how much psi can i pump safely? - Page 2 - Fuelly Forums

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Old 11-07-2007, 01:50 PM   #11
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Originally Posted by theclencher View Post
we need a sticky on this
INDEED! well, skewbe and theclencher have great ideas. either paint a line across the tread or drive on a dirt road. then, see where the paint/dirt ends. adjust psi accordingly.
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Old 11-07-2007, 01:51 PM   #12
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I heard the car talk guys say tires are rated up to 200PSI for blowout. In other words, less than 200PSI and they won't blow out. My personal experience is that the tires have better traction in dry but perhaps worse traction in wet when over inflated.
Possibly even higher than 200psi Engineers don't design load bearing items to meet their load - they design to exceed with a certain factor of safety... I have had a hard time finding the FoS for radially belted tires, but for bias tires, I found a paper claiming a FoS between 5 and 11 with 7 being ideal. That is, if it is rated for 1,000 pounds - it should fail at 7,000. Then convert to whatever psi that corresponds to But that's outdated tire tech. The Fos has likely not decreased though.

I should have mentioned before with regards to wet conditions... Yes, you'll have less traction purely because wet road+rubber has a lower coefficient of friction. But I should have mentioned that I live in Florida Lots of rain in a short period of time. Hydroplaning is a big danger - I'd rather have slightly less traction to reduce the risk of hydroplaning. I can always give more space between me and the person in front of me while keeping with traffic (which typically goes too fast anyway)
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Old 11-07-2007, 01:59 PM   #13
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Originally Posted by trebuchet03 View Post
Possibly even higher than 200psi Engineers don't design load bearing items to meet their load - they design to exceed with a certain factor of safety... I have had a hard time finding the FoS for radially belted tires, but for bias tires, I found a paper claiming a FoS between 5 and 11 with 7 being ideal. That is, if it is rated for 1,000 pounds - it should fail at 7,000. Then convert to whatever psi that corresponds to But that's outdated tire tech. The Fos has likely not decreased though.

I should have mentioned before with regards to wet conditions... Yes, you'll have less traction purely because wet road+rubber has a lower coefficient of friction. But I should have mentioned that I live in Florida Lots of rain in a short period of time. Hydroplaning is a big danger - I'd rather have slightly less traction to reduce the risk of hydroplaning. I can always give more space between me and the person in front of me while keeping with traffic (which typically goes too fast anyway)
For me the issue of wet roads and high PSI is that I like to take corners fast in order to be able to go into third gear when I come out of the turn since I have to accelerate to a minimum of 1500RPM in second before I can go into 3rd. And if I shift that early, then I will have no power. So what happened the other week was that I went into the turn, slower than normal since it was wet, but still not slow enough! The car started to slide. My front tires are at about 52 or 53PSI and are rated at 35. I was quite surprised that they slid. I tapped the brake and the car regained traction before I hit the brick wall of the underpass. (it's a nasty S turn railway underpass) I did the turn in neutral. In dry it really does handle better, though. I do a 90 degree turn at 28mph which normally would have squealed the tires, but at the higher PSI it just has no problem, even in neutral. I will still run the high PSI, and will just know that I have to be extra careful in the wet and maybe keep it in gear while turning during wet driving. It doesn't rain all that often here, so it's worth it for me. (It's been sort of a droughty year here)
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Old 11-07-2007, 02:14 PM   #14
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Krousdb had 60PSI in his 44PSI rated Potenza RE92 14" tires. I looked up these tires and the description didn't mention anything about being LRR. Which makes me wonder... does one really need to buy LRR tires? Might not any decent tire overinflated work just as good or maybe even better than a LRR tire? I can't think of anything else that lent Krousdb's superior fuel economy to other VXes on this board. He wasn't even hypermiling. If you look at his gas log, you will see even at 75mph he wasn't getting less than 60mpg. I don't think one single gas log was below 60mpg. It defies comprehension. The only thing I can think of, aside from a wonky odometer, is his tires ended up being very very LRR when inflated to 60PSI. I'd like to hear from Krousdb how well his car rolls. Hard to make a comparison of something like that tho.
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