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Old 02-22-2012, 08:05 PM   #1 (permalink)
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Wheel bearings

I was going to re-pack the bearings in my 2007 kia spectra with 160k miles. Found out that the bearings are sealed. Does anybody know if putting new bearing assembly would decrease friction and resistance and help mpg?

Thanks in advance

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Old 02-22-2012, 08:52 PM   #2 (permalink)
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Unless there is a defect or major flaw or maladjustment, the drag contributions of wheel bearings is so small as to be ignorable. Replacing bearings that aren't bad won't improve anything, except maybe the time interval for bearing replacement, which oftentimes never happens because the bearings outlive the rest of the vehicle.
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Old 02-22-2012, 11:28 PM   #3 (permalink)
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Old 02-26-2012, 12:31 AM   #4 (permalink)
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and someone was just telling me about some vw guy that was swapping out bearings in bugs with high end bearings... maybe scammin... :P
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Old 02-26-2012, 12:54 AM   #5 (permalink)
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I like to think about these types of questions like this:

Friction = energy lost to heat

Suppose I am loosing 1hp of energy due to friction. That means I am loosing 746 watts of power in the form of heat. That is a lot of heat! I can't imagine bearings that are in decent shape heating up by any significant amount. Certainly not anywhere near 1hp, which itself is a very modest amount of power.

The pads on disc brakes remain in contact with the rotor even when the brake pedal is released. This constant friction is so low as to be negligible because the force of the caliper is not pressing the pads against the rotor.

I'm sure a brake system could be designed that retracts the pad away from the rotor and eliminates friction altogether, but the tiny savings would not justify the added complexity.

Where am I going with all this; if it ain't getting hot then it ain't reducing your MPGs.
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Old 02-26-2012, 12:57 AM   #6 (permalink)
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Frank is dead on, sure on a bicycle you can get a tiny bit by switching to $300 ceramic bearings with lube that costs nearly that much as well, but it's not much and the bearings you can get for a car are not going to be that much different then OEM, so unless the current wheel bearings are bad they don't need to be replaced, good chance that they produce so little friction that they never get warm and bearings getting warm is a ok way to tell if there is something wrong with them.
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Old 02-26-2012, 02:00 AM   #7 (permalink)
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Old 02-26-2012, 05:07 AM   #8 (permalink)
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Old 02-26-2012, 08:19 AM   #9 (permalink)
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Most modern disc brake systems use the seals as a means to retract the pads from the rotors, although very slightly.

You could use a laser thermometer to check the temp of the individual wheels to see if there was any wheel that produced higher temperatures than the others, which would indicate excess brake drag or a potential wheel bearing problem.

The newer sealed type bearings do have additional resistance compared to the older type that are precisely adjusted for lower resistance, but that is not the case here.

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Old 02-26-2012, 08:42 AM   #10 (permalink)
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Food for thought: Mazda sells blueprinted wheel bearings for Miatas that SM racers use. I've spun one by hand and was very impressed at the reduction in resistance compared to an OE bearing assembly. When you guys are talking about ~5-10hp of total energy use at ~50mph, I could certainly see a bearing like this having a measurable impact on economy.

That said, its unlikely that replacing an OE bearing with a new OE bearing would make any difference.

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