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Discussion Starter #1
As I researched new tires for my Element, the one question that kept coming up was "If I change tire size, what is the right inflation pressure?". I had a heck of a time looking for a load inflation table at tire sites. They all mentioned it being important to check, but if they had one it was well hidden.

Today I found a manual that lists thousands of different tire sizes by wheel size, width and ratio, and for each shows the pressure for a range of maximum loads. The 55 page manual goes up through 22" rims and is too large to upload, so here is the link:

http://www.tiresafety.com/images/Tire Replacement Manual.pdf

As an example, I'm installing P225/70R16 tires, which is not a big increase over the OEM size, but I didn't know what to do when I saw the new tire rated at 51psi! The tables and notes explain this. Listings for 16" rims are pages 33-36.

The original tire specified for the Element P215/70R16 had a load rating of 1709#. If you scan across the table for new new tire size, you'll see that at the door plate pressures the new tire 32F/34R psi can support 1753/1793#, easily surpassing the original tire. The maximum carrying capacity for this 101 tire,1819#, is reached at 35psi, even though the particular tire I have is rated at that load at 51 psi (see note A at the bottom of the page.)

So the door plate numbers can still be safely used as the low end of my range. My experience with the OEM tires was that the the best pressures for me were 33F/35R, which corresponds to a load imbalance of 73#. To get the same effect with the new tires, the pressure of the rear tire will need to be more than 3psi higher than the front. The pressure above 35psi won't increase load capacity, but it will increase stiffness in response of the rear to load changes up to that capacity.

In my case this was something I knew intuitively, but it's nice to have objective confirmation. My guess is that most people using this size tire on an Element would end up with pressures of 33F/37R psi +1/-0 psi by experimentation. A small pressure change should have a noticable effect on handling and ride. (This makes an accurate tire gauge very important.)

I think that tables may be more useful for people making more radical wheel/tire size changes.
 

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The weight - size - pressure tables that I found in the past applied to big truck size tires. This table does cover our sizes, but I'm not sure how useful they are.

For the 215/70/16 size, the max load at max pressure (44pis on tires?) is 1709lb, but at Honda's recommended 32 (front) 1620lb. Not much of a change. If I lookup 1620lb in the 225/70/16 row I find 27psi. (Toyota recommends 28 psi for 215/70/16 tires on the much lighter RAV4)

According to the door sticker the front axle load is 2300 lb, or 1150 per tire. Does that mean I could safely drop the stock tires to 26psi or less? People do that when driving on sand (down to 15psi or less), but they are cautioned to pump them back up before hitting the highway. The danger with soft tires at highway speeds is that they flex too much, creating heat in the layers, and possibly damaging the structure.

I think Honda chose these tire pressures to balance handling, tire wear, and gas use, not because of the load rating in a table like this.

Because the stock tires tend to wear fast on the shoulder tread, some of us think that pressures higher than the door sticker will improve tread life (putting more wear on the center tread). Higher pressure may also improve water drainage (Tirerack has info on this).

I run my 225/70/16 tires 2-4 psi above door sticker, and am getting more wear in the center tread. Maybe I should run them softer, even down to 30. But that puts the coarse shoulder tread in firmer contact with the ground, creating noise, and scraping in low speed turns.
 

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Q: Why are airplane tires filled with nitrogen instead of air like car tires?

Air contains moisture and freezes at high altitudes, where average temperatures hover at -57°C. Nitrogen freezes well below this and contains little to no moisture. As well, tires can warm up quickly upon landing. Nitrogen handles the heat much better than air and also prolongs tire life by preventing oxidation and rust from forming inside the wheel.



I wonder if we can put nitrogen in our tires?!
 

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Discussion Starter #6
I don't know how useful they are either, but they do show the designed load capacity for each inflation level, so at least it's not a guessing game any more.

Most P series radial tires are optimized for handling and rolling resistance in the 32-35psi range, they are matched to vehicles weight by their maximum load capacity. The reason that the recommended tire pressure is less than the max load pressure is a trade off between the actual weight per axle, comfort and a safety margin against road impacts that can sharply increase the internal pressure.

I suppose you could lower the pressure in an oversized tire below 32 psi, but the footprint and handling would be negatively affected, and I've read that radials operated at less than 80% of their max load bearing pressure are prone to "zipper" failures due to "excessive sidewall flexing".

The tire I chose is a touring model; I do mostly highway driving. I'm looking at the extra load capability rating as an extra safety margin should I decide to load my car more heavily than suggested.

FYI If read that when P-series tires used on light trucks, the rules having been written for pickup trucks that could carry heavy loads, the tire capacities are de-rated by 10%. I don't know whether the Element is classified as a light truck or a passenger vehicle under these rules.
 

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Discussion Starter #8
Since I'm running non-stock tires (as anybody should be...), I generally go with the "Max PSI - 10%" rule of thumb.
That might be safe as far as static load-bearing, but if it's too much above 35psi, it could make for an unnecesarily harsh ride and wear the center tread down prematurely. Indy cars run with tires at high pressures, but they also run on very well maintained surfaces, and wear out their tires in a few hundred miles. . .
 

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Discussion Starter #10
The Element is based on the CR-V chassis which is based on a stretched and beefed up Civic chassis, which is why it handles like a tall car. It's also relatively light for its size. I would classify its tire needs as a mid-size sedan, yet a lot of us also need off-road and bad weather snow/mud/slush/whatever capability.
I wouldn't say the Element was light for its size. It is 4 inches taller, one inch wider, 12" shorter in length, 900 lb heavier than the 2005 CR-V , which get better gas mileage,
has a payload weight of 1022 vs the Elements 875 on 98 series tires using the same drive train.

I classify it's tire needs as similar to a similarly equipped minivans' if driven under the same conditions. Our box is just a little smaller, more versatile and nicer IMHO.
 

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Discussion Starter #11
My max is 51 psi I believe, I run them at 45 or 46. No problems so far, seems to be wearing just find and rides great.
My max is 51 also. What I know now is the safe minimum pressure. After I've broken them in I'll see what raising the pressures by 1 psi at a time does to the overall handling on the highway.
 

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Discussion Starter #13

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Tire Pressures

Take your tire pressures after a nice 1 hr run on the interstate and see how much difference there is between cold and hot.

Nitrogen for you tires is old school. Recently banned i believe in F1 the hot ticket is hydrocarbons to fill the tire. You get a constant temp and pressure
etc. None of the downsides of nitrogen.

And if you have to ask how much you can't afford it.

If I had coilovers on my E like some of you guys I would corner balance my E for fun if I could afford it since ride height is adjustable.

Fred
 
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