Overinflation - Is there a tire mileage penalty? - Fuelly Forums

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Old 11-14-2007, 10:22 AM   #1
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Overinflation - Is there a tire mileage penalty?

Is there any penalty to be paid in the total miles traveled on a tire that has been overinflated all its life? With the vehicle weight on a smaller patch, do they still get 30-60k miles?

Sure, the MPG driver isn't going to do much tire squealing, but surely it would affect the life span, wouldn't it?
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Old 11-14-2007, 11:18 AM   #2
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I've been running mine at max sidewall for over a year now and my tires still look barely warn
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Old 11-14-2007, 11:30 AM   #3
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I'd think that as long as the over inflation isn't causing abnormal wear, then there is no mileage-of-tire penalty.
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Old 11-14-2007, 11:59 AM   #4
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Mr Incredible -

I think the tire sellers will tell you that the center of the tire wears out more quickly. This was true before steel-belted tires came along. Today, the steel belt won't allow the tire to deform. I think other people on this site have gotten 80K miles on their overinflated tires without any problems. I like this website for learning about tires :

The wheel and tyre Bible
http://www.carbibles.com/tyre_bible.html
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Tyre pressure and gas-mileage.

For the first two years of our new life in America, I'd take our Subaru for its service, and it would come back with the tyres pumped up to 40psi. Each time, I'd check the door pillar sticker which informed me that they should be 32psi front and 28psi rear, and let the air out to get to those values. Eventually, seeing odd tyre wear and getting fed up of doing this, I asked one of the mechanics "why do you always over-inflate the tyres?" I got a very long and technical response which basically indicated that Subaru are one of the manufacturers who've never really adjusted their recommended tyre pressures in line with new technology. It seems that the numbers they put in their manuals and door stickers are a little out of date. I'm a bit of a skeptic so I researched this on the Internet in some of the Impreza forums and chat rooms and it turns out to be true. So I pumped up the tyres to 40psi front and rear, as the garage had been doing, and as my research indicated. The result, of course, is a much stiffer ride. But the odd tyre wear has gone, and my gas-mileage has changed from a meagre 15.7mpg (U.S) to a slightly more respectable 20.32 mpg (U.S). That's with mostly stop-start in-town driving. Compare that to the official quoted Subaru figures of 21mpg (city) and 27mpg (freeway) and you'll see that by changing the tyre pressures to not match the manual and door sticker, I've basically achieved their quoted figures.

So what does this prove? Well for one it proves that tyre pressure is absolutely linked to your car's economy. I can get an extra 50 miles between fill-ups now. It also proves that it's worth researching things if you think something is a little odd. It does also add weight to the above motto about not trusting forecourt pressure gauges. Imagine if you're underfilling your tyres because of a dodgy pressure gauge - not only is it dangerous, but it's costing you at the pump too.

What's the "correct" tyre pressure?

How long is a piece of string?
Seriously though, you'll be more likely to get a sensible answer to the length of a piece of string than you will to the question of tyres pressures. Lets just say a good starting point is the pressure indicated in the owner's manual, or the sticker inside the driver's side door pillar.I say 'starting point' because on every car I've owned, I've ended up deviating from those figures for one reason or another. On my Subaru Impreza, as outlined above, I got much better gas mileage and no difference in tyre wear by increasing my pressures to 40psi. On my Honda Element, I cured the vague handling and outer-tyre-edge wear by increasing the pressures from the manufacturer-recommended 32/34psi front and rear respectively, to 37psi all round. On my Audi Coupe I cured some squirrelly braking problems by increasing the pressure at the front from 32psi to 36psi. On my really old VW Golf, I cured bad fuel economy and vague steering by increasing the pressures all-round to 33psi.
So what can you, dear reader, learn from my anecdotes? Not much really. It's pub-science. Ask ten Subaru Impreza owners what they run their tyres at and you'll get ten different answers. It depends on how they drive, what size wheels they have, what type of tyres they have, the required comfort vs. handling levels and so on and so forth. That's why I said the sticker in the door pillar is a good starting point. It's really up to you to search the internet and ask around for information specific to your car.

The Max. Pressure -10% theory.

