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Old 08-29-2015, 02:18 PM   #1
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Tire Specs

Anyone running tires that can handle over 5,000 pounds each? Also, did you swap your rims? Looking to see if there is a 16" tire available.

Assuming a GVWR of just a squeak over 