NHW11 tire size study

Discussion in 'Generation 1 Prius Discussion' started by bwilson4web, Jul 3, 2010.

  1. SteamRollerCC

    SteamRollerCC Junior Member

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    My external GPS system is not connected. I'll have to go by close ranges.

    I'm looking at possibly getting the Michelin X-Ice Xi3 tires.
    X-Ice Xi3 | Michelin Tires

    They're extra load and have low resistance for the type of tire they are. The only place around my area that seems to have them is Sears. I might be trying these out!

    I'll let you everyone know how they handle if I do get them!
     
  2. Jeff F

    Jeff F Member

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    I have the earlier X-Ice tires on my other car and they are great. Highly recommended, along with most Michelin tires.

    Bob, have you had a fully loaded vehicle with the 195-70-R14 tires on the rear? They seem awfully big, and I can't help but wonder if there is enough vertical clearance with a couple of people in the back and/or a loaded trunk.

    I've gone for lower profile tires on my car because I'm less concerned with straight line stability and fuel economy and more interested in sportier handing. I really didn't like the turns with the 175-65-R14 that came with my car, although that may have been a function of the (cheap) brand rather than the sizing. Probably a bit of both.

    My winter tires are 195-60-14 on BMW rims, which have about 1/2" less offset and stick out slightly. I kind of like the look, but with 5 people in the car they make minor contact with the rear wheel well on big bumps. I just recently picked up a set of 15" Honda rims with 195-55-R15 performance tires. Had them on the other day and they fit perfectly. The Honda wheels have the same offset as Toyota, so I don't have the wheel rub problem. I'm actually thinking that my next summer tires might be 195-50-R15, which would be a slightly smaller diameter than the OEM rather than the slightly larger configuration I have now. But as I said, I'm a fan of the snappy handling that comes with the lower profile tires.
     
  3. bwilson4web

    bwilson4web i3 and Prime

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    The best I could do were some high-speed passes over speed bumps. I just didn't have an extra 500 lbs of people. <grins>

    I am only running the larger tires on the front and there is plenty of clearance. The rear are something more standard but I don't have their specs handy. It might be in the thread.

    Bob Wilson
     
  4. jonathan T

    jonathan T Junior Member

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    Hi Bob
    Jonathan here, i was reading your post on tire size and i wanted to get clear as i need to replace all 4 tires on my 03 prius but absolutely needed to put the largest tire sizes on for ground clearance(my under body well thank me for it!!). I realize there is more room in the front wheel well , then the rear. So with that said what is the largest size tires i can put on even if the fronts are different then the backs ? and how much clearance will i gain from it?
    Thanks
     
  5. bwilson4web

    bwilson4web i3 and Prime

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    I use Sumitomo T4, 195/70R14 on the front but I don't see them at Tire Rack. There is a Sumitomo Touring LS T that looks similar.

    As for rise, it depends upon your current tires. If you have something like the stock tires:
    • 24.9" - 23.3" = 1.6" diameter change -> 0.8" radius is the rise
    I have not read of any effort to raise the car but this is not an area I've had an interest. I would expect there might be challenges in the steering linkage. Now I have looked at air-bags that are inflated in the rear springs but just to handle heavy towing loads.

    GOOD LUCK!
    Bob Wilson
     
  6. jonathan T

    jonathan T Junior Member

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    So could i use the 195/70/r14's on the rear and something larger on the front because of more front well room?
     
  7. bwilson4web

    bwilson4web i3 and Prime

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    Buy one and mount on a full size rim. Test it by mounting on a front and later a rear wheel. Then drive in the worst conditions to check for interference.

    Remember that my goal was improved, highway, straight-line stability. My worst case condition were speed bumps. So my testing did not worry about the reduced motive forces.

    The torque at the front, drive wheels is fixed by the Prius design. The longer radius of a larger tire means the forward thrust and rear braking forces are proportionally reduced. This may become a problem if you have to negotiate a steep grade.

    Bob Wilson
     
  8. bwilson4web

    bwilson4web i3 and Prime

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    Ending status: 2014/09/05
    Thread started: 2010/07/03

    So here are the tread depths, no swapping, just running:
    position driver passenger Sumitomo T4
    1 front .053 .097 .110 .079 .071 .104 .104 .079 P195/70R14
    2 rear .077 .158 .148 .122 .064 .076 .068 .058 P175/70R14

    2/32 = 0.0625 - legally worn out
    3/32 = 0.09375 - close

    Lessons learned:
    • Because of the different sizes front and rear, left-right swaps would be the only practical option
      • Left-right rotation could probably have gotten another year
    • Higher tire pressures than normal 51 psi (max sidewall) needed
    • Check camber on driver rear as the inner and out wear ratio is too high
    • Data suggests driver rear wheel is relatively unloaded compared to passenger side rear wheel
    Background:

    Earlier this week, I had an unexplained, tire slippage while on a rain-slick street. The car handled it fine but I knew it was time to look at the next tire. So I ordered a pair of Yokohama, P195/70R14, which are slightly wider tread than the Sumitomo T4, P195/70R14. But testing revealed they have interference with the rear wheel well on a dip. I tried to map out the problem but it looks like major surgery would be required. Fortunately, they work just fine in the front.

    A quick test this morning found, 22.8/21.1 ~= 108.0% +/- 0.5% over size. It is amazing to see 60 mph indicated and GPS reporting 65 mph true. But they have interference with the rear wheel well.

    So I've ordered a pair of Yokohama, P185/70R14, that are slightly smaller than the Sumitomos scheduled to arrive Tuesday. These will go in the rear and the old driver-side tire and rim will become the new spare.

    We'll have Firestone mount them and do an alignment. I'll check their numbers against the wear pattern of the last set and adjust the shims as needed before fully inflating them. Then I'll restart the driving stunt.

    Bob Wilson
     
    #28 bwilson4web, Sep 5, 2014
    Last edited: Sep 5, 2014
  9. bwilson4web

    bwilson4web i3 and Prime

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    I ran a preliminary test, not even fully inflating all tires, just to see how the P195/70r14 Yokohamas might work out:
    [​IMG] [​IMG]
    • 55.8 / 52.0 = 107.3% +/-0.2 %
    • 52 / 74.7 = 0.696 gallons
    • 55.8 miles (GPS)
    • 55.8 / 0.696 = 80.17 MPG (true)
    Correction, a 954 mile tank. We won't really know until the new rear tires are mounted, wheels aligned, and fully inflated tires.

    Bob Wilson
     
    #29 bwilson4web, Sep 6, 2014
    Last edited: Sep 6, 2014
  10. bwilson4web

    bwilson4web i3 and Prime

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    Adding the results of tire alignment:
    position driver passenger Sumitomo T4
    1 front .053 .097 .110 .079 .071 .104 .104 .079 P195/70R14
    2 camber 0.1 -0.1
    3 toe -0.02 0.06
    4 rear .077 .158 .148 .122 .064 .076 .068 .058 P175/70R14
    5 camber -1.3 -1.0
    6 toe -0.12 0.39

    2/32 = 0.0625 - legally worn out
    3/32 = 0.09375 - close

    Excessive toe on the right rear would have driven the rear to the left or clockwise looking down at the car. This probably induced the outer wear on that tire and likely led to the excessive wear on the front left tire and others.

    Bob Wilson
     
    #30 bwilson4web, Sep 11, 2014
    Last edited: Sep 11, 2014
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