter

That makes more sense.
My chart shows a rolling circumference for a "typical" 16" tire to be 89.10", which would put you at 57.1 MPH at 2400 RPM with a 3.54 rear. With the variation in tires, you could be spot on at 58

Thanks GRutter

12-29-2018, 04:51 PM	#1
1929 Senior Member Join Date: Jan 2015 Location: New York Posts: 943	RPMs? Took the car out for its weekly winter exercise, speed was 58 mph at 2400 rpms, is that about normal for a 3:54 in the rear?

12-29-2018, 06:59 PM	#2
HDowse Senior Member Join Date: May 2010 Location: Hancock, New Hampshire Posts: 375	Re: RPMs? Try this link on rpm, rear end ratio, tire diameter and speed. You can plug in your values and check the rpm or change any three values to get the fourth. http://www.advanced-ev.com/Calculators/TireSize/

12-29-2018, 08:27 PM	#3
sphanna Senior Member Join Date: Jun 2010 Location: Polk City, Iowa Posts: 526	Re: RPMs? That is correct __________________ Steve Hanna, Polk City, IA

12-29-2018, 08:29 PM	#4
GRutter Senior Member Join Date: Sep 2017 Location: Mint Hill, North Carolina Posts: 386	Re: RPMs? It depends on wheel diameter. Assuming from your user name that it is a 1929 model. If you have 21" wheels with a dia of approx 30" your speedometer should show close to 62 mph for a 3.54 rear. If a 30-31 with 19" wheels, your speedometer would be closer to 60 mph with a 3.54 rear. If you are reading 58 mph I would believe you have a standard 3.78 rear and not a 3.54. Why do you think you have a 3.54 rear? Did you rebuild and change ring & pinion?

12-30-2018, 11:04 AM	#7
GRutter Senior Member Join Date: Sep 2017 Location: Mint Hill, North Carolina Posts: 386	Re: RPMs? That makes more sense. My chart shows a rolling circumference for a "typical" 16" tire to be 89.10", which would put you at 57.1 MPH at 2400 RPM with a 3.54 rear. With the variation in tires, you could be spot on at 58