Cambered Tires Can Improve Fuel Economy

thecarchik writes with an excerpt from Green Car Reports: "We already know that it's possible to curb your fuel consumption just by having your tires properly inflated, or better yet, installing a set of low rolling-resistance tires, however, soon there may be an additional avenue to look at when picking the most fuel efficient rubber for your ride. The answer is the camber of your tires, more specifically, the negative camber. This is when the tops of your car's tires are angled inwards towards the chassis. Of course, there are negative effects too — namely increased tire wear and impaired ride quality — which is why production cars almost always have zero camber." The linked article, as well as the New York Times article from which it draws, describe a new tire which is designed to minimize those negative effects.

Comments

How?

[Sarten-X]

How does this help fuel economy? More to the point, how is this story anything but an advertisement for some guy's new tire?

Re:How?

[DevConcepts]

In a pure theory aspect, less tire on the road, less rolling resistance.

Re:How?

[LurkerXXX]

On a poorly designed suspension setup you could get more grip in corners thana narrower tire
like this, but that is in effect a design fault.

Just about every sports or race cars out there ( including Formula 1) have negative camber. You are saying that is a design default? Righhhhhht.

Re:How?

[thesupraman]

Sigh, go and learn something you retard.

They dont, any competent and not class limited suspension design dynamically adjusts camers in corners to develop the desired cornering camber, while not causing issues in strange line.

A lot of moronic 'boy racers' like to think a ton of negative camber is the sign of a race car, mainly because some suspensions designs develop a lot of un-adjustable negative camber when cars are over-lowerd.. This of course is terrible for handling (but they like to think it is not.) but since those cars cannot have it adjusted out with spending real money....

And F1 most certainly does NOT run static negative camber, it would be a disaster for straight-line handling. They run DYANMIC camber in corners due to the uneven A arm suspension geometries.

I suggest you start here.

http://www.amazon.com/Competition-Car-Suspension-Construction-Motoring/dp/085429645X
http://books.sae.org/book-pt-90

Re:How?

[JWSmythe]

    Race cars are made to turn quickly. Street cars are made to drive on relatively straight roads. There's a huge difference in the setup of the vehicle.

    Oval track cars give negative camber to the right side, and 0 camber on the left. That's because they always turn left. They even adjust their brake systems to assist in this (more braking power on the left side). As the car turns left, the body rolls to the right, shifting the weight to the right, and increasing the surface area on the right contacting the track.

    Street track cars (like Formula 1) expect to turn both left and right, so they get negative camber on both sides. Regardless of the direction they turn, the body rolls (much less, but it still does), and the weight is transferred to the outside of the turn. As that happens, the negative camber comes closer to 0. At a stop, sure it looks odd. In practice, it's what keeps them on the track.

    If you set up a race car like a street car (0 camber), you would see a race car that fails to perform as well as its peers.

    If you set up a street car like a race car, you'll be able to corner a lot better, but you'll reduce your braking ability in straight line stops, and your tires will wear significantly faster.

    With the negative camber tires, as the body rolls, they'll suffer the same fate. Instead of riding on the largest part of the tire (the tread), they'll roll up onto the outer edge.

    We won't see these tires showing up on production cars any time soon. If they are even produced, they'll be a sad fad like the Aquatred tires. The original version (circa 1991) They increased resistance to hydroplaning, but reduced overall traction due to less surface area contacting the road. The better innovation was improved groove patterns to reduce hydroplaning while still maintaining a large contact area. The Aquatred II and Aquatred III kept the brand name (and hype), but operate like a normal tire with good tread patterns.

    If this does make it to market, I'd shelve it right along with the fuel line magnets that align the atoms of the gasoline (or whatever); the electric supercharger that is only a marine bilge fan; and my all time favorite the battery cover insert for your cell phone that will increase your signal by 1000%.

    I'd never compare it to a tinfoil hat though, those really work. Aliens, nor the government, have ever read my thoughts from space. :)

Re:How?

[Sycraft-fu]

Also I wish that people would stop looking at how race cars do things and assume that it is good. Race cars are specialized machines designed for a specific purpose. They are good at what they do, but that doesn't mean they are good at everything.

