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Tires - Load Range C and D capabilities


bufbooth

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Hello All,

I have been seeing some discussion lately on Class C and Class D tires and was hoping to get some more detailed information. I have been having a hard time getting specs on Yokohama tires so I was hoping that Yokohama tire owners could provide what the actual load rating in pounds on their tires are. From the information that I could find on the internet for 185R14 tires, the max. load range varies depending on brand. For example, I have see Max. load range (both C and D) tires have a range different of up to 210 lbs,

for example, one brand Load C had a max load of 1500 while another brand Load C had a max load of 1710. So far it appears to me that Load C and Load D does not mean much, it is

the actual max load rating that really matters. With a 210 lbs load swing, I believe

we can find examples of some Load C tires having more load capability than some Load D

tires. I am either seeing fasle information, or the tire companies can define what a Load range lbs number is, or the tire Industry has a min/max load range in each load ranging.

I currently have Goodyear 185R14 Wrangler Load Range C tires on my Toyota, they have

a max load rating of 1,710 lbs (at 55psi), 1,555 lbs (at 55psi) if used as duellys.

Her rear axle weights 4,050 and the front axle 1800 lbs. From my calculations my rear tires can handle 6220 lbs and my front tires can handle 3420 lbs.

Thanks,

Dennis...

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I have the Yokohama Y356 tires D load rated. The tire reads single load 1850 lb. dual load 1765 lb. at 65 psi cold. Funny I would have thought dual would have carried more load than a single.

X2? 3530#

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Hello All,

I have been seeing some discussion lately on Class C and Class D tires and was hoping to get some more detailed information. I have been having a hard time getting specs on Yokohama tires so I was hoping that Yokohama tire owners could provide what the actual load rating in pounds on their tires are. From the information that I could find on the internet for 185R14 tires, the max. load range varies depending on brand. For example, I have see Max. load range (both C and D) tires have a range different of up to 210 lbs,

for example, one brand Load C had a max load of 1500 while another brand Load C had a max load of 1710. So far it appears to me that Load C and Load D does not mean much, it is

the actual max load rating that really matters. With a 210 lbs load swing, I believe

we can find examples of some Load C tires having more load capability than some Load D

tires. I am either seeing fasle information, or the tire companies can define what a Load range lbs number is, or the tire Industry has a min/max load range in each load ranging.

I currently have Goodyear 185R14 Wrangler Load Range C tires on my Toyota, they have

a max load rating of 1,710 lbs (at 55psi), 1,555 lbs (at 55psi) if used as duellys.

Her rear axle weights 4,050 and the front axle 1800 lbs. From my calculations my rear tires can handle 6220 lbs and my front tires can handle 3420 lbs.

Dennis...

A lot of it has to do with the ply rating a "C" is rated 6 ply and load pressure of 50 psi and a "D" rated tire is rated 8 ply at a load pressure of 65 psi. When I bought my Toyota it had "C" rated tires on it one of them split right in the middle of the tread it did not come apart but the next day I bought 6 new "D" rated tires.

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I have the Yokohama Y356 tires D load rated. The tire reads single load 1850 lb. dual load 1765 lb. at 65 psi cold. Funny I would have thought dual would have carried more load than a single.

Would dual load be the sum of both tires 1765 plus 1765 or 3530?

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Would dual load be the sum of both tires 1765 plus 1765 or 3530?

Correct.. but don't forget you have 4 tires on the back. So you max rear tire load is over 7000lb. Of course your axle and brakes can't deal with that much weight.

Also that is why us po'folk with the 5/6 lug combo RVs can safely limp into the next town, in the event of a flat rear tire, with only 3 good tires on the rear.

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Thank you for all the replies.

The point that I was trying to make was that one that is buying new tires

should probably check that the tire has an acceptable Max Load capabilies

and just not go on the Load Class rating (ie. D). For example, one should

ensure that a Class D tire has at least an 1800lbs capability.

Thanks,

Dennis...

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Mine is a 92 Winne 21ft I seem to remember the book stating C at 50psi which is what is on it now,due to age plan on tire's this year so far have only found D rated tires which would be somewhat higher rating, and I hope the ride doesn't suffer. Someone posted here about a similar unit with a very harsh ride I'd hate to buy 6 new tire's and find out afterwards. Overkill

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Mine is a 92 Winne 21ft I seem to remember the book stating C at 50psi which is what is on it now,due to age plan on tire's this year so far have only found D rated tires which would be somewhat higher rating, and I hope the ride doesn't suffer. Someone posted here about a similar unit with a very harsh ride I'd hate to buy 6 new tire's and find out afterwards. Overkill

I would think that the ride stiffness would have more to do with the tire pressure than the extra plys in a D rated tire. I have seen a lot of discussion regarding the bet psi to run the d rated tires at for best ride and performance.

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tirerack.com has a pretty good site and they give a good run down on sizes,loads etc. The ply rating of a tire does not mean it has as many ply as the rating just that it is rated to be as strong as having X number of plys so the ride is not adversely effected. The Toy Home has a long wheel base so the ride is not bad regardless, higher pressure might make you notice little bumps more.

