my F150 is getting some new shoes

Discussion in 'Tow Vehicles, Hitch & Towing' started by G. Will Ickers, Jul 14, 2015.

  1. G. Will Ickers

    G. Will Ickers New Member

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    Factory tires on my truck are 265/55/r20 Pirelli Scorpions. I don't love them. I think they look too "slim" and "streety" for a truck, always have.

    I'm getting close to 50k miles, so I decided to get some new Cooper Discoverer RTX tires, but a step up in size (LT265/65/r20) and with an "E" rating.

    This kind of tire comes on heavier duty trucks like 2500's and F250's. I expect about a 1.5" lift from the tires alone, and a much stiffer ride, which I won't mind. They'll help when towing my heavier car trailer and should get better wear, from what I've read.

    I have them installed next week.
     
  2. exploreco

    exploreco Active Member

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    Post a pic when you get them on. You have the 20 inch chrome i take it? I have never seen anything aggressive on those rims so curious what that will look like.

    Sent from my Samsung Galaxy S4 using Tapatalk
     
  3. G. Will Ickers

    G. Will Ickers New Member

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    They're the smoked out rims. Not chrome. The paint scheme is "tuxedo black", so everything from the factory, including lights, rims, windows, is some version of "blacked out".
    For that reason, I made it very clear this morning when dropping off the truck that I wanted the tires mounted "white letters IN".
     

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  4. exploreco

    exploreco Active Member

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    Gotcha, the FX package. Looks nice. How do the ride? Gives it a nice aggressive look.

    Sent from my Samsung Galaxy S4 using Tapatalk
     
  5. G. Will Ickers

    G. Will Ickers New Member

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    It sits almost 2 inches taller, and has a bit of a stiffer ride due to the E rated tires. They're quiet though. So far I really like em.
    No rubbing, no issues.

    Paid $850 out the door. Buy 3 get 1 free at Merchants Tire.
     
  6. Keith Hawkins

    Keith Hawkins Active Member

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    Just remember, you will be travelling faster than your speedometer reads so adjust accordingly. Tire 1 in the chart below is the original 265/55/r20 and tire 2 is of course the new 265/65/r20.

    Tire 1 Tire 2
    20 mph 21.3 mph
    30 mph 32 mph
    40 mph 42.7 mph
    50 mph 53.3 mph
    60 mph 64 mph
    70 mph 74.7 mph
    80 mph 85.3 mph
    90 mph 96 mph
     
  7. G. Will Ickers

    G. Will Ickers New Member

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    Right. I knew that going into it, and may take it to the Ford dealer for a speedo recalibration. I don't suspect that I'll have any negative impacts with shift points or anything else.
    The only differences between the old and new tires are the size and weight, which really only means that I'll have more distance per revolution and the truck will think it's got about 20 extra pounds in the bed.
    Somebody in an F150 forum mentioned something called "unsprung weight". I'm not sure what the hell he's talking about, so I'm doing my research on it now.....
    But he said that each new tires weights about 20 extra pounds heavier than the stock tires (which I find hard to believe - maybe 8-10, but not 20). And he then went on to say that this is "unsprung weight, not sprung weight, so the truck thinks it's go an extra 800 pounds in the bed".
    What?
     
  8. gruss

    gruss Active Member

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    unsprung weight is anything "under" the suspension, and since unsprung weight is typically rotating, the effects of increasing it are amplified, steering will be a little slower brakes have to work a little harder etc etc. There is a lot of math involved if you really want to dive in.

    If this were a sports car, you may see some negative effects, or if you put some gargantuan rims on the truck (metal is heavier than rubber) you should worry about it. Jumping up a tire size on a pickup truck it's unlikely there will be any noticeable negative effects unless you like to autocross with it.
     
  9. G. Will Ickers

    G. Will Ickers New Member

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    Thats what I assumed by the name "unsprung". But 800lbs?
    I can feel a little bit of sluggishness upon accelerating, but not braking at this point.
     
  10. gruss

    gruss Active Member

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    Not sure where he came up with 800lbs, probably an excel spreadsheet someone came up with that calculates rotating mass at X MPH, but isn't really relevant to actual payload or anything.
    Acceleration will take a hit, essentially your trying to spin up more weight and have a taller gearing now so it's a combination of the 2.

    Something I was mildly interested in when I had a car where things like that mattered, it is pretty interesting, but I wouldn't worry about it on a pickup truck. Plus those look way better than the Scorpians anyway so there is that!
     
  11. Wrenchgear

    Wrenchgear Near Elmira, Southern Ontario

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    Looks good, you might want to think about putting some wheel locks on those.
     
