http://autozine.kyul.net/techn...1.htm
This is very good!
The Truth About Handling
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Q45tech
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Unfortunately he is still promalgating the [WRONG] idea that wider tires have more contact patch AREA..........the patch is wider but comenserately shorter so equal weight loaded, equal psi tires always have the same area.
Of course since rear sideways sliding is nice to control in a RWD car........wider is better in this application.
Of course since rear sideways sliding is nice to control in a RWD car........wider is better in this application.
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Q45tech
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The 33 psi inflation pressure means you have 33 psi per square inch of tread ALSO.
People don't seeem to understand how many square inches of tread they have...........all you have to do is weigh the load on each tire...........ur calculate it from the real loaded weight and weight distribution ratio.
People don't seeem to understand how many square inches of tread they have...........all you have to do is weigh the load on each tire...........ur calculate it from the real loaded weight and weight distribution ratio.
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Q45tech
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Duh! watch the contact patch change as you slowly lift the car up. Ink the tire and use different sheets of paper to show you [the tread] as you change the weight on the tire lowering the car [incrementally] to the paper/ground.
Take all the ink contact drawings and measure the area of each................you will need a scale to measure the load under the paper as the tire takes more and more weight.Boyle's Gas Law states that the pressure must be equal everywhere not just the rim.........do the experiment with a ballon and a triple beam drug scale.
I just don't understand how people can believe - obviously they didn't pay attention in College Physics and advanced mathematics and Solid Geometry.
This is why I have so much trouble getting Automotive Engineers to forums such as this. They get fustrated with the education level of most users........trying to debunk common myths and explain how Physics works - takes all their time.
Take all the ink contact drawings and measure the area of each................you will need a scale to measure the load under the paper as the tire takes more and more weight.Boyle's Gas Law states that the pressure must be equal everywhere not just the rim.........do the experiment with a ballon and a triple beam drug scale.
I just don't understand how people can believe - obviously they didn't pay attention in College Physics and advanced mathematics and Solid Geometry.
This is why I have so much trouble getting Automotive Engineers to forums such as this. They get fustrated with the education level of most users........trying to debunk common myths and explain how Physics works - takes all their time.
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s13sr20chris
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s13sr20chris
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Q45tech
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The question is one of instantaneous grip [1 second] vs sustained grip [road race where multiple curves keep adding heat to tire.........quickly overheating the rubber compound and exceeding the ideal temperature for max friction.
Another variable is the tread pattern [the so called void ratio] which by definition to voidier in all season tires vs summer vs slicks [which are all tread no voids].The voids don't add to the contact patch only the square inches of rubber in actual molecular contact with the road surface.
There are smooth roads and high void asphalt [high drainage rough] roads, so each tire may react friction wise differently on different road surfaces. Why all friction specs are given as a range not an absolute number plus they vary with tire and road temperatures.
Ever notice that some car test show right and left turn differences in handling [g %].....the drivers weight to one side and slight differences in alignment.........why the Q battery, alternator, ABS, and compressor is on the passsenger side to try to offset the divers weight to some degree.
Another variable is the tread pattern [the so called void ratio] which by definition to voidier in all season tires vs summer vs slicks [which are all tread no voids].The voids don't add to the contact patch only the square inches of rubber in actual molecular contact with the road surface.
There are smooth roads and high void asphalt [high drainage rough] roads, so each tire may react friction wise differently on different road surfaces. Why all friction specs are given as a range not an absolute number plus they vary with tire and road temperatures.
Ever notice that some car test show right and left turn differences in handling [g %].....the drivers weight to one side and slight differences in alignment.........why the Q battery, alternator, ABS, and compressor is on the passsenger side to try to offset the divers weight to some degree.
there is some really interesting stuff in the new issue of "racecar engineering" concerning tires and optimum temperatures for avrious grip and slip planes.
much of it is actually counter-intuitive, and contradicts some of the classic traction models.
especially, it is presented that the optimum tire temperature is fairly low (below the temp at lowest load peak force)
it sort of brings together the temperature gradients of a dynamic system with the classic steady-state traction models.
also claims that wide tires give more traction in all cases...
very cool.
much of it is actually counter-intuitive, and contradicts some of the classic traction models.
especially, it is presented that the optimum tire temperature is fairly low (below the temp at lowest load peak force)
it sort of brings together the temperature gradients of a dynamic system with the classic steady-state traction models.
also claims that wide tires give more traction in all cases...
very cool.
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Q45tech
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"wide tires give more traction in all cases..." they surely do in slipping sideways...........unfortunately there are significant differences in racing tires and street tires designed for more than a few days use.A street tire with 8,000 miles on it is so significantly different than the tire brand new because of ozone/oxygen and the interreaction of the heat cycle.Once tires get above 160F the vulcanization continues at an accelerated pace.........owners don't understand how hot tires get internally.
