Warm Wheel Hubs: Troubleshooting & Causes

Hello,

Because the "Fuel Saver" factory-fitted tires on my Polo have an unreasonably high rolling resistance, I initially thought it might be due to dragging brakes.

After a drive, the brake discs are usually only moderately warm (depending on when and how hard braking occurred). However, I also notice that after each drive, all four wheel hubs are noticeably warm, even when the rims and brake discs are practically cold.
(Currently, I'm using the bare factory steel rims without the hubcaps or wheel covers.)

Today, I lifted the rear axle and spun the wheels.

OK, 195-size tires on 15" rims already have a significant amount of rotational mass, but they seem to "recover" normally after spinning out, with equally "normal" light scraping noises from the disc brakes.

I noticed this warming of the wheel hubs for the first time on my Polo.
Is this normal, or can a "modern" wheel bearing develop significant internal friction losses under load, while running almost freely without load?

Hello Ulf!

Wheel hubs typically use preloaded conical or tapered roller bearing sets in an O-arrangement.
Specifically, tapered roller bearings require a certain break-in period before the friction torque decreases to its normal value. The same principle applies to angular contact ball bearings, although the effect is not as pronounced.
A slight increase in temperature is therefore perfectly normal and nothing to be concerned about.
I think that after approximately 5,000 to 10,000 kilometers (or miles), the wheel bearings should be properly broken in.

Excessive heating could also indicate that the bearing is overfilled with lubricant. However, in your case (a new car), I can almost completely rule this out, as the bearing is filled with lubricant by an automated process during manufacturing.

Regards,
Alex.

donalexo wrote:

In particular, tapered roller bearings require a certain break-in period before the friction torque drops to its normal value. For angular contact ball bearings, the same principle applies, although the effect is not as pronounced. A slight increase in temperature is therefore perfectly normal and nothing to be concerned about. I think that after approximately 5,000 to 10,000 kilometers (or miles), the wheel bearings should be properly broken in.

Hi Alex,

thank you for the explanation

At outside temperatures around 15°C, the outer part of the rim feels cold to the touch, but everything within the area of the wheel studs is almost pleasantly warm... it's quite noticeable.

On the other hand, the issue is present on all four wheels, despite presumably different bearing designs at the front and rear, which suggests that the problem is not limited to a single wheel.

I'll keep an eye on it.