07-12-2017, 05:55 PM
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#1 (permalink)
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Master EcoModder
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How much fuel does brake pads dragging waste?
I was doing a brake job the other day and I noticed that the brake rotors are much easier to turn with the pads and calipers off than on. That started me thinking that if the pads were somehow spring loaded so they fully retract and do not rub on the rotor when not using them, that would reduce drag and extend pad life. Would it not? I must be missing something. If that would save fuel, why do car companies not do it from the factory?
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07-12-2017, 06:39 PM
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#2 (permalink)
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Corporate imperialist
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I have heard of a system like that on drag race cars.
The system of springs and tensioners needs almost constant adjusting.
The OEMS use square O-rings on the pistons that are supposed to reduce brake drag by pulling the piston back a little when pressure in the brake system is released.
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1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
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07-12-2017, 06:55 PM
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#3 (permalink)
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Human Environmentalist
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07-12-2017, 07:17 PM
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#4 (permalink)
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Master EcoModder
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Oh wow. I never heard of drag reduction clips. I could be wrong, but I do not think that the few ounces of pressure the drag reduction clips apply to try to pull the pads off the rotors would be effective since the pistons in the calipers are so hard to push back in anyway. But is the drag of the brake pads rubbing on the rotors enough to have a measurable effect on gas mileage anyway?
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07-12-2017, 08:32 PM
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#5 (permalink)
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Corporate imperialist
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Drag race guys say it gives higher trap speed.
So it could be measurable in fuel economy.
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1984 chevy suburban, custom made 6.5L diesel turbocharged with a Garrett T76 and Holset HE351VE, 22:1 compression 13psi of intercooled boost.
1989 firebird mostly stock. Aside from the 6-speed manual trans, corvette gen 5 front brakes, 1LE drive shaft, 4th Gen disc brake fbody rear end.
2011 leaf SL, white, portable 240v CHAdeMO, trailer hitch, new batt as of 2014.
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07-13-2017, 10:09 AM
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#6 (permalink)
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Master EcoModder
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Quote:
Originally Posted by EcoCivic
I noticed that the brake rotors are much easier to turn with the pads and calipers off than on.
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Now take this one step further and measure the drag. Jack up a wheel, wrap a string around the tire, and pull with a spring scale. Then push back the brake pads and repeat. The difference is a direct measure of brake pad drag for that wheel.
Repeat for the other three wheels. Then report the total drag here, and we can estimate the effect on gas mileage.
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07-15-2017, 01:43 PM
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#7 (permalink)
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Master EcoModder
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I think the drag is noticeable at very slow speed on an unloaded wheel but does that drag stay constant or increase with speed and load? I'm betting it is always the same otherwise your brakes would be burning after a freeway run and they aren't. That little bit of drag you can feel with the wheel jacked up at slow speeds probably doesn't amount to anything measurable economy wise.
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07-15-2017, 03:29 PM
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#8 (permalink)
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Master EcoModder
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The one way to find out is to measure. The best way to measure drag is to coast to a stop without using the brakes, jack up a wheel, and measure. Then push back the piston and measure again. The drag after driving may be different from the drag after stopping because brake disk wobble can push the pistons back.
I can calculate the effect of the measured brake drag on mileage.
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06 Canyon: The vacuum gauge plus wheel covers helped increase summer 2015 mileage to 38.5 MPG, while summer 2016 mileage was 38.6 MPG without the wheel covers. Drove 33,021 miles 2016-2018 at 35.00 MPG.
22 Maverick: Summer 2022 burned 62.74 gallons in 3145.1 miles for 50.1 MPG. Winter 2023-2024 - 2416.7 miles, 58.66 gallons for 41 MPG.
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