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Post by silverdragon on Mar 15, 2014 7:46:28 GMT
During a recent conversation with a mechanic whilst I was getting a puncture repaired, the subject of Hub caps comes up.
Are they really that aerodynamic compared to just a wheel?....
To be honest, I have mine just because the steel rims I have are but-ugly.
But does having the plastic trim over those wheels actually help in aerodynamics or not?...
I suspect, as always, this may depend on a few other factors, the type and size of wheel, design of wheel, design of Hub cap etc?...
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Post by kharnynb on Mar 19, 2014 19:37:09 GMT
I always thought hubcaps were to keep dirt and such away from the nuts and brake disc?
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Post by the light works on Mar 20, 2014 5:56:11 GMT
I can see some wheel covers making an aerodynamic difference. - but it may not necessarily be positive. my wheel covers are essentially a duplicate of my wheels, but chrome plated - so I suspect they produce a little bit of added turbulence.
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Post by silverdragon on Mar 21, 2014 7:06:17 GMT
My Hub-caps/Wheel covers are designed to suck air through the wheel.
Two benefits, one it sucks the caps onto the wheel which helps prevent the buggers flying off, and two it sucks air out from under the car which cools the brakes and creates downforce?...
Edit.... they day after, after thinking this through... I am now confused......
Disk brakes, Vented, suck air from the centre of the wheel and throw it out towards the tyre.
So....
Having air flow THROUGH the wheel......
How does that affect the air being sucked through the vents on the disk?....
Does it suck the air from the exit of the vent?...
I may have to return to this.
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Post by the light works on Mar 21, 2014 14:10:26 GMT
My Hub-caps/Wheel covers are designed to suck air through the wheel. Two benefits, one it sucks the caps onto the wheel which helps prevent the buggers flying off, and two it sucks air out from under the car which cools the brakes and creates downforce?... I have seen cars with non vented wheel covers have trouble with the brakes overheating - but I'm not convinced there is any significant downforce advantage. - we could do a minimyth on how many CFM a hubcap at 60 MPH can move. |
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Post by silverdragon on Mar 22, 2014 11:20:37 GMT
I suppose this all depends on how the brakes work.
If the disks are small and inside the wheel, they will overheat if not cooled.
If the brakes are large and behind the wheel, that is a better design, no?...
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Post by the light works on Mar 22, 2014 12:49:52 GMT
I suppose this all depends on how the brakes work. If the disks are small and inside the wheel, they will overheat if not cooled. If the brakes are large and behind the wheel, that is a better design, no?... larger brakes are nearly always better than smaller brakes. but if they are larger than the wheel, that can present problems as well. |
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Post by c64 on Mar 22, 2014 13:56:15 GMT
The Hub cap has a serious impact on aerodynamics at high speeds.
First of all, you need an air flow to cool the brakes. In case of normal driving, you don't brake that hard very often so it doesn't really matter. I you brake as hard as you can and accelerate as hard as you can alternately as in race conditions, you need air flow to cool the brakes. This is less the job of the hubcap as for the car body to redirect air through the brake system. But the hubcap needs to match the brake ventilation system to prevent "stealing" the air flow or to prevent to pressurize the wheel housings. Pressurized wheel housings cause a lot of drag and can reduce wheel grip.
What's really bad is that the holes in the wheel rotate with the wheel so the intake and outlet positions of the air constantly alternate. This chops the air flow which mixes with the rest of the car's aerodynamic so you have alternating air flow conditions over your entire car. This prevents that you can have an ideal setup since your setup needs to accept those fluctuations.
That's why in Formula 1 the wheels have no holes at all. And some F1 cars have stationary hubcaps which don't turn with the wheel to keep the air flow around the wheels and the car a constant.
So if you want a perfect hubcap, it needs to be stationary, it may not spin with the wheel. But beneath 60mph, the common speed of ordinary driving, and never pushing the car even anywhere near its limits, the hubcap doesn't matter much.
On my race car (back when it still worked), I had really ugly hubcaps someone told me I should try. They made a difference at very high speeds. I now have them on my ordinary car. On both cars, the chopped air flow starts to make the rear of the car vibrate at around 90mph but not significantly below 115 mph. It's worse without hubcaps and the original VW hubcaps are good for 110mph I'd say. At this kind of speed, the race hub caps don't make any significant difference but I have them, I use them even if I receive ugly comments about them. I always tell them "I don't care how they look like, when I sit inside the car, I can't see them!"
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Post by the light works on Mar 22, 2014 14:06:14 GMT
of course, the hub cap used to be to keep the axle grease in. (some models of axle still have these)
in the 70s, most decorative wheel covers had no ventilation at all, and were essentially to hide the plainness of the steel wheels. - some were modeled to imitate fancier wheels, but most were simply a decoration.
most high performance wheels I have seen don't have a "hubcap" mainly because it is one more thing to fuss with in a situation where changing tires in a hurry can make a difference on the outcome of the race.
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Post by c64 on Mar 22, 2014 15:03:29 GMT
most high performance wheels I have seen don't have a "hubcap" mainly because it is one more thing to fuss with in a situation where changing tires in a hurry can make a difference on the outcome of the race. Correct, but now some F1 cars DO have them for aerodynamic reasons. They need to remove them in the pit which takes time, but they figure they save more time on the track. |
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Post by silverdragon on Mar 23, 2014 12:21:26 GMT
Now outlawed.
Changes are happening this season.
Next season you will see tyre warmers outlawed as well.
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Post by the light works on Mar 23, 2014 14:05:22 GMT
Now outlawed. Changes are happening this season. Next season you will see tyre warmers outlawed as well. F1 appears, from my perspective, to be a balancing act between keeping it feeling like a competition, keeping it from feeling like they are all driving the same car, and keeping it from being a race where any baboon can drive - its the car that wins the race. |
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Post by silverdragon on Mar 27, 2014 10:59:56 GMT
You are now going to have to watch for Formula "E"...
I will have to open a new thread for this, but aerodynamics just got new toys, ELECTRIC Formula racing.
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Post by c64 on Mar 28, 2014 15:18:58 GMT
most were simply a decoration. Not quite, they protect the bolts. Especially during winter with salty roads, they prevent corrosion of the bolts. Doesn't matter that much in case of bolts you remove to change the wheel instead of nuts sitting on fixed bolts. When the fixed bolts corrode, you need to replace the brake disc or drum to fix them. It's funny that people who don't want to afford a second set of hubcaps drive their wheels without during winter to keep their caps shiny for the summer. |
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Post by the light works on Mar 28, 2014 16:16:11 GMT
most were simply a decoration. Not quite, they protect the bolts. Especially during winter with salty roads, they prevent corrosion of the bolts. Doesn't matter that much in case of bolts you remove to change the wheel instead of nuts sitting on fixed bolts. When the fixed bolts corrode, you need to replace the brake disc or drum to fix them. It's funny that people who don't want to afford a second set of hubcaps drive their wheels without during winter to keep their caps shiny for the summer. nope, here you just knock out the studs if they get damaged, and put in new ones. (the only time I have seen that was when the tire center didn't torque them properly and the lug nuts loosened - never from corrosion - and actually, unless the caps are sealed and heated, they will actually trap the moisture inside.) |
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Post by c64 on Mar 28, 2014 17:43:03 GMT
Not quite, they protect the bolts. Especially during winter with salty roads, they prevent corrosion of the bolts. Doesn't matter that much in case of bolts you remove to change the wheel instead of nuts sitting on fixed bolts. When the fixed bolts corrode, you need to replace the brake disc or drum to fix them. It's funny that people who don't want to afford a second set of hubcaps drive their wheels without during winter to keep their caps shiny for the summer. nope, here you just knock out the studs if they get damaged, and put in new ones. (the only time I have seen that was when the tire center didn't torque them properly and the lug nuts loosened - never from corrosion - and actually, unless the caps are sealed and heated, they will actually trap the moisture inside.) The ones on the common European cars leak out the moisture but prevent a constant (salty) spray while driving. The studs can rust solid if you don't have hubcaps, then you can't just change them. Well, I like the interchangeable bolts you remove to get the wheel off a lot better  |
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Post by the light works on Mar 29, 2014 1:04:51 GMT
nope, here you just knock out the studs if they get damaged, and put in new ones. (the only time I have seen that was when the tire center didn't torque them properly and the lug nuts loosened - never from corrosion - and actually, unless the caps are sealed and heated, they will actually trap the moisture inside.) The ones on the common European cars leak out the moisture but prevent a constant (salty) spray while driving. The studs can rust solid if you don't have hubcaps, then you can't just change them. Well, I like the interchangeable bolts you remove to get the wheel off a lot better If those rust spall and seize, then you'll shear off the head and they're done. mine are drawn through the hub, so if they get damaged (like I said, the nuts weren't torqued properly) they can be hammered out, and new studs drawn in. but even on the water rescue rigs, which get routinely dunked in the ocean, I haven't seen them rust. |
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Post by silverdragon on Mar 29, 2014 9:05:24 GMT
The pictured Galvanised bolts(?) will not seize up as old as non treated bolts, therefore wont snap off either?...
This is developing a separate myth?... are we drifting here?...
If this is topic drift should we get a new thread here?.. can a Mod split this?...
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Post by c64 on Mar 29, 2014 19:20:42 GMT
but even on the water rescue rigs, which get routinely dunked in the ocean, I haven't seen them rust. Those used to use brass or hot-dip zinc bolts and nuts or nowadays stainless steel ones for such applications. Hot-dip zinc became the norm over here in the early 90s even for ordinary cars. The trouble is that the disc or drum needs to match or you make a battery out of your wheels when there is enough moisture. I need to use the rusty kind and on 3 wheels, it makes an ugly sound before they start to turn when I remove the bolts and one wheel has always bolts rusted in place which can't be removed with my pneumatic nut runner. This is the wheel all cats p** on for some reason. |
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Post by silverdragon on Mar 30, 2014 7:38:18 GMT
Which is when you get the length of scaffolding bar on handle of the wheel wrench.
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