chromedome

ES300h, 17" rims, Dunlop SP Sports, and I'm getting a lumpy and uncomfortable ride first thing in the morning. Outside temps are 10C or lower and tire pressure is 210 kPa or 30 psi, although the tires warm up to 230 kPa or 33 psi after a few minutes.

Is it normal for all season tires to feel lumpy when cold? I don't want to pump it up higher because the tires would probably hit 36 psi when warm.

Dave Mac

I think that is normal - just inflate your tires "when cold" and I wouldn't worry about the rough ride as long as it goes away when they warm up. Some tires may be more affected by the cold than others.

Dave Mac

Freds430

What you are experiencing is called a flat spot. When the tire sit especially when cold a flat spot forms from the weight of the car. This is more of a tire manufacturer problem and more prevalent on the lower profile tires. I had this on my SC430 but not on our RX or ES. I would try a couple pounds more air pressure. I remember reading this somewhere that for every ten degrees drop in temperature a tire will lose one pound of air. I run 33 cold on my ES300h and when tires get warm they will increase to 36.

don1

I live in Ontario and have no flat spotting in cold weather. The type of tire is more likely the culprit IMO. My 2014 300h has all season Michelins and I have had these same tires on several generations of Acura TLs without ever experiencing cold weather flat spotting. I generally use the manufacturer recommended tire pressure shown on the inside door panel.

Maikerusan

I don't think it is normal. Even when I lived in places that regularly hit -25 to -30, that was not a problme for me.

TechNut

I had Toyo tires on our last RX and it was lumpy after sitting for a few days. They would settle down after just a few minutes so while a bit annoying, it wasn't worth replacing them. They were really quiet so I just put up with it. I never tried increasing the pressure to see if that would resolve it. So I don't think it is all that common and I have only seen it with one set of tires.

SLH

The weight of the car makes a flat spot on the bottom of the tire, under all conditions. The spot is larger when the pressure is low, as when it is cold. When the car is sitting still. the flat spot is in one place on the tire. During cold weather, the rubber becomes stiff. Then when you start driving, the flat spot is still there... As long as the tire is cold and stiff, the flat spot rotates with the tire. After the tire warms up, the rubber moves more easily, and the flat spot stays on the bottom (where the tire is touching the road) even while driving at high speed.

With higher tire pressure, the flat-spot is smaller, and so is less noticeable. With lower tire pressure, the flat-spot is larger. The size of the flat spot is just the weight of the car divided by the pressure in the tire. With lower tire pressure, the flat-spot is larger. The imbalance of the tire depends on how much rubber tread is dislocated toward the axle. Larger amount of tread, dislocated a larger distance, makes a larger imbalance.

To minimize the effect of the imbalance, you can do several things. Fill the tires with air while they are cold, or fill to a higher pressure than you do in the summer. (Both compensate for the fact that air shrinks with temperature, and so pressure drops with temperature.) If you can, drive at low speed for a few kilometers to warm-up the tires before starting to drive at high speed.

If the unbalance persists after the tires are warm, you may have a flat spot on the tread. This is usually caused by skidding with the brakes locked. In this case, the only real fix is to replace the tire (but having it re-balanced with weights may suffice, if the imbalance is not too bad). It is also possible that you have lost a lead weight, and that having it re-balanced will actually fix the problem...

chromedome

I should've said the ride was hard and not well damped with cold tires. It's not lumpy as in flat spot lumpy or unbalanced. I've pumped up the tires to stock 230 kPa or 33 psi and the ride is much better now. Tire pressure does go up to 240-250 kPa when running on the highway but it's still more comfortable than before. I guess some tire designs don't like being run at low pressure when cold.