16 or 18in wheels?

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by Necred, Jun 9, 2013.

  1. Necred

    Necred Member

    Yea, I fitted one tire on front to see if I had clearance, as I said, there was 2in diff in height.
    Stchman, this was my concern is the 2in in height diff gonna confuse tranny & reduce my mpg...On my camry I put 195/75/14 over 195/70/14 and I notice a diff in both response & mpg,,mostly in response ....
  2. stchman

    stchman Active Member 2 Years 1000 Posts

    There are a lot of aftermarket ECU programmers that will re-program the ECU. Hypertech makes power programmer (#32500), but the unit will run you ~$325. There might be less expensive ones out there.
  3. Necred

    Necred Member

    I think I will stay with 16in & replace with 265/75 tires.. that way I wont have set tires/wheels to get rid of...
  4. McClintoc

    McClintoc ɹoʇɐɹǝpoɯ Staff Member 3 Years 1000 Posts

    You said you are currently running 265/70/16s. Do they rub any? If they do, you probably don't want to go 265/75/16s as they'll be taller and will rub more. If your current tires do not rub, have the tire shop test fit a 265/75/16 before you buy all four.

    Only reason I ask is, I had a set of 265/65/16s that rubbed.
  5. buckmeister2

    buckmeister2 Rockstar 4 Years 100 Posts

    You might be getting confused with all the different answers. Like another poster wrote, what matters is the outside diameter of the tire, width of tread (not "thread"), type of tread, and weight of tire. If you go to a 265/75, you are increasing the outside diameter 1.1"...not enough to worry much about. The 265/75 is also .7" narrower. The weight will be about the same.

    So, if you go to 265/75, your speedo will run about 2mph slower than your current tires indicate (IDK if your speedo is currently right or wrong, but that will be the diff), and your odometer will record about 2% fewer miles than with current tires.

    If the tread pattern is similar, you will not see a diff in MPG due to that.

    good luck....
  6. Necred

    Necred Member

    now that you mention it,, as per my garmin my speedo is couple miles off...truck came with 75s....I can get 18s with xlent tread for $900, it will cost me that to put 16s new on it.
  7. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    265/70 means .7x265x2=371mm of sidewall= 371/25.4=14.6 14.6"+16"=30.6" tall

    265/75 means .75x265x2=397.5mm of sidewall 397.5/25.4=15.6" +16"=31.6"

    31.6/30.6=1.033=3.3% taller.
    so you will be going 3.3% faster than indicated and 3.3% farther
    at 60 indicated roughly 62mph
  8. Necred

    Necred Member

    No sir they don't rub, even the 18in one I tried on front didn't scrub turning, I never got on raod with it since I had took one wheel home to try. Nor do the 265/70 rub....265/75 are stock as per door.
  9. buckmeister2

    buckmeister2 Rockstar 4 Years 100 Posts

    Not exactly. I did the math quite well by myself, thank you, and got the same result as you (a bit surprised you took that route, though. Much easier to look at the height diff, see it is 1", and just realize that is 3.3%...to each his own). However, real world...it isn't quite accurate. Possibly due to height diff's from calculations when weight is added, compressing the rubber, or possibly due to expansion of air pressure once the tire heats up, or other issues I can't think of off the top of my head. I used those final result numbers because they are what I came up with over several years of travel through a single, metered 5 mile run, with many different tire combinations. Did it maybe 500 times, because I am a bit anal about getting actual results. I gave the OP a very good approximation of real world results. BUT, I am glad someone is checking the math....
  10. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    No offense meant.
    Just thinking out loud.
    Yes calculated and height measured numbers never seem to match up with good numbers based on actual distances-road markers etc.
    I'm also compulsive about measuring things-but mainly in respect to mpg ,and weight.
    With bicycles motorcycles and various trucks I have done various things to drop weight.
    On the 98 Suburban I pulled the 3rd row-78 lbs- and the single seat from 2nd row- almost 60 lbs-
    Of course we didn't need them-and use the flat space to sleep when traveling -dog likes the big flat space too..
    I can't actually measure any improvement in city FE-150 lbs on 5200 lb Suburban-almost 3% less-might get 1/2 of that in improved city FE- but that is barely .1mpg-no way I could measure that in any way that mattered since just letting my wife drive the Suburban ruins my FE

    In any case-no offense meant-just compulsive
    PS-There are lower rolling resistance tires available-but most are more passenger car than truck.
    Since I'm a mpg nut-I would stick with stock height width tires.Besides taller sidewalls usually give a more comfortable ride.

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