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PK in CA
06-05-2012, 04:26 PM
Hi folks, currently I have Tow Max tires by Power King size ST205/75 R 14 on my 2012 Passport super lite 238ml.
I have not heard one good thing of these tires and have been told several times and have even read forums about how bad these tires are and that I should replace them before they have a blow out.

The big question is, With what?? I've heard bad things about GY Marathons, Carlisles, and Michelins as well. Does anybody have any suggestions? Thanks a bunch!

f6bits
06-05-2012, 04:45 PM
1) While there are many complaints about those tires, many people, including myself, use them without incident. For now, make sure they’re in good condition and inflated to 50 psi.

2) Many people recommend MAXXIS tires. My local tire shop is a Goodyear dealer and I plan to research their trailer tires and hopefully find no issues with them. I’d like to give my business to this particular shop.

PK in CA
06-05-2012, 04:54 PM
Thanks Scott. I'm glad to hear someone isn't having a problem with them. I think I may take your advice and just try to make these last as long as possible.

I too have a neighborhood goodyear around the corner from me but I haven't heard many good things about Marathons. I'm really beginning to think all of these tires are the same and that maybe it really is just about keeping them inflated properly etc. Thanks again!

flc
06-05-2012, 05:00 PM
I have a camper on order (it's here, looks great - pick it up next week) and will work with the tires that comes on it (for a while.) On previous trailers I have gone to the Maxxis and found they worked very well. They are made in Thailand. If the Goodyear Marathon is being made in the states again I would also consider them. I've heard lots bad about the Marathons made in China.

fla-gypsy
06-05-2012, 06:01 PM
I switched to Maxxis and have been very pleased with the performance of them.

Momamac
06-05-2012, 06:06 PM
We have a 2010 Passport 300bh and have the same tires you do.
In 2010, we went from Michigan Lower Pennisula down and around until we got to South Dakota...including one bad move that had me pulling the trailer over a short section of road construction that was tore down to the road bed (including large asphalt chunks) and had the trailer leaning 30 degrees toward the ditch!:eek: Went back home through Minnesota, Michigan UP and home. In 2011 we stayed in Michigan but camped about every weekend 2 hours from home. Right now the tires look as good as new. Keep your pressure right and always look at them at every stop (I looked at every inch after the construction debacle!). When it is time to replace mine, I will look at American made but in a higher load range...mine are at the max right now!I also may move from 14" to 15"...not sure yet. If you read enough, you will find bad reviews of every tire...along with the political angle, too! I hate Communists as much as anyone and would rather not send them my money either! Happy Trails!:wlcm:

CWtheMan
06-05-2012, 06:15 PM
Hi folks, currently I have Tow Max tires by Power King size ST205/75 R 14 on my 2012 Passport super lite 238ml.
I have not heard one good thing of these tires and have been told several times and have even read forums about how bad these tires are and that I should replace them before they have a blow out.

The big question is, With what?? I've heard bad things about GY Marathons, Carlisles, and Michelins as well. Does anybody have any suggestions? Thanks a bunch!

According to the specs for your trailer you have nothing to worry about when it comes to the tires Keystone has provided with it. Keystone is not known to provide tires with much load capacity reserves but in your case they have giving you max over kill tires. Your trailer tops out with just a little less than 5000# on the axles and your tires provide 7040# of load capacity at 50 psi. Like almost any ST tire, the Towmax will give you great service if properly maintained and not abused with under inflation, overloading or speeding.

Here are some references for information.

http://www.keystone-passport.com/index.php?page=specs&year=2012

http://www.towmaxtires.com/Default.aspx

www.towmaxtires.com/catalogs/towmax-str-roadside-assistance.pdf

CW

PK in CA
06-05-2012, 06:40 PM
Thanks a bunch everyone! I really appreciate the input as well as the pep talks! I think I will just ride these into the ground for a bit longer and then go to Maxxis when need be.

Again, I really appreciate everyone's advice.

KanTC
06-05-2012, 07:33 PM
PK,

Here's a specific thread about Tow Max Tires... more good info. :thumbsup:

http://keystonerv.org/forums/showthread.php?t=6111

Given your CA location, I'd recommend using "tire covers" if your trailer is stored outside.

