Another NHW11 tire thread . . .

Discussion in 'Generation 1 Prius Discussion' started by bwilson4web, Sep 8, 2010.

  1. bwilson4web

    bwilson4web i3 and Prime

    Nov 25, 2005
    Huntsville AL with 2014 BMW i3-REx
    2017 Prius Prime
    Prime Plus
    After getting their OK, I'm posting some PM comments:
    I wanted to address some thoughts in a public forum: brand and alignment.

    Consumer Reports lists the Sumitomo T4s as one of 4-5, low rolling resistance tires. My local Toyota Service shop sells them as replacements for both of our Prius. Better still, they are affordable. Their only drawback is they are not highly rated on ice and snow. But these are what I consider the important specs from Tire Rack:
    Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7
    0 size revs per mile comments
    1 175/65R14 919 Same aspect ratio (the 'size') as OEM tire slightly smaller diameter leads to speedometer reporting faster than true speed and trip meter slightly better than true MPG even if calculating MPG from the pump. The indicated distances are longer than real. Due to weight rating of original tires the 51 psi maximum sidewall makes up the difference. If non-technical folks often drive the car these tires work best by leading to more modest speeds and the appearance of 'rosy' MPG numbers.
    2 175/65R14 902 Original OEM tires were XL rated at 1 102 lbs at 35 psi. Sad to say tire shops use the door jam pressure rating and will deflate tires leading to an over weight condition. Just get used to fixing the tire pressure after leaving the shop.
    3 175/70R14 886 Slightly larger diameter than the OEM tire the speedometer display lower than true speed and MPG shows lower than real. However the adjusted calculated MPG is solid and driving the posted speed limit no problem.
    4 195/70R14 849 These are the largest that fit without interference but with significant speedometer and tripmeter error. Only recommended if using a GPS speedometer (aka. Garmin nuvi works nicely.) So far little or no impact on the adjust MPG but it does allow hybrid operation up to a true speed of ~45 mph versus 42 mph on the OEM tires. This extra 5 mph of hybrid operation (aka. engine off) can significantly improve city mileage.
    There are at least 3-4 other, low rolling resistance tires but I don't have operational data with them.

    My original tires were Master Craft (Sears) and they showed:
    • Inner edge wear - the center tread was still good but the inner edges were down to the wear makers.
    • Scalloping - felt more than visible, it was obvious something was wrong with the alignment.
    I bought Firestones life-time alignment service from Firestone which I use every Spring and Fall when I have them rotated. This lets me spot problems before the rubber is worn off the tires. At ~$140, it is not a trivial expense but I've gotten two dozen alignment reports, about $6/alignment. Best of all, it is for the life of the vehicle, not the tires. I've just started my 3d set of Sumitomo T4s. <GRINS>

    The alignment showed two problems:
    • passenger camber excessive - the top of the front tire tilted too much towards the vehicle. Attempts to release and tighten the bolt failed to make a measureable change so I ordered the next size up, front caster alignment bolt, ~$5.00 and brought both front tires well into the "green zone" on camber. Toe is easly handled by any stop.
    • rear tire toe and camber too much - the rear tires were both tilted in too much at the top, camber, and their front too much towards the center of the car, toe but these are normally not adjustable. That led to metal shims eventually replaced by EZ-shim. Note that the rear axle is supposed to 'pivot' a little so the toe-to-toe values can change but the total toe would remain the same.
    NOTE: I have no business relationship with Specialty Products other than being a satisfied customer.

    You might see if whoever is doing your tires might be willing to estimate getting the camber bolt and front camber reduced to minimum and EZ shims on to optimize the rear tire camber and toe. As for life-time alignment, you could offer to let them do two tire rotations per year, fair price, and double check the alignment. That is what life-time alignment means to me, I bring my car in for Firestone rotation, they report 'I don't know about that water pump belt' which I decline and everyone is happy. (Heck, I think they are just happy to have a customer who doesn't bitch and knows what he is talking about.)

    One last suggestion, go ahead and take a flash photo of all four tires. The flash will throw shadows and let everyone get a feel for what has been going on and you can't beat our rates!

    Bob Wilson
  2. kmc6566

    kmc6566 Junior Member

    Dec 2, 2008
    England, AR
    2009 Prius
    I will go ahead and take some pictures of the old tires. The shims are a good idea but I'm not good enough to go that route. I will have to live with just getting the car aligned.

    Once I have the car aligned with the sumitomos on it I will post the results as far as gas mileage goes and what the change is to the speedometer as opposed to what the actual speed is.