Another Tire Question
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Junior User
Joined: Jul 2005
Posts: 82
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From: Duluth, MN
Another Tire Question
Ok guys, I know this has been beaten to death, but I can't find any advice that directly addresses my issues.
I have a 1989 F-150 4x4, Borg Warner T-18 (4 speed manual w/ granny) and 3.55 rear gear ratio. I'm running stock tires wich are Cooper 235/75R15.
My tires are shot and need replacement. I want to reduce my RPM's at Freeway speeds b/c in the 4th gear (1:1) i'm turning about 3000 RPM's @ 70mph. I did the math and at first it didn't seem to add up, but then I measured my tires and found out that they are actually only 27.5" in Diameter. Go figure.
So here is my question: Can I upgrade to 31x10.5 tires to drop the RMP's or will those be too large of a tire to push with my setup? Does anyone else have a similar setup? Ideally I'd prefer to get a gear splitter or new transmision but can't afford either. Any comments would be great.
I have a 1989 F-150 4x4, Borg Warner T-18 (4 speed manual w/ granny) and 3.55 rear gear ratio. I'm running stock tires wich are Cooper 235/75R15.
My tires are shot and need replacement. I want to reduce my RPM's at Freeway speeds b/c in the 4th gear (1:1) i'm turning about 3000 RPM's @ 70mph. I did the math and at first it didn't seem to add up, but then I measured my tires and found out that they are actually only 27.5" in Diameter. Go figure.
So here is my question: Can I upgrade to 31x10.5 tires to drop the RMP's or will those be too large of a tire to push with my setup? Does anyone else have a similar setup? Ideally I'd prefer to get a gear splitter or new transmision but can't afford either. Any comments would be great.
Fleet Mechanic
Joined: Aug 2004
Posts: 1,276
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From: NE Tennessee
What motor? You'd gain top end if the motor can pull em. Your gonna be a little sluggish on the take off. With the 3.55s you will probably be okay. Also if you have a long-bed you may have to lift it to fit those depending on how saggy your springs are.
Junior User
Joined: Mar 2006
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I run 31X10.50's on my 91 with 302, E4OD, and 3.55's with no problem, even with overdrive. My dad runs them on his 95 4X4 with 351, E4OD, 3.55's, supercab and longbed as well. Also, I think that they look better on both trucks than the stock 235's.
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Junior User
Joined: Jul 2005
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From: Duluth, MN
Opps. I have the I6-4.9L (300) with the 8-ft box.
So you think there might be a problem if my rear leafs have a bit of a sag? What other size tires might you suggest that would be bigger than the 235/75's that might work?
So you think there might be a problem if my rear leafs have a bit of a sag? What other size tires might you suggest that would be bigger than the 235/75's that might work?
Fleet Mechanic
Joined: Aug 2004
Posts: 1,276
Likes: 7
From: NE Tennessee
Only way to really know is to put a set on it 
Would be nice if ya had a friend with some that you could try on.
Longbeds usually sit a tad lower in the front than short bed 4x4's. Not sure about the back. Just keep in mind that you may have to get a 2" lift if ya get some bad scrubbing.
Would be nice if ya had a friend with some that you could try on.
Longbeds usually sit a tad lower in the front than short bed 4x4's. Not sure about the back. Just keep in mind that you may have to get a 2" lift if ya get some bad scrubbing.
Fleet Mechanic
Joined: Feb 2004
Posts: 1,448
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From: CA Central Coast
I have a 93 F-150 4x4 Supercab Longbed AOD, with 31x10.5's. Off hand I don't recall what rearend ratio I have, but I like the look and have no problems with tire rubbing.
Fills the wheel wells nicely without looking like I'm trying to make a point. (Note: tires right now are a highway tread Bridgestone HT Dueler set probably 6 year old. The newer tread is more aggressive).
I haul a 2 horse trailer or a dump trailer averaging #4000 lbs total, and it's slow with the 5.0 but it gets the job done. Since the truck came to me like this, I can't tell you anything about comparison with stock.
Fills the wheel wells nicely without looking like I'm trying to make a point. (Note: tires right now are a highway tread Bridgestone HT Dueler set probably 6 year old. The newer tread is more aggressive).
I haul a 2 horse trailer or a dump trailer averaging #4000 lbs total, and it's slow with the 5.0 but it gets the job done. Since the truck came to me like this, I can't tell you anything about comparison with stock.
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Junior User
Joined: Jul 2005
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From: Duluth, MN
Thanks guys, I appreciate all of your advice. I was having second thoughts about going through with it but I ended up getting the new rubber this afternoon and went with the BF 31x10.5's.
It looks like the front tires will rub slightly on the radius arms at full lock and the rear will be fine. A little rubbing shouldn't hurt. Sure does look nice and fills up those wheel wells good. I like the stockier look and the little bit higher stance.
I've only driven it the 20 miles to home but so far so good. No real ******* from on a start from a stop. I'm probably benefitting from the low gears of the BW T-18. I sure did enjoy the lower RPM's on the ride home. No longer screamin' at 3000 at 65 mph. I'll drive it around some more tommorrow and let you all know how she does. Thanks again.
It looks like the front tires will rub slightly on the radius arms at full lock and the rear will be fine. A little rubbing shouldn't hurt. Sure does look nice and fills up those wheel wells good. I like the stockier look and the little bit higher stance.
I've only driven it the 20 miles to home but so far so good. No real ******* from on a start from a stop. I'm probably benefitting from the low gears of the BW T-18. I sure did enjoy the lower RPM's on the ride home. No longer screamin' at 3000 at 65 mph. I'll drive it around some more tommorrow and let you all know how she does. Thanks again.
