tire question
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Elder User
Joined: Nov 2005
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From: Cottage Grove, Minnesota
tire question
I have a 97 F150 4x4 auto w/ 16in standard wheels. I plan on going from the tires I have now which are 255/70R16 to 265/75R16. I am wondering if my speedo will be off at all?
Any input welcome.
P.S. I read the post on the top of the forum about tire sizes and didn't see anything about the speedo being off.
Any input welcome.P.S. I read the post on the top of the forum about tire sizes and didn't see anything about the speedo being off.
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tire size
i did exactly the same swap, and i think it is about 5% off now. in other words, it is off more the faster you go. at 0 it wouldn't be off any and at 100 you would really be going 105. hope this helps. i have found at 65ish on the highway, it's about 3 off.
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Elder User
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From: Cottage Grove, Minnesota
One of my dad's buddies from church has a 97 F150 4x2 and I think he put on 265/75R16 his truck. They really filled out the wheel well. Oh yeah they are Bridgestone Dueler AT Revo's.
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Depending on the brand of tire you go with can also change height. A 265/75/16 generally is sized to a 32-11.50 where as a 255/70/16 is basically a 30.5 true height with most brands. If you have any difference at all it will be between 2-3 mph on your speedo. But however I have mounted many 265/75/16 tires at my shop to replace the 255's and have never had a customer come back in my 7 years with a complaint of the speedo being off.
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Yes your speedo will be off. I just did the same swap, but I went from 245/75/16's to 265/75/16's. I needed a 19 tooth speedo gear to correct for the new tire size. I would say go for the bigger tire, it makes the truck look a lot better and did not really affect my gas mileage.
This site will tell you how much different tire sizes affect your speedo:
http://www.miata.net/garage/tirecalc.html
This site will tell you how much different tire sizes affect your speedo:
http://www.miata.net/garage/tirecalc.html
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Elder User
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From: Cottage Grove, Minnesota
Originally Posted by 54_Ford_F100
Yes your speedo will be off. I just did the same swap, but I went from 245/75/16's to 265/75/16's. I needed a 19 tooth speedo gear to correct for the new tire size.
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I'm not sure if there are any web sites that tell you the speedo gear you currently have, I had to take mine out of the transfer case and count the teeth that were on it. My original was a 21 tooth with the 235/70/16's. I would guess yours is a 20 tooth, if you have the 3.55 rear end. The 19 tooth would correct it for the bigger tire size for that gear ratio. If you have a different gear ratio you would want to find a speeo gear that has approx. 5.3% less teeth.
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Elder User
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From: Cottage Grove, Minnesota
How hard is it to remove the speedo gear? Can it be removed with the truck sitting on all 4 wheels or do I have to put it on jack stands? I'm a skinny guy and can crawl underneath mine with no problem except for the running boards hanging down.
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It is real easy to get at. I changed mine by just crawling under my truck. It is held in by one nut in the transfer case (4x4) or transmission (2wd). It will be on the drivers side of the truck. Once you get the nut off just pull the assembly out. The gear is held on by a little clip.
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Elder User
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From: Cottage Grove, Minnesota
Ok so I found the speedo location I think. Correct me if I'm wrong but is it at the tail of the transfer case towards the top? How do I go about removing it/ It is cold and don't want to break any parts. But I know I have to go to a 19 tooth gear to correct the speedo for larger tires if I do get them.
Last edited by skilife17; Mar 3, 2006 at 01:11 PM.