OEM Tires, Optional OEM tires, and totally off-the-wall tires

E Meyer wrote in article ...

...

"The Racing & High-Performance Tire" by Paul Haney

ISBN 0-9646414-2-9

Available through SAE - or directly from Haney at:

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Page 70 and 71 "Load and Internal Pressure"

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I've just answered Mr. Meyer's question.........

When can I expect you to answer the questions I have posed to you?

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  • wrote in article ...

Quote from Page 70, third paragraph down......

"The contact patch area (A) is equal to the vertical force (Fv) in pounds divided by the internal pressure (P) in pounds per square inch."

500 pounds of vertical force (amount of vehicle weight supported by that wheel) divided by 25 p.s.i. inflation pressure equals a 20 square-inch contact patch.

500/25=20

OTOH.....500 pounds of vertical force divided by 40 p.s.i. inflation pressure equals a 12.5 square-inch contact patch.

500/40=12.5

Simple, eh?

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[...]

How much does any of that matter in a passenger car? Really, I can understand worry over those stats with a race car since they tend to push the limits, but in an econo? FWIW, running a tire at a higher pressure will reduce contact area as you have stated over and over, but it will also increase ground pressure. I have seen nothing from you addressing the tradeoff--only an assertion that less area means less traction. And with some conditions, such as water on the road, higher ground pressure is far more valuable than contact area. As long as there is enough pressure to keep the side wall from bulging excessively and the tire isn't grossly above the max pressure printed on it, just about any pressure will do. But running low (as most people do since they don't ever look at their tires until one goes flat) accelerates tire wear. He's not talking about race cars, so tire spring rate, sidewall stiffness, and fancy tire dynos are irrelevant. A pressure gauge and some eyeballs are sufficient.

Reply to
B.B.

Go ahead!

I'll STILL sleep tonight.......

.....and, YOU will avoid answering the questions I have asked you.

Reply to
*

Tire manufacturer "recommendations" are based more on potential litigation than actual applications.

We regularly mount race tires on wider and narrower rims to gain circumferential differences for chassis tuning pruposes.

I have run many, MANY brands of street tires - including Firestone/Bridgestone - on much-wider-than-recommended and much-narrower-than-recommended rims at one time or another - under racing conditions and at racing speeds - with no ill effects.

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*

Ah, but I do drive windy, twisty roads as fast as possible.

Since changing from the 185/70-14s to 185/60-14s, I am able to take the twisties an average of about 6 MPH faster. Also, fuel economy increased about 10%. (Yes, allowing for odometer inaccuracies...the 'course' has been measured with two other cars. now all three agree on mileage...)

But, the point is missed.

My original quandry was this: on the old tires, acceleration was sluggish at best, and often going up very short, steep grades required dropping a gear (usually from 4th to 3rd). It would also mean winding out the engine longer into higher RPMs to get any kind of 'adequate' acceleration, esp for a small, light car with a 145 HP engine.

Now, the car FEELS like a small,light car w/ 145 HP. Acceleration is what I would expect, I reach the 'power band' quicker and can upshift to a higher gear at lower RPMs and still have plenty of grunt, whereas before the car would be wheezing under the same circumstances.

This was REALLY the quandry I was looking to answer...why the car took on completely different characteristics by changing the tires...

Reply to
Hachiroku

This looks like the reference I was seeking. Thanks.

Reply to
E Meyer

Damn, Sam, if you're such an expert, you should know what I'm talking about!

Reply to
Hachiroku

Um, the way the car responds?!

I used to test aircraft components, spacesuits, and do Underwriter's Lab testing. Trying different sized tires isn't Rocket Science...

Yeah. It ain't too hard to figure out...

Reply to
Hachiroku $B%O%A%m%/(B

I doubt if your local library has a copy of this book, but if your local college/university participates in the "Formula SAE", it's a safe bet that there is one on campus somewhere.

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*

You are, without a doubt, the MASTER of the non-answer.

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*

More precisely, the question is if YOU know what you're talking about!

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Hachiroku $B%O%A%m%/ wrote in article ...

If it's all so simple, and you have it "figured out", why do you feel compelled to ask about it on an internet group?

Sounds as though its too hard for YOU to figure out with your extensive training and background in tires.

What did you mean by "....a certain percentage of OEM spec....."?

Reply to
*

Your continued use of non-answers is quite telling.

Since you are unwilling - more likely UNABLE - to substantiate or clarify ANY of your statements that I have asked you to substantiate or clarify, I have come to the conclusion that you are a bag of wind - flatulent wind, but wind, nonetheless.

You use buzz words, terms and outrageous statements you found in enthusiast magazines in order to look like you actually know something.......

.....but your actions in ducking questions give you away as a bullschidt artist.

I STILL would like to understand just what you mean by "....a certain percentage of OEM spec...." as it applies to your assessment of tires.

Reply to
*

You don't know what I mean by being within a 'percentage of OEM spec'? Huh? It ain't Rocket Science here. Dooddamath...

Either that, or you're even more clueless than I think you are, no matter how many racing tires you claim to have mounted.

And if you want to continue the insults, exactly *HOW* did you 'mount them', buddy? ;P

Reply to
Hachiroku

And you wasted three responses on the same post.

Reply to
Hachiroku

Perhaps a poorly worded post, and an even more poorly worded response.

I was wondering more about how the characteristics of the car's performance changed.

And you can't figure out what I mean by staying 'within a percentage of OEM spcification'?

Reply to
Hachiroku

...

Okay, I'll play along with your assinine game.....one more time, then I'm gonna' let you troll on........

Exactly what OEM specifications are you talking about? What are you allegedly applying these acceptable percentages to?

Tire size....?

Circumference....?

Cross section....?

Sidewall height....?

Sidewall flex.....?

Tread Squirm....?

Bead concentricity.....?

Carbon black content.....?

Cord material....? (How do you figure a percentage on one fiber versus another?)

Slip angle....?

Coefficient of friction....? (Of course, if you even considered this - and assured yourself that your new tires were within an acceptable percentage of the OEM tires - you wouldn't have had to ask your original questions concerning traction.)

And, where are you coming up with both the OEM specifications and those of the tires you are considering as replacements?

You're a bullschidter.........

Reply to
*

OK...you've proven you're not really much other than a trool yourself, so if I have to spell it out for you:

The Mazda is a stock '89 626 with no modifications. As the header in the original message says, "OEM Tires, Optional OEM tires, and totally off-the-wall tires"

The manufacturer specifies a certain tire size for a number of reasons. The original spec on this car was 185/70-14, 195/60-14 or 195/60-15. The DX (the one I have) got the 185 tires, the top model got the 15s.

This has a lot to do with a lot of things: speedo accuracy, sterring and suspension geometry, etc. According to different tire size calculators I have seen, I am running a tire that is 6% lower than 'spec'.

So, I don't know what this means in terms of steering and suspension goemetry. It does throw my speedo off...by 6%. Also should throw the odometer off by 6%; however, where the odometer was reading lower than actual mileage, it is now correct.

Also in the mix is the drivablility response of the car. Prviously I had to downshift to get up short, steep grades; now I can take those same grades in 4th gear and sometimes even have some acceleration to spare. Overall performance of the car has increased considerably, to where it actually feels like a car with 145 HP under the hood, whereas before acceleration was sluggish and often had to drop a gear to reach speed.

But, if you had read the original post, you would have seen these were my original concerns, instead of jumping into a thread halfway.

Reply to
Hachiroku

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