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Tires can be very confusing but critically important to RVers. There are several links below with some great information. Most modern tires will have a sizing something like P185/75-14 78S or LT185/75-14 88T. The first part of this description tells what type of use the tire is for. P=Passenger car tire also know as a P-Metric tire. The LT means it is a Light Truck tire. Generally speaking an LT tire is going to be of stronger construction than a P-Metric tire. You may also run across an ST at the front of a tire size. This would be a Special Trailer tire intended only for use on a trailer. After the initial letter or letters the first number, in our example "185" is the width of the tire in millimeters. This measurement is taken at the widest part of the tire, not at the tread. Remember the sidewall (side of the tire) almost always bulges out wider than the tread. You should also know that this measurement is taken on a specific width wheel. If you mount the tire on a wider or narrower wheel it will not be the same width. Most tire manufacturers will tell you on their detailed spec sheet what width rim they measured the tire width on. They also typically give an approved minimum and maximum wheel width. After the slash we see a "75" in the example tire. This means that the sidewall height (also known as aspect ratio) of the tire is 75% of the width of the tire. In this case 185mm X 75%=138.75mm sidewall height. Some older tires like the original equipment 185-14 tires on the earlier Toyota motor homes are missing a number. What this means is that the sidewall is the exact same height as the width of the tire. Essentially 185/100-14 if you will. You'll never see the 100 on a tire it's just understood that when this number is missing that is what it means. After the dash we see "14" in the example. This means the wheel size is 14 inches in diameter. Back to the first example we see "78S". This tells us two things. The two (sometimes 3) digit number is the Load Index NOT to be confused with the Load Rating. The Load Index allows us to directly compare two tires to know which one has a higher capacity to carry weight. A higher number ALWAYS indicates a tire with a higher weight capacity. The Load Index is the more modern system. Now the last thing we have on example 1 is "S". This is the Speed Rating. In this case "S" means the tire is rated for sustained speeds of up to 112mph. The "T" in example 2 is 118mph if you are interested. Speed Ratings are not straight forward, you just have to compare the letter rating to a chart to determine the speed rating. Generally speaking a tire with a higher speed rating will run cooler at a given speed which reduces pressure build up and tire wear. Unless you've put a small block Chevy in your Toyota this really is not that important to us! The last thing is the Load Range which is found on most truck tires. We typically see C and D in our applications. Generally speaking the higher the letter, the higher the weight carrying capacity of the tire for a given tire size. The Load Range is the older style of rating this and loosely correlates to the number of tire plys or more often tire ply equivalents. Decades ago before steel belted radials you had nylon, rayon, etc. plys in the tires and more plys usually equaled a stronger more puncture resistant tire. Load Range also tells you the maximum inflation pressure you can run in the tire. To get more load carrying capacity out of a tire you need more air pressure. A Load Range C has a max pressure of 50psi, Load Range D 65psi and Load Range E 80psi. There are more load ranges for other vehicle types.

If your are still with me here are two great links for reference and to help document what I have said. The first will show you Speed Ratings, Load Ratings and Load Ranges. There is also some other info I didn't cover. Note at the bottom this info was obtained from Bridgestone/Firestone. It's a dead link but I found the original info which you will see in Link 2. The charts in Link 1 can be found by digging in Link 2. It's not real easy to find (or link to) but I did verify the links in Link 1 came from Link 2. Link 3 page 47 shows LT Tire Inflation vs. Load Charts which I talk about further down.

http://www.dualport.com/bustech/load_tires.html#anchor-load

http://www.tiresafety.com/

http://www.tiresafety.com/images/Tire%20Replacement%20Manual.pdf

There are a few more important things to discuss. You only get the full load carrying capacity of a tire at a certain inflation pressure. It is VERY important to weigh your rig fully loaded and know how much weight you have not only on each axle but each wheel. Only then can you decide on an appropriate tire pressure to run based on the tables for your specific tire model and size. Not all tire manufacturers make this data available on the web. Usually calling the corporate office will get you the info you need once you get past the secretary who has no clue what you are talking about.

If you are upgrading in Load Range you need to consider what is the max PSI your wheels are rated for. Sometimes this is stamped on the wheel itself either on the outside or the inside (as you have to dismount the tire). If you have aftermarket wheels a call to the manufacturer may answer this question.

If I have a blowout on the dual rear wheels, I can just keep driving right? Well, not necessarily. Let's say for example the left rear of your rig weighs in at 2500 pounds. Your tires are rated at 1800 pounds single and 1500 pounds dual. With both duals in good condition inflated to where they will achieve the max weight capacity we have 500 pounds reserve at the left rear. Let's look at the math: 1500lbs load capacity X 2 tires = 3000lbs available minus our 2500lbs load at this corner. Now if we blew one of the tires we only have 1800 pounds of available load capacity. Unless we shed some weight or move some weight around we are absolutely overloaded. What can happen in this situation is that we damage the remaining tire by driving on it overloaded. This weakens the structure of the tire and it now has a much lower failure point. We might now set up a situation where we get a new tire to replace the first one we blew and then 200 miles later we blew the tire we overloaded. This is more of a problem with heavy 5th wheel trailers but you should be aware of it.

Old tires are failure prone tires. Tires age in many ways. One is sitting in the sun under UV rays that drys them out. Another is thru moisture inside the tire that may start to rust the belts and weaken them. A big one for RVs and trailers is sitting for extended periods in the same spot. Each tire manufacturer has a recommended (not required) age for discarding their tires, often 5-7 years regardless of how much tread is remaining. I personally don't run my RV or trailer tires over 5 years and that has dramatically reduced my rate of blowouts. If you do some searching in the RV.net forums you will find many people who agree with the 5 year point. Do you really want your vacation ruined by a blowout? Even more importantly for us Sunrader owners can you afford to destroy your really hard to find fender flare if the outer tire blows?

I hope this helps provide some insight on tires and clear up some misconceptions. If you are a Tire Geek like me you might want to check out http://www.tirereview.com/ It's a free industry publication for those in the tire business. I've read the print version for 17 years and learned a lot. I believe you can access articles on the site and subscribe electronically.

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