Occasional severe vibration on highway

Its a bad tire. I'd suggest having them re-balanced and if that doesn't fix it - replace them.

 

With all the rain you get in Vancouver, I'd be changing the tires now. I'd also get an expert to look at the front end bearings.


Tread Depth Matters

I'll cheat and just give you the results from a TireRack testing session. The difference between a new tire and one worn down to 2/32 (legal limit in many US states) in a test on a water soaked surface was an almost doubling of stopping distance! 4/32 deep tires took about 50% longer to stop than new tires.

New - 195 feet

4/32 - 290 feet

2/32 - 378 feet

Even more startling to me is that on a 2/32 tire, in stopping tests in the wet from 70MPH the new tire would have stopped the car where the worn tire would only have slowed the car to 55MPH!!!! 4/32 would only have slowed the car to 45!!!!

They don't cite skidpad tests but the same issues that affect stopping distance would affect your staying on the road as you round the curve in the very wet. The tire needs the depth in order to evacuate the water beneath the tread and get the tire "rubber" into contact with the pavement. If it rides up on the water, it is like driving on ball bearings. I recall driving behind a car once and seeing it hit a puddle just as it came to a bridge and then going off like a pinball bouncing off both the sides of the bridge. When I stopped, sure enough he had balding tires.

Measuring Tread Depth

Measure in 3 places across the width of the tire. The lowest depth is the one you use in comparing tread depth. You can find the original tread depth in the "specs" area for each tire at Tire Rack. Their home page has videos showing how you can measure using a coin and what the recommended tread depths are and how they affect handling. Or you can buy a "professional" tread-depth gauge from most auto parts stores for around $3.

 

Radial tires can have an assortment of issues that produce an equal assortment of symptoms relating to vibrations. Even balancing problems can cause intermittent vibration, especially if more than one wheel is involved. And lets not forget that those were super cheap tires when new. They are not the same as the Michelin Energy Saver-AS tires that many of the Prius owners use.

 

You've put 82000 kms on a set of tires, and you're running them at less than legal minimum tread depth. Heading into winter. C'mon, do the right thing, for anyone who shares the car with you, and vehicles that share the road with you.

 

Hard to say, but OEM tires are generally of cheaper construction than retail, even if they have the same name on the sidewall. In any case, the tires are your first and best bet for the cause.

 

Bad harmonics, probably caused by several wheels being slightly out of balance. At certain speeds and relative wheel-rotational positions, the vibrations resonate with each other, making it much more noticeable. That's my guess.

 

You might also consider Michelin Premier A/S, if only because the Energy Savers are hard to even find, locally. The Premier's almost certain to give up some mpg (vs Energy Savers), but are very good for traction, stopping distance. Premiers are in stock at Costco, for one. Unfortunately, the Michelin promotion, $70 off on set of 4, is over for now.

 

Another cause of severe vibration is a blown shock absorber but those are nearly continuous once above a certain speed and don't typically fade in and out at a constant vehicle speed.

 

"Balancing issues" are generally tied to the person doing the balancing, but there are cases of improper radial run-out that can mimic bad balancing. That's essentially a "lumpy tire" issue caused by sidewall or tread construction problems. Its a more common problem on tall tires like 4x4 tires.
I might agree with others that in a cold climate there might be a better all-around choice than the ES-AS, but there's no better choice for MPG.

 

I agree, except would replace the phrase "resonate with" with "reinforce" (i.e., the imbalances are additive) at some certain orientation of wheels relative to each other. Then several seconds or a minute later when those wheels are 180 degrees from that relative orientation (due to one turning very slightly faster than the other), the imbalances will cancel each other. Then the cycle repeats ... .

 

Resonance - Wikipedia, the free encyclopedia

 

Not an easy calculation. For me, the gas savings (compared to OEM tires) from the ES-AS amounted to about 1/2 the entire cost of the tires over their projected life. But that was at $3/gal for gas with a 4 MPG boost from the ES-ES.
Anyways, be sure to include fuel savings into your numbers.

 

We have bought tires in the USA and brought them back to Canada many times, only paid the HST on them. Some were installed and some were loose. Some places in WA. you can ask for tax exempt, show D/L to prove you are from BC and save some $$.