Tire Size
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Joined: Dec 2003
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From: South Texas Coast
Tire Size
I have a 96 F250 PSD with automatic and 3.55 rear end.
I am currently running stock 235 tires.
The rear end ratio is a little tall for towing my fiver unless I run in 3rd gear never in OD. In 3rd at 65 mph I'm turning about 2500 RPM maybe a tad under. I have no problem doing that but would perfer to drop the RPM about 200 so I am operating on the up side of the power & torque curves instead of near the peak.
I am considering increasing tire size as a means of affecting the final drive gear ratio to gain that 200 RPM. I have a friend that has run 285 tires on an identical truck. He had no body contact or rubbing problems so I should be able to go that large.
does anyone know how to calculate or get a good estimate of the effect of increased tire size?
I am currently running stock 235 tires.
The rear end ratio is a little tall for towing my fiver unless I run in 3rd gear never in OD. In 3rd at 65 mph I'm turning about 2500 RPM maybe a tad under. I have no problem doing that but would perfer to drop the RPM about 200 so I am operating on the up side of the power & torque curves instead of near the peak.
I am considering increasing tire size as a means of affecting the final drive gear ratio to gain that 200 RPM. I have a friend that has run 285 tires on an identical truck. He had no body contact or rubbing problems so I should be able to go that large.
does anyone know how to calculate or get a good estimate of the effect of increased tire size?
Senior User
Joined: Feb 2004
Posts: 392
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From: Lamesa,Texas
my 97 has the same set up. ive found that i can pull almost anything in od with the stock 235 85's. i just have to speed up to around 74 or so. that speeds up the motor enough that it is making enough to pull hills. i pull a 24' gooseneck stock trailer loaded this way and only down shift on the steepest of hills. just a thought. you might not want to run that fast but it would keep you from having to buy new equipment. ive been running and towing this way for 170,000 so i wouldnt worry about wearing out the truck. just my .02 good luck!!!
Elder User
Joined: May 2004
Posts: 637
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From: Forest Hill, MD
