edited to protect the company and individual identity:
Dennis, attached you'll find a bit of information that will probably only make you more curious, but it's all that I can put my hands on given the time that I have available. One of the overworked guys at our development headquarters schlepped me a couple of graphs that you should find interesting and hopefully not too frustrating.
As I indicated to you earlier, we don't have much cornering force characterization data on the xxxxxx X4 if you consider all the sizes in the tire line. The tires characterized in the graphs are the 205/55-16 size, the 225/60-16 size, and the 235/60-16 size. From the similarity in the graphs, you get an idea of the "character" of a typical xxxxxxxx X4, no matter what the size.
The top graph in the attachment is cornering stiffness versus vertical load. The data is generated on a flat-track cornering force machine, and the data portrayed here is based on zero degrees camber and caster (a common standard). We frequently refer to these kinds of plots as "Pacejka curves" since they're generated from the Pacejka coefficients determined from the data acquired from the flat-track machine. Think of cornering stiffness as a kind of "lateral force spring rate." It's literally the initial slope (at zero slip angle) of the curve of lateral force versus slip angle for a given vertical load. XXXXXXXXX tirenerds pay a lot of attention to these kinds of curves because, over time, we've learned something about how to anticipate the steady-state handling behavior of a tire-vehicle combination by interpreting the shape of the curves. The first thing to note is how basically similar all these curves are although the tire sizes vary significantly. This says something about the "character" of XXXXXXX H4; it's a "signature" for the tire line that is determined by the tread pattern, the stiffness of the tread compound used, the type of angled-ply composite used to reinforce the crown of the tire, the pneumatic and structural stiffness components of the tire design, and so on.
A second interesting thing to note within the family of tire sizes on the "Pacejka plot" is how the 205/55-16 size differs from the two 60-series 16" tires. You'll note that the 55-series tire has a somewhat "straighter" curve. We would interpret this shape to indicate--all other things being equal--that the 205/55-16 size has a tendency to be relatively more efficient at higher loads than at lower vertical loads. This is an effect that is typical. Lower aspect ratio tires tend to produce "straighter" curves than higher aspect ratio tires. This kind of cornering force behavior would, for example, tend to reduce the understeer tendencies of a vehicle that would characteristically transfer a significant amount of its static load to its outside front tire in heavy cornering--all other things being equal. You may recall my experiences with my wife's Q45 in moving from the OE 215/65-15 size to a 235/45-18 or 245/45-18 solution. As expected, I observed just this sort of evolution in the car's handling behavior.
A "rounder" Pacejka plot would tend to suggest the opposite tendency (an increase in steady-state understeer for such a vehicle). The trick is to balance this steady-state balance with good transitional handling characteristics. For example, you wouldn't want to have a tire solution whose efficiency at the front axle environment (relative to the back-axle environment) was such that you couldn't attempt an emergency lane-change without looping the car.
The "straightness" and "roundness" can be affected substantially by inflation pressure, with lower pressures tending to "round" the curves (more efficient at lower loads), and higher pressures tending to "straighten" the curves (more efficient at higher loads). That's why tuning the inflation pressure to the expected load-transfer behavior at each axle is such a good idea. If you know the characteristic behavior of the car and tire, you can dial in the combination quite nicely. Unfortunately, because of the need to respect all kinds of regulatory requirements, many car manufacturers choose a single inflation pressure for each axle--even though it's not optimized for each axle--just to keep things simple. Companies like XXX, however--just as an example--recognize and place a lot of stock in the tire/vehicle marriage, and will have inflation pressure recommendations as a function of load and speed for their various car models.
The second plot is a simple plot of lateral force (or cornering force, if you wish) versus slip angle for a given load (5000N in this case--and by the way, the "2.4" in the plots refers to 2.4 bars, or 35psi, for the test inflation pressure). As expected, just because they're bigger and fatter, the 235/60-16 and 225/60-16 tend to generate more sheer "grunt" than the little 205/55-16 at the given 5000N vertical load. That's what you'd expect.
