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Friday, August 7, 2020

Another question on "Cold Inflation" vs your "Set Pressure"

Got this question from a reader of an RV Forum:

Thank you for all of your informed comments regarding proper tire care. I need one clarification. I have always considered the cold psi on the side of my 22.5 RV tires to be the minimum to carry the maximum rated load, but have assumed that psi was also the maximum COLD psi the tire should see. From your recent post, am I to understand that unless the tire states that it is the maximum cold pressure, I can exceed it by 5-10 psi?
Thank you for your time, Doug


My Answer:


The wording on tire sidewall IMO was written by lawyers, not engineers or users. Info on the sidewall is the inflation needed to support the Max load.  The difficulty is that few understand that the pressure changes with temperature and the only meaningful pressure, measurement is when the tie is "cold". This still confuses some because some want to apply Chemistry Lab practice of adjusting to theoretical 72.5°F when what "cold" really means for tires is at "Ambient Temperature" and does not include any pressure build-up"   In real life terms this means "Not warmed by being driven on or in direct sunlight for the previous 2 hours"
Now we need to address what is meant by "Cold Inflation" vs the psi to set your tires to or what I like to call your "Set pressure".
I like to suggest the "Set Pressure" for motorhomes to be the minimum needed to support the maximum load on the tires PLUS 10% inflation. 
RV trailers are different because of their Interply Shear problem.
For RV Trailers,  I would like to see a minimum of +15% load capacity over the measured heaviest loaded tire, with +20% to +25% Reserve Load capacity being better. Sadly most RV trailers come with tires that provide +0% to +10% load capacity vs GAWR
NOTE: I am not even addressing the tendency for most RV owners to overload their tires.
So for trailers I try and simplify:
- To lower, but not eliminate the Interply Shear problem I suggest the "Set Pressure" when the tires are "Cold" to be the pressure on the tire sidewall. BUT I still want trailer owners to confirm they have at least 15% "Reserve Load" over their measured scale reading.

Friday, July 31, 2020

Can't "Balance" your tires? Bad ride?

Can't remember the number of times I have seen someone post about the "bad ride" they had in their Motorhome and that they took the vehicle to their RV dealer but was told they could not "Balance" the tires or that they were balanced and the ride was 'What it is".

The ride can be affected by a number of different contributing factors.

1. One or more tires may be out of balance
2. The tire may not be properly mounted to the wheel
3. The wheel could be out of round
4. The brake drum/rotor may be out of balance
5. The wheel may not be mounted to the hub correctly
6. The tire may be out of round
7. The tire may have internal structural "uniformity" problems.

Many times people jump to the conclusion that the tire must be "Out Of Balance" and they want to ignore all the other possibilities.

Back in Nov 2011 I covered a number of possible contributing factors when I answered the question of Do You Need To Balance Your Tires? Obviously, those that just focus on "balance" did not review this blog post.
In that old post, I said it was possible to balance a cinder block. You might consider reviewing this post as it has some good pictures of the other conditions that can give poor ride.

I have used this comment a few times in my RV Tire Seminars but I bet few believed me. Well here is the proof.
This first shot is of my "Bubble" Balancer and my test cinder block. Yes, the balancer is old ( from the 70's) but I have balanced hundreds of tires.








Even those used on my Camaro race car

where high speed (125+) would quickly show up if the tire was out of balance.

Now first I confirm the balancer is adjusted to a near-zero level of out of balance itself. We can see the bubble is very near to perfect balance with it right at the center point.

Next, I loaded the cinder block onto the balancer. I chose to not try and pile standard wheel weights on the block, so just grabbed some hand wrenches. After some moving these "balance weights" around I ended up with a
very acceptable level of balance.

I do hope this clears up some of the confusion on Ride vs Tire Balance.