Saturday, August 26, 2017

Downside of 4WD

One of the tires has a nail in the sidewall, so not repairable.  But tires on a 4WD need to be replaced with similar levels of tread depth, so one nailed tire means four new tires.  It is a shame there is not an exchange where tires of your type with 11,000 miles on them could be purchased.

Oh yeah, the the tire store's estimate included nitrogen fill at $5 per tire.  I've seen this scam being pushed for several years now: nitrogen weighs less than air.  Yeah, probably about 2 grams per tire.  (Air is 78% nitrogen.)  Of course, saving Mother Earth is part of the nitrogen hype, so that's a good sign that it makes no sense.  I am surprised that Congress hasn't created a tax credit for it. gets me H-rated Sumitomos for $359 delivered (with road hazard warranty) and $131.80 for installation, compared to $659 for a tire brand that I do not know.  The Sumitomos have a UTQSG rating of: 600 A A.

I have put the other three tires on craigslist in case someone needs that size for a non-4WD, or has tires at 11,000 miles of wear.  Even a few dollars makes sense, because I have to pay a tire disposal fee to the installer.  Do tire stores still sell used tires?


  1. You could create a device to artificially "wear" the tread on a new tire by grinding it down to match the others. The tire shops would love that.

    I have no idea if that's even feasible.

  2. It is called tire shaving. One of the tricks to SCCA racing is driving on 1/2 depth shaved tires. Many street tires do better with the soft squishy part gone. And what incentive would a dealer have to reduce demand for tires?

  3. I heard a more sophisticated excuse for using nitrogen - that using air, the oxygen would slowly react with the tire, losing pressure.

    I doubt that makes a difference. Not a $5 difference, at least.

  4. They claim oxygen and water vapor corrode the rubber and the wheel. Apparently only on the inside.

  5. Really dry air might be worth paying for, if you had some odd alloy wheels that were more sensitive to corrosion than normal.

    Putting a dessicant pack in your tire probably wouldn't work as well.

  6. The water vapor issue is valid. Compression and cooling whether it's airbrake systems (wet tank, dry tank water drains and such earn their place), a shop air compressor or anything else promotes condensation. This matters for things like paint spraying. The reason damage is on the inside more than on the outside is that what starts as water in compressed air tanks ends up as steam when the tire rolls down the highway - hot oxygen and steam on the inside really does do more damage than cooler oxygen and ambient water or mist does on the outside. A conscientious shop will minimize water in the compressed air system. Nitrogen also matters for consistent that is accurate speedometer and odometer readings as in rally cars. Water will change the rolling radius of the tire as water goes to steam and condenses back to water.

  7. I've found that a N2 filled tire maintains it's pressure better in cold weather than a normal air filled tire. This was really noticeable in Ontario, when the temps got to -30 or lower....

  8. I think the original claim was less pressure change with temperature increase.

    My take on it:
    100% Dry nitrogen can cause some rubber types to break down, literally.

    I worked at a company that built machines (steppers) that ran that to float the stages on air bearings. O-rings had to be made of certain materials, otherwise the o-ring would turn to powder, and contaminate the system. Years later, I pointed out to the engineer that was working on the laser environmental package of a communications laser that a mistake had been made in material selection. His retort was YOU try telling the head of Engineering he has goofed. Dept head got reamed by one of the founders after the lasers started failing due to atmospheric contamination. It was right there in the o-ring book. Israeli egos. Sheesh.

  9. Here in Cincinnati, there are numerous stores selling used tires. they tend to be in ghetto areas.

  10. I'm pretty sure some tire places do have a tread shaving machine for the purpose of matching a new tires wear to the others for AWD. I'm a dinosaur driving rear wheel drive vehicles, but seem to recall a place that could do that for my mom's Subaru. I think they use the same machine as they use for the other scam known as siping.

    Nitrogen's is hype for passenger cars/light trucks. Now for big rigs and aircraft tires it has some justification because of loading and temperature extremes. If you lived in a place like North Dakota or Alaska it might also make sense.

    Now when you get it for no additional charge it might be worth it. I understand Costco does it for free. They will even mount new tires you bring in just for the mounting fees. At least I also understand that is the case as one of the guys I used to work with out at HP told me that when I came across him out at Costco a few years ago. So if you really want the green valve stem caps (that is what those indicate) then go to Costco.