Minimum oxygen transport is the goal for minimum rubber oxidation so I’d like to understand this.
Are you saying that the actual number of O2 molecules being transported through the tire wall due to the 3.1psi exterior O2 partial pressure (in a 100% nitrogen fill) is trivial compared to the number of O2 molecules randomly transported through the tire wall due to Brownian motion?
Or is there some other ‘driving force for transport across the wall’ Dr. Murphy neglected to mention that I’m unaware of?
No, it correctly tells you the net flow of oxygen. That’s the difference between the oxygen leaking in, and the oxygen leaking out. If you want that difference to be zero, then pick an oxygen concentration that gives equal partial pressures.
On the other hand, if you want to minimize the total number of oxygen molecules that pass through the membrane, then Murphy’s formula, although correct, is not useful for this. If the pressure inside the tire is a given, and the external pressure and oxygen concentration are both given, then there will be a fixed amount of oxygen molecules leaking into the tire. You can’t control that. But you can minimize the oxygen molecules which leak out by simply not having any oxygen in the tire to start with.
Yes, but there is O[sub]2[/sub] migration into the tire in any case. It’s just that if you set equal partial pressures inside and out, the oxygen leaking in will balance the oxygen leaking out. And in that case, you’ll have twice as many oxygen molecules making the trip through.
penumbrage, I’m not sure how to answer your question. It has been pointed out that the main source of leakage is either poor seal with the rim or bad stem. Transport of molecules through the tire is a smaller factor. With that said, if you get a good seal and a good stem, then start with pure Nitrogen in the tire, you will have less oxygen transport through the tire because there will be no initial transport rate from the interior to the exterior.
Rate of transport through tire = Rate of transfer in + Rate of transfer out.
If there is zero oxygen inside to begin with, then the Rate of transfer out is initially zero. As the Oxygen comes into the tire, there will then be molecules to go out, and the Rate of transfer out will go up from zero. Sum total net result will be some period with zero transport out, then some limited transport out, then reaching equilibrium.
If you start with oxygen in the tire, then you will get transport out through that whole time period.
How much difference that makes I can not quantify.
I really don’t know for sure, but suspect that brownian movement is an order of magnitude or smaller than pressure driven transport. It is essentially irrelevant to the question, which is why Dr. Murphy ignores it.
Suppose you have a piece of rubber. It has two sides: side A and side B. The number of molecules of a particular type (say, oxygen) that get transported *from *side A through the rubber *to *side B is a function of how many of those molecules bang into the rubber on Side A. So a higher pressure or greater concentration of the molecule (oxygen) on side A will result in more molecules migrating from side A through the rubber to side B.
But the transport of molecules from side A to side B is not affected by the number of molecules on side B. The number of molecules on side B only affects transport *from *side B through the rubber *to *side A. It’s certainly possible to have the number of molecules transported from A to B exactly equal the number of molecules transported from B to A, in which case the net flow of molecules is zero (by definition), but having a net zero flow does not mear no transport at all is occuring, it just means that the transport in each direction is zero.
I would say, “it just means that you end up with the same amount of molecules on each side that you started with” or “it just means that the transport balances out.”
Otherwise, good post.
Sorry it took so long to get back to the board, life you know.
Yes, we beat it to death. inner-liner oxidization, it was pointed out that the amount of oxidization would be minimal because as something oxidizes it uses up the oxygen in the air. So the oxygen would be used up. Water was about the only benefit anyone could come up with for the average driver, rim corrosion I haven’t seen a rim corrode in over 20+ years now, that’s do to fewer steel rims than in the past. And if you get dry air, that advantage is minimal. Pressure variability over temperature at almost the same rate, IF the air is dry. It’s the water vapor that causes the greatest pressure variation, again if the air is dry almost no benefit.
Fire safety, and just how many tires have seen that have caught fire from driving or even from a car accident? In 35+ years of driving I’ve never met anyone who’s tire overheated to the point of starting on fire, I’ve only seen a few accidents where the tire started on fire, and in those cases the sidewall failed and the air quickly leaked out. But if you really are worried about fires, use CO2, it’s a larger molecule, which would mean even less air loss.
“doubling the tire body life” The tire body is only good for 10 years. A 60,000 mile tire will be about half way through its life when it’s ready for it first retread and at its end of life before the second.
