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Old 02-02-2008, 09:03 PM   #21 (permalink)
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If you have access to 200 psi compressed air, you might be right.

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Old 02-03-2008, 02:14 AM   #22 (permalink)
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Blackbird great thread. A lot of interest. Personally i have never had any trouble with narrow tires in poor traction situations only wide tires. IMHO wide tires injure more people than narrow tires. The more warning the tire gives, the safer the tire. Wide tires are great in ideal conditions. Wide tires have their uses don't get me wrong, i run 275 Hoosier rains on my vette. But when it comes to moddin', i like to find the outer limits and then worry about the details later. That's what i like about this site the name economodder rather than econostocker.
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Old 02-03-2008, 12:59 PM   #23 (permalink)
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DPOV -
I'm very sorry to hear abot your friend .
I agree with you (and I'm sure all of us will) that a lot of accidents out there happen because people don't maintain their vehicles a they should.
A friend of my sister died just a few months ago when someone decided that applying the parking brake isn't necessary, the car rolled down hill and killed her. Stupid negligence (sp?).

I do however feel that the car's tires, being your only connection with the ground, should not be the right place to reduce the car's fiction from the reasons I listed earlier.
We may agree to disagree on it.

Diesel John -
I'm all up for tinkering with cars in order to improve them and didn't miss the part that says "modder" in the site's name .
There are many ways to improve FE.
Some can be applied to every car in any situation, some can be applied in some situations and some should be applied unless they are in fully controlled enviorment IMHO, which public roads wouldn't qualify as.

Take P&G driving for example, it may work well for someone that drives in a small town area or a place the roads aren't filled with millions of cars, but I have no doubt that you'll be a victim of road rage in no time if you try it here in Los angeles ...

A lot of you mentioned hydroplaning being a problem of wide tires, all of which is true, but I doubt you find hydroplaning a major problem in most of cars that see that folks here drive, as the average tire size on a Metro is about the size of a roll of electrical tape.
I personally never found hydroplaning to be a problem on any tire sized 205 and under as long as it has good tread depth.

Moti
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Old 02-03-2008, 11:59 PM   #24 (permalink)
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Quote:
Originally Posted by Blackbird View Post

Take P&G driving for example, it may work well for someone that drives in a small town area or a place the roads aren't filled with millions of cars, but I have no doubt that you'll be a victim of road rage in no time if you try it here in Los angeles ...
Didn't happen to me I did quite a bit of driving in LA two weeks ago. I was doing quite a bit of anti-traffic driving too, and surprisingly, less people cut in front as compared to Orlando or South Florida. I have no problems with road rage people (I do occasionally have to deal with them) - as soon as they pass (and they will), I dial non emergency police and call in their plate. Tailgaters? Bring on the washer fluid.

Quote:
Originally Posted by Blackbird View Post
A lot of you mentioned hydroplaning being a problem of wide tires, all of which is true, but I doubt you find hydroplaning a major problem in most of cars that see that folks here drive, as the average tire size on a Metro is about the size of a roll of electrical tape.
I personally never found hydroplaning to be a problem on any tire sized 205 and under as long as it has good tread depth.

Moti
Meh - you just didn't have the correct conditions for it I personally call it black water as it's just as unidentifiable as black ice. Freshly paved roads (asphalt) seem to drain water very poorly - add a puddle and it's a mess. You can't see the puddle because the shininess from the rest of the poorly drained road blots it out... This happened to me with 14" 60x215's.

Quote:
Modern day cars are made for driving idiots who are clueless about driving physics.
Everything in this current generation of cars is engineered to save the life of the talentless moron that's driving it.
For god sake, there are cars out there that will activate the brakes on their own accord if the engineer that designed the system think that you went too hot into some corner ...
Would you prefer those features be removed? (Just not quite sure what you're getting at). I personally don't mind these things being there...

Quote:
Some drivers, myself included, who have developed their car control skills by taking performance driving courses and lapping racetracks in a variety of cars for some thousands of miles (I logged well over 10K track miles), know that there situations where applying the throttle will do much better than applying the brakes.
I saw many accidents that could have been prevented altogether had the driver sent his foot to the pedal on the right.
I've also seen (and nearly been in) accidents that happened because the driver freaked and pushed their foot down on whatever pedal was closest (the one on the right ). I have avoided accidents like this by applying throttle (that doesn't change that it's not defensive driving) - but I'm not about to advise the masses about this. In all likelihood - we'll see more accidents because people will go for the closer pedal because they can't make the proper decision.

It's great and all that you've got driving experience on the track - this means you're more aware of how driving technique can change the entire driving dynamic. A similar notion goes for hypermilers - the ones that are changing their driving technique (which is the key defining characteristic of a hypermiler). It seems you don't have any issue with neither of these groups - instead, you have a problem with the aforementioned morons. I tend to agree.

And that said, with all due respect, telling us we have a problem because of our trade off between higher pressure and highly tuned driving techniques seems to be a bit misaligned with where your problem is - the moronic drivers we all have to deal with.
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Old 02-04-2008, 12:41 AM   #25 (permalink)
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Lets understand max.psi sidewall is not overinflation, above and beyond max.psi sidewall is.

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Originally Posted by Blackbird View Post
Understanding the connection between tire size and friction and how it translates into FE, I see why one would think that reducing the friction from the tires would improve FE.
BUT, are those who over inflate their tires or reducing tire width (or reducing the size of the contact patch in any other way) forgetting the purposes of the tires to start with?