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Mayhem_J30
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Which street tire on which car ? Sizes mean very little [other than the load rating]. Load rating may have a correlation with tread temperature in that stronger may mean better. Different manufactures have different tread widths in the same size. Also tread void ratios vary with different tread designs.
The problem is 245 vs 255 may require a different wheel width for optimum loading......the 255 wheel may be heavier negating any gain by the wider tire.Obviously the less load a tire has [in relation to its max load] the lower the slip angles will be for a given load. Thus the higher its G capability.........why higher load index tires can handle better.
Some test by Pirelli say that you divide the increase in load index pounds by 2.5 to get a rough percentage of increase. Say a 1640 vs 1521 is 7.8%/2.5=3%........ the increase in G measured something like 0.75>0.7725G from going up from a 215/65 to a 235/60 or in 16" a 245 vs a 255.
There are a half a dozen specs tire manufacturers never releash [even to the Government] these [trade secrets] are the ones one needs to determine how a tire will behave.
Independent rear suspensions are not best for drag racing where solid axles shine........not sure you can compare cars with different rear suspensions.
Nissan tried to compensate for IRS by installing LSD to help with launch. But the viscous LSD is no where as good as a mechanical locking LSD for drag racing.
The problem is 245 vs 255 may require a different wheel width for optimum loading......the 255 wheel may be heavier negating any gain by the wider tire.Obviously the less load a tire has [in relation to its max load] the lower the slip angles will be for a given load. Thus the higher its G capability.........why higher load index tires can handle better.
Some test by Pirelli say that you divide the increase in load index pounds by 2.5 to get a rough percentage of increase. Say a 1640 vs 1521 is 7.8%/2.5=3%........ the increase in G measured something like 0.75>0.7725G from going up from a 215/65 to a 235/60 or in 16" a 245 vs a 255.
There are a half a dozen specs tire manufacturers never releash [even to the Government] these [trade secrets] are the ones one needs to determine how a tire will behave.
Independent rear suspensions are not best for drag racing where solid axles shine........not sure you can compare cars with different rear suspensions.
Nissan tried to compensate for IRS by installing LSD to help with launch. But the viscous LSD is no where as good as a mechanical locking LSD for drag racing.
Everything in the post above addresses the cold facts and theories of tire performance and Q45Tech nails it pretty much across the board. However, for most of us, the straight numbers do not directly correlate to the one item most of us care about. How much confidence can we have in our car's handling characteristics, or "how does it feel?"
All tires slip while generating cornering forces. When the forces get large, some tires need larger slip angles to generate a given cornering force. For most of us, the larger the slip angle, the less confidence we have that the car is doing what we tell it. A large slip angle means the car is not moving in the direction the tires are pointing. Steering gets lighter, your buttmeter registers "odd" feelings, and you instinctively lift off the throttle.
Basic rules of thumb: Wider tires = smaller slip angles Stiffer sidewalls = smaller slip angles (Not necessarily shorter sidewalls) Warmed up tires = smaller slip angles (cold tires = big slip angles and overheated tires = really big slip angles) Less tread voids = smaller slip angles Stickier compounds = smaller slip angles
The last rule: If the tire works great on another type of car, it won't work on yours.
I suspect that maybe 1 out of 10 of us Q owners will ever consistently get anywhere near these limits. I think we should pay much more attention to braking performance. That is a completely different set of rules.
All tires slip while generating cornering forces. When the forces get large, some tires need larger slip angles to generate a given cornering force. For most of us, the larger the slip angle, the less confidence we have that the car is doing what we tell it. A large slip angle means the car is not moving in the direction the tires are pointing. Steering gets lighter, your buttmeter registers "odd" feelings, and you instinctively lift off the throttle.
Basic rules of thumb: Wider tires = smaller slip angles Stiffer sidewalls = smaller slip angles (Not necessarily shorter sidewalls) Warmed up tires = smaller slip angles (cold tires = big slip angles and overheated tires = really big slip angles) Less tread voids = smaller slip angles Stickier compounds = smaller slip angles
The last rule: If the tire works great on another type of car, it won't work on yours.
I suspect that maybe 1 out of 10 of us Q owners will ever consistently get anywhere near these limits. I think we should pay much more attention to braking performance. That is a completely different set of rules.
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Q45tech
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1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
It is truely amazing how Q owners turn a car that could once stop in 129 feet into one that is lucky to stop in 175 feet [maybe 190 feet with bling bling wheels] on a good day. Worse they tell everyone how great their brakes are till they rearend some newer car........with plain old oem tires and pads.
I put a note on the dash to remind me every morning that even with great [ high reserve] pads my Michelins are much harder than the oem tires.........why I use extra soft front AVS in Summer when I might get frisky or drive 85 mph in traffic.
I put a note on the dash to remind me every morning that even with great [ high reserve] pads my Michelins are much harder than the oem tires.........why I use extra soft front AVS in Summer when I might get frisky or drive 85 mph in traffic.