Big brakes causing worse MPG?

[Spike00513]

I guess we all want brake upgrades, right?
They look cool, and allow for better braking feel, possibly.

I don't know about you, but my stock B6 A4 1.8T brakes didn't feel very good. I don't know if that's due to brake parts choice, or the size alone.

So I installed a B7 A4 kit I had laying around, and it feels better.
The problem is, it's using Centric High Carbon Premium rotors. Which are heavy.

Also, the calipers were rebuilt (by me) using Centric piston seals. Probably a bad move, considering I hear these seals are shitty quality, and tend to be too tight on Volkswagen/Audi calipers, resulting in a piston that doesn't fully retract off braking, and ends up dragging the brakes constantly. Even when you're not using them, such as when accelerating or cruising.

In addition to a big heavy wheel and tire combo, these brakes probably add weight.

The main point: I noticed my MPG drop, and don't really like this. And they're just 321mm B7 A4 brakes.
Is the B7 2.0T engine THAT much more efficient, that B7's can handle these brakes?
Also, I heard of someone using S4 brakes (345mm) on a B6, without reduced MPG. How?

Basically, is it just these damn Centric seals that are to blame?
Lesson learned. It probably wasn't worth saving a few bucks skipping out on getting OEM brand parts such as Ate or TRW.

I have not measured rotor temps with a thermometer to try and see if they drag.
The wheel bearings (old, high miles) probably aren't helping either, nor are worn control arm bushings failing to keep the wheel perfectly straight.

Am kind of tired of getting automatic V6, V8 or lower MPG
from a tiny manual 1.8L 4-cylinder that has no power




This leaves me with the question of which brakes to choose next, since I can probably find any (B7, S4, 3.0L, etc.) and which wear parts (pads, rotors)
I hear ECS Geomet slotted is good.

If I find out S4 345mm will result in horrible MPG, then maybe I'll choose something smaller,
such as 3.0L 312mm,
or even go back to stock 288mm

One problem is that with B7 or S4, supposedly it could use rear e-brake cable adjustment, or installation of a new different one ($)
Not to mention, rear brake parts varying. For example, rear S4 might require changing to an S4 rear hub, with bolt-in bearings.

Thank you

[agentsmith988]

I would check for dragging brakes. I swapped to a B7 setup and saw no change in mileage.

[Spike00513]

I would check for dragging brakes. I swapped to a B7 setup and saw no change in mileage.

Oh. With a laser thermometer maybe, or touching by hand?

There's a road near me that I can drive up hill without braking, if there's no traffic. And then slowly coast to a stop, then pull the e-brake at the last second. Then get out and measure.
And honestly, last time I did that as a test, I think the brakes were hot. I imagine they shouldn't be. Leading me to believe they're dragging.

The cluster reads about 23mpg, which is not friendly on the wallet. If that's the best I can expect from this car, then I need to sell it.
Would be a sad thing to get S4 MPG (340hp V8), from the cheapest car offered in the Audi model line-up with an engine smaller than a soda bottle. That regularly gets honked at for being too slow. (unacceptable and obsolete, imo)



I'm not sure if anything else could be a contributing factor. Such as abrasive local roads, low quality fuel, etc.

[jj94tt]

In my experience, during normal, everyday driving... brakes get hot. But if you have a caliper piston hanging - they get HOT to a totally different level. You should feel heat rolling off the brakes just by holding your hand above the outside of the wheel. You should also smell a distinct odor from the friction material off-gassing. A noticeable drop in MPG would mean you have a decent amount of energy being absorbed by the rotors/pads. It also tends to get worse, the longer you drive as things really heat up.

Drive around for a while and get things hot, then see how freely it coasts on a gentle grade in neutral.

[fR3ZNO]

One suggestion would be to pick up a cheap infrared thermometer from Amazon. Would be fairly easy to pinpoint if an individual caliper is dragging without having to get it crazy hot.

[DarkoNova]

When I replaced my clutch master cylinder and reinstalled the knee booster incorrectly, it caused brake drag. It was pushing on the brake pedal all the time.

So much so that there was visible smoke outside the car and it took a ridiculous amount of throttle to go up a small hill on the freeway.

I'd imagine that the temperature difference between the front and rear brakes would be HUGE and easily visible with a laser thermometer.

I don't know the exact numbers for brake temperatures from normal driving, but I know it's something you can Google. I want to say 300° is like the max temp you'd see with normal city/highway driving.

[agentsmith988]

Just spray the rotors with a small bit of water after a short drive (like the one you mentioned). If the water boils off, you're probably dragging. Or spend some cash and get an infrared thermometer from Amazon.

[BARRY]

when i went with upgraded brakes...my rear pads were dragging from being too thick....took about 3 weeks of driving for them to wear down to no longer drag.

good thing those 2 piece rotors seemed to do their jobs as i'm sure they were glowing red on the highway.