Being the only contact of the car with the pavement, I don't think that the tires are the right place to improve gas mileage.
Don't forget if you go past max.psi you'll also wear the tires down the center, there's argument concerning this but I can assure you my GTAS tires run $120 each and I take NO chances.

What good does it do to increase my mpg by 10% if I wear my tires prematurely I get to shell out dang near $600 for a decent set of passenger treads, wth I just threw all that saved money out the window and then some, on top of compromising my ride's safety.

On that note my car calls for 195's and I run 205's, I never compromise traction for mpg.

Then a lot of this is for competition only and there are some who want to re-invent the wheel but I'm with you 100%, don't believe all the hype.

btw max.psi sidewall is the correct inflation.

Use yer noggin'
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Old 02-04-2008, 12:54 AM   #26 (permalink)
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8307c4, instead of implying that people exceeding the maximum sidewall aren't using their noggin, why not use yours' by encouraging them to test this on their tires thereby spending their money if they're wrong and their tires wear out prematurely.

If you can't go by the door plate, why should the sidewall be any different? You can excuse yourself from doing this experiment but please don't trivialize it by labeling it as hype.
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Old 02-04-2008, 01:00 AM   #27 (permalink)
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Quote:
Originally Posted by 8307c4 View Post

What good does it do to increase my mpg by 10% if I wear my tires prematurely
Not sure what good it is... But, by design, my tires have yet to wear out prematurely, unevenly, or have any of the aforementioned anomalies I'm running 55/50 (front/rear)
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Old 02-04-2008, 11:50 PM   #28 (permalink)
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Blackbird -

Quote:
...
I do however feel that the car's tires, being your only connection with the ground, should not be the right place to reduce the car's fiction from the reasons I listed earlier.

We may agree to disagree on it.

...
I understand your concern and I agree with being "cautious first". I am not going to talk about the contact patch issue for the moment because I think I would need to do more research on that.

Instead, I am going to talk about the load specifications of the tire. Here is my tire :

Continental ContiProContact
http://www.tirerack.com/tires/Spec.j...rtnum=965HR5CP

The load index is 91, which means each tire can support up to 1356 lbs. The speed rating is "H", which means the tires are good up to 130 MPH. I got these tires because they have the highest max PSI rating (51) available for my car and have an "LRR Pedigree" in independent tire testing.

What does this mean from my POV? This means that the tires are rated for the following maximum loads :

51 PSI @ 130 MPH @ 5424 lbs

The 5424 lbs is because each of the four tires are rated at 1356 lbs, so 4*1356 = 5424 lbs. Now, my car is placing the following loads on my tires :

2806 lbs / 5424 lbs = 0.5175 => 52% of maximum weight load.
I added about 350 lbs to include myself, one passenger, and crap.

80 MPH / 130 MPH = 0.6154 => 0.62% of maximum load.
Now, I never hit anywhere near 80 MPH, but I want to show the upper limit of how fast I would be willing to push the car if I was forced to.

From the above, it is my opinion that I am operating well within the "maximum load" of the tire. I am conservative in the sense that I am running at 51 PSI, the maximum rating for the tire. However, because I know that my other loads on the tire are at or below 60%, I don't think I would have a problem upping the pressure to 60 PSI.

CarloSW2
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Old 02-05-2008, 12:57 AM   #29 (permalink)
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so am I suposed to go by the door plate, the owners manual, or the max side wall presure? my door plate says 34psi, my manual says 34psi UNLESS I'm going over 55mph and if I'm driving on the highway to increas my tire presure by 4psi, now my old tires had a side wall max presure of 36psi, my current tires are 51psi, and I check my tread depth every time I rotate tires, and tred wear is well within reason as far as uneven wear is concerned for the last 30,000 miles, so those steel belts seem to be doing their job.
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Old 02-05-2008, 07:21 AM   #30 (permalink)
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I just want to try and clarify a few misconceptions about car tires and friction. When you increase the psi of the car's tires the mpg increase is not from less friction with the road, it is from less deformation of the tyre. Rolling resistance and road friction are two separate things. As the tyre comes in contact with the road a section deforms to become flat against the road. As the tyre rolls away the rubber returns to its original shape. This compressing and expanding of the tyre creates heat which wastes energy. This can be reduced by higher pressures. The other part of rolling resistance is adhesion forces where the tyre sticks to the road and is then peeled off. Adhesion is more directly related to grip but is more a function of the tyre compound than the pressure. The reason wider tyres are reported to have more grip is because the wider contact patch gives more surface area for the tyre to cool down in high performance situations, i.e. situations where grip is lost due to temperature. This seems to be the source of the myth that a bigger contact area gives greater friction. The maximum grip of tyres before skidding is proportional the coefficient of static friction (i.e. for rubber on concrete it is 1.0) times the reaction force in newtons. A quote from my university Physics textbook "Physics for Scientists and Engineers" by Serway, Jewett:
Quote:
The coefficients of friction are nearly independent of the area of contact between the surfaces. We might expect that placing an object on the side having the most area would increase the friction force. While this provides more points in contact... the weight of the object is spread out over a larger area so the individual points are not pressed so tightly together. These effects approximately compensate for each other, so that the friction force is independent of the area.
I'm not trying to sound like an expert or anything I just wanted to clear up some myths being thrown around.

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