The Ford Barn

rer_239 · 10-27-2017, 08:13 AM

tried the search but couldn't fine the answer. i have a 4.11 gear set and plan on using 16" wheels (tire dia 28.36). that figures out to 2440 rpm. is that too high for a stock engine/trans?

Tom Wesenberg · 10-27-2017, 10:06 AM

You need to measure the road surface to the center of the axle to get the radius, then multiply it in the formulae. This is because the tire has a shorter radius where it contacts the road.

Jim/GA · 10-27-2017, 10:52 AM

Quote:

Originally Posted by rer_239

tried the search but couldn't fine the answer. i have a 4.11 gear set and plan on using 16" wheels (tire dia 28.36). that figures out to 2440 rpm. is that too high for a stock engine/trans?

2440 RPM at what speed?

I have run my Model A engine at that RPM at times. It is very well balanced, so quite smooth.

PM me for details.

modelAsteve · 10-27-2017, 11:21 AM

There really isn't enough info on your car. I can tell you that for a street/ touring car you will soon tire of the 2440 rpm. You want to be down around 2000 rpm for a pleasant enjoyable car. The A motor has a lot of torque and you can be happy with the lower rpms. Henry had it about right!

woodiewagon46 · 10-27-2017, 11:55 AM

Here are the formulas, MPH= RPM x Tire diameter, divided by Gear Ratio x 336. RPM= MPH x Gear Ratio x 336 divided by Tire Diameter. Gear Ratio = RPM x Tire Diameter, divided by MPH x 336. Tire Diameter = MPH x Gear Ratio x 336 dived by RPM.

sphanna · 10-27-2017, 10:27 PM

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With a 3.78 rear end and 14.4 inches from road surface to center of wheel, the rpm / 44 equals the mph. So on the 3.78 rear end 2440 rpm divided by 44 = about 55.5 mph. to correct this for the 4.11 rear end take the 3.78/4.11 = .92 55.5 times .92 = about 51 mph at 2440 rpm. I do not think that 2440 rpm is too high. I like 2200 rpm better, but I think you are OK.

Jim Brierley · 10-29-2017, 10:53 AM

2440 is too high for cruising, aim for 2,000 - 2100. You'll be happier and so will your engine.

10-27-2017, 08:13 AM	#1
rer_239 Senior Member Join Date: May 2010 Location: muskegon, mi Posts: 297	gear ratio and engine speed and mph. tried the search but couldn't fine the answer. i have a 4.11 gear set and plan on using 16" wheels (tire dia 28.36). that figures out to 2440 rpm. is that too high for a stock engine/trans?

10-27-2017, 10:06 AM	#2
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: gear ratio and engine speed and mph. You need to measure the road surface to the center of the axle to get the radius, then multiply it in the formulae. This is because the tire has a shorter radius where it contacts the road.

10-27-2017, 11:21 AM	#4
modelAsteve Senior Member Join Date: Nov 2010 Location: Penn Valley (Nor-Cal) Ca Posts: 128	Re: gear ratio and engine speed and mph. There really isn't enough info on your car. I can tell you that for a street/ touring car you will soon tire of the 2440 rpm. You want to be down around 2000 rpm for a pleasant enjoyable car. The A motor has a lot of torque and you can be happy with the lower rpms. Henry had it about right!

10-27-2017, 11:55 AM	#5
woodiewagon46 Senior Member Join Date: Jun 2012 Location: Long Island,NY Posts: 1,562	Re: gear ratio and engine speed and mph. Here are the formulas, MPH= RPM x Tire diameter, divided by Gear Ratio x 336. RPM= MPH x Gear Ratio x 336 divided by Tire Diameter. Gear Ratio = RPM x Tire Diameter, divided by MPH x 336. Tire Diameter = MPH x Gear Ratio x 336 dived by RPM.

10-27-2017, 10:27 PM	#6
sphanna Senior Member Join Date: Jun 2010 Location: Polk City, Iowa Posts: 526	Re: gear ratio and engine speed and mph. Sponsored Links (Register now to hide all advertisements) With a 3.78 rear end and 14.4 inches from road surface to center of wheel, the rpm / 44 equals the mph. So on the 3.78 rear end 2440 rpm divided by 44 = about 55.5 mph. to correct this for the 4.11 rear end take the 3.78/4.11 = .92 55.5 times .92 = about 51 mph at 2440 rpm. I do not think that 2440 rpm is too high. I like 2200 rpm better, but I think you are OK. __________________ Steve Hanna, Polk City, IA

10-29-2017, 10:53 AM	#7
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,107	Re: gear ratio and engine speed and mph. 2440 is too high for cruising, aim for 2,000 - 2100. You'll be happier and so will your engine.