“than 2/3 the leak down”
" The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting. "
http://news.consumerreports.org/cars/2007/10/tires-nitrogen-.html
I haven’t read how many tires they used but as you can see, you still have pressure loss, it happens slower, so aren’t those pushing nitrogen give people a false since of security. “Hey, I have nitrogen I don’t have to worry about my tire pressure.”
No matter what you still need to check your tires.
BTW is I put the stress on my tires that aircraft and the space program puts on their extreme temperature changes 30 F or colder to 100+ in a very short time, 0 to 200+ mph I would use nitrogen too. My car doesn’t even come close to those conditions. Like I said a buck or two I might use it.
Irishman/CurtC – If it’s not Brownian movement that makes so many O2 molecules migrate in and out of the tire that they render balancing the O2 partial pressure irrelevant, then what is the transporting force?
I understand that there are losses from the bead seal (all 8ish feet of it) and valve stem (stem base to tire rim and internal check valve), but here’s my problem giving it as much weight as you do.
The calculated permeability of the butyl rubber innerliner (designed to hold inflation pressure and resist oxygen degradation) for air inflation and for N2 inflation is the sum of the gas proportions times their specific permeability in butyl rubber:
Air: P = (0.78 * Pnitrogen) + (0.21 * Poxygen)
95% N2: P = (0.95 * Pnitrogen) + (0.05 * Poxygen)
Using permeability values of 50 for N2 and 195 for O2 (from the butyl rubber column in table IV at Apa Info : votre actu habitat n'a jamais été aussi accessible !) we get:
Air: P = (0.78 * 50) + (0.21 * 195) = 79.95
95% N2: P = (0.95 * 50) + (0.05 * 195) = 57.25
Which means 95% N2 has 71.6% the permeability of air.
If the leakage from the bead and valve stem were an order of magnitude greater than the leakage from tire diffusion, the best possible improvement from nitrogen inflation we could achieve would be 6.5% (71.6% of the tire diffusion losses which would be 9% of the total gases lost).
To explain the 37% improvement Consumer Reports found in real world testing of the whole tire (3.5psi for air, 2.2psi for N2), either the bead/valve stem losses are considerably less than you assume or else the rubber under pressure conforms to the various metal surfaces so well that the bead/stem losses are largely due to miniscule (non-Graham’s Law sized) passageways that discriminate between the N2 and O2 molecules nearly as well as the butyl rubber itself.
“To explain the 37% improvement Consumer Reports found in real world testing of the whole tire (3.5psi for air, 2.2psi for N2), either the bead/valve stem losses are considerably less than you assume or else the rubber under pressure conforms to the various metal surfaces so well that the bead/stem losses are largely due to miniscule (non-Graham’s Law sized) passageways that discriminate between the N2 and O2 molecules nearly as well as the butyl rubber itself.”
You still have pressure loss only at a slower rate. I can make it even slower by using CO2. And have all the benefits listed for nitrogen. It’s dry, having even a slower leak down when compared to nitrogen, it won’t burn, in fact many fire extinguishers use it to put out fires.
Like I said all along there is a only a very small benefit for the average driver. You still need to check your tires, (I check at least one a month). But I can get compressed air just about anywhere, and in most cases I get it for free.
My bad (or rather, my lazy) for cut and pasting from my original post.
My subsequent research shows that the deterioration is in the structural rubber of the tire due to highly reactive oxygen that migrates through the innerliner,
which using N2 cuts in half over the life of the tire (http://www.branick.com/uploads/NitrogenInflationforPassengerCarandLightTruckTires-Daws.pdf).
To be fair in my update, however, I’ll have to add increased tire pressure monitoring sensor reliability (especially in cold weather) to my list of slight to moderate advantages for N2 inflation.
Don’t feel bad about not being able to add to the two disadvantages, cost and availability (which don’t apply to me as I get it free right on my commute), no one else has managed to find any either.
With more and more places offering nitrogen for less and less (many for free) as they pay off their N2 separation equipment, the decision will soon be a total no-brainer anyway.
As I noted upthread, “… all my comparisons have been to hydrous air, the kind most gas stations and all home and pay compressors provide (water traps only remove droplets, virtually all the water vapor remains unless expensive desiccant or active air drying stages are added).”
