The Ford Barn

Curly · 08-15-2017, 11:00 PM

I was reading a thread earlier today on figuring out gearing ratios. I can't seem to find it now. Forgive me if this is a re-post.

I lifted one rear wheel and cranked the handle exactly 15 revolutions. The lifted rear wheel made 8 full revolutions. The truck was in 3rd gear. This is a 1939 transmission.
Can anyone tell me what gears I have in the rear end?

Tom Wesenberg · 08-15-2017, 11:45 PM

Sounds like you have the 3.78 ratio.

Curly · 08-16-2017, 12:43 AM

Thanks Tom. 2250 RPM's = 48 mph. 16 inch wheels. Might be time to look into some higher speed gearing from Snyders. Is there a chart or formula to see how many mph I might gain? I wouldn't mind gaining 5 mph.

Synchro909 · 08-16-2017, 01:00 AM

Quote:

Originally Posted by Curly

Thanks Tom. 2250 RPM's = 48 mph. 16 inch wheels. Might be time to look into some higher speed gearing from Snyders. Is there a chart or formula to see how many mph I might gain? I wouldn't mind gaining 5 mph.

Larger tyres will give you a little more speed and more rubber on the road.
I gain 5% by using 5.25X21 tyres instead of the original 4.5X21 with better road holding and no adverse affects.

Tom Wesenberg · 08-16-2017, 04:46 AM

I would install the 3.27 ring and pinion. Best bang for the buck to gain some speed through gearing.

Dodge · 08-16-2017, 04:51 AM

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Ditto, 3.27. I went 3.54 not enough with my motor.

Bruce of MN · 08-16-2017, 05:04 AM

Do you have enough motor to handle uphill grades with the lower ratio?

V4F · 08-16-2017, 07:59 AM

takes a little hp to power the 3:27 gear

BILL WILLIAMSON · 08-16-2017, 09:41 AM

3:78 is a good all around gear. Why spend time & money for just 5 MPH gain????---"Maybe" your speedo's not even accurate, anyhow????
Bill Cheep

Will N · 08-16-2017, 10:02 AM

Help me with the math here please- 8 divided by 15 is 1.875, not 3.78. Do you have to double the 1.875 because one wheel was left on the ground, causing the differential action, and the spider gears have half the number of teeth than the axle gear?

Curly · 08-16-2017, 11:24 AM

Mr. Cheep,

5 mph gain is pretty good when on club rides you are always about 5 mph slow. By the time I get to the pie stop all the good pie is gone.

Curly · 08-16-2017, 11:25 AM

I think I have enough motor. Its a Ron Kelly touring. 6:1 head.

Tom Endy · 08-16-2017, 12:03 PM

The attached may help answer the original question. Document provided by MAFCA.

Tom Endy

Patrick L. · 08-16-2017, 12:29 PM

A 3:54 should give about 4 mph at same engine speed over a 3:78
A 3:27 would be about an 8 mph increase over the 3:78

Curly · 08-16-2017, 02:42 PM

Thanks Patrick.

jhowes · 08-16-2017, 03:30 PM

Wilk N; Take the 8 and knock it in half since only one wheel is turning. Then divide the 4 into 15 and you should get close to 3.78. 3.75 to be exact but the standard ratio was 3.78 so that's what he has. Jack

Will N · 08-17-2017, 03:28 PM

Thanks Jack- and i suspect that the reason you knock the 8 in half is due to the number of teeth on the axle gear vs. spider gear. When both wheels are turning the same speed, there is no relative movement between the spider and axle gears. When one wheel only moves, the spider spins the axle gear.

08-15-2017, 11:00 PM	#1
Curly Member Join Date: Dec 2014 Location: Alaska Posts: 94	What gear ratio do I have? I was reading a thread earlier today on figuring out gearing ratios. I can't seem to find it now. Forgive me if this is a re-post. I lifted one rear wheel and cranked the handle exactly 15 revolutions. The lifted rear wheel made 8 full revolutions. The truck was in 3rd gear. This is a 1939 transmission. Can anyone tell me what gears I have in the rear end?

