Tire sizes

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Oct 9, 2017 | 11:57 AM

MTP55

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From: Michigan

Tire sizes

How much can you change your tire size before it effects your speedometer. My VIN tag says it had 235s and it now has 265s. My boss's truck has 285s. What's the pros and cons of larger tires?

Oct 9, 2017 | 12:29 PM

seville009

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Supposedly less than 3% change. Depends on the aspect ratio too. There are online tire size calculators you can use to compare two separate tire sizes to see how different they are.

Oct 9, 2017 | 03:35 PM

MTP55

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What would be the process of resetting the computer to read the speed of a bigger tire? A PCM reprogram? I know the dealer did one before I got the truck because it's written on a tag under the hood. Also does the tire size effect pulling power in anyway?

Oct 9, 2017 | 03:47 PM

seville009

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Dealer generally has to do it, but some tuners can - there’s alot of threads by people who have dealt with it.

Oct 9, 2017 | 03:47 PM

don123

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From: Massachusetts

Quote:

Originally Posted by MTP55

A smaller tire will give you the net effect of shorter gears.

Oct 9, 2017 | 04:00 PM

MTP55

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Can you explain what "shorter gears" means? Gearing is something I haven't got involved with yet but am curious about.

Oct 9, 2017 | 04:40 PM

don123

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From: Massachusetts

You have gear ratios in the differentials of your truck. The 6.2 comes with two choices stock 4.30’s or 3.73’s. The 4.30’s are shorter or deeper gears which put a bit more torque to the ground. 3.73’s are taller gears allowing less rpm’s and slightly better mileage. If you had 35” tires on your truck and then switched to say 30” tires it would be the same as swapping gears in your truck. Like going from 3.73’s to 4.30’s.

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Oct 9, 2017 | 06:09 PM

don123

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From: Massachusetts

Bigger tire will equal less torque to the ground. Smaller diameter tire equals more torque to ground.

Oct 9, 2017 | 06:31 PM

#10

MTP55

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From: Michigan

Ah ok. So not much gain from a larger tires is what I'm getting. The difference between 265 and 285 shouldn't be too much though. There's a one inch sidewall difference and if I'm right the aspect ratio is the same. I'm switching from the Falken Rocky Mountains to Cooper Discoverer STT pros. I'm in fields and snow too much with my job for highway tires and the old tires are wore out now anyway.