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  #1  
Old 07-23-2004, 12:39 AM
Matthew Groves Matthew Groves is offline
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Differences between 285/75/16 and 235/85/16

Hello,

I'm replacing tires in my stock 97 F250 HD PSD CC. I'm choosing between these two tires, I think. Anyone savvy on the differences between them?

I already know the factual differences like the slight difference in Diameter and it's effect on the speedo, etc. I know what 75 and 85 stand for etc.

Will the 285/75/16s, being an 8 ply tire give me a softer ride than the 10 ply 235/85/16s?

I don't do any towing, but I have 4.10s in the rear. I'd like the tallest tire I can get to gain back some RPMs at highway speed. (At 70mph I'm turning about 2300rpms)

Is there some other reason that I should stick with the stock size of 235/85/16? Equally good in the snow?

Thanks,

Matthew
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  #2  
Old 07-23-2004, 09:04 AM
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nuclearmonster nuclearmonster is offline
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If for no other reason, looks should lead you to the better choice. 235s just don't look right on a big diesel truck.
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  #3  
Old 07-23-2004, 09:53 AM
mtncrawler mtncrawler is offline
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Don't know about that. Like my tires like I like my women. Tall and narrow.
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Old 07-23-2004, 10:29 AM
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nuclearmonster nuclearmonster is offline
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Really its what makes you happy. I run a 315/75/16 in a mud terrain. Love the tires. Go anywhere I want and feel like my truck has shoes that feet it's feet. If a small street tire will do what you need, that is what you should get. The bigger tires soften the ride because they have a lot more give.
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Old 07-23-2004, 11:18 AM
mtncrawler mtncrawler is offline
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And alot more rolling resistance. From my hot rod days I always felt wide tires had more "road wander" too but I always ran them anyway. But yea I agree, it's all personal preference. There are those that feel a well dressed vehicle requires windshield dingle ***** and fuzzy dice.
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Old 07-23-2004, 11:32 AM
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Matthew. The 285/75/16 is a little over an inch taller than the 235/85, do you will drop your rpm's a little bit, but at a full two inches wider than the 235 you will add more rolling resistance so your milage may suffer a bit.

I have run the 285's since the truck was practically new and other than them still being too small (looking) for the truck I've been happy with them. My milage didn't really change any...and they do fill out the wheelwells better. They perform substantially better in mud/snow than my stock Firestones did.
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Old 07-23-2004, 03:10 PM
Matthew Groves Matthew Groves is offline
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I went with the 285/75/16s today. Having 4.10s in the rear end and hardly ever ever pulling anything, I wanted to gain back some rpms on the highway, and give my engine at least *something* to work it some.

I have some rubbing on the front bumper, which I was suprised at, so I'll start another thread to deal with that after I search the archives of course.

Thanks for all your help on the tires.
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  #8  
Old 07-23-2004, 03:23 PM
PSDJOE PSDJOE is offline
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Formula for tire measurements if needed.

235/85/16
235 divided by 25.4 =9.25 is the actual width
take 9.25 and multiply it by 85% will = 7.86
take 7.86 and muliply it by 2
then add the 16 inches for the wheel
will give you 31.72 inches tall
actual measurements are 9.25 wide by 31.72 tall

formula will work on all sizes of course
285/75/16 is 11.22 wide and 32.84 tall
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Last edited by PSDJOE; 07-23-2004 at 03:33 PM.
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  #9  
Old 07-23-2004, 05:25 PM
Diesel Daddy Diesel Daddy is offline
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Matthew, I had put some 33X12.50R 16.5 on my 94 F250. When I put those on, they rubbed the bumper slightly. So, I took a sawzall ( ) and cut just the inside edge of the front bumper at an angle and no more rubbing!!
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Old 07-23-2004, 09:56 PM
Matthew Groves Matthew Groves is offline
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I'm trying to decide between 1. cutting the bumper 2. shimming the bumper, and 3. Putting 265/75/16s on (or even 255/85/16s)
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Old 07-24-2004, 11:12 PM
Matthew Groves Matthew Groves is offline
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I went with the non-destructive method. Took less than an hour to remove the 4 bolts and replace them with 4 longer ones plus an inch stack of wide washers.

