That looks pretty sweet! I imagine changing the batts would be a 'con'. Any others you remember?
-Spike
Tire Inflation- The Ultimate Answer
- Thread starter cary
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That looks pretty sweet! I imagine changing the batts would be a 'con'. Any others you remember?
-Spike
Some cons.
The batteries in the tire senders were sealed so had to be sent back to the company for replacement. They were supposed to last six or seven years.
Each tire sender had its own frequency or way to identify itself. If I rotated the tires I had to make notes where each tire was so I would know the tire location of which pressure and temperature the receiver was showing. Each wheel had to be marked with a number to identify it.
In order to preserve the battery in the tire sending units, the units shut down when not moving. So until the wheels turned several times, there was no pressure or temperature reading.
The tire sender units came with a counterweight that offset the weight of the senders. It made it more difficult to balance the tires depending on where the sender units ended up being placedin the wheel.
Care had to be taken when mounting/dismounting the tires as the sender units stick out from the wheels and the tire easily would catch on them, possibly ruining the sender.
Money. IIRC, I paid $600 or $700 for the RV (recreational vehicle) package to get six sending units because I carried two spare tires and wheels.
I have no idea how much these things are now or if changes have been made to them. It was nice to have a warning light and audible signal if a tire was going low or getting hot and to monitor the tire temperature and pressures without having to physically check them. These things would also be great for pulling a trailer as the trailer tires could give a warning and/or be monitored from the towing vehicle. HTH
Bill
Here is the chart that Discount Tire emailed to me at my request. It provides a method for converting from P-metric to LT tyre sizes. You can get the load index ratings for both the OE Michelin LTXs and your new tyres from TireRack dot com.
View attachment Discount Tire - Load Inflation Tables.pdf
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For BFG KM2 315...
So if I read all this correctly, and used the newly provided Inflation guide.
Knowing that the BFG Km2's 315/75/16 are Load Index/Range 121, and they must be C Load Range due to the web specs of 3195@50.
See km2 specs here Mud-Terrain T/A KM2 | BFGoodrich Tires
To achive the necesary stock load (2355 or so), and the KM2 315 PSI set to 35 would put me at a 2535 load Range?
This would mean we would just need about 30 PSI for the 315 KM2 to meet the 2355 stock load range. (even though the new provided chart does not go down to 30 psi for a C load Range tire, im just extrapolating about 200lbs of load range per 5 PSI)
I'm currently at 40 PSI and they feel good. I might go down to 35 to see how they feel. Don't really know about going all the way down to 30 PSI?
So if I read all this correctly, and used the newly provided Inflation guide.
Knowing that the BFG Km2's 315/75/16 are Load Index/Range 121, and they must be C Load Range due to the web specs of 3195@50.
See km2 specs here Mud-Terrain T/A KM2 | BFGoodrich Tires
To achive the necesary stock load (2355 or so), and the KM2 315 PSI set to 35 would put me at a 2535 load Range?
This would mean we would just need about 30 PSI for the 315 KM2 to meet the 2355 stock load range. (even though the new provided chart does not go down to 30 psi for a C load Range tire, im just extrapolating about 200lbs of load range per 5 PSI)
I'm currently at 40 PSI and they feel good. I might go down to 35 to see how they feel. Don't really know about going all the way down to 30 PSI?
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Aids10
xploraz.net
Not me but.....
I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air pressue in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.
So how do I get a 2 Rivet rating? Does this long explanation help or hurt?
I worked for Michelin Tire Corporation for 7 years and Yokohama Tire Corporation for 11 years. I have given numerous tire seminars on tire maintenance and especially how to determine the correct tire pressures. So here goes.
The pressure on the sidewall of the tire is the maximum pressure at the published load at approximately 55 mph. (The speed can vary somewhat but it is not important for our discussion).
The air pressure is required to support the load that the tire must carry in such a manner that the tire flexes at the designed place on the sidewall of the tire.
If the load on the tire changes then the air pressure should change accordingly to keep the tire flexing at the proper place.
The reason for correct air pressure is to prevent the tire from overheating. It was put together with heat and it will come apart the same way. An under inflated tire will eventually self destruct due to excessive heat build up. An over inflated tire will ride harshly and be more likely to burst upon impact. Sorry for the long explanation but here is the bottom line.
To determine the correct air pressure, check the pressure when the tire is cold. Run the tire for several miles at highway speed. Stop and immediately check the air pressue in the tire. It should be higher than we cold but no more than 10% higher.
Now here is the hard to believe part. If the pressure is more than 10% higher you must ADD AIR and test again. For example if you start with 50 psi cold. If the pressure is 60 when hot, you have exceeded the (10%) in this case, 55 psi maximum safe heat build up pressure. You must ADD AIR. In this case I would add 5 psi which would take the tire to 65 psi when hot. After you run the tire again you will find the pressure to actually drop because the tire will run cooler. The heat build up causes the tire pressure to increase when under inflated.
On the other hand, if the 50 psi cold pressure does not change when hot. You have more air than needed. You can remove 5 psi or so and test again when they return to cold. Like the next trip you take.
So a fully loaded rig will require more air in the tires than one with empty tanks and a light load on board. Always error on the side of over inflation. Thus the maximum sidewall pressure indicated on the tire is usually used. It usually is more than needed. Each axle has its own requirement based upon the load on that axle.
So how do I get a 2 Rivet rating? Does this long explanation help or hurt?
