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rpmerf · 06-12-2019, 11:30 AM

My suburban is a 97 - overdrive with lockup. I can plug it into a calculator and see 34.7 MPH per 1000 RPM.

To get ~35 MPH / 1000 RPM with a 0.7:1 gear ratio and a 4.10 rear, you would need to have ~33.5" tires.

I'm assuming you have 235/85R16, as that's what came on my 70 C20. They are 31.7". With OD and a 4.10 rear that should give 32.9 MPH / 1000 RPM. You should be closer to 2,125 RPM at 70 MPH.

Here is a calculator to get the speed at a given tire size, trans ratio, rear ratio, and RPM.
https://spicerparts.com/calculators/...rpm-calculator

06-12-2019, 11:30 AM	#11
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Rear end ratio help? My suburban is a 97 - overdrive with lockup. I can plug it into a calculator and see 34.7 MPH per 1000 RPM. To get ~35 MPH / 1000 RPM with a 0.7:1 gear ratio and a 4.10 rear, you would need to have ~33.5" tires. I'm assuming you have 235/85R16, as that's what came on my 70 C20. They are 31.7". With OD and a 4.10 rear that should give 32.9 MPH / 1000 RPM. You should be closer to 2,125 RPM at 70 MPH. Here is a calculator to get the speed at a given tire size, trans ratio, rear ratio, and RPM. https://spicerparts.com/calculators/...rpm-calculator __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z