Used 10.9 class bolts, shouldn't be a problem.

Thanks for all the help from here. On to the next project........frozen lock solenoids.
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Old 07-24-2004, 11:52 PM
Bluesbandit Bluesbandit is offline
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Matthew I did the same swap on my 97 also with 4.10's. I lost about 100 miles of travel per fill up, but I didn't recalibrate the computer or anything so I'm interested in what you come up with for your milage. Traction is much better off road with the 285's but wet weather pulling is worse..more resistence yadyadayada.....I would think that a thinner tire would be better in snow as it would be less likely to sit on top of snow. Kinda like a snow shoe versus a bare foot. But I live in Texas, so what do I know about snow? One thing I have noticed is at full turn the tires rub on radius arms. You didn't mention if your's was a 2wd or not, so this may not be a concern for you. If I had it to do over again, I think I'd splt the difference and go with the 265's.
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Old 07-26-2004, 11:25 AM
Matthew Groves Matthew Groves is offline
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I haven't checked rubbing at full turn. I need to do that.

M7 97 is a 4x4, yours?

I'm on my first tank of gas, so I don't have mileage yet. I did recalibrate my speedometer, took about half an hour because it was my first time. Kinda scary knowing that you've only got 6 changes. I don't know if it's ever been changed, so hopefully I've got 5 left now.

It took me a 61 seconds to drive a mile at 60mph on the speedometer, so I'm a little off still, but not much.

What do you mean about worse wet weather towing? I will be driving in snow here in Nebraska for sure. Won't be doing any serious off roading though. Maybe I should have saved my money and went with the 265s or back to the 235/85/16s. If I would have known about the 255/85/16 I might have gone that route. Those would be some stiff tires for sure, though.

It's a done deal, so I'll say I'm happy with my 285s.

What else have you done to your 97? I take all advice. I'll be shimming the FPS next. Maybe a home made intake after that.
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Old 07-26-2004, 11:33 PM
Bluesbandit Bluesbandit is offline
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No, mine is a 2wd. Your 4X4 won't have radius arms so no worries there. Did you get the info for the recal. off the site, I've been too lazy to search it? As for worse in wet weather, you have a much wider tire now so when it encounters water there is more surface area that has to break through the water to stay in contact with the pavement. Hence more pull through puddles, and increased ability to hydro-plane. Think of it as trying to skip a small round rock, and a large flat rock in a lake. Same thing in snow. You have more tire area to support the weight of your truck, and thus it is more likely not to contact pavement. Not that I think you'll have any problems at all, just some things to consider in your driving habits. I'm very happy with my 285's and their ride. Next time I may try something different. Only other mod I've done to my truck (spent too much fixing other stuff....old girl has 300K on her) is to put on a Tymar intake. In my opinion that is a must, but that's a whole 'nother thread. Good luck and enjoy your rig.
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Old 07-27-2004, 12:13 AM
Matthew Groves Matthew Groves is offline
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Thanks for your info.

Yes, I got the speedo calibration info from this site. It is very easy to do. All you need is one jumper wire and then you work a sequence of buttons.

You DO need to do some measuring of your tire first (not just knowing it's "size"). I assume that this recalibration affects the speedometer, odometer, and maybe even the transmission shift points, though on second thoughts those are run off the tach instead (which is not affected by the speedo recal)

Tell me more about your Tymar? i've read all the threads. Are you happy with yours? I'm pondering the home made open air intake myself. That and shimming the Fuel Pressure Regulator are the only mods I'm planning on.

I'm sure that's what everyone says starting out though, huh.
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Old 07-27-2004, 12:13 AM
 
 
 
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