Welcome to the forum, and happy trails.
Terri, the Chevy co-pilot & DH Kevin :)

raytronx
06-05-2012, 07:37 PM
I just replaced my original set of TowMax tires, they had 15000 + miles on them basically looped around US on all kinds of roads and the treads were worn down from use, tires performed great. I went with another set of TowMax.

Halibutman214
06-05-2012, 07:48 PM
PK,

Here's a specific thread about Tow Max Tires... more good info. :thumbsup:

http://keystonerv.org/forums/showthread.php?t=6111



And you will see from this thread that the vast majority of people have had NO problems. I feel good enough about the responses from this thread that these tires will be with me on my Alaska trip.

Johnnyfry
06-06-2012, 02:25 PM
I have the original Towmax tires on my 5er and have had no problems in 16K miles. I keep them inflated to 80 PSI and have them balanced. I also don't tow over 60 MPH. I expect them to last at least another 7 to 8K miles.

Three tire dealers have told me that NO trailer rated tires are made in the USA, even if they are branded by a US manufacturer. Some people have suggested using LT (truck) tires but, no manufacturer or dealer I have encountered recommends this because trailer tires have definite manufacturing differences and would not perform well.

IMHO
John

Outbackmel
06-06-2012, 03:33 PM
2011 Outback, 36ft, triple slide. Just returned 2 months ago from 6700 miles x US from GA to AZ; southern route, I 20 to I 10 going and back across I 40. All types of weather from cold to heat to hail. Roads were HELL in some areas. Never ANY issue in the 6700 miles. Period. Tires look brand new. Next RV trip early August from N GA mountains to the beaches of Charleston and Myrtle Beach (Pirateland) rrrrr, matey!

Usually set speed control at 63-65 mph for safety and fuel economy. 11mpg at this range. TV...2008 Dodge, quad cab. 6.7 Cummins turbo diesel. Often have to look back to see if the RV is still there....Have a slider hitch, but, never needed it in "manuever" position. Can do a full 180 degrees without touching slider window. LOVE THIS THING.... :D

AlCorr
06-07-2012, 04:39 AM
I always add 10 psi more than the max. tire rating. On my truck and trailer. Hope this helps.

http://www.tirerack.com/images/tires/goodyear/Marathon_Special_Trailer_Applications.pdf?GCID=C13 674x032&code=yes

AlCorr
06-07-2012, 05:20 AM
My last trailer had GY Marathons. The tire pressure on the sidewalls was max. 60 psi. I always inflated to 70 psi and never had a problem. I always replaced them every 4 years. Also, on long hauls, I always tow 70-75mph.

seahunter
06-10-2012, 09:35 PM
Regarding speed safety:

•All "ST" tires have a maximum speed rating of 65 mph.
•As heat builds up, the tire's structure starts to disintegrate and weaken.
•The load carrying capacity gradually decreases as the heat and stresses generated by higher speed increases.

Festus2
06-10-2012, 10:42 PM
Greg -
Your information regarding speed rating of ST tires in your above post, taken from Discount Tires website, does state that if a tire is designated as "ST", the maximum speed rating is 65 mph.
However, if you visit this Goodyear site (www.goodyearrvtires.com/pdfs/rv_inflation.pdf), Goodyear lists a number of RV tires which are not designated at ST but have a speed ratings in excess of 65 mph - some as high as 75 mph.

I am assuming that these tires, which Goodyear has listed as being RV tires, are suitable for RV's.

seahunter
06-11-2012, 12:04 AM
Hi Festus2,

Some of the Goodyear RV tires are rated at 75 mph, but as far as I know they are all LT tires. For example, I'm getting the Goodyear G614 on our new Montana, which are LT235/85R16 and rated to 75 mph. However they also run at 3750 @110 psi and require a special high load capacity wheel and high pressure tire valve as per the Goodyear site. I'm still learning all the time :) so I might be incorrect, but all the Montana's that are not Big Sky's are running the ST RV Marathons and the limit I continue to see is 65 mph.

Jim & Kay
06-11-2012, 04:42 AM
IMHO, replacing rv tires every four years is a very smart move, But towing an rv at 75 mph is Very DUMB !!!!! :dizzy:

Festus2
06-11-2012, 07:12 AM
Jim:
No argument from me on that!

rhagfo
06-11-2012, 07:46 AM
IMHO, replacing rv tires every four years is a very smart move, But towing an rv at 75 mph is Very DUMB !!!!! :dizzy:

Jim:
No argument from me on that!

