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AH_AK

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Posted: 04/11/21 12:30am Link  |  Quote  |  Print  |  Notify Moderator

Like every other truck camper owner, I am looking to increase the safe load carrying capacity of my truck (2012 Chevy 3500HD SRW). I get that you can't increase the payload, but I also know that 90% of TC's on the road are overloaded (some egregiously) and you don't hear a lot about catastrophic failures. I imagine this is likely thanks to the healthy factor of safety that auto- and tire-makers build into their designs. Perhaps the nature of heavy haul driving (slow, cautious) helps to provide an additional buffer.

When I looked into the limiting factor for the payload, it appears to be the tires. The wheels, axles, suspension, and brakes all seem capable of handling a larger GVWR/GAWRR. Handling (sway, squat, etc.) is a different beast, but can be addressed with upgrades. So here is the rub (pun intended), my truck is very limited in terms of upsizing the tires ( with the intention of bumping the load index). I considered Rickson 19.5x6.75 wheels with 225/70r19.5 G or H tires, but Rickson is sort of MIA in terms of communications...also $$$. Vision wheels would be great, but the 19.5x7.5's can only run 245/70r19.5 and I am told they will rub...also $$$.

So I start looking for load range F tires in the stock size (265/70r18) and I find that one company makes them https://www.prioritytire.com/kanati-armo........7-124q-f-12-ply-at-a-t-all-terrain-tire/. Now these get me to a load index of 127, which I am satisfied with, but they have a speed rating of Q (99mph). No worries, I am not planning on racing around with my TC. Looking at S-rated (112 mph) tires, the absolute largest I can fit without lifting the truck is 275/70r18, and the load index is only 125 on these.

This gets me thinking about the basis for the load index and I find this http://www.trucktrend.com/how-to/towing/1407-understanding-tire-load-ratings. Apparently, it is based on temperature, which is a function of load, speed, materials/mass, pressure, and ambient conditions. So hypothetically, if I commit to never driving faster than 60 mph, would I actually have a greater factor of safety on the 125 index, S-rated tires due to the additional speed margin? I wonder if these calculations are done by tire makers using models, or, if they physically test every model.

Now before you all light me up: YES, I know I could buy a dually. YES, I know I could buy a smaller camper. YES, I know I can reduce the driving weight by emptying tanks and lightening my gear load. YES, I know that I can just relax and the extra 200-300 lb per tire probably won't kill me and my family. I am genuinely curious as to what these tires can handle practically speaking. I also believe that the more you know about the likely cause of failure (e.g. overheating) the better you can manage you operations to mitigate risks (e.g. drive slow/empty tanks when it is hot).

The tread on those Kanati's is probably going to wear fast, but the steel construction and the increased load index are awfully tempting. Plus, I don't need to solve the Rickson puzzle to actually buy them. What say ye?

JimK-NY

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Posted: 04/11/21 07:08am Link  |  Quote  |  Print  |  Notify Moderator

High temps and underinflation are major risks for tire failure. Slowing down can make some difference. My first truck had 17" rims with limited tire choices so I eventually paid well over $3000 for Rickson wheels and 19.5 tires.

My current truck has 20" wheels with somewhat better tire ratings. I guess I will stick with the current wheels and tires even though they are loaded to approximately max load. I have a TPMS and check it at least daily. I also drive at a maximum speed of about 65-70 mph.

Lwiddis

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Posted: 04/11/21 07:20am Link  |  Quote  |  Print  |  Notify Moderator

Assumption One...90% of TCs are overloaded.
Assumption Two...you don't hear a lot about catastrophic failures
Assumption Three...The tread on those Kanati's is probably going to wear fast
Assumption Four...thanks to the healthy factor of safety that auto- and tire-makers build into their designs
Assumption Five...Perhaps the nature of heavy haul driving (slow, cautious) helps to provide an additional buffer.

* This post was edited 04/11/21 08:42am by Lwiddis *


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BurbMan

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Posted: 04/11/21 07:28am Link  |  Quote  |  Print  |  Notify Moderator

I've not heard of that brand of tires, but the tread pattern looks very similar to the Nitto Ridge Grapplers that I'm running on my SRW. I'm very happy with these tires and will probably buy again.