As I noted upthread (twice, in fact) “I’m just talking about the difference between releasing a pressurized burst of explosive gasses when the tire fails (even without the containment and internal ignition required for an explosion) compared to merely releasing more flammable gasses into the combustible gas rich environment of a car fire – basically the same difference as using a lit match to pop a balloon filled with acetylene and air or popping one filled with acetylene and nitrogen - the same combustible gas energy is released much more rapidly and violently when pre-mixed with oxygen, generating more heat and pressure to intensify and accelerate your car fire.”
Not being someone who is regularly dispatched to car fires, I asked my firemen/EMT friends to check with their colleagues on the subject rather than risk my own limited experience being wrong.
When I can get environmentally neutral CO2 for free half a block off my commute, I’ll consider the pros and cons of CO2 inflation.
We probably won’t take advantage of nitrogen increasing our tire body life from 2 retreads to 4 retreads like truckers do, but as I noted upthread “I don’t think it makes sense to pay an extra $200 or more for a set of premium quality tires (and the subsequent safety and peace of mind they provide) only to cheap out on a few dollars of N2 (presuming you’re unable to find it for free), fill them with air and slowly degrade them to the quality of cheap Chinese rubber before they wear out.”
2.2 isn’t 62.9% of 3.5?
As I noted upthread (in reply to your own post) “It’s not magic, of course they have to be filled correctly and regularly checked for pressure (they just get slightly better gas mileage between checks).”
You’ll get slightly better mileage, safety and tire life if you check them weekly, or at least twice a month, especially with air’s faster leak down rate.
You’re certainly entitled to your opinion and if you can adequately refute the dozen or more sources I provided that claim differently (from tire industry and university papers to government reports and double blind, 110 million tire mile studies), you’ll probably even change my opinion. Like I said, “…that’s why I come here, to sort the bogus from the bona fide.”
Hum. Here are what other folks in the thread have said:
I agree with penumbrage here: for a correctly mounted and undamaged tire, permeation through the tire structure is the main source of pressure reduction. Although that leakage is small, for some definitions of small, it’s not negligible. postpic200’s CR cite says about 3.5psi per year, which seems ballpark reasonable. I’d like to see a cite that this tire leakage “comes from either an incomplete seal at the bead seat, incomplete seal at the valve stem joint, or leakage through a defective Schrader valve, not due to permeability through the tire body.”
In fact, do a back-of-the-envelope calculation on tire permeation. Assuming a 1mm butyl innerliner and roughly guesstimating tire dimensions, I get a yearly permeation rate close to the measured CR rate. Or, as a general example, these folks at Exxon-Mobil seem to think that changing innerliner formulation has a substantial effect on pressure loss rates–not at all what you’d expect if sealing ot the rim or stem was the promary loss pathway.
What, exactly, is your claim, and how does it differ from postpic200’s statement that “there is a only a very small benefit for the average driver”? I actually went through the calculations for the cost of gas I’d save, driving 30,000 miles per year and refilling my tires quarterly, if I switched to nitrogen. It’s about $2.00 per year. That’s a pretty small benefit, and a negative one at that if I pay any extra at all for nitrogen inflation.
I’ll grant that nitrogen inflation improves rubber life, but what does that mean for me? I replace my tires every couple years or so anyway. Translate reduction in oxidation of rubber into something meaningful in terms of cost or safety, because right now that sounds like a very small benefit for the average driver to me.
That does sound reasonable to me. 3.5 psi per year = 0.29 psi per month. My gauge, one of those standard sliding stick pressure gauges, has tick marks every 2 psi. 0.3 psi is not going to show up very well. After 3 months, that is 0.875 psi, which is still fairly small with respect to the scale. After 6 months (1.75 psi), I might notice the reading is a bit lower than I left it.
“…To be fair in my update, however, I’ll have to add increased tire pressure monitoring sensor reliability …“
TPMS doesn’t really care if the pressure is from air or nitrogen, it only measures pressure, the sensors are designed to be in plain old air and most of the faults from the sensor are from the batteries going dead.