I agree with both of you, while I have no issue with getting up to speed going 60 pulling 11+K of trailer your chances of recovering from an emergency move go way down over 60 and get pretty slim at 70+.
Watched some idiot tailgating a working snow plow over Oregon 6 to the coast at about 45 mph, he was about 50 to 60 feet off the plows bumper on snow he was pulling a out a 35' toy hauler just pushing the limits in my book!

CWtheMan
06-11-2012, 05:48 PM
Regarding speed safety:

•All "ST" tires have a maximum speed rating of 65 mph.
•As heat builds up, the tire's structure starts to disintegrate and weaken.
•The load carrying capacity gradually decreases as the heat and stresses generated by higher speed increases.

Just a note here: Carlisle only recommends 60 MPH for their trailer tires.

CW

ls1mike
06-11-2012, 08:33 PM
I think you only really hear about the bad things on the internet. I had Carlises on the old trailer for 4 years and 10,000 miles. People said they would blow up and wear out. I kept them air up end checked the temps with an infrared temp checker from time to time while on the road towed at 60 and under. I never had one problem.

Stuff happens but take care of the tires properly and you should have no problems.

azlee56
06-11-2012, 08:39 PM
Now that I am being brave. I looked at our Montana tires and said WOW. I never hear of E tires before, so I had to go ask the guys here what is E tires? So this guy told me. Then there was some other tire and I said "what the heck is that?". One day the BF and I were out in the yard so I was reading our Montana tires and I said. hmmm. What are G tires that need 110 lbs of pressure? He said WHAT? I said that is what it says, come look. He had them at 85. I said again what is G tires? So I had to go look. I guess they are heavy duty. Then I looked at the truck and said HEY they are E tires.

What a lesson I am getting here.

azlee56
06-11-2012, 08:41 PM
wow I am a senior member (which I am not)!!!

seahunter
06-11-2012, 09:00 PM
Now that I am being brave. I looked at our Montana tires and said WOW. I never hear of E tires before, so I had to go ask the guys here what is E tires? So this guy told me. Then there was some other tire and I said "what the heck is that?". One day the BF and I were out in the yard so I was reading our Montana tires and I said. hmmm. What are G tires that need 110 lbs of pressure? He said WHAT? I said that is what it says, come look. He had them at 85. I said again what is G tires? So I had to go look. I guess they are heavy duty. Then I looked at the truck and said HEY they are E tires.

What a lesson I am getting here.

Another thing to realize too is just because that G-rated tire says 110 psi, does not mean you need to be running it at 110 psi. You need to look at the actual load you are running. If you're not running at maximum load, you can run them at 90 or whatever matches the load guides. Otherwise you will just have a rougher ride and keep the higher pressure unneccesarily. I am getting the Goodyear G614 tires which are the G-rated tire and will probably be running at 90-95.

azlee56
06-11-2012, 09:06 PM
thanks. I will tell the BF that, but I have a question in the AZ hot weather it is better to do less cause they get hot?

When he first put pressure in the tire, he did the stand back and look and that is where he came up with 85 pressure (he drove semi's) when I read 110 psi and said don't know and he said that is what it says so ok, he really was surprised. In AZ at 100+ degrees they do get hot. The others that saw my weight might add on here.

seahunter
06-11-2012, 09:22 PM
thanks. I will tell the BF that, but I have a question in the AZ hot weather it is better to do less cause they get hot?

When he first put pressure in the tire, he did the stand back and look and that is where he came up with 85 pressure (he drove semi's) when I read 110 psi and said don't know and he said that is what it says so ok, he really was surprised. In AZ at 100+ degrees they do get hot. The others that saw my weight might add on here.

As you probably already know, always check when they are "cold", meaning they have not been driven on yet. Actually if you have them lower in psi, it will cause more friction and raise the tire temperature. I do not live in an extremely hot climate so I'll let others chime in on this more. One other thing to consider is possibly a tire pressure monitoring system (TPMS) - one tha not only monitors pressure, but also temperature of each tire...

azlee56
06-11-2012, 09:34 PM
the tire monitoring system will probably be his xmas present...or I should say our xmas present.

CWtheMan
06-12-2012, 01:18 AM
RV trailer tire pressures for Original Equipment (OE) tires need to be kept at the recommended pressure (s) found on the tire placard/certification label or in the owner’s manual. There is zero justification for using less pressure than what has been recommended by the vehicle manufacturer with the exception of special circumstances found in the owners manual.

