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09-12-2022, 03:22 AM | #31 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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09-12-2022, 06:15 AM | #32 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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The pressure inside the tire matches the pressure outside the tire. The main factors in determining the size of the contact patch are the tire pressure and the weight of the vehicle. A 3000lb car with 30psi of pressure in each tire is going to have a total of 100 square inches of contact. With equal weight distribution, that's 25 square inches per tire. If you took that same car, and lowered the rear tires to 20psi, they'd have 37.5 square inches of contact patch... a 50% increase. |
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09-12-2022, 07:10 AM | #33 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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having a bigger contact patch, hell we'd all be driving on tires as wide as some road bicycle. “ What I was postulating in my original post was that, all other things equal, widening the wheel & tire package changed not the area of contact patch, but the orientation of said patch. So no, I do not believe that a narrower combo would have a larger area of contact. |
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09-12-2022, 07:16 AM | #34 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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It is unfortunate, though, that it led to giant rims/wheels becoming ‘a thing’ in the off-track passenger car segment. Last edited by RidingOnRailz; 09-12-2022 at 08:04 AM. |
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09-12-2022, 07:24 AM | #35 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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In my case, a 2010 Honda Accord EX with a wider 50R17 package, the specified cold tire pressure is 2psi higher(32) than for the 2010 base Accord LX: 30psi in 60R16. So it is quite likely that the contact patch area under both above Accords is equal, or possibly 5-10% more area in the LX, with its lower cold pressure spec of 30psi. Another interesting fact: The 2008-2010 Accord LX OEM tire load index was 94, vs 93 for the HIGHER trim EX. I sought out the EX because it has niceties like a moonroof. But I suspect that the LX trim, with its narrower, higher profile tires and a higher load index, was the more practical version of the Accord for those model years. Question: as far as the whole “wider lower profile tires require lower tire pressure” line of thinking, then why does Honda specify, on several models, not just Accord above, higher cold pressures on trims with bigger wheels and wider, lower profile rubber? |
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09-12-2022, 08:38 AM | #36 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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It is such a common misconception that you can calculate the size of the footprint knowing only the inflation pressure and the load on the tire, I wrote a webpage debunking it. http://barrystiretech.com/Footprint.html |
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09-12-2022, 11:56 AM | #37 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
Quote:
-Rod |
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09-12-2022, 01:15 PM | #38 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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Although the EX trim level across Honda's lineup has historically been more of a 'mid' trim level. In my Accord, the only extra weight might be the moonroof unit. 30-40lbs? I don't know how much heavier a 6-CD changer is compared to a single disc AM/FM stereo unit. And the difference in the weight of a power driver's seat vs a manual one is probably negligible. Cloth interior on the EX, unlike EX-L(eather) or EX-V6. |
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09-12-2022, 01:40 PM | #39 | |
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
Power seat to manual can be as much as 40lbs.
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09-12-2022, 02:02 PM | #40 |
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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09-17-2022, 10:51 AM | #41 | |
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
Semi-related to this thread:
What is the actual change in air pressure per 10deg F temperature delta - 1.0psi, or 0.8? I've read read estimates of tire pressure loss/gain from half-PSI up to two-PSI on this objective internet we use! Which one is iiiiiit?? |
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09-18-2022, 04:46 AM | #42 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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It also depends on the starting inflation pressure. You'll get a different answer if you are starting with 30 psi than if you start with 100 psi. Having said that, if you have a 30 psi tire at 70°F at sea level, and the temperature rises to 80°F, the increase in pressure is 0.84 psi. On the other hand if you start out with 65 psi (like on some LT tires), the pressure increases 1.50 psi. I've worked with other tire engineers and have worked out a "Rule of Thumb" - 2% for every 10°F. It's close enough and easy to remember! |
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09-18-2022, 10:06 AM | #43 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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My takeaways, and confirmations, of what you just explained: 1. Delta in air pressure per given temperature change varies depending on existing air pressure. The lower the pressure, the less the change. The higher, the more the change. I can attest to this - bleeding down a 35psi tire for two seconds, with my particular gauge, reduces pressure only around 1psi. But: bleeding down a 60psi spare ‘donut’ for two seconds, using that same gauge, reduces pressure 4-5psi! So I do understand now that an equivalent temperature change will affect the higher pressured tire more drastically than will affect the lower pressured tire. 2. At altitude, I know the cold pressure I set near sea level will increase a bit with every 1,000 feet up I go into the mountains. Because there is less atmospheric pressure imposed on the tire up there. So at sea level, a 10°F increase in temperature would increase that 35psi tire to about 35.9psi? At, say, 4,000 feet up, that same temperature increase might increase that 35psi to…. 36-37psi? Interesting stuff to know, and it helps me to estimate how high a pressure I should set it for based upon the altitude or temperature conditions where the tire is being driven to. |
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09-21-2022, 09:47 PM | #44 | |
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
One more brain cell I'd like to pick of Barry's:
Given: Two days with the same temperature, same humidity, pre-dawn conditions with no sun hitting the car, cold tire pressure set, IE: 32psi. Change one thing: Lower or raise the barometric pressure approx. one inch on the second of the two days. What effect will that one change have on the cold tire pressure? |
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09-22-2022, 07:51 AM | #45 | ||
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Re: The MYTH Of Wider Tire Contact Patch Dispelled!
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That's 0.49 psi. |
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