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Friday, October 23, 2020

How much Air Compressor do you need?

 Some things to consider before making a purchase.

When making a purchase decision for air compressor the number one feature to consider is the max pressure capability. You must be able to get up to the max for your tires. You can learn that number by simply reading the sidewall of your tires.

All tires will have a statement that reads something like "65 psi ( 450kPa) air pressure Max load 2,500 lbs (1,135 Kg)". That tire is telling you the MINIMUM pressure needed to support the stated MAX load for that tire.

RV Trailers usually come with Load Range C (50 psi) to LR-E (80 psi) tires. Some large Class-A Motorhomes may say 100psi but there are a few tires that have higher inflation pressure associated with the Max load.
Whatever the highest inflation number on any of your tires, you need to have a bit more capability. I suggest at least +10 Psi with + 30 psi being desirable.
The reason for the extra is that if you need 80 psi in your tire and the compressor is only rated for 80 psi you may never actually get to 80 because the rate of inflation slows down for all compressors as you approach their upper rating.

The second number to look at is the Rate of inflation which will be something like 1.5 CFM (Cubic Feet per Minute) @ 100 psi or maybe 3.0 CFM @ 50 psi. Now you need to pay attention to the "At" number because all compressors will put out more air volume at lower pressure but that 3.0 CFM @ 50 psi unit may only be capable of 0.1 CFM @ 100 psi which means if you are inflating to 105 it might take you a long time ( 20 minutes?). Some compressors, may mislead you with high CFM number but state it at a low inflation number so read the fine print.

Finally do not "over-buy" more capability than you need. If you do you may be wasting money on the purchase and also end up with a physically larger and heavier compressor than you realistically need.

Hopefully you will only need to "top off" a tire by adding 5 psi. If you need to add more than 20% of the goal inflation you may have a problem because if a tire has lost 20% of its air and it was driven there may be damage to the tire structure. Re-inflating a tire that has been damaged could result in a tire explosion. If you need that much air I strongly recommend you call a professional. They should have the training and tools that might even include a "Safety Cage" designed to prevent injury.


Friday, October 16, 2020

Load Range E or F or even G. What's the difference?

I found a discussion on Load Range in a Forum where the question was: How strong of a tire do I need? was being discussed. Here is some of the discussion:

Below you see what is stamped on my tire sidewall:
Load Range is rated at "H" 4940# single tire That's at max pressure!!
Load Range 4675 Dual tires.
Tread is 5 ply of steel. Good puncture protection with 5 steel treads.
Sidewall is 1 ply of steel. Maybe this is why they ride smoother with only 1 steel side wall.
Am I missing something since your Load Rating info does is not the same as mine. There's not enough plies to be rated an "H" tire???

Well, I felt that a better understanding of the "strength" of the Steel ply, in the subject tires, might help people understand the concept of different tire constructions 

The number of 'Ply" or layers of cord (textile or steel) are not in themselves any proof of strength. Individual cords of steel are made up of many strands. The steel or other material used to make the strands can have a wide range of strength. Also the number of strands and even the "twist" of the strands can affect the strength and flexibility in the end product. Here are some basic examples of steel cord/cable.

Each has a different configuration. Without more information it would be impossible to know which is "stronger". Don't forget tires have to flex and bend millions of times so just max strength may not be the best choice as you need flexibility too.
If we get to more complex cords we "twist" cords together and can get different properties. As seen here.

So an obvious question is how is the material selected by the tire engineer? 
There are a number of different tests conducted on tires to establish their "strength" rating and the different materials can help a tire meet the different tests. It is completely possible for a given tire to pass some tests associated with a given level. Lets say "G". BUT if a given tire only passes the "F" level of one test, then the tire would be rated as "F" even if it passed the "G" level in the other tests.

Now if the sales dept wanted a "G" rated tire then they would ask the engineer to change the specification so the tire could pass all the "G" level testing. This change or "improvement" may or may not result in more layers of steel. I can relate to an actual example of such a process in a tire I developed. It turned out in this case that the only change I needed to make was the wire in the "Bead" of the tire. This is the "cable" of wire that holds the tire on the wheel. It is kind of an anchor for the body ply. Here is a very basic image of tire components. The feature I want you to understand is where the "bead" is located.

As you can see the 'Ply" can be very complex and simply looking at the number but not the Load range can be misleading.

The bottom line is you need to know the Load Capacity in pounds that you need for your specific application. In the same size you may have different Load Range such as E, F, or G. Each Load Range has a different inflation level for the size tire you are considering and a different load capacity. So you need to consider much more than just the number and type of "Ply".