CW

seahunter
06-12-2012, 01:50 AM
RV trailer tire pressures for Original Equipment (OE) tires need to be kept at the recommended pressure (s) found on the tire placard/certification label or in the owner’s manual. There is zero justification for using less pressure than what has been recommended by the vehicle manufacturer with the exception of special circumstances found in the owners manual.

CW

CW,

I respectfully disagree. That is what a "Load Inflation Table" is for. In my case I do not need to run my tires at 110 psi if I am not fully loaded. In fact, if I run them at full load (3,750 X 4 = 15,000 pounds) I would exceed my particular axle weight rating.

I submit this link:

http://www.goodyearrvtires.com/tire-selector.aspx

and then hit "Download Load Inflation Table"

to show the various tire load limits based on psi.

Festus2
06-12-2012, 06:38 AM
Goodyear also has another link on the same site page in addition to the table mentioned above. Click on "RV Tire and Care Guide" and it explains there that the "tire inflation should be adjusted to the tire carrying the heaviest load". It also goes on to say that you need to weigh your set-up to find out what the load on each axle will be and then adjust your pressure accordingly within the load limits of the tire.
Someone who has a GoodyearG614 for example, as does seahunter and geo, can adjust their tire pressure to less than 110psi if it results in a "softer" ride. The Tire Load Inflation table would indicate what the recommended pressure would be for the axle load of their RV's.
This Goodyear guide makes for excellent and informative reading.

jsmith948
06-12-2012, 06:45 AM
Hello SeaHunter,

Well, I get all that, but; how do you avoid the sidewall flex (and the heat build up) resulting from running the tire under-inflated? In other words, if I am loaded up for a long trip, I should be at 65psi, but if I drain the water and remove all of our gear (say to go to the dealer for service) then I should run less air pressure?
When I drove OTR (2.5 million miles) I ran 105 psi in my trailer tires regardless of how heavy the load was. I think there might be more than one way to read the tables to which you refer.
No argument intended - just IMHO

azlee56
06-12-2012, 06:56 AM
the tires that are on the montana are different then what is on the label. The label says type E and 85 lbs, but the tires on it are type G and the tire says 110 psi. I read that type G tires are 14 ply. Not sure I read the right thing but I was surprised. Both are 16 inch though.

seahunter
06-12-2012, 09:47 AM
Hello SeaHunter,

Well, I get all that, but; how do you avoid the sidewall flex (and the heat build up) resulting from running the tire under-inflated? In other words, if I am loaded up for a long trip, I should be at 65psi, but if I drain the water and remove all of our gear (say to go to the dealer for service) then I should run less air pressure?
When I drove OTR (2.5 million miles) I ran 105 psi in my trailer tires regardless of how heavy the load was. I think there might be more than one way to read the tables to which you refer.
No argument intended - just IMHO

Hi Jack and Marty,

I guess the best way to look at it is more of a range of tire pressure built into the tire than actually being under-inflated. As per the Goodyear literature, the G614 has a "premium casing and mold shape design" and "solid, rounded shoulder ribs (which) increase rib stability".

Technically yes, anytime you adjust the load by a substantial amount, you would be able to adjust the tire pressure for the maximum quality ride. You can run any tire at full maximum all the time, it just may be that it is unnecessary air pressure for the given weight and just results in a harsher ride.

You're probably right on more than one way to look at it :), and I'm not an expert by any means and learning all the time...

Take care.

seahunter
06-12-2012, 10:01 AM
the tires that are on the montana are different then what is on the label. The label says type E and 85 lbs, but the tires on it are type G and the tire says 110 psi. I read that type G tires are 14 ply. Not sure I read the right thing but I was surprised. Both are 16 inch though.

Yes, E-rated are 10-ply and G-rated are 14 ply rated. Current Montanas that are not Big Skys, come with Goodyear Marathon E-rated tires. If they have the Big Sky package, they come with Goodyear G614s which are the G-rated tires. They just began allowing a stand-alone option of upgrading the tires on any Montana to the G614s which is what I was able to do. They are not cheap tires, but offer a lot of peace of mind especially with a not-so-great reputation of the Marathons amongst a lot of RVers. Not to get into a huge hornets nest, just stating fact, but the Marathons are not made in the U.S., and the G614s are made in the U.S.

azlee56
06-12-2012, 10:44 AM
OH! thanks for that explanation and now I know our little ark has the Big Sky package and 10 anniversary stuff.

seahunter
06-12-2012, 10:58 AM
OH! thanks for that explanation and now I know our little ark has the Big Sky package and 10 anniversary stuff.