Don't just go by "Load Range F"...you need to look up the actual load rating for the size you are interested in. If you look at the specs on any tire that comes in multiple sizes, you will note that load rating varies by size even when all tires are catty the same letter rating.

Here is the spec chart for the Ridge Grappler in various sizes, note that some the E-rated sizes have higher load ratings than the one size that is F-rated.

[image]

The right way to do this is load the camper up and head to a scale. Find out how much you're carrying on the rear axle and size your tires accordingly...


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JimK-NY

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Posted: 04/11/21 08:16am Link  |  Quote  |  Print  |  Notify Moderator

Kanati, Nitto Grapplers, or others do not seem to make any tire in 285/60r/20 that exceeds a load capacity of 3640. I had the same issue when I shopped for tires for 17" rims.

Buzzcut1

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Posted: 04/11/21 08:43am Link  |  Quote  |  Print  |  Notify Moderator

just an FYI on the 19.5s Having owned both 19.6s and 16s on my old truck 245/70R19.5s are the same size as 285/75R16. They are tall but the can handle 4500+ per tire


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Slymer

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Posted: 04/11/21 10:47am Link  |  Quote  |  Print  |  Notify Moderator

I went with the Visions for our F350 SRW. That was to allow me to go to commercial tires as I felt the rubber would be the weakest link. I went with Michelin XDS2's. 16 ply with load range H. Camper on, I run them at 120 PSI. Camper off I run them at 80. Supposed to be good for 100,000 kms. and so far it looks like they just may. I got drive treads for the rear but steer treads for the front (quieter up front). I also upgraded the TPMS valves at $35 each but they have never worked. The truck won't recognize them. Every time I ramp up to 120 psi I get a dashboard message,..."low tire pressure". Go figure. I just feel much safer with these tires.

AH_AK

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Posted: 04/11/21 03:23pm Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

High temps and underinflation are major risks for tire failure. Slowing down can make some difference. My first truck had 17" rims with limited tire choices so I eventually paid well over $3000 for Rickson wheels and 19.5 tires.

My current truck has 20" wheels with somewhat better tire ratings. I guess I will stick with the current wheels and tires even though they are loaded to approximately max load. I have a TPMS and check it at least daily. I also drive at a maximum speed of about 65-70 mph.


I feel like if they are under their max, you likely have a comfortable (unofficial) safety margin. How did you feel about the 19.5’s? Any issues with balancing? So much money, but nice to have that peace of mind.

AH_AK

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Posted: 04/11/21 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

BurbMan wrote:

I've not heard of that brand of tires, but the tread pattern looks very similar to the Nitto Ridge Grapplers that I'm running on my SRW. I'm very happy with these tires and will probably buy again.

Don't just go by "Load Range F"...you need to look up the actual load rating for the size you are interested in. If you look at the specs on any tire that comes in multiple sizes, you will note that load rating varies by size even when all tires are catty the same letter rating.

Here is the spec chart for the Ridge Grappler in various sizes, note that some the E-rated sizes have higher load ratings than the one size that is F-rated.

[image]

The right way to do this is load the camper up and head to a scale. Find out how much you're carrying on the rear axle and size your tires accordingly...


Sorry, I probably wasn’t clear. I am going off the load index. I am only looking at the F-range because they get me to a higher load index. They might be stiff/loud as all get out though. I assume if you are happy with the grapplers that the tread life wasn’t too bad on them. That is the gripe I see most often. I would love to just upsize my tires to get load index I want, but the front end on Chevy 3500 is so tight. Tough to do without rubbing or doing some trimming and/or lifting. A lift is out for obvious stability reasons.

AH_AK

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Posted: 04/11/21 03:33pm Link  |  Quote  |  Print  |  Notify Moderator

JimK-NY wrote:

Kanati, Nitto Grapplers, or others do not seem to make any tire in 285/60r/20 that exceeds a load capacity of 3640. I had the same issue when I shopped for tires for 17" rims.

It seems like the r18s have the best selection. Perhaps because base one tons run 18s? The 20s seem more focused on the “aesthetics crown”. Bum deal if you have 20s and want to haul. At least you have enough room in your fenders to play with larger tires.

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