Tireman Needs Your Assistance

[tireman9]

OK this is a long post and may put some folks to sleep, but if you can wade through it I would appreciate feedback.  Comments appreciated or direct email might be best for some folks.  Tireman9 at gmail.com

I am trying to develop a comprehensive statement oh how to set both Cold Inflation Pressure and TPMS warning levels. I also need to keep this simple enough so anyone can follow the instructions. So what do you think?

I feel the CIP should it be the minimum inflation based on actual measured load of that individual RV plus a margin, even if the RV industry doesn't want this because they would have to provide larger or higher rated tires to future models. Owners can read their inflation and calculate the CIP. Suggesting a margin on load involves the tables and additional interpretation.
 

 

+++++++++++++++++++++++++++

Steps for setting CIP and TPMS pressure warning levels:
 1. Weigh the coach and learn 4 corner weights or at least get axle weights and assume a 47/53 side to side load split on each axle to accommodate some of the identified unbalance in RVs.

 

2. Using the heavier end load for each axle or the 53% figure, use Load Inflation table to learn the minimum inflation needed to support that load.

3. Establish the CIP to be the minimum inflation in step 2 + 10% + round up to next higher 5 or 10 inflation level to get an easy to remember inflation for the CIP.  Example  Load table gives 80 psi  + 10% = 88psi  and round up gives 90 psi.  Example Load table gives 110 psi +10% = 121 and round up to 125

4. Set the low pressure warning level of a TPMS to the inflation level in step 2 above to ensure the tires are never operated in an overloaded condition.

5. Set the high pressure warning level to 120% of CIP

++++++++++++++++

Reasoning for #1.  IMO a 45/55 would cover more RVs but might be too much unbalance and not reflect the majority (lets say 90%) of motorhomes so I am suggesting the 53% as a compromise. I can only guess at the statistics needed to cover 80 or 90% of the market.

Reasoning for #4 Some TPMS sellers say to set the low warning level to -10% and other say -15% or possibly lower, of the "baseline inflation" but they do not seem to be clear or consistent seller to seller on what they mean by "baseline". Some will say placard inflation others say the inflation in the tables. I believe the -15% inflation level for warning level for TPM was taken from the passenger car warning level but that ignores the fact that passenger car inflation levels are not set to the pressure needed to support the load but at a higher level some significantly higher as handling or fuel economy are a driving force for light ( under 10,000#) vehicles.

Reasoning for #5 With pressure increasing by about 2% per 10°F a 20% rise in pressure would translate to a temperature rise of 100°F which would be significant and may indicate some problem or excess speed for the conditions.. Note the default TPMS High temperature warning of 158°F is not reflecting the actual tire temperature as there is cooler of the sensor and the hottest part of the tire is hotter than the contained air average temperature.

====================

Are the suggested guidelines clear enough?

Do you think my reasoning is logical?

 

[wildebill308]

54 minutes ago, Tireman9 said:

OK this is a long post and may put some folks to sleep, but if you can wade through it I would appreciate feedback.  Comments appreciated or direct email might be best for some folks.  Tireman9 at gmail.com

I am trying to develop a comprehensive statement oh how to set both Cold Inflation Pressure and TPMS warning levels. I also need to keep this simple enough so anyone can follow the instructions. So what do you think?

I feel the CIP should it be the minimum inflation based on actual measured load of that individual RV plus a margin, even if the RV industry doesn't want this because they would have to provide larger or higher rated tires to future models. Owners can read their inflation and calculate the CIP. Suggesting a margin on load involves the tables and additional interpretation.
 

 

+++++++++++++++++++++++++++

Steps for setting CIP and TPMS pressure warning levels:
 1. Weigh the coach and learn 4 corner weights or at least get axle weights and assume a 47/53 side to side load split on each axle to accommodate some of the identified unbalance in RVs.

 

2. Using the heavier end load for each axle or the 53% figure, use Load Inflation table to learn the minimum inflation needed to support that load.

3. Establish the CIP to be the minimum inflation in step 2 + 10% + round up to next higher 5 or 10 inflation level to get an easy to remember inflation for the CIP.  Example  Load table gives 80 psi  + 10% = 88psi  and round up gives 90 psi.  Example Load table gives 110 psi +10% = 121 and round up to 125

4. Set the low pressure warning level of a TPMS to the inflation level in step 2 above to ensure the tires are never operated in an overloaded condition.

5. Set the high pressure warning level to 120% of CIP

++++++++++++++++

Reasoning for #1.  IMO a 45/55 would cover more RVs but might be too much unbalance and not reflect the majority (lets say 90%) of motorhomes so I am suggesting the 53% as a compromise. I can only guess at the statistics needed to cover 80 or 90% of the market.

Reasoning for #4 Some TPMS sellers say to set the low warning level to -10% and other say -15% or possibly lower, of the "baseline inflation" but they do not seem to be clear or consistent seller to seller on what they mean by "baseline". Some will say placard inflation others say the inflation in the tables. I believe the -15% inflation level for warning level for TPM was taken from the passenger car warning level but that ignores the fact that passenger car inflation levels are not set to the pressure needed to support the load but at a higher level some significantly higher as handling or fuel economy are a driving force for light ( under 10,000#) vehicles.

Reasoning for #5 With pressure increasing by about 2% per 10°F a 20% rise in pressure would translate to a temperature rise of 100°F which would be significant and may indicate some problem or excess speed for the conditions.. Note the default TPMS High temperature warning of 158°F is not reflecting the actual tire temperature as there is cooler of the sensor and the hottest part of the tire is hotter than the contained air average temperature.

====================

Are the suggested guidelines clear enough?

Do you think my reasoning is logical?

 

I think it is fairly clear. I would make it simpler in just use 10 lbs over and set the TPMS to 2 lbs over the minimum inflation pressure. This way you get a warning before you are under the minimum allowable pressure for the load. This still gives an 8 lb cushion before you get a low pressure warning.

Bill

[manholt]

Since it's an across the board item, I agree with Bill.  KISS !  In Summer, I run 15/2...rest off the year, 10/2. 

Carl C.

[tireman9]

Thanks for input.  I want to KISS Sooo

Steps for setting CIP and TPMS pressure warning levels for Motorhomes:
 1. Weigh the coach and learn 4 corner weights or at least get axle weights and assume a 47/53 side to side load split on each axle to accommodate some of the identified unbalance in RVs.

 

2. Using the heavier end load for each axle or the 53% figure, use Load Inflation table to learn the minimum inflation needed to support that load.

3. Establish the CIP to be the minimum inflation in step 2 PLUS 10 Psi

4. Set the low pressure warning level of a TPMS to the inflation level in step 2 PLUS 2 Psi to ensure the tires are never operated in an overloaded condition.

5. Set the high pressure warning level to 120% of CIP. If your pressure increases by 20% there is something is wrong like too much Load or too much speed or too large an increase in Ambient over the morning temperature. Take a break, let the tires cool down and figure out what changed and make a correction.

[wildebill308]

I might go 45/55 on the axle.  

Bill