Who's running 285/65R20 tires? Will they fit?

Discussion in '3rd Generation Ram Forum (NO engine/transmission topics) Archive' started by WOT, Feb 8, 2017.

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  1. WOT TDR MEMBER

    I currently have 275/65R20 (on 20x9, 5.75 back spacing) and it looks like I could go up to 285 (~1/2 larger diameter and slightly wider) but it would be close. Hoping someone is running something similar and can let me know for sure. Where it gets really close is if I want to add fender flares as they take up a little more space on the lip. FYI, looking at BFG All Terrain KO2s and running stock height/no lift.

    Thanks in advance!
     
    WOT , Feb 8, 2017
    #1

  2. GroceryHauler


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    Exact tires I have on my 06. They are close on rear of front fender when turning. Mine have never hit. I think a leveling kit would look nicer but unsure about changing stock geometry of truck. Don't know what my offset is, but dish on rim is about 2".


     
    GroceryHauler , Feb 8, 2017
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  3. GroceryHauler

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    Here's 1 more pic. Wish I knew the exact back spacing on on my rims. Do know that tire combo is 34.6" tall. I haven't had any issues, but putting fender flares on would make it "real close". If you want different pics let me know.



     
    GroceryHauler , Feb 8, 2017
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  4. cerberusiam Staff Member

    You could to a 305 or maybe even a 325 tire with that back spacing. A 285 is pretty minimal tire for what can be there.
     
    cerberusiam , Feb 8, 2017
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  5. WOT TDR MEMBER

    GroceryHauler,

    Nice looking truck. Your offset looks similar although hard to tell for sure. From KMC's website (http://www.kmcwheels.com/wheelSpecs/2067/1/11539/xd795-hoss) it looks like you have either model #XD79529080212N (4.53 offset) or XD79529080218 (5.71" offset). Do you have any issues with those tires picking up rocks and slinging them out? Also, did you get them road force balanced and if so do you know the run-out they had?

    Can you get a picture of the front wheel turned so I can see the proximity to the fender?
     
    WOT , Feb 9, 2017
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  6. GroceryHauler

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    Hope this pic helps. I purchased this truck approximately 3 months ago, so I'm not sure if these tires were load force balanced. As far as picking up and throwing stones, I don't really notice it and I have a gravel drive.

    I'm very happy with the BFG's, very smooth and fairly quiet. I'd say the tread is about 50% with 30,000 miles on them.



     
    GroceryHauler , Feb 10, 2017
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  7. cerberusiam Staff Member

    The 285\65\20 is a 33.5" tire and not wide enough to worry about on 5.75 back spacing. Would be better with the stock 6.25 but it works. Forget the BFG's, worst choice of a tire you can make for a heavy truck. There are much better tires from Nitto and Cooper that will outlast and outperform the crappy BFG's. You could even go to a 295 or 305 tire and not have issues with that back space.
     
    cerberusiam , Feb 10, 2017
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  8. GroceryHauler

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    Cerb must be talking about a 60 series tire, because that 285/65r20 is just shy of 35". I really don't think you'll get a taller tire on a stock truck with out at least scraping fender.


     
    GroceryHauler , Feb 11, 2017
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  9. cerberusiam Staff Member

    Not just shy of 35, a lot shy of 35. That is a calculated number of a tire that is not mounted and is not actual height as installed. I haven't found one yet that measured up to the published diameter because it is a calculation, they all come out at about an inch shorter when mounted and installed. If you flattened the tire out that is what it would be if it was a perfect circle, they aren't. The face of the section flattens out to accommodate the tread width so actual is always less than calculated on a metric tire.

    You can run up to a 34" tire and not have issues, depending on back space. You can run a 35" tire on the stock back space rims with only minor interference and full turn and compression at stock height. A 2" level will allow a 35" tire to work with only minor rubbing on the control arm.
     
    cerberusiam , Feb 11, 2017
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  10. GroceryHauler

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    OP , here's a couple more pics for you to decide by.

    You know what, I'm not a tire engineer. I'm just going by manufacturer specs, but if you can get a 305/65r20 on a stock 3rd gen 2500 and not rub please send me a pic. I'm just running the same setup the OP was asking about and giving my opinion.
     
    GroceryHauler , Feb 11, 2017
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  11. cerberusiam Staff Member

    When you put too small back space wheels on it that tends to limit the tire sizes you can run. You can run a taller wider tire with no issues if they are tucked back into the fender well instead of sticking out too far. Like I said a 34" tire on a stock back space works fine, a 35" tire will fit but hit the control arms, fenders if you adjust the back space out. With a 2" level it is good all the way around. The back space and suspension height are critical.
     
    cerberusiam , Feb 11, 2017
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  12. WOT TDR MEMBER

    Appreciate the pics. The calculated dimensions are pretty close to the MFG specs. I had emailed BFG to confirm the specs:
    Also, I've had good luck with my current BFGs...I have 60K on them and have about 1/32 left before the wear bars and are evenly worn. A friend has had 3 sets of Nittos...the most any set lasted was about 30K miles.
     
    WOT , Feb 13, 2017
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  13. cerberusiam Staff Member

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    MFG specs and calculated diameter are the same number. They do not take into account the section top is flattened to accommodate the tread and create a contact patch. When installed on a rim and vehicle the actual diameter is always less than the calculated number, about 1" difference than published. Calculated numbers assume a 1 dimensional aspect while the actual application is 2 dimensional. Real easy to validate, measure the actual height of the tire as installed on the vehicle.
     
    Last edited by a moderator: Nov 15, 2018
    cerberusiam , Feb 13, 2017
    #13

  14. WOT TDR MEMBER

    I would agree that the radius as measured from the ground is less due to compression. The radius near the fender where the interference might happen would not have any compression and therefor should be the "advertised" radius/diameter. Would that not be correct?
     
    WOT , Feb 13, 2017
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  15. cerberusiam Staff Member

    Nope. There is less than 2/10 of inch difference horizontal vs vertical or static vs rolling. If you air them down to 5 lbs there would be more difference but not the normal 1" between actual and published. They will get shorter under a load as much as 1/4 though but that is expected. The back space will have more effect on rubbing fenders than differences in compression. A 33.25" tire will scuff the fender at full compression with a 4.5" back space rim. A 34" tire won't with a 6.25" back space rim.
     
    cerberusiam , Feb 13, 2017
    #15
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