  12. G. Will Ickers

    G. Will Ickers New Member

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    I haven't considered that because of where I live. I know that's a horrible excuse, and it's one that people use to rationalize not locking their windows, or carrying a weapon, but I just never considered that my wheels would get stolen.

    Are wheel locks pretty dependable as far as staying torqued, and being a replacement to the lug nut? I've never used them, so I don't know.
     
  13. Keith Hawkins

    Keith Hawkins Active Member

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    I worked at an Automotive dealership in the service department and must say, we had more problems getting the locks off than the actual lug nuts. Yes they stay tight....just don't lose the key for them.
     
  14. JeffC

    JeffC New Member

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    Unsprung weight increase affects your suspension by increasing kinetic energy. Now when you hit a bump, the mass of your unstrung weight will increase how far it travels....more mass, more energy. Your springs are less able to slow and stop that mass so you end up with a suspension that is working harder....as if it had more weight. Now add a heavily loaded car trailer (F250 tires do dot an F250 make) and you're setting yourself up to kill both your suspension and your rear end. Or you live in a pothole free place where it won't matter. Those spreadsheets people seem to doubt are generally conjured up by engineers who are very familiar with physics. I don't know why everyone's first impulse is to doubt it. They do make mistakes, but I'm guessing they get it right more often than not.
     
  15. G. Will Ickers

    G. Will Ickers New Member

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    Understood, and not doubted. What I doubted was what some armchair physicist said on some online truck forum, which was that my truck would think it's hauling 800 lbs. I understand the concept of unsprung weight, just never knew what it was called.

    I personally think the factory put a shoddy pair of street tires on the truck. They were too low profile for me, and if I'm going to get new tires, I'm going to get larger ones that actually look like they belong there from the factory. It just so happens that finding a non-LT tire one size up size was difficult. Add to that a buy-3-get-1 free deal, and I couldn't afford not to.

    I spoke to a technician at the dealership and explained to him what I did. He told me that the only adverse affect would be the speedo reading.
    "Anything else? Transmission shift points? Any other things I may need to worry about?" I asked.
    "Nope. Just the 5 miles off on the speedometer reading. Thats it."

    I've done a tiny bit of research on sprung vs unsprung weight and there are two camps:
    Camp 1 says that 1lb of unsprung weight = 10lbs of sprung weight and that's gospel, amen.
    Camp 2 says that the difference is so miniscule that it's not even worth worrying about.

    So I'm now sitting about 2" taller, with about 20 lbs in extra rubber below the truck, and my tire revs/mile went down due to the new circumference. It handles great, and feels better driving it. Not sweatin' it.
     
  16. gruss

    gruss Active Member

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    Doubting proven math is different than disagreeing with someone on the internets interpretation of a spreadsheet they googled and didn't provide. (not sure where the 800 lbs comes from)

    If G.Will said "i put f250 tires on, now I can tow 20,000 lbs" then yes that would be silly and dangerous. Doing what he is already doing with the truck, I don't see going up a tire size being all the detrimental or dangerous.
     
  17. JeffC

    JeffC New Member

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    Gruss,
    for clarification I did not verify or comment on the accuracy of the spreadsheet, just tried to explain the concept of unsprung weight as the OP didn't seem to understand the concept when he wrote this yesterday:
    But clearly does understand it today:
    Though he didn't say he was towing 20,000 pounds, the comments
    are what I was addressing with the F250 comment. I must have read it all wrong so my apologies to all.

    Jeff
     
  18. G. Will Ickers

    G. Will Ickers New Member

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    Jeff-

    I can see why you interpreted what you did, and I appreciate your input.
    The unsprung weight issue makes complete sense to me. Although I think some folks are confused by it. Heck, I may even be one of em!
    When I used to race mountain bikes, I always found it fascinating that a static tire/wheel combo felt lighter than it did when it was spinning at decent revs. It wasn't truly heavier, but it "felt" heavier. More mass spinning means there's more weight being thrown around and around, so while the weight of the object never changed, the object was harder to move while spinning. I THINK thats unsprung weight. But again, I could be wrong.

    As for the car trailer thing, yeah thats kinda my fault for misleading you. I work at a cabinet manufacturing facility and we have two box trucks, and one car trailer. It's seen cars in it's heyday, but now it is used as my personal errand trailer to pick up sheet goods, cabinets, etc. There's never more than 1,000 of "stuff" inside. So in total, the trailer might weigh 4,000 lbs at any given time. Well within the capacity of an F150.
    The stock tires did fine with it, but they had too much squish when driving that thing around. So instead of airing up and down every time I hooked up, I wanted to upgrade to a beefier tire for towing applications.

    It's all good man. Thanks for the comments.
     

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