Cambered Tires Can Improve Fuel Economy 317
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.
Re:"Negative Effects" (Score:5, Informative)
Perhaps you should get your shocks replaced....
Re:How? (Score:5, Informative)
In a pure theory aspect, less tire on the road, less rolling resistance.
No fuel efficiency bonus (Score:5, Informative)
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.
Re:How? (Score:5, Informative)
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? (Score:1, Informative)
Not just camber my little friend.
Caster, scrub radius, toe. Reverse every manufacturer recommended settings and you'll be well on your way to giving big multi-nationals the finger.
Seriously, this is total BULLSHIT. From some shilling journalism idiot.
Camber is set to give optimal contact for your tyres. Which results in optimal handling, braking, safety, reliability.
If you want minimal tyre contact, you are looking for a bicycle, not a car.
Re:BMWs, Minis (Score:2, Informative)
Not uncommon. I have an older volvo wagon (245) Many owners have modified the stock arrangement to allow for a small increase in negative camber. Most people end up with -.5 to -1.5 degrees after some grinding and or drilling (nothing drastic). Upshot? A pretty much universal agreement that it improves cornering DRASTICALLY, and improves tire wear also. That's right most people report a noticble *improvement* in tire wear. (my car is stock and wears the tires unevenly FWIW) There are alot of variables at work here, suspension systems move, tires flex and the sort. People here are making the assumption that it increases tire wear, it doesn't always. In the case of an older volvo it's win-win, with perhaps the only negative being a small reduction in straight line handling, but not one that's very noticable.
Re:BMWs, Minis (Score:4, Informative)
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:How? (Score:5, Informative)
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.
And as usual, the Japanese... (Score:4, Informative)
have to take it to the logical extreme:
http://www.youtube.com/watch?v=_r6ltUgtFWI [youtube.com]
Pretty soon, all stock Toyotas and Hondas will look like this! XD
Re:How? (Score:1, Informative)
In a pure theory aspect, less tire on the road, less rolling resistance.
Is that general theory or specific to tires? Doesn't most of the rolling resistance from a tire come from deforming the tire? So then wouldn't any camber just load one side of the tire more heavily than the other, so there would be more deformation on that side of the tire? This would only be beneficial if there were some net reduction in rolling resistance.
From TFA the patent is for a new tire with an asymmetrical side wall height where the outside would be higher than the inside. Based on the diagram there is still the same amount of tire in contact with the road, so it seems it is not just a matter of putting less tire on the road.
Re:How? (Score:5, Informative)
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? (Score:4, Informative)
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:BMWs, Minis (Score:5, Informative)
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.
Mechanical Engineer give U advice (Score:2, Informative)
WAIT hold on guys, I just took a land vehicle dynamics class last semester and if I find my notes.....
Oh here they are one sec let me find the section on Camber caster, and kingpin inclination angles
alright first off rolling resistances
influenced by:
applied load
inflation pressure
tread design
compound
The primary cause of rolling resistance is hysteresis (or internal friction) of the tire material, which occurs as the tire flexes
it increases with
higher load
higher tread design agressiveness (net to gross footprint ratio)
higher tread depth
and decreases with
increasing tire pressure (i.e. less contact patch)
it can be calculated at the contact patch as
F_r= [(s+1)(t_in/R_l)-F_x]cos(a)-F_y*sin(a)
where
F_r is the rolling resistance
s is the slip ratio= (Omega*R_l/V_0)-1
F_x is the longitudinal force (+ driven - braking)
F_y is lateral force
Omega is the angluar velocity of the wheel in rads/second
V is the forward velocity (in ft/s)
a is the slip angle
R_t is the tire radius
and T_in is the driving torque
so on to camber angle
camber angles is the tilt of the center of the tire patch axis from vertical
camber is positive (if viewing from the front of the car) if the tops of the tires are further away from each other than the bottoms
Trucks run positive camber to account for different loads
a small camber is used to account for road crown
some trucks have different camber settings to account for the huge torque their engine can output (this counteracts the torque of the engine's affect on the suspension
mechanics used to bend axels to give cars positive camber ( they shouldnt be doing this anymore >)
so some reasons why camber angle would increase gas efficency
well for one, it makes the effective tire radius larger (by a tiny bit) which should decrease rolling resistance, also, it makes the contact patch smaller, however, depending on the sidewall strength of your tires, this could merely cause more internal hysteresis friction and decrease your effective gas milage
one of the big reasons you probably should not do this is... most consumer tires are manufactured assuming no camber angle, so you'd probably run into some issues with tires wearing out quickly. Also, if you, like most people, forget to check tire pressure before every ride, it would probably be fairly easy to blow out your sidewall in a tight corner, especially if you were running with a heavy load
and if you're especially stupid, and put too much negative camber, you could probably screw up your suspension geometry enough to make your tires move further than the designed rattle space in you car (the open area where the suspension can move) and perhaps your tires would rub on the inside of the wheel wells before the suspension bottomed out.
