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Old 08-12-2014, 11:43 AM   #11 (permalink)
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I think I've seen or heard of tires being melted off the rims due to the heat from the brakes, so I'm certain that the wheels are removing a substantial amount of heat by conduction. The wheel usually has a fair amount of contact area with the hub part of the brake disc, so the heat is being drawn out there.

That being said....This IS ecomodder! Why the heck are we worried about over heated brakes?!? It has been said, "If you have to use your brakes, You're Doing It Wrong." Really this whole conversation could get us BANNED from the site, lets hope the moderators go easy on us. I suppose we could talk about this "Hypothetically" as well, like, "Suppose I was to one day go down a very long steep hill and my clutch/transmission went out preventing me from engine braking, and I could only use my brakes...." Yeah, that's the ticket.

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Old 08-12-2014, 01:03 PM   #12 (permalink)
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So I was thinking, there are aero spoke bicycle wheels, why not cars? Would the improvements be too small?
Yes.

In the case of the bicycle you have a minimal rim and tire, with the spokes open to the airstream on both sides. Would aero spokes would the flat carbon fiber spokes? They cut though the air better than a round wire spoke.

In the case of the car, you have a massive rim and tire with a relatively small opening in the middle. Which is typically full of brakes. So you can see daylight though some small slots? ChazInMT's point holds, so divide by two. The path is intermittently shuttered by the moving spokes, so deduct some additional points. The wheelwell is full of turbulence, so the inside/outside pressure differential probably changes direction at random.

When you have to pump the brakes, it's because the parts expand from the heat, requiring more fluid than the master cylinder contains. The correct way to cool brakes is to ventilate the rotors and cross-drill the rotors and drums.
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Old 08-12-2014, 03:04 PM   #13 (permalink)
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Quote:
Originally Posted by freebeard View Post
Yes.

In the case of the bicycle you have a minimal rim and tire, with the spokes open to the airstream on both sides. Would aero spokes would the flat carbon fiber spokes? They cut though the air better than a round wire spoke.

...The path is intermittently shuttered by the moving spokes, so deduct some additional points.

The correct way to cool brakes is to ventilate the rotors and cross-drill the rotors and drums.
Fair enough wrt to the fat rim. With the moving spokes though, when the spokes get to the top of the rim, they are moving at almost 2x the speed of the car relative to the air, and so even though the spoke is small and not fully exposed to the air flowing around the car, I would think that there is some significant energy expenditure there.

I don't know about your brakes but I've never seen a non-ventilated rotor. As far as brake cooling goes a lot of cars are designed so that brake cooling air goes to the brakes from the inside and leaves through the outside of the wheel, but you could probably easily reverse this, as a partially covered wheel would act like a fan that pulls air through the hub.

The main reason people don't want to do this though is for looks, which is why I started this discussion. Like I said, brake cooling is not an issue for 99% of people.
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Old 08-12-2014, 03:43 PM   #14 (permalink)
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I was thinking about brake cooling, as I've had some minor episodes where the brakes fade to the point that the pedal goes all the way and there are no brakes, so you have to release the pedal an apply the brakes again (it was an old Nissan Sunny '87 or so).
That's no brake cooling issue IMO.

Hypermiling, you shouldn't have any brake issues at all
(Oh well, aside from glazed pads and rusty disks maybe )


I'd look into improperly bled brake lines ; brake fluid gone past its prime and absorbed too much water; or spongy brake lines that expand under pressure - or any combo of these.
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Old 08-12-2014, 03:52 PM   #15 (permalink)
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Originally Posted by serialk11r View Post
I don't know about your brakes but I've never seen a non-ventilated rotor.
They're not rare though.

You'll find them on rear axles, older motorcycles (i.e. not drilled), disk kits for oldtimers to replace drums, ...
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Old 08-12-2014, 05:35 PM   #16 (permalink)
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Quote:
Originally Posted by serialk11r View Post
So moon disks and pizza pans are great and all but some people do care about brake cooling, and many people (not here) think covered wheels look weird. So I was thinking, there are aero spoke bicycle wheels, why not cars? Would the improvements be too small?

Some cars already come with "aero spokes", in that the spokes get a lot wider as they hit the edge of the wheel where the air would be moving the fastest.

Painted black, spoke fairings could look pretty good IMO. Kind of like if you took these concept wheels and made the black bits bigger:
A typical stamped steel wheel has a windage drag which adds 0.005 to a car.
With spokes,there'd be increased windage since it's a primitive 'fan.'
At zero crosswind,the entire wheel is for the most part shielded,shredding the air next to it,air blowing through it,and by it.
In a crosswind,the windward and leeward sides of the car will see different effects.
A void cannot support airflow.Without a full wheel cover there must be turbulence there.
If your not going to skirt the openings you're never gonna get low drag anyway,so maybe it's unimportant whether or not the spokes are 'optimized.'
Ford's concept truck wheels have active shutters which close during highway operation.They evoke the testosteronephilia at rest,then go full-girl when underway.
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Old 08-12-2014, 06:03 PM   #17 (permalink)
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Quote:
Originally Posted by serialk11r View Post
I don't know about your brakes but I've never seen a non-ventilated rotor. As far as brake cooling goes a lot of cars are designed so that brake cooling air goes to the brakes from the inside and leaves through the outside of the wheel, but you could probably easily reverse this, as a partially covered wheel would act like a fan that pulls air through the hub.
Some of the fastest cars I've ever seen use solid disk brakes with no venting whatsoever. They stop from 250mph or more just fine.

Once.

Then the car sits and cools down for a while before it makes another pass down the drag strip...

Air flowing around the body of the car should create a low pressure zone outside the wheels. I think forcing air to flow the opposite direction would be challenging (except maybe open-wheel cars).
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Old 08-13-2014, 01:52 AM   #18 (permalink)
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Originally Posted by aerohead View Post
A typical stamped steel wheel has a windage drag which adds 0.005 to a car.
With spokes,there'd be increased windage since it's a primitive 'fan.'
I understand the inside of the wheel itself being a big void probably contributes more drag than the spokes, but say you had streamlined spokes instead of the typical rectangular chunks, how much of a difference would that make? Would you be better off with a partial cover (a full cover missing a circle in the middle)?
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Old 08-13-2014, 11:06 AM   #19 (permalink)
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Quote:
Originally Posted by euromodder View Post
That's no brake cooling issue IMO.

Hypermiling, you shouldn't have any brake issues at all
(Oh well, aside from glazed pads and rusty disks maybe )


I'd look into improperly bled brake lines ; brake fluid gone past its prime and absorbed too much water; or spongy brake lines that expand under pressure - or any combo of these.
That was an old car and I suppose that it may not be ideal for that kind of driving. It was exactly as ChazInMT described. Very steeped hills with speed bumps at the end when going downhill, repeatedly, in summer.

Anyway, that could count as an exception (and maybe, or most probably, some adjustments on the brakes system). For ecomodders I don't think it will be a problem. That was many years ago and I don't even have that car anymore
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Old 08-13-2014, 11:20 AM   #20 (permalink)
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Quote:
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You'll find them on rear axles, older motorcycles (i.e. not drilled), disk kits for oldtimers to replace drums, ...
..the front of a current model Fiat 500 & Panda...

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