Dennis, I'll be honest with you and tell you that I typically don't have the opportunity to spend too much time on these sorts of exchanges (especially at a rate of right around 100 e-mails/day plus my real job). This is gonna have to be about it, bro'. Unfortunately, the tirenerds at our R&D center don't have readily available the data on your Q45-specific sizes, nor have we provided any relevant data from similar tires from other companies. We can't typically share that kind of comparison data anyway, since it's for internal use and not "third-party validated." Our legal eagles get pretty constipated about that, and rightfully so. I hope that you'll understand.
In responding (at least in part) to your inquiries, I've just wanted to at least give you a feeling that we really do look at this stuff carefully. We don't just fling a bunch of different solutions at car manufacturers when we're involved in OE programs, and we don't just arbitrarily decide the performance characteristics for tire line families or even individual sizes within those lines when we're developing replacement-market-only products. While any family of tires from a given tire company will have "stronger" and "weaker" sizes within the line, we at XXXXXXXX attempt to seek out and destroy the "dogs" before they get into the hands of knowledgeable enthusiasts such as yourself. That's why, typically, the experience that the owner of an M5 with XXXXXXX XXXXX will be similar to, but not exactly like (because of the car, of course), the experience of an owner of a G35 Coupe with completely different tire sizes in the XXXXX XXXXX line. You will notice (I hope) similar overall "character" from the 215/65-15 and 235/60-15 solutions on the first-gen Q45 to that which you would note with other XXXXX XXXXXX XX sizes on other cars"
This guy may kill me but just wanted members to know I spend every day thinking about your problems plus this email was so precise and well written. Once published on the web it get achived in search engines forever.Can't publish the graphs.as they seem to be taylored for my 90Q front static weight........the overworked tire nerd back at the lab must have created them.
Tires
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Q45tech
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- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
The question concerned the 255/50/16 size vs the 235/60/15. NON STANDARD Q SIZES.DATA on the 215/65/15 but I new use that size.What is the difference in cornering stiffness vs load? What will the difference be in slip angle at x load.
The CRAY super computer is crunching as we speak.
Not every tire in every size is tested to the depth necessary to answer my question, but 3 given tires can be used to reverse engineer Pacejka coefficients .
He gave me everything I need to solve it, just have to work at it.Kind of an intelligence test to see if I am worthy of continued help.
The answer will be ~~ 1700 N/degree Vs. 1620 N per degree with an 8.5 KiloNewton load.
What is the maximum theorectical G handling possible in a 90Q at x camber and z caster on y [mu] road surface.The limiting factor is the weight on the front tires, the ambient temperature and load index.How much incremental improvement can be expected from increasing load index from 95V/H to 98 V/H at 35 psi [>7%]......my theory is that at 8.5 kiloNewtons that 35% of the difference can be gained [119x 0.35=~~42 lbs..........0.023G improvement with 0.8 degree less slip angle.
Real world conditions always defeat mathematics because the models are not perfect.
245/50/16 vs 255/50/16 have the same 95 vs 98 load index ratio vs 215/225-15" vs 235/60/15.
What would really be nice is some 15 vs 16 vs 17 vs 18" in the same load index........then only sidewall height variations.
The CRAY super computer is crunching as we speak.
Not every tire in every size is tested to the depth necessary to answer my question, but 3 given tires can be used to reverse engineer Pacejka coefficients .
He gave me everything I need to solve it, just have to work at it.Kind of an intelligence test to see if I am worthy of continued help.
The answer will be ~~ 1700 N/degree Vs. 1620 N per degree with an 8.5 KiloNewton load.
What is the maximum theorectical G handling possible in a 90Q at x camber and z caster on y [mu] road surface.The limiting factor is the weight on the front tires, the ambient temperature and load index.How much incremental improvement can be expected from increasing load index from 95V/H to 98 V/H at 35 psi [>7%]......my theory is that at 8.5 kiloNewtons that 35% of the difference can be gained [119x 0.35=~~42 lbs..........0.023G improvement with 0.8 degree less slip angle.
Real world conditions always defeat mathematics because the models are not perfect.
245/50/16 vs 255/50/16 have the same 95 vs 98 load index ratio vs 215/225-15" vs 235/60/15.
What would really be nice is some 15 vs 16 vs 17 vs 18" in the same load index........then only sidewall height variations.