“…releasing a pressurized burst of explosive gasses…”
A tire for a 15-inch wheel measures approximately 26 inches in outside diameter and 9 inches in width needs about 4.8 cubic feet of air at standard pressure. That would mean there is about 1 cubic foot of oxygen in a tire. Assuming instead of nitrogen you filled it with acetylene and oxygen. Acetylene has about 1470 btu’s per cubic foot, and lets say you filled the tire and that we managed to get 5 cubic feet of energy into the tire That would give you 7350 btus of energy. So how much explosive gasses could a degrading tire produce from the inside of it? Not much so that’s not a worry.
“…We probably won’t take advantage of nitrogen increasing our tire body life from 2 retreads to 4 retreads like truckers do…”
But even they can’t run some types of retreads on their steering axel the kind they can run on their steering axel have a shorter body life. But when was the last time you even saw a retreaded tire on a car? Once a tire hits 10 years old, it’s wore out, even if there is a ton of tread left. My classic car friends make a point of checking the date on the tires they buy. Some of them are odd ball sizes and it’s not that unusually to see a new tire that is over 10 years old. They won’t put it their car because the rubber isn’t safe anymore.
“2.2 isn’t 62.9% of 3.5?” and “As I noted upthread (in reply to your own post) “It’s not magic, of course they have to be filled correctly and regularly checked for pressure (they just get slightly better gas mileage between checks).”
The point was that the people start to think “I don’t to worry about my tires because I have nitrogen in them so they won’t lose air.” Or they will start checking them less and less. What do you think TPMS are going to be standard and required on new cars? Because people are already terrible at checking tire and nitrogen give them one more bad reason not to check them.
“You’ll get slightly better mileage,…”
Really, can you explain why nitrogen would give anyone better mileage, assuming they check their tire pressure monthly?
I can understand why big trucking firms would use nitrogen, first who checks trailer tires? The drivers don’t own them, and other than the thump test, they really don’t check trailer tire pressure. So if a trucking firm can keep them full longer they save money. But just because a big trucking firm uses it doesn’t mean you’ll see any real benefit. It all about scale, you might save $0.001 per mile and if you drive 12,000 a year you saved $12, no much but if you’re running 10,000 trucks a 120,000 a year, it adds up. (the thumb test is when you use a small bat or rod and hit the tire, the harder it bounces back the more air is in the tire)
Once again a small benefit for the average drive, and again if it cost a buck or two I’d probably use it.
Even if you managed a 1% increase in fuel mileage how much money would you save. Assuming your car manages 30 MPG a 1% increase would mean you are now getting 30.3 MPG over 12,000 miles you’d use 4 gallons less fuel for a saving of $16 at $4 per gallon. So if it cost more than $4 a tire to fill them with nitrogen (the prices I’ve seen run from $3 to $10 a tire) you are losing money.
If you check them weekly, you’ll likely lose more air getting the gauge seated than you will from leak down. As irishman noted, few tire gauges have granualarity better than one psi and even fewer are accurate to that level.
If the bead seals well and the valve is good, pressure variation is entirely controlled by ambient temperature. If either the bead or valve is not optimum, or you have a puncture, it won’t matter what the tire is filled with.
I agree with weekly pressure checks, but only because they will reveal a slow leak due to puncture. If nitrogen fills become free, I’m on board. Otherwise, I’ll stick with what comes out of the compressor.
Both the talking digital gauge my wife bought me (for blind drivers I suppose) and my old $12 digital gauge have a resolution of 0.5psi and are within 2psi of Costco’s calibrated gauge. Digitals are much more repeatable (even if you have to compensate a psi or two) and only use a tiny sip of air since they don’t have to push a piston out an inch.
My original point was, with all the slight and moderate advantages N2 inflation has compared to hydrous air (assuming reducing rubber degradation by half at any point in the tire life cycle doesn’t qualify as a significant advantage) that it wasn’t a hard call to pay less for my top quality tires at my local Costco where the nitrogen purge/fill and lifetime top offs were free.
If some newly developed rubber technology cut your chances of having a blowout in half (while still driving on your very favorite tires), would you pay a couple more bucks a tire (or shop wisely and get them for the same price) to take advantage of it?
The tire innerliners are ‘designed to be in plain old air’, yet they work much better in N2.
While most failures are electronic (10 year batteries that last 2 or wheel impacts exceeding the rated PCB/component G loads), the water vapor in air (when frozen) causes false low pressure alerts that are eliminated with N2 and the sensor element is protected from the highly reactive oxygen in the air by a very thin synthetic rubber diaphragm which O2 degrades and permeates.
