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I do alot of driving on the highway, so it makes sense to try overinflating my tires to reduce rolling resistance. To those who have tried this, at what pressures are you noticing diminishing return? Does overinflation impact emergency handling, especially in rain?
What about tire wear?
Thanks

Hi Techman41973:

___Welcome to CleanMPG!

___Tire pressure has been discussed forever and you will see a diminishing return from 5 psi below placard on up to double Max sidewall. The FE vs. tire pressure graph rolls off to a flatter rate as you climb but there is an ever increasing FE capability no matter where you decide.

___Emergency handling is usually improved as there is far less sidewall flex (turn-in) with a tire at Max Sidewall vs. placard. In rain, less hydroplaning.

___Tire longevity and more even wear is always improved with higher pressures.

___Good Luck

___Wayne

I drove last night in the rain with my tires at 40 PSI. I noticed much better handling when turning and the car just felt more sure-footed.

Hydroplaning is proportional to the square root of the tire pressure. The lower the pressure the more likely a tire is to hydroplane.

I have some concerns regarding my own tire pressure and rather than starting a new thread I figure I will ask in here. (I don't mean to hijack your thread, techman :o )

I pressed my tires up to 60 PSI! :eek: I am wondering if this is dangerous, because I tend to push things like this to the limit. (You know, "Well... 44 was okay so I'll try 45. Okay that didn't kill me, so how about 55. Ah hell, let's just make it 60!" :rolleyes: )

So, do any of you veterans have any idea of what I can expect? What should I look out for?

My placard says something like 32, but even the dealership inflated a bit past that. The max sidewall pressure is 44 PSI. I am in South Florida and it gets HOT down here. Winter is coming soon though. (Although, winter here is really more like a light breeze.)

So, do any of you veterans have any idea of what I can expect? What should I look out for?

My Insight tires are rated for 44 and I have them at 65 no problems.

(1) There is a large safety margin built into the tires: if they're rated for 44 they aren't going to blow up at 45.
(2) That said, as xcel pointed out there's a diminishing return the higher you go, so I wouldn't bother taking them much higher.
(3) I believe that you really get the best payback from higher pressures doing pulse and glide, since the higher pressures lengthen the glide portion, so you should try P&G.
(4) I watch the road surface and avoid potholes and debris, but I'd do that anyway no matter what the tire pressure was. I also don't corner at the absolute limit, always leave myself a safety margin (I never tried to take a turn at 100% anyway, but now I leave a slightly bigger margin).
(5) Pressure buildup in hot weather should be LESS with higher pressures in the tires because there will be less flexing and therefor less heat goes into the tire. You can convince yourself of this by checking the pressures first thing in the morning, then driving a good distance on a hot day, and checking them again. In the Subaru at 51psi it went up by only 1-2psi.

That's my 2 cents.

...
So, do any of you veterans have any idea of what I can expect? What should I look out for?

My placard says something like 32, but even the dealership inflated a bit past that. The max sidewall pressure is 44 PSI. I am in South Florida and it gets HOT down here. Winter is coming soon though. (Although, winter here is really more like a light breeze.)

One thing to consider is that the contact patch (the part of the tire in contact with the road surface) will get somewhat smaller with higher inflation pressures. This will affect traction whether starting, stopping or cornering.

I'm surprised to read fixedintime's "formula" of hydroplaning inversely proportional to the square root of the tire pressure. This indicates to me it changes very little in relation to pressure changes, but where did that formula originate, fixedintime?

Personally I'm running at max -2 (42 lbs) in both vehicles, and I can definitely feel the slightly harsher ride characterstics in both of them.

It's true, the contact patch is smaller. However, the pressure on that patch is higher as well, and traction is the product of both those factors. Comes out the same, but with a stiffer sidewall, roadholding ability comes out ahead.

That hydroplaning function is well known and discussed. NASA figured it out first.

I have some concerns regarding my own tire pressure and rather than starting a new thread I figure I will ask in here. (I don't mean to hijack your thread, techman :o )

I pressed my tires up to 60 PSI! :eek: I am wondering if this is dangerous, because I tend to push things like this to the limit. (You know, "Well... 44 was okay so I'll try 45. Okay that didn't kill me, so how about 55. Ah hell, let's just make it 60!" :rolleyes: )

So, do any of you veterans have any idea of what I can expect? What should I look out for?

My placard says something like 32, but even the dealership inflated a bit past that. The max sidewall pressure is 44 PSI. I am in South Florida and it gets HOT down here. Winter is coming soon though. (Although, winter here is really more like a light breeze.)

The placard for my PT says 32 PSI. The tires say minimum PSI should be 32, maximum 44 psi. I do keep mine at 44 psi...BY CHOICE. However, I read somewhere that you could go up to 74 psi, but I'm not sure where I read that.

I've been running 55-60 for the last 15,000 miles and no problems.

I know others have run even higher and for longer, too.

I'm surprised to read fixedintime's "formula" of hydroplaning inversely proportional to the square root of the tire pressure. This indicates to me it changes very little in relation to pressure changes, but where did that formula originate, fixedintime?



The links I came up with are in this thread. (http://www.cleanmpg.com/forums/showthread.php?t=15489&page=2)

Read down a bit as well as there are some corrections/clarifications.

Remember, Xcel said there is diminished gain in going higher and higher, but YES there is still gain. So from 40psi - 50 psi you will net more gains than going from 60psi - 70psi
but you will still NET GAIN for better FE. This is worthy of remembering, as some here have written that there is no point in going beyond sidewall max as gain is lessened, but I say you are darn right there are gains in FE to be had well beyond that.