I see yours is a 2008 - is it new to you? It should say "Big Sky" on it if it is a Big Sky. If you bought it used, they may have just replaced the tires at some point with the G-rated tires.

azlee56
06-12-2012, 11:06 AM
It was used when we got it, some military high up guy had it and traded it in for a $100,000 motorhome. It was a friend of the salesman. No it doesn't say big sky on it. 3500RL Montana. I do know it is the anniversary addition and had all kinds of upgrades to it.

Outbackmel
06-12-2012, 12:59 PM
8000 miles and look and ride as new. Recent 6000 mile trip, never an issue.
If I 20, 10 & I 40 are not a good durability test, what the heck is?
Second only to PA pothole turnpike.

Check pressure and lug nuts and pull that sucker.

CWtheMan
06-12-2012, 02:16 PM
CW,

I respectfully disagree. That is what a "Load Inflation Table" is for. In my case I do not need to run my tires at 110 psi if I am not fully loaded. In fact, if I run them at full load (3,750 X 4 = 15,000 pounds) I would exceed my particular axle weight rating.

I submit this link:

http://www.goodyearrvtires.com/tire-selector.aspx

and then hit "Download Load Inflation Table"

to show the various tire load limits based on psi.

I’m sorry for the bluntness of this answer.

Load inflation charts are a product of the freedom of posting non confidential information on the internet.

Load inflation charts provide the information necessary for experienced and certified mechanics to apply them.

The first rule in the application of load inflation charts with regards to Original Equipment RV trailer tires is to NEVER use less air pressure than recommended by the vehicle manufacturer.

When replacing OE tires with tires that deviate in pressure/load requirements the minimum load requirement must be equal to or greater than the OE tires. From that load requirement a new recommended tire pressure is established and displayed near the OE placard (s).

CW

p.s. I have a couple of valid references to support those statements if needed. I hate to post them because they are lengthy and often quoted out of context.

seahunter
06-12-2012, 03:05 PM
I’m sorry for the bluntness of this answer.

Load inflation charts are a product of the freedom of posting non confidential information on the internet.

Load inflation charts provide the information necessary for experienced and certified mechanics to apply them.

The first rule in the application of load inflation charts with regards to Original Equipment RV trailer tires is to NEVER use less air pressure than recommended by the vehicle manufacturer.

When replacing OE tires with tires that deviate in pressure/load requirements the minimum load requirement must be equal to or greater than the OE tires. From that load requirement a new recommended tire pressure is established and displayed near the OE placard (s).

CW

p.s. I have a couple of valid references to support those statements if needed. I hate to post them because they are lengthy and often quoted out of context.

Hi CW,

I think we may be looking at two different topics now. Your reply discusses the proper way to replace an OEM tire, and the other topic is whether that given tire can operate at different pressures under different loads. The Goodyear site I reference above is a consumer website, not commercial. Montana delivers trailers with G614 tires on the unit I have ordered, so that is an allowable OEM tire. I could see a problem going "backwards" or downgrading from a G614 to a Marathon, so I understand what you are citing above. Given that a proper specification tire has been mounted, then the charts are showing what the different inflation values will yield for weight capacity. So, say I have two 7k pound axles. I only need to run my tires between 95 and 100 rather than the maximum of 110 psi because any higher and my trailer's maximum weight would be exceeded. The tire allows for this, so there is no need to run at 110 psi, but I can if I want to. I can't recall what the 80 psi ST Marathons are rated at, but as long as I am over that equivalent for the LT G614 (which is what you are saying :) ) then I am okay - say it's 85 or 90 psi or whatever. In any case it gives me an operating range of say 85 to 100 in my case.