08-15-2017, 11:45 PM	#2
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: What gear ratio do I have? Sounds like you have the 3.78 ratio.

08-16-2017, 12:43 AM	#3
Curly Member Join Date: Dec 2014 Location: Alaska Posts: 94	Re: What gear ratio do I have? Thanks Tom. 2250 RPM's = 48 mph. 16 inch wheels. Might be time to look into some higher speed gearing from Snyders. Is there a chart or formula to see how many mph I might gain? I wouldn't mind gaining 5 mph.

08-16-2017, 04:46 AM	#5
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: What gear ratio do I have? I would install the 3.27 ring and pinion. Best bang for the buck to gain some speed through gearing.

08-16-2017, 04:51 AM	#6
Dodge Senior Member Join Date: Nov 2011 Location: Sonoma, CA. Posts: 1,496	Re: What gear ratio do I have? Sponsored Links (Register now to hide all advertisements) Ditto, 3.27. I went 3.54 not enough with my motor.

08-16-2017, 05:04 AM	#7
Bruce of MN Senior Member Join Date: May 2010 Location: VA Posts: 1,410	Re: What gear ratio do I have? Do you have enough motor to handle uphill grades with the lower ratio?

08-16-2017, 07:59 AM	#8
V4F Senior Member Join Date: May 2010 Location: ca. Posts: 2,522	Re: What gear ratio do I have? takes a little hp to power the 3:27 gear __________________ V4f

08-16-2017, 09:41 AM	#9
BILL WILLIAMSON Senior Member Join Date: Dec 2010 Location: FRESNO, CA Posts: 12,560	Re: What gear ratio do I have? 3:78 is a good all around gear. Why spend time & money for just 5 MPH gain????---"Maybe" your speedo's not even accurate, anyhow???? Bill Cheep __________________ "THE ASSISTANT GURU OF STUFF"

08-16-2017, 10:02 AM	#10
Will N Senior Member Join Date: Jul 2010 Location: Pennsylvania Posts: 1,101	Re: What gear ratio do I have? Help me with the math here please- 8 divided by 15 is 1.875, not 3.78. Do you have to double the 1.875 because one wheel was left on the ground, causing the differential action, and the spider gears have half the number of teeth than the axle gear?

08-16-2017, 11:24 AM	#11
Curly Member Join Date: Dec 2014 Location: Alaska Posts: 94	Re: What gear ratio do I have? Mr. Cheep, 5 mph gain is pretty good when on club rides you are always about 5 mph slow. By the time I get to the pie stop all the good pie is gone.

08-16-2017, 11:25 AM	#12
Curly Member Join Date: Dec 2014 Location: Alaska Posts: 94	Re: What gear ratio do I have? I think I have enough motor. Its a Ron Kelly touring. 6:1 head.

08-16-2017, 12:29 PM	#14
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: What gear ratio do I have? A 3:54 should give about 4 mph at same engine speed over a 3:78 A 3:27 would be about an 8 mph increase over the 3:78

08-16-2017, 02:42 PM	#15
Curly Member Join Date: Dec 2014 Location: Alaska Posts: 94	Re: What gear ratio do I have? Thanks Patrick.

08-16-2017, 03:30 PM	#16
jhowes Senior Member Join Date: Jul 2010 Location: upstate NY near Mass border Posts: 789	Re: What gear ratio do I have? Wilk N; Take the 8 and knock it in half since only one wheel is turning. Then divide the 4 into 15 and you should get close to 3.78. 3.75 to be exact but the standard ratio was 3.78 so that's what he has. Jack

08-17-2017, 03:28 PM	#17
Will N Senior Member Join Date: Jul 2010 Location: Pennsylvania Posts: 1,101	Re: What gear ratio do I have? Thanks Jack- and i suspect that the reason you knock the 8 in half is due to the number of teeth on the axle gear vs. spider gear. When both wheels are turning the same speed, there is no relative movement between the spider and axle gears. When one wheel only moves, the spider spins the axle gear.