As I noted upthread, my firemen friends report car fire tire failures that go BOOM, send trim pieces flying and distort wheel well sheet metal - most likely pinhole sidewall failures that allow ignition propagation inside the partial containment of the tire where the unavoidable combustible gasses (you did watch the welding demo I linked to upthread didn’t you?) are premixed and preheated with the entirely avoidable oxygen from air inflation.
Although I said we probably won’t be using them, passenger car retreads are making a comeback with the environmentally conscious due to improved safety technology and using less than a third of the oil a new tire takes - as oil prices inevitably climb we could be back to the 1 in 5 ratio of the 1970’s soon.
I wouldn’t trust a 10 year old tire, even one that’s been N2 filled it’s entire life and has twice the rubber strength of an air inflated one.
TPMS has been required in the US since 2007 and is much more misleading as people assume they don’t have to check pressure at all (see upthread) when the system only warns of dangerously low tires, not inefficiently low tires. At least with N2 you really can check them 2/3 as often with no sacrifice in gas mileage, safety or tire life (or check them just as often with slight improvements).
The smart, informed folks will still check pressures and (at the risk of inciting Cecil’s ire for undermining the The Straight Dope’s stated purpose) while you can often remedy uninformed, “You can’t fix stupid.”
Because tire inflation nitrogen is an oddly specific hallucinogen that subtly warps the mind of anyone who scientifically analyzes it or does any real world testing on it, universally resulting in a distorted perception of improved efficiency (no doubt due to a Darwinian survival adaptation).
I’m sure this can be the only rational explanation as to why you can’t find any sources to support your contention that it’s no better than air.
The truckers I know (even if they don’t buy their own fuel) check pressures regularly since it means the difference between big black stripes in their lane and jackknifing in a panic stop.
$12 times 250 million US cars (ignoring the thousands of tons of pollutants and the 2 – 3% gas mileage improvement most studies show) is 3 billion dollars, do you own stock in OPEC or will gas have to be $15 ?
A whole laundry list of slight to moderate benefits, and if you got it for free it would obviously be a no-brainer.
"Because tire inflation nitrogen is an oddly specific hallucinogen that subtly warps the mind of anyone who scientifically analyzes it or does any real world testing on it, universally resulting in a distorted perception of improved efficiency (no doubt due to a Darwinian survival adaptation).
I’m sure this can be the only rational explanation as to why you can’t find any sources to support your contention that it’s no better than air. "
ALL the studies I’ve read the improvement is because you lose pressure more slowly, not because nitrogen has some magical proprieties. You get no better mileage with properly air filled tire then a nitrogen filled one.
If you think about it according to your numbers the amount of nitrogen is increasing in MY tires every time I top them off with plain old air. Think about it according to your number nitrogen leaks out at 1/3 the rate, so 2/3 of the pressure I lost was oxygen and other gasses and only 1/3 of it was nitrogen. So over time the amount of nitrogen in my tires increases over time. So say (to keep it simple) it takes 5 cf to fill a tire to 30 psi and that 1 psi = .167 cf. When I fill my tire for the first time my tire has 78% nitrogen and 22% oxygen and other gasses. My tire loses 1 pound .167 cf, of that .130 cf would normally be nitrogen but we know nitrogen leaks out at one third the rate so of the “air” I lost only .043 cf of nitrogen (.130/3) that means of the .167 cf lost .124 cf was oxygen and other gases. But when I fill my tire I’m replace it with air that contains 78% nitrogen. After I topped off my tire I would have about 79% nitrogen so over time the amount of nitrogen would increase. In the studies I’ve read you reach a balance at right about 92.5% nitrogen. Like I said we beat nitrogen to death on my other board.
“The truckers I know (even if they don’t buy their own fuel) check pressures regularly since it means the difference between big black stripes in their lane and jackknifing in a panic stop.
$12 times 250 million US cars (ignoring the thousands of tons of pollutants and the 2 – 3% gas mileage improvement most studies show) is 3 billion dollars, do you own stock in OPEC or will gas have to be $15 ?”