CWtheMan
06-12-2012, 06:47 PM
Hi CW,

I think we may be looking at two different topics now. Your reply discusses the proper way to replace an OEM tire, and the other topic is whether that given tire can operate at different pressures under different loads. The Goodyear site I reference above is a consumer website, not commercial. Montana delivers trailers with G614 tires on the unit I have ordered, so that is an allowable OEM tire. I could see a problem going "backwards" or downgrading from a G614 to a Marathon, so I understand what you are citing above. Given that a proper specification tire has been mounted, then the charts are showing what the different inflation values will yield for weight capacity. So, say I have two 7k pound axles. I only need to run my tires between 95 and 100 rather than the maximum of 110 psi because any higher and my trailer's maximum weight would be exceeded. The tire allows for this, so there is no need to run at 110 psi, but I can if I want to. I can't recall what the 80 psi ST Marathons are rated at, but as long as I am over that equivalent for the LT G614 (which is what you are saying :) ) then I am okay - say it's 85 or 90 psi or whatever. In any case it gives me an operating range of say 85 to 100 in my case.


The DOT regulation for tire fitment on RV trailers at the time of first sale is very direct. The tires on the trailer MUST match the description on the certification label/tire placard. Brand is not an issue. Size, load capacity and recommended tire pressure are the issue.

The dilemma is the load inflation chart. A very basic issue comes into play. Who sets tire pressure? The DOT says that responsibility belongs to the vehicle manufacturer. Therefore what the vehicle manufacturer has recommended on the placard is the minimum standard for that vehicle.

There is no OOPS allowed for the tire placard. It MUST be correct at the time of first sale. It protects both the buyer and seller. If replacement options are installed by the dealer before the sale date the dealer has the authority and responsibility to install a new placard. Even after the papers have been signed any installer has the responsibility to change (pen & ink) the information on the trailer and in the owner’s manual.

Now, if you have a trailer that came from the factory with 16” LRG tires and the placard depicts 16” LRE tires you have a situation that requires a RECALL for all like vehicles by that manufacturer. It has already happened for other Keystone trailers.

Here is a reference that clearly states not to use tire pressures below those recommended on the tire placard. Look on page two - "Find the recommended inflation pressure".

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

CW

seahunter
06-12-2012, 07:25 PM
The DOT regulation for tire fitment on RV trailers at the time of first sale is very direct. The tires on the trailer MUST match the description on the certification label/tire placard. Brand is not an issue. Size, load capacity and recommended tire pressure are the issue.

The dilemma is the load inflation chart. A very basic issue comes into play. Who sets tire pressure? The DOT says that responsibility belongs to the vehicle manufacturer. Therefore what the vehicle manufacturer has recommended on the placard is the minimum standard for that vehicle.

There is no OOPS allowed for the tire placard. It MUST be correct at the time of first sale. It protects both the buyer and seller. If replacement options are installed by the dealer before the sale date the dealer has the authority and responsibility to install a new placard. Even after the papers have been signed any installer has the responsibility to change (pen & ink) the information on the trailer and in the owner’s manual.

Now, if you have a trailer that came from the factory with 16” LRG tires and the placard depicts 16” LRE tires you have a situation that requires a RECALL for all like vehicles by that manufacturer. It has already happened for other Keystone trailers.

Here is a reference that clearly states not to use tire pressures below those recommended on the tire placard. Look on page two - "Find the recommended inflation pressure".

http://www.trucktires.com/bridgestone/us_eng/press/zip/WeighForm.pdf

CW

Thanks CW,

I remember seeing this guide before. It will be interesting to make sure when we pick up the trailer that the tire installer has updated the placard. Once we have the trailer, I will be doing exactly what your reference states:

"Find the RECOMMENDED Inflation Pressure

Always determine correct tire inflation pressure based on actual loads on the tires. Use the tiremakers’ recommendations (which you will
find in load and inflation tables). Never use inflation pressures lower than those printed on the vehicle placard."

So lets say my trailer weight is 14,200 after taking off the pin weight. So 14,200 is on the two trailer axles. Take 14,200 divided by four (tires) equals 3,550 pounds per tire. Since they happen to be Goodyear, I go to their inflation table and find 3,550 and it says the inflation pressure is 100 psi per tire. That is what I can run them at, I don't need to inflate them to 110 psi - but I can if I want too.

So, we are assuming (ha) that the new placard will be correct, but the source you have given is exactly the way to figure out the recommended inflation pressure based on ACTUAL LOADS on the tires. I guess my only point being one needs to reference the placard, but also needs to calculate the actual load to know how to properly inflate the tires.

Greg