I had mine at side wall max + 5 psi. FE improved nicely. I went + 10 and it improved nicely. I went + 20psi and got more. I went max plus 30 and got even more.
I went max plus 35 and netted just a bit more. I am at 70 psi all around on 35 sidewall max rated tires.

I'm just letting all tire pressure wonderers or naysayers that this is my experience.
Also, dry or wet I have never had better and safer grip on the road and much better handling. High Pressure is KING for FE after your driving techniques.

Whether you are a Hypermiler or Gas Hog, the softer the tire, the more fuel is burned.

The burst point of a tire according to tire engineers is around 200psi. So 80 psi is really a joke. 70 even easier. 50-60 psi is childs play to a modern tire.

Remember, Xcel said there is diminished gain in going higher and higher, but YES there is still gain. So from 40psi - 50 psi you will net more gains than going from 60psi - 70psi
but you will still NET GAIN for better FE. This is worthy of remembering, as some here have written that there is no point in going beyond sidewall max as gain is lessened, but I say you are darn right there are gains in FE to be had well beyond that.

I had mine at side wall max + 5 psi. FE improved nicely. I went + 10 and it improved nicely. I went + 20psi and got more. I went max plus 30 and got even more.
I went max plus 35 and netted just a bit more. I am at 70 psi all around on 35 sidewall max rated tires.

I'm just letting all tire pressure wonderers or naysayers that this is my experience.
Also, dry or wet I have never had better and safer grip on the road and much better handling. High Pressure is KING for FE after your driving techniques.

Whether you are a Hypermiler or Gas Hog, the softer the tire, the more fuel is burned.

The burst point of a tire according to tire engineers is around 200psi. So 80 psi is really a joke. 70 even easier. 50-60 psi is childs play to a modern tire.

Thanks for the great info! This is all really true!

-Last night, I've inflated my tires from 30 PSI to about 50 psi, which is 15 psi over the side wall rating. Granted, at first I was a little afraid, however, everything worked out fine!

The drive was a tad harsher, however, FE increased, AND coasting and gliding were extended, faster, and MUCH better sustained.

Pierce, you are already and expert! You will be elite in no time. Listen to the guys with the highest numbers they know what's up in this Hypermiling game.

Pale Malenesian is one to listen to as well as of course Xcel, Right Lane Cruiser, and the other greats. They can get you to really high numbers. I'm always here to help when I can as well. Take care, and try some more air! Ha!

Very helpful, and very clear, fixedintime; thank you! I'd still be concerned about more rapid wear and potential failure of suspension parts due to their being engineered around a lower tire pressure recommendation, thus transferring a substantial portion of road shock from the now less-compliant tire to the suspension.

Very helpful, and very clear, fixedintime; thank you! I'd still be concerned about more rapid wear and potential failure of suspension parts due to their being engineered around a lower tire pressure recommendation, thus transferring a substantial portion of road shock from the now less-compliant tire to the suspension.

Trust me, you'll be avoiding anything that would cause much road shock anyway -- first because EVERYTHING reduces your glide distance (yup, that stick in the road, too) and second because you can really feel it. ;)

I started out just like everyone else here -- just keep putting in the effort and you'll keep surprising yourself. :)

60 psi (will probably go to 65) sidewall=44 no problems

showbiz, if you are concerned about suspension, just look at all the people here doing it for years such as none other than Wayne himself, for example on all kinds of cars-no problems much longer wear, and better safer handling, by the way.

Remember the firestone deaths on the Ford Explorers that exploded? The vehicle was "engineered" around that low 26 psi pressure, yet they killed people. The tire flexed
to absorb shock from the road, but with more of the tire than the suspension flexing and absorbing shock the tires heated up and blew killing some unfortunate people. So don't put so much stock in that idea. Suspension is the last thing that will suffer - and had the Ford Explorer tires been at let's say a nice 50-60 psi those people would be alive today.

There ya go-concern gone!

Xcel convinced me to get my pressures up today at MPGfest, and the FE was amazing.

Somebody should be selling really nice metal valve stems at these MPG festivals. The cheapo rubber ones are not really appropriate for the 'hyperbaric' driver.

DAS

...Remember the firestone deaths on the Ford Explorers that exploded? The vehicle was "engineered" around that low 26 psi pressure, yet they killed people.

I work for Firestone (now Bridgestone/Firestone). I suffered (with thousands of others) through that mess, when our then-CEO broke ties with Ford over their refusal to accept responsibility for, and to correct, that literally fatal recommendation. I remember with sadness...

Along this line RightLaneCruiser, you make a very valid point; but my WRX, at 42, rides as hard as I want. Now my "Blue Ox" Veracruz, with 18-inch FAT tires also is at 42, but is probably the better candidate for max + pressures, since the tires are so large, and more than likely will produce less harshness at higher pressures for that very reason. I'll try [nearly] anything to get that beast over 22. My best to date is shown in the mileage logs: 20+. :(

Here is my info:

Side wall max is 51psi - I have been at 60psi for a little over 10k and I have been riding at 65psig for 500miles. The tires have 41k on them with a patch in two of the tires. I haven't heard of anyone (non-hypermilers) getting over 30K out of these tires. Around 15K I had the tires at 50psi and before that they were around 33-40psi. My tread depth as of last week was at 6/32". I have had my tires rotated and balanced at least 3 times(possibly more but I am not so sure it is worth it from what I have read here). I feel the enhanced grip of the road, the longer glides/coasts and the harshness(I have learned to like that) and all are a plus in my book. ;)

I hate tires that don't have harshness now. Harshness is another word for better control and safety and fuel economy. Soft tires just suck in so many ways.