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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Feb 2001 Posts: 81 Shop Shark | | Shop Shark Joined: Feb 2001 Posts: 81 | My 62 1/2 ton Chevy truck needs bigger tires on the rear to help lower RPMS. I have a 235 c.i. six with a 390 rear end. Presently have 235/70/15 tires. How large can I go without a problem? I have a three speed three-on-the tree trans. Thanks for any information.
Green Machine
| | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | I've put 32x11.50s on them before without issue. You will need wider wheels, though (8-9").
Bill Burmeister
| | | | | Joined: Apr 2003 Posts: 942 'Bolter | | 'Bolter Joined: Apr 2003 Posts: 942 | I went from 235/75R/15's to 265/75R/15's on the back of my '72 C-10. It made a notice-able difference. They look good too.
Bill
'60-'72 Chev/GMC Fan
GMC 9500 Fan
Detroit Diesel Fan
| | | | | Joined: Jul 2008 Posts: 1,262 Shop Shark | | Shop Shark Joined: Jul 2008 Posts: 1,262 | Might I suggest you use a calculator to pick which diameter gets you into the RPM range your engine likes? http://www.ringpinion.com/Calc_RPM.aspxAs an example: With your current set-up you are turning 2574 RPM at 55 mph Change to a 32 inch diamter tire and you will be turning 2252 RPM at 55 mph. Keep in mind that if you go too big you will affect your launch ratio, which simply means you will have to slip the clutch to get going. | | | | | Joined: Feb 2001 Posts: 81 Shop Shark | | Shop Shark Joined: Feb 2001 Posts: 81 | Thanks for the replies to my question! I previously ran a three speed borg warner overdrive trans but it needed an overhaul-kept jumping out of high gear so I put the regular three speed back in. Rather than spend a lot on the overdrive thought I would try larger tires first. Sure miss those higher gears. Any other suggestions are appreciated.
Green Machine
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