LCPhil,
That makes sense. Never seen it explained that way.
Thanks.
That makes sense. Never seen it explained that way.
Thanks.
Correct. It often seems unreasonably difficult to get folks to understand the simple words on the sidewall that state the maximum pressure for the maximum load...
Certainly it's dangerous to have an under-inflated tire, which has received much attention in recent years because of people's unwillingness to perform simple safety checks/maintenance like checking their tire psi.
There are inflation charts that list how much tires of a certain size are rated to carry at a specific psi. Many would be amazed at how much weight most large RV/flotation tires will support at a mere 35 psi.
Since most people with modified trucks these days are running relatively large and heavy-duty tires (historically speaking), often load range D or E, even heavy Land Cruisers don't need anywhere close to the maximum psi (65-80 psi) for their axle loads. Weighing a rig on a truck scale will remove all the conjecture and offer a proper starting point of what psi should be used.
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Helpful thoughts. Thanks, guys!!
OK, I have an opinion on this, and maybe Ive been doing it wrong. But heres what I have always done to get a baseline pressure. Now this does not take into account different springs or chassis modifications that could affect the Gross Axle Weight Rating (GAWR). Once you get the baseline though, you really should monitor your tire wear for longterm durability.
Deleted the rest of my post. My math really was way off and did not add anything to this thread.
Deleted the rest of my post. My math really was way off and did not add anything to this thread.
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- Thread starter
- #32
Here is another chart from Toyo that provides a more complete explanation.
http://toyotires.com/tires-101/load-and-inflation-tables
Good post, but remember that the weight of the truck divided by 4 is not the proper pressure. The best way to do it is start with the factory recommendation and figure out what pressure you should be using for the tire you are running. So lets take the stock tires:
Stock is a P275/70/16 tire with a recommended inflation of 32 psi. Looking at the load table we see that this provides a load capacity of 2480 pounds. We now multiply this by the .91 correction factor for P-Metric tires which gives us a load capacity of 2256 pounds.
Lets now take the replaced tire, say the common 33" tire of LT285/75/16. We now need to find a pressure that corresponds to carrying a weight of 2256 pounds per tire. Looking at the Toyo chart page 9 we see that 35 psi provides a load capacity of 2130 pounds and 40 psi 2340 pounds. So we know for this size tire the baseline pressure (and the pressure we should never go lower than on the street) is about 38 psi to give the minimum load capacity recommended by the manufacture.
Now lets say you have added sliders, bumpers and a winch and want to adjust. If you figure your static load is 1000 pounds more than stock, looking at the chart for the LT285/75/16 tire tells us that 45psi supports 2540 pounds. This gives us a good idea that for a truck running all this extra gear that a good baseline is in the 42 psi range.
For those guys running 35s in a LT315/75/16 size the load chart shows that at 35 psi the load capacity is 2535 pounds. So the minimum street pressure for the 35" tire is going to be close to the stock 32 psi.
Remember the foregoing numbers are to establish the baseline minimum pressure for the new tires. You should not run lower pressures than this on the street or the tire will be under inflated and could fail. People will often run higher pressures, but in many cases it is not necessary.
In my case with measure tread wear over a long time in LT285/75/16 tires, I have found that about 42 psi provides the most even wear. This is 4 psi above the minimum pressure that should be run. I would suggest that anything above 10psi above the minimum pressure will be over inflated and result in decreased handling and poor tire life.
- Thread starter
- #33
Your methodology is incorrect for two reasons. First because it assumes that the load carrying capacity of a tire is linear to its pressure from the max load: it is not. Second, the GVRW/4 is not the load on each tire for computer pressures. This is the reason you need to use the load table starting with the factory recommendations, figuring out the minimum pressure for you new tires, and adjusting from there as necessary.
I agree...you can do all the calculations you want but in the end if you are creating heat your pressure is not safe no matter what the numbers say.
Thanks.
For a few years I've had that Toyo PDF saved on my computer. It's informative, but there are others out there too. What one needs is the industry standard Tire & Rim Association (TRA) data for their specific tire size, with which it's very easy to figure the minimum psi needed if you know the weight. I’ve been using TRA charts to fill my tires for twenty years.
I don't weigh the truck and divide by four. I weigh my rigs at trucks stops on commercial trucks scales (cost about $10) where the steer axle and drive axle are weighed separately. Though there is some variance side-to-side, it's not the same concern as fore-aft. Knowing this data I use the charts the engineers agree on.
If I have a trailer in tow, there are separate scales for the trailer axles that give that data as well.
Precisely why I use commercial scale. All of my trucks are modified and heavier. I establish a baseline at the beginning of the build after I purchase a vehicle, then a new baseline once the rig is built.
Often my trucks are used and loaded similarly for similar types of trips. So after weighing a couple times loaded with a typical load I know the weight for the next time. I've also weighed items before they were loaded, but this is not always accurate because you don't know the split between the front and rear axles. When in doubt, one can always add another 5-10 psi to be safe, up to the maximum recommended psi for which the tire is rated.
I’m talking about relatively heavy loads here 16-17k gross, 7,500 pound truck (F-350) with approx. 1,000 pounds in the bed, an 8,000 pound travel trailer, etc. Even with a moderately heavy load like this (for an F350) I don't need or use 80 psi in the front tires if that's their maximum psi rating, because there's less weight on the front axle, substantial (load distribution bars) but still less.