but it really depends on the type of suspension your car has (and there's wayyyyy to many to list) to get a definite answer as to whether this is doable or advisable. I would go with the factory recommended settings personally and just firkin keep your tire pressure high enough (the recommended amount) and you'll save a TON on gas
oh and a warning, ALWAYS REPLACE REAR TIRES if you're only gettin 2 tires, if you replace the front tires (regardless of a front or wheel rear drive car) only, you could potentially put your car in an oversteer condition, and that is what causes people to lose control, and spin out, unless you're a formula 1 driver and you know WTF you're doing, always keep your car in an under steer condition (i.e. more traction in the back dawg)
This is what i got for taking a land vehicle dynamics class, i hope you find some of it useful
Except it's not just racers (Score:5, Informative)
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 (Score:5, Informative)
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:hmmm (Score:3, Informative)
I agree. We're talking about tires shaped like a slice of a cone. Anyone that has played with a cone shape as a child may recall that when laid on its side and rolled, a cone will pivot around its apex. So, these cone-segment tires would try to do the same thing. Even without the cone analogy, it should be apparent that the smaller inner-edge diameter will try to travel a shorter distance with each rotation than the outer-edge diameter. That difference will make the tire roll on a circular path if left to its own devices. Forcing it to follow a linear path rather than a circular one would require some degree of lateral scrubbing, the severity depending on the pitch of the cone.
In the cone-tire's defense, the non-zero toe-in that some cars' alignment specs call for also causes lateral scrubbing. You could adjust toe so the two scrubbing forces fight each other but that would only neutralize the forces against the car's suspension, not eliminate the scrubbing.
Re:"Negative Effects" (Score:3, Informative)
Have you ever driven a zero camber set car? They are twitchy as hell. even slight negative camber is still a challenge to drive. Considering what I observer daily in the lack of skill in driving that most of the population has, I really don't want to encourage making the job harder.
Yes Zero or slightly negative camber increases gas mileage and it has been done for decades for mileage challenges, and is certainly not new. Having driven a car that had zero camber setup for max fuel economy and running on tires that were at 72psi I can tell you I do NOT want 95% of the population driving such a car. It takes all your concentration and requires the power steering to be removed from the car to make it somewhat tolerable for a 5 hour drive.
You end up after 1 hour feeing exhausted and afraid to look at the instrument cluster.
Re:BMWs, Minis (Score:3, Informative)
Ha ha, very funny. My Mini came from the factory with Dunlop SP Sport 9000 DSST Run Flat Tires (size 205/45/R17). The dunlop equivalent is $319-ish on tirerack.com.
Try replacing those on the cheap. I've gone through several sets (including an abysmal set of Kumhos), and am currently running Continental ContiProContact SSR's. They go for $219/each on tirerack.com.
Re:How? (Score:2, Informative)
Re:I bet they work even better... (Score:3, Informative)
It will help, marginally, in corrosion resistance and pressure maintenance. Not enough to matter for most folks, but it's not snake oil...
My local oil change price does it for free, so I get it. I wouldn't pay extra for it, but given the choice N2 versus air, I'll take the N2..
Re:"Negative Effects" (Score:3, Informative)
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.