Every tyre has a maximum inflation pressure stamped on the side somewhere. This is the maximum pressure the tyre can safely achieve under load. It is not the pressure you should inflate them to.
Having said this, I've given up using the door pillar sticker as my starting point and instead use the max.pressure-10% theory. According to the wags on many internet forums you can get the best performance by inflating them to 10% less than their recommended maximum pressure (the tyres, not the wags - they already haves inflated egos). It's a vague rule of thumb, and given that every car is different in weight and handling, it's a bit of a sledgehammer approach. But from my experience it does seem to provide a better starting point for adjusting tyre pressures. So to go back to my Subaru Impreza example, the maximum pressure on my Yokohama tyres is 44psi. 10% of that is 4.4, so 44-4.4=39.6psi which is about where I ended up. On my Element, the maximum pressure is 40psi so the 10% rule started me out at 36psi. I added one more to see what happened and it got better. Going up to 38psi and it definitely went off the boil, so for my vehicle and my driving style, 37psi on the Element was the sweet spot.
If you still are uncomfortable, then do alot of homework and try to find LRR tires for your car rated at 51 PSI. When I needed new tires, that's what I did :

New shoes (aka tires)
http://www.gassavers.org/showthread.php?t=3699

I am running these at max tire pressure of 51 PSI. I know I could easily go to 60, but it's bumpy enough as it is.


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Old 11-14-2007, 12:24 PM   #5
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Perhaps I'm not saying what I'm thinking...(as my wife always says)...

Over the years I've put many different size tires on many different sized rims...car/truck/motorcycle. The key to getting total wear out of those tires was to find the sweet spot pressure for that combination.

I've seen many tires wear out on the edges faster (pressure too low) and others wear out in the middle first (pressure too high). But I've never put in high pressure for extended spans.

You can easily see now on my tires where the edges of the tread have no contact with the road. Thus, obviously, the tires are wearing in the middle rather than all the way across in a uniform fashion.

Tires that are highly inflated will deform less, thus creating less heat and frictional losses. But they will wear in the middle first, garonteed. Is this tradeoff equal? Or is there a penalty I'm not thinking of?
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Old 11-14-2007, 12:28 PM   #6
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^^^ what size/brand/psi are you running now? IIRC something in a 175/60/13 correct?

If the tires are in fact wearing out the center of the tread more so than the outer tread, then you might try lowing psi just until the outer tread is touching the ground. This way, due to cornering weight forces, your tires should wear more evenly.

I think I got the gist of what you were thinking now.
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Old 11-14-2007, 12:30 PM   #7
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Interesting. I need to put more air in my F-150 tires to get better mpgs out of that beast.
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Old 11-14-2007, 01:19 PM   #8
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TomO, thanks for your thinking on this. And thanks to you all.

I currently am using 175/70/13s. Front/rear is 40/38 psi.

I would think that any tire would wear evenly across the tread at PSI-X. Anything more or less would make it wear at the center or at the edges.

I would think that every single tire of every single forum member that overinflates their tires here would wear not evenly across the tread, but more in the middle. It is the nature of the beast of overinflation. At least, that is how all the tires I've ever had until now have worn, and I fully expect that out of these.

Has anyone here been highly over inflating long enough to see this happen, and did you get reasonable mileage out of your tires?
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Old 11-14-2007, 01:47 PM   #9
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Quote:
Originally Posted by Mr Incredible View Post
I would think that every single tire of every single forum member that over inflates their tires here would wear not evenly across the tread, but more in the middle. It is the nature of the beast of overinflation. At least, that is how all the tires I've ever had until now have worn, and I fully expect that out of these.

Has anyone here been highly over inflating long enough to see this happen, and did you get reasonable mileage out of your tires?
Of course, you'll have to go with what works for you. Which is the reason most (if not all) of us check our tires frequently for abnormal wear, damage, etc.

Personally, I've put ~23K miles on over inflated tires.... No abnormal tread wear. Given the wear rate thus far, I have no intentions of replacing my current tires early on account of tread wear I'm inflating 55/50 (front/rear) cold.

Quote:
I would think that any tire would wear evenly across the tread at PSI-X. Anything more or less would make it wear at the center or at the edges.
Keep in mind that the rating printed on the tire is the pressure to support the max load rating for the tire And also keep in mind that engineers don't design to meet the spec rating - it's designed with a factor of safety (so if something has to support 10 pounds with a safety factor of 5, it shouldn't fail until 50 pounds). I found an old technical paper on bias tires that had stated the safety factor will range from 4-11 with a target of 7.
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Old 11-14-2007, 05:02 PM   #10
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For those of us driving older cars who have problems trying to find the narrower tires that were the OEM tire sizes for these car, overinflation is a way to reduce that overwide tire's footprint down to the size of the OEM tire's footprint. If they wear out faster in the center, that's fine, since that worn area is close to the width of the OEM tire's tread.
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