[Spike00513]

One suggestion would be to pick up a cheap infrared thermometer from Amazon. Would be fairly easy to pinpoint if an individual caliper is dragging without having to get it crazy hot.

I put Centric seals on the front two,
but fronts also do the majority of the braking in a car, I hear.

When I replaced my clutch master cylinder and reinstalled the knee booster incorrectly, it caused brake drag. It was pushing on the brake pedal all the time.

So much so that there was visible smoke outside the car and it took a ridiculous amount of throttle to go up a small hill on the freeway.

I'd imagine that the temperature difference between the front and rear brakes would be HUGE and easily visible with a laser thermometer.

I don't know the exact numbers for brake temperatures from normal driving, but I know it's something you can Google. I want to say 300° is like the max temp you'd see with normal city/highway driving.

Interesting. I retrofitted a Euro one with a cubby. I hope it doesn't push the pedal.
It didn't trigger your brake lights?
I'll check to see if it's installed properly, or even fits right. It's still a B6 part, but I had to remove some metal bracket for it to fit.

It does take some throttle to go up hills, but I chalked that up to it being a small engine (1.8T. No smoke though.

[IndoReef]

My S4 brakes did not cause any loss in my Mileage.

Mainly highway driven

[Kevin C]

Some cars have what's called brake drag clips that assist in pulling the pads back slightly. I would give each wheel a spin and to get an idea of how much drag you have. One other thing is if you have perfect rotors you may end up with a bit more drag. Rotors will always have some runout, a tiny bit ( less than what what you ever feel when braking) actually helps to reduce drag by slightly knocking the pads back.

Things that affect how well the pistons pull back.

1: Obviously the seal.
2: How the upper edge of the seal groove is cut. A chamfer lets the seal flex more and increases retraction.
3: Piston friction in the bore.
4: How well the pins slide on floating calipers.
5: Rotor runout, a tiny bit can help.
6: Piston assist springs.
7: Pads that hang in the housing.

https://www.autoserviceprofessional....eduction-clips

https://www.carlsonqualitybrakeparts...e-brake-clips/

[BARRY]

oh....yes anytime you change your rear pads you need to release your ebrake cable automatic adjuster. sometimes they don't fully retract when you release so you might have to push on the cables a bit. just make sure you don't cause them to fall off the hooks.

[Kevin C]

oh....yes anytime you change your rear pads you need to release your ebrake cable automatic adjuster. sometimes they don't fully retract when you release so you might have to push on the cables a bit. just make sure you don't cause them to fall off the hooks.

I was assuming that Spike rebuilt all the calipers... So they should be retracted. That and ever try putting fresh pad in calipers with the pistons out? Not going to happen... Still worth taking a look to make sure the E brake is not dragging.

[texasboy21]

Switching from the heavy B7 S4 calipers and rotors (345mm) to my StopTech calipers (monoblock 4 pots) 331mm two piece rotors made a drastic improvement. I lost about 10lbs on each side.

[SleeperAvant]

Switching from the heavy B7 S4 calipers and rotors (345mm) to my StopTech calipers (monoblock 4 pots) 331mm two piece rotors made a drastic improvement. I lost about 10lbs on each side.

Wallet must be a lot lighter too.

[texasboy21]

Wallet must be a lot lighter too.

Not really.. after selling the stock B7 setup, the S4 set up, and getting a killer price on the StopTech BBK it was only a couple hundred out of pocket.

[fR3ZNO]

Switching from the heavy B7 S4 calipers and rotors (345mm) to my StopTech calipers (monoblock 4 pots) 331mm two piece rotors made a drastic improvement. I lost about 10lbs on each side.

Sticking with the topic of this thread... did you notice an improvement in MPG?

[TMeschke]

Put the car in neutral, jack up the front, and rotate the wheels by hand. Should be pretty obvious if the brakes are rubbing.


Sent from my iPhone using Audizine

[texasboy21]

Sticking with the topic of this thread... did you notice an improvement in MPG?

MPG? Probably not, but I dont drive the car daily so its hard to tell.

What I can confirm is that the weight loss is very evident immediately.

[Charles.waite]

I went from b6 288mm fronts to s4 345mm fronts and 245 rears to b7 288 rears on my b6 and noticed now MPG difference. I did notice a difference in how the suspension soaked up bumps driving on the crappy roads here (it was noticeably less controlled and almost bouncy from the extra brake weight), but no MPG difference.

Think about it. Once you're at a steady state, cruising for instance, you have inertia in your favor. The energy required to keep the wheel and rotor assembly spinning is so vasty outweighed by the aerodynamic drag and friction from the tires, that its pretty much negligible.

So I wouldn't worry much about it, unless you have a dragging caliper in which case fix that asap.