My dad was a truck driver for 30+ years, and in the many trips I’ve been with him, I NEVER saw a truck driver do more than a thump test on trailer tires, they were more careful on the tractor tires but even then it was generally the thump test. Only a few times did I see a driver check his tires with a gauge. They would have the tractor tired check when they changed oil. And using the upper number of the “increase” the average driver would save $36 a years, and if you only pay $3 per tire to fill it or $12 the average driver would only save $14 or a little more than a buck a month the first year, and assuming you got refills for free, $3 bucks a month until the tires wore out (assuming you never got a flat). That last part is really funny, no I don’t own stock in OPEC, nobody can. OPEC is not a public company. And MY car already gets over 40 MPG. We are talking about the advantages of nitrogen, and as I have pointed out the benefit to the average drive is minimal. It basically depends on how much you paid for the nitrogen, free sure, $10 a tire no thank you.
I might. Does filling with nitrogen cut my chances of having a blowout in half?
There’s a *Consumer Reports *cite upthread that gives avereage tire pressure loss of 3.5 psi per year, which is 0.3 psi per month. According to you, pressure gauges you’ve used are precise to within 0.5 psi (and accurate to only 2 psi or so). If the inaccuracy of your *initial *pressurization is greater than any potential *loss *of pressurization over the measurement period, I think it’s fair to say that nitrogen is no better than air at keeping tires inflated (given postpic’s check interval caveat).
The equalization due to O2 partial pressure slows down logarithmically and takes years to hit the sweet spot. I’d rather my tires rotted at the slowest possible rate right from day one.
I paid extra to get the highest rated tires that would fit my vehicle, it wouldn’t be cost effective to do burnouts, run them underinflated, curb them, fill them with air or otherwise intentionally shorten their useful life span.
OPEC is more universally understood to mean foreign oil interests that have us over a barrel (no pun intended), would you have known what I meant if I’d said NIOC or ARAMCO?
I couldn’t say what the exact odds are but slowing sidewall aging would certainly reduce your chances. Refer back to the sources I provided for Mithras in post #60, all those studies and papers address rubber degradation and tire aging from oxygen migration. This pdf has summaries of several of those studies including oxygen migration at different N2 purity levels and total lifetime O2 flow data (http://www.branick.com/uploads/NitrogenInflationforPassengerCarandLightTruckTires-Daws.pdf).
I don’t care what my gauge offset is as long as I know the amount (with an immediate read after a calibrated top off) and it’s repeatable. I always overfill slightly and use multiple reads to slowly drop pressure until my desired value first appears and since the digital uses so little gas (15 reads or so to drop 0.5psi) I’m confident that the tire is within 0.1psi of ideal.
In the Drexan/Harris 110 million tire mile study (Nitrogen Tire Inflation in a Long Haul Trucking Fleet, Konrad Mech / Drexan Corporation / Harris Transport 2007) the author expresses his surprise that the fuel efficiency of the nitrogen inflated equipment increased by 3.3 percent in spite of the double blind methodology aggressively maintaining correct pressure in the air filled tires. It would seem that premature aging of the sidewall rubber has a measurable effect on rolling resistance.
That’s nice. However, recall my original question:
I’m already granting that nitrogen inflation improves rubber life. What I’m asking is what is the actual reduction in blowout risk? If slowing sidewall aging certainly reduces the chances of a blowout then you should be able to demonstrate how much. Right now you haven’t show that there’s a connection at all.
Again, that’s nice. In what way does this give you better mileage with nitrogen compared to air? My point above is that monthly tire pressure losses are in the range of inflation accuracy, which is true of both you and typical drivers. Pressure changes due to temperature are also more significant than the pressure difference due to nitrogen filling.
And, now that I think about it, here’s a question for you: your tire-pressure checking routine seems pretty thorough. How *often *do you check your tire pressure? Given that, how much better fuel economy do you think you’re getting?
First of all, trucks are different than cars. One would expect rolling resistance to be a higher proportion of losses in a truck. Second, the authors give no definition of the “aggressive” pressure maintainance schedule. Were tires checked monthly? Quarterly? Yearly? Third, although the author refers to a decrease in aging, I can’t find where he states that “premature aging of the sidewall rubber has a measurable effect on rolling resistance.”
Finally, I think most people in this thread agree that using nitrogen in a truck fleet application; where tire, fuel, and maintainance costs are high; could very well make sense. The problem is converting this to passenger cars. Again, how does anything you claim differ from postpic200’s statement that “there is a only a very small benefit for the average driver”?