Shuddering partly depends on speed and steppiness on gas pedal

Question

The facts

I've had my tires balanced twice in the past two weeks, but I have shuddering over the speed range 115-120kph. As I continue to accelerate, it comes back as I approach 130kph. I don't intend to drive at 130kph (at least not consistently), but it was just a test to see whether I can repeatably cause the vibration at certain speeds. The fact that it is associated with certain speeds suggests that it is a balance problem, but the complicating factor is that even though it only occurs at those speeds, it doesn't always do so. It seems to be somewhat dependent on how much I'm stepping on the gas, and tends to show up when I'm stepping on the gas more, e.g., accelerating through the problematic speeds, or climbing a hill, in contrast to slowing down, holding steady, or travelling downhill.

Somewhat contrary to the above observation, I found that it seemed to occur more often when I was driving West (our main highway runs east-west), and the wind was coming from the East. So it seems more noticeable when I'm travelling with the wind, which sort of goes against the perception that the shuddering is more likely to occur when stepping more on the gas pedal.

Navel-gazing sense-making conceptual modelling

As someone with engineering schooling, I tried to dream up a mental model for the shuddering. If it was a balance issue, then the reason why shuddering occurs at certain speeds is due to resonance. So I pictured a linear system with resonance peaks across the frequency spectrum. Whatever the mechanical input disturbance is, the frequency components at the resonances would be most pronounced in the output. At certain speeds, the imperfections in the rotating tires yield input disturbances with a lot of power at those resonances, leading to the pronounced shuddering at the output as, felt by the driver at the steering wheel and where the feet touch the floor.

However, it's not just the right frequency spectrum of the input that yields pronounced shuddering. The amount of power (or in audio terms, volume) of the input also affects the power in the output (i.e., the strength of the shuddering), even if the input spectrum mismatches the system spectrum. I figure that this might explain why stepping on the gas more seems to yield greater shuddering. The tires are pushing harder, so any non-roundness and lateral shimmying might translate into more forceful bumpiness, and same with variability in the springiness of the sidewalls. As well, I seemed to notice that shuddering is less when traversing newly paved dark road surface, as opposed to more light-gray (more solid and concrete-looking) old pavement. Perhaps the newer pavement is smoother, leading to less power at the input due to random disturbances from the road, and hence, less shuddering. Random "noise" has a flat-ish spectrum, but it does contribute power at the resonance frequency ranges.

The questions

I have several questions about my characterization of the shuddering.

1. Does the fact that the shuddering is not just speed dependent, but also present only sometimes (depending on other conditions) indicate whether it is a balance problem, roundness problem, or gross variation in sidewall springiness problem?

2. Does the observation that it is at least partly depending on steppiness on the gas pedal provide any further clue?

3. Even with even pressure on the gas, on level ground, the vibration wavers in and out over a 5 second cycle. The tire changing outlet says that vibrations due to imbalance don't wax and wane like that, and I'm wondering if anyone can corroborate that statement?

4. Is my rationalization in terms of linear system model with resonances approximately reflective of what is happening at a gross level?

I haven't yet decided to go for road force balancing.

2017-12-13 New Info

There seems to be negligible shuddering this evening, and the only difference is that the wheel changing outlet tightened the nuts this morning (they recommend torquing it to a specific tightness after driving on the changed tires for 80km) and it's darn cold. -15 degrees Celsius. I've heard that coldness can make the resonance go away, and that makes sense since the rubber is of a different softness. I found data on the past week or so to see if there has been such cold temperatures. This following graph shows that the answer is no (during driving hours, 9-10am and 7-8pm), so I have more confidence in the coldness as a primary factor.

Note that on the very next day, 2017-12-14, 12 hours later, the same tire establishment was willing to make another attempt at re-balancing. The person who did this found that all tires were significantly out of balance, and could not explain why this was the case after two visits. I suspect that it may have been related to the crazy demand and schedule for tire changes in the two weekends that I visited previously. I haven't found that this 3rd balancing changed the vibration noticably. It is still present, and approximately as subdued as yesterday (but still noticable). But then, the temperature is just as cold tonight as it was last night. The acid test will be during warming temperatures, when the vibration was much worse in the past.

In fact, I'm not sure if very cold temperatures provide for a fair test of what's acceptable, since there will be many days that are not that cold, especially toward mid-day. What is the prevailing idea on this, both as an explanation for the presence and absence of shuddering, and as a fair condition of what is acceptable in a tire? Thanks.

On an tangentially related matter, is there anything I have to do to re-obtain attention to my question after adding such significant new info?

Answer 1

Out of balance tires will shudder at different speeds. Since you just changed the tires, this is where I would start.

You can try rotating the tires yourself. Swap the front tires, one at a time to the rear and see if the problem improves, in terms of steering wheel wobble.

If so, the tires/wheels are causing the issue.

EDIT:

It may be intermittent in a case like this: Both front tires are out of balance roughly by the same amount. As you turn the car they rotate at different speeds, causing their respective balances to be exactly out of phase or otherwise cancel each other out.

It may be a defective tire(s) and/or wheel(s). If it cannot be balanced out, even with road force balancing, I'd see about taking the tires off and checking the wheels out.

If you have a full-size spare, I'd start swapping it out with the others to try and find the culprit(s).

Answer 2

Is there any reason you are only looking to the tires as the possible issue? You should have a suspension alignment done and have them check suspension components.

While tires can cause shuddering if they are imbalanced, rounded, or anything other than their functional shape, the suspension would likely be your culprit. Components there wear out and cause what is known as "death wobble" aka the shuddering you are experiencing only at certain speeds.

Check ball joints and bushings at several steering and suspension component locations for ovaling or other normal/excessive wear and see if this diagnoses and if repair/replacement solves your issue.

Answer 3

Five+ months later and I think you are well on your way to answering your own question: No amount of "balancing" can remove the problem of a distorted/wounded/mis-manufactured tire.

Granted, there are several mechanical problems that could cause this effect, but the fact your "summer" tires are fine, pretty much sums up all the diagnostic information you need.

Unless an aftermarket "winter" wheel is bent (and you could see this) I sincerely doubt it's about any "flimsy" characteristic of a rim. A "flimsy" rim might have some odd handling characteristics, but it should be consistently flimsy all around. I doubt it would only be flimsy in one spot. The grand experiment would be to mount your current summer tires on the "flimsy" aftermarket rims and test. This would be a costly and tedious effort, and I suspect we already both know the outcome.

The fact that it is more noticeable when accelerating only points (as you surmised) to the same thing - the effect is most prevalent on a loaded tire, and is accentuated by the carcass distortion caused by acceleration. Truly a "road force" condition. And further condemning the tire(s), but only the tire(s).

Clearly "roadforce" type balancing is better, and may mitigate some of the effects in the hands of a trained expert - someone very likely in a different class than the guys that change tires as their vocation and have no other skills. And of course there comes a price for such service... A good "roadforce" type machine is likely 5 to 10 times the cost of a perfectly serviceable dynamic balancer that relies on radial strain gauge sensors deflected by mere weight differences.

I can't afford such a beast in my shop. I rely on an aged Snap-On manual balancer (you have to crank it by hand) and I balance to a 1/4 ounce. I also keenly observe the tire and rim as it spins, watching both beads and the overall flat road-contact surface. I have encountered many tires over the years in which I can obtain a perfect "displayed" balance "000", but yet roll my eyes and sigh because I now have to inform the customer that this is meaningless and by mere observation: this tire or tire/rim combination is shot, incurable, and I can only make it somewhat better by "band-aiding" with compensatory weights.

I suspect your ultimate solution is two new front quality Nokia, Blizzak, or Haappiklatica [yes, that's seriously spelled wrong - but made by the folks that have winter 13 months of the year] winter tires . . . and be done with this nuisance. Or just put up with it and avoid 115-130kph.

Best wishes.

Answer 4

The following might not be the answer to all such situations, but it seems to go a long toward explaining my situation.

All my navel gazing as to the conceptual reasons for the observed vibration under certain conditions were washed away when I brought the car to mechanic rather than the wheel-changing establishment (actually, they sell and store tires, too). I can't recall whether he used road-force balancing, but he did say that the tires were well out of balance. He also confirmed the pronounced non-roundness of one tire's rim. His balancing removed (subjectively) 80% of the shuddering. With oval rim on the rear passenger side, the vibration was tolerable. I did not feel that the car was having the heck depreciated out of it. I tolerated it throughout the winter. Just last week, I switched back go all-seasons, and the smoother ride is like a dream.

I did have a talk with the wheel-changing place, and they are at a loss to explain the ineffectiveness of their balancing by various staff. They did say that for the future, one option was to not mess with the better balancing by the mechanic, and to keep the oval tire at the rear rather than switch them to the front every other years (the tires are directional, so there's no left/right switching). The front wheels would simply wear out faster, since they do the pulling.

I also learned from both the mechanic and Honda that the winter tires were on after-market rims, which are significantly flimsier and susceptible to deformation by potholes. That might explain why the one of winter rims were oval while the all seasons were still round -- the latter were on beefier OEM rims. This only explains the non-roundness, but not the balancing issues. If I'm really bothered by rear ovalness, I could replace the rims on those two tires. I'm not sure whether it would be wise to just replace the one oval rim. From our conversation, it seemed OK to do so, as long as the size specs matched.

On the winter tires, the suggestion to not mess with the existing balance done by the mechanic simply means that if I ever run into a balance problem, I cannot trust that it will be properly done by the wheel changing establishment. Having to bring it elsewhere is extremely costly in terms of time, but no more so than repeatedly bringing it back to the tire changing place, each visit costing several hours. if things go that way, I may switch to Honda to store, change, and balance tires. They do road force balancing.

Another alternative would be to have these services provided by the mechanic who did the good balancing. I would check if his balancing is road-force balancing, though frankly, I don't have any evidence to date that would have been beneficial in my case. I would be forgoing the reputation of Honda, but sometimes, the local reputation of an individual is just as good if not better than a chain (though Honda's rep is a high bar to beat). My only concern is that the track record I have on the mechanic is limited, at least presently. If it works out, however (and this can only be recognized in hindsight!), it wouldn't have been a bad thing to have taken a chance and gotten onto his roster before he shot to stardom.