For example you would find that many kinds of race cars would have real trouble handling on normal roads. They rely on the downforce generated by their high speeds and the heat changing the properties of their tires. On regular surface streets and speeds, they don't perform so well.

Likewise you wouldn't want a racing engine. Not only could you not use it but those things aren't built for longevity. The cars badly tear themselves up over the course of a race. The engines are pushed to extremes. However they needn't survive for more than a single race, another one can be had next time around. Wouldn't be so nice on a regular car though (even though it would last longer due to being used less intensely).

If you want to drive a car on the street then, well, you want a street car. It turns out the engineers behind them are usually fairly savvy and the design decisions are made for a reason. This includes things like the camber of the wheels.

If you are going to race a car, great, then you probably do want to modify it and there are some cool classes of racing purely on modified street cars. However realize that it is expensive, and generally you have to do a good deal of mods for it to be worthwhile. Don't just lower your car and think that matters to any real degree. While lowering the suspension is likely to be something done in converting a car for racing, that doesn't mean that lowering it alone is going to get you anything driving around town, other than some scrapes from speed bumps.

And really, if what you want is more performance in a street car, you just need to spend more and buy a more performance street car. Go get an Audi S4 or something. It'll have more power and speed than you can use on any street outside of the autobahn.

Re:How?

[LurkerXXX]

Also I wish that people would stop looking at how race cars do things and assume that it is good.

No one said a negative camber is good in all circumstances just because most sports cars use it. Heck, on Indy cars, they often have positive camber on one side of the car because they always turn one direction. Even among racers, they adjust the amount of camber by what type of course they are going to be racing on. In many cases for every day personal cars, 0 or close to 0 camber is the best setting, for others a slight negative camber is going to work best. The point was not that every car should use negative camber. It's that saying "negative camber is a a design defect" is moronic.

Re:How?

[Lotana]

In a pure theory aspect, less tire on the road, less rolling resistance.

Now I am completely new to this whole area, so please don't flame me too hard if what I ask is something stupid and obvious.

It is logical that less friction, less power is needed to keep the wheel spinning. But in poor, wet or icy conditions I need every unit of friction possible for safety (Aside: What is the unit of measure for friction?). Therefore, isn't this new tire design makes it more difficult for me to brake and thus more hazardous?

Saving me money in fuel is good, but if some child runs out in front of my car on local road and I can't stop in time with these tires...

Re:How?

[chrylis]

The coefficient of friction is dimensionless; it's the ratio of the maximum frictional force (opposing motion) to the force pressing the two objects together (such as the upper object's weight).

Re:How?

[R.Mo_Robert]

Aside: What is the unit of measure for friction?

Friction itself a force; therefore, you can measure it in Newtons (or poundals or your unit of choice). However, most non-physicists (that's me! ...so correct me if I'm wrong, by the way) run into the coefficient of friction far more frequently. This number (usually represented by the Greek letter mu) is just a ratio, so there are no units. (This probably explains the confusion in the first place.)

Re:How?

[tknd]

That wouldn't solve anything. You'd want to change the properties depending on if the driver is trying to stop or not. Such a tire you're suggesting wouldn't do anything for me if I'm trying to stop at 70mph.

The best I can imagine is a self-inflating/deflating tire. If the driver presses the brakes and the tire starts to lose grip, the tire would deflate some to increase contact with the road. Similarly, when the tire is not in any pressure to stop/accelerate or turn, the tire would over inflate to reduce resistance.

Such a device might be feasible. It would require a wirelessly controlled pump attached to the tire and it would probably be integrated with the TPMS system (which is already wireless). But the pump would need to be powered somehow. Seems a bit complicated and expensive to design and another point of failure. Who knows, maybe we'll hit a point where fuel/energy is that much more expensive so implementing a device is worth it.

We could also simplify the problem and just over inflate in optimal conditions and have a special valve that resets tire pressure to normal when bad conditions are detected. A pump would still be necessary, it just wouldn't have to be as demanding since the under-inflated case is out of the equation.

But for some people this system could be a net loss. Some drivers jam the hell out of their brakes that their brake pads go like nothing. I knew a friend's dad that burned through new brake pads in just a few months. The system would probably spend more energy adjusting tire pressure because it could never tell when the driver really needed to stop.

BMWs, Minis

[Raleel]

Apparently, BMWs and Minis (and probably other sport-ish cars) are negative cambered because it helps with handling. I found this out replacing the tires on my mini... the ones that I burned through in 1.5 years because I drive it like a sport-ish car ;)

Re:BMWs, Minis

[SydShamino]

I have a BMW, not a mini, but my car's tires (645ci) are completely different front-to-back, plus the tires are designed for single-direction turning only (i.e. grip works one way, not the other). Put those together and my car's tires can't rotate. They stay where installed until they wear out, which the rear tires already have done once in less than a year.

Then again, there's these really nice, sharp corners on the freeway that I can take at posted speed (though never higher, of course) when most people slow down to 45... $350 tires (each) is part of what I bought when I picked the car.

My rear tires have a static negative camber. I have no idea if it helps the abysmal fuel economy or not, nor does it really matter. I offset the carbon in other ways and I don't care about the cost.

Re:BMWs, Minis

[aXis100]

The salesman must have loved you. Would you like some special monster cable for your headlights too?

I can do posted speeds on my $110 tyres, pretty sure it's not that lofty a goal.

Re:BMWs, Minis

[Anonymous Coward]

Whether he needed it or not is debatable, but the points about different front/back tires and unidirectional tread are not snake oil.

Particularly in rear-wheel drive cars, it is not uncommon for the drive wheels (which need to apply torque) to be wider, while the steering wheels (which may need to cut through water/snow) are narrower.

Unidirectional tread is less common, but it does help reduce hydroplaning.

If you have just one of these, you can still move your tires in one direction (not full rotation, but front/back or side/side). If you have both, you have to keep your tires in the same location.

Re:"Negative Effects"

[JazzyJ]

Perhaps you should get your shocks replaced....

Exaggerated?

[grantek]

TFA is light on details, and I fail to see how anything other than zero camber can be optimal for straight-line travel. I can see how it could reduce rolling resistance during cornering (in the same way it improves grip), but if you're looking to improve braking as the article claims, I'd be looking at caster (angling the wheel forward like the front wheel of a "chopped" motorbike) before camber.

Well DUH!

[BLKMGK]

Gee, less contact patch equals less friction and rolling resistance - and less traction with more treadwear on a narrower part of the tire if you get stupid about it. The car may also feel darty in a straight line but caster can also cause this. Auto manufacturers set alignments for more than just ride comfort and I'm pretty sure zero is NOT how many are set. Sheesh!

I know, lets put bicycle tires on cars and bump pressure to 120PSI. Bet it will get great MPG! Never mind the side effects...

A little help

[gmhowell]

I don't really understand TFA. Could someone post a car analogy for me?

No fuel efficiency bonus

[Sierran]

The summary and the article it was taken from are misleading and poorly written. They only use the term 'fuel efficiency' to describe one possible effect of mucking around with your tires in general, probably by increasing their pressure or using harder tires. However, the CamberTire appears to have nothing to do with tire rigidity - and hence fuel economy - whatsoever. What the article appears to describe is a tire which is optimized by shape for negative camber, in order to improve handling of the vehicle, without the faster tire wear that putting negative camber on regular symmetrical tires produces.

WIth negative camber, the tire will be able to withstand more lateral force since it is angled out at the bottom, 'into' the turns. Thus it will be able to corner harder without losing grip.

When it is a car thing..

[Junta]

It has to be a computer analogy. This is kinda like when you are uploading files, but need them to go faster. You do that by leaning the computer back so the bits flow out of the back of it faster. Same deal here.

Re:"Negative Effects"

[aoteoroa]

I wonder if the increased fuel efficiency is simply the result of creating a smaller contact patch for the tires and reducing the rolling resistance. Maybe the same result could be acheived by using skinnier tires...but they wouldn't look as cool.

Ummm, sometimes the answer is in a book

[Sycraft-fu]

Sorry if that goes against the short attention span mentality we generally have these days, but that's life. Sometimes there isn't a good or reliable reference for something online, you have to go get a book.

"either way I win"

No not really. You may "win" in your own mind but that is meaningless. If you mean "win" as in convince others you are right, you have failed. Sorry.

Re:I bet they work even better...

[tsalmark]

Sir, I do believe you've been sold.

Re:"Negative Effects"

[Lt.Hawkins]

if thats so... I don't want one (or four?). I want larger contact patches for better stopping. Screw 1 MPG, I don't want to hit that kid / dog / train that ran out in front of me.

And as usual, the Japanese...

[wickerprints]

have to take it to the logical extreme:

http://www.youtube.com/watch?v=_r6ltUgtFWI

Pretty soon, all stock Toyotas and Hondas will look like this! XD

Re:"Negative Effects"

[Gordonjcp]

That's exactly what it is - the outer edge of the tyre has a lot less loading than the inner edge. Not only does this make the ride unpleasant but it drastically reduces grip and makes the car handle like a greasy weasel. If you want to know how to get the best out of your suspension, look at how tarmac rally cars are set up. That's going to be about the closest in "performance" suspension to what will be suitable for a daily driver. You'll find it has little camber, very soft springs with a lot of travel, and very stiff damping. On the road, this would give you a soft, comfortable ride with excellent grip on uneven road surfaces. Having really hard suspension means you have no grip at all, on anything but a perfectly glass-smooth racing track.

Re:"Negative Effects"

[FlyMysticalDJ]

I'm just imagining a boy with a dog running out in front of you along the railroad tracks. Or even more absurd, a train flying out in front of you in the middle of the suburbs with no tracks in sight.

Why do I suddenly feel like watching back to the future?...

Except it's not just racers

[poptones]

I was a mech for many years and grew up in Detroit. Just about ewveryone I knew worked in the auto industry, and I myself worked in the auto industry as an engineer.

And just about every car I have ever worked on or known about specifies some amount of negative camber right from the factory. You can call this anedote if you like, but the fact is I've worked on LOTS of cars and seen a LOT of specs and have seen zero or positive camber specified on a car so few times I could probably count them all on one hand.

  Because it's NOT just about how the car grips in the corners, but how it handles in a straight line; Too much negative camber will make the car twitchy as it bump steers over every wave or truck rut, but NO negative camber also makes the steering feel lighter, which is also not a good thing when it means the car has absolutely no "return to center" correction. Any rear wheel drive car will try (to some degree) to straighten itself out, but half a degree to two degrees (depends on car) negative camber is pretty much standard. Part of this is also because cars tend to get knocked out of alignment because of neglect, and POSITIVE camber is really no fun - it tends to make the car even more vague in steering. So a little negative camber is built in just to help make certain things don't go positive.Of course too much is also no fun, since it will make the car try to steer away from the crown in the road and heavily crowned roads will make you feel like the front end is badly out of alignment (because it is).

The same holds true for caster: toe the front wheels out a bit and the thing will wander all over the place; toe them in and the car will tend to center itself. Both of these also will tend to increase friction as well, which also it seems would negatively affect mileage. Given many cars nowdays run on low profile tires inflated to 40psi or more I have a hard time believing it's going to make much difference on a properly tuned and aligned vehicle, however.

Re:Except it's not just racers

[mungtor]

The same holds true for caster: toe the front wheels out a bit and the thing will wander all over the place; toe them in and the car will tend to center itself. Both of these also will tend to increase friction as well, which also it seems would negatively affect mileage. Given many cars nowdays run on low profile tires inflated to 40psi or more I have a hard time believing it's going to make much difference on a properly tuned and aligned vehicle, however.

I'm hoping you just mis-spoke here, or that you're not a suspension engineer. Caster and toe are completely different entities. Toe is whether your tires are pointed inward (toe-in) or outward (toe-out) when viewed from the top. Caster is a measurement of how far the center of the contact patch is behind the steering axis. Caster is what makes the wheel want to straighten out. Both toe and caster are much more important for straight line stability than camber is.

Re:I bet they work even better...

[zippthorne]

True that. I fill all my tires with a low-grade nitrogen mix (only about 20% impurities.)

Re:"Negative Effects"

[Anonymous Coward]

I think you may mean Toe? Most cars have zero camber, or very close to it. Toe at zero or toe out is what causes a very twitchy car.