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Downsizing Wheels & Tires

matt_e_boymatt_e_boy Posts: 4
edited July 11 in Toyota
Yep , gas is $3 a gallon round here and gonna rise. Anyone know if I can take my 2005 LE 15X6.5 wheels and trade down to 14x5.5 wheels from a 2000 Camry so I can run 185/75 14s instead of the wider stock 205/65 15's ? Has anyone done this? Can they hopefully clear the caliper - front and rear?

Comments

  • capriracercapriracer Somewhere in the USPosts: 800
    Matt,

    The best information I have is that doing the downsize the way you are doing it actually is the wrong direction for better fuel economy. It seems that load carrying capacity is directionally better for fuel economy: More capacity = better fuel economy.

    But careful selection of tires is by far the most important thing if you want to get better fuel economy by changing tires. Just be aware that in tires, fuel economy, traction, and treadwear are tradeoffs. You can't get good values for one without sacrificing one (or both) of the others. That's why you will hear many complaints about treadwear and traction from OE tires, where the tire are designed with rolling resistance as a very important parameter.
  • matt_e_boymatt_e_boy Posts: 4
    edited April 2010
    Thanks Capriracer,
    Though to explore the discussion I disagree with your load capacity belief. I used to sell tires in the early 90's and we watched the beginning of the 75 series aspect ratio phase out and in later years the 70 series and 14"tire. They were often replaced with 15"tires with lower aspect ratios as manufacturers would use this to increase handling as a selling point (for a while every car commercial I saw cars were drifting sideways!) Those cars' mileage was diminished however manufacturers still had to meet CAFE requirements so to compensate for their SUVs and performance cars and enhancements they were now building Prius' and other hybrid's to boost the overall gas mileage of their entire vehicle line. To the consumer this meant cars suddenly had wider, speed rated tires (like an H rating) that could take off ramps at 60mph because of the reinforced sidewalls but simultaneously phased out the average tire - suddenly average $60 tires were nonexistent or junk. The only decent ones I see nowadays are the foreign made ones that are in that price range. With the overall industry pushing performance everybody's tires are now wider and have more load capacity (especially with 44psi casings). But this also means lower mileage, increased hydroplaning (less pressure per square inch over the larger contact patch) and more expensive construction. Heck,I can remember the first dodge minivans had 195/75SR14s on their 4cyl model. So I do see the tradeoffs with tires but they are not with fuel mileage in mind on most cars. Don't get me wrong, the performance increase in the industry is actually nice as we have better performing vehicles overall and there are many more choices for the gearheads and tuners but that luxury has come at a price - both literally and figuratively.
  • capriracercapriracer Somewhere in the USPosts: 800
    edited April 2010
    Matt,

    Here is what I am basing my statement on:

    http://www.energy.ca.gov/transportation/tire_efficiency/documents/2007-12-07_wor- - kshop/presentations/Lambilotte_Bruce_Task%204%20Rolling%20Resistance%20Testing.p- - df

    This is a study performed by Smithers Scientific Services for the California Energy Commission to explore rolling resistance in tires and what effect certain laws might have on the general public.

    On page 31 is a graph showing the Rolling Resistance Coefficient (RRC) for various sizes of tires but all the same make/model. I think it is easy to see that small tires (load carrying capacity wise) have better RRC.

    They actually calculated a correlation value - and it was pretty poor at 50% - but the trend is there.

    Conclusion: If you want to improve fuel economy by changing tire size: More load carrying capacity = Better
  • Ummm Capriracer, did ya see page 35?
    Looks like a positive correlation between rolling resistance and load index to me.....
    It's also interesting to note rolling resistance increases with UTQG ratings and tire weight.
  • capriracercapriracer Somewhere in the USPosts: 800
    Matt,

    Be very careful here. The way tires are tested for rolling resistance includes compensation for the load carrying capacity of the tire. What you get is rolling resistance force. To compare tires of a different load carrying capacities, you need to divide by the load to get rolling resistance coefficient (RRC). When you change tires on a given vehicle, the load on the tire doesn't change - so you have to use rolling resistance coefficient (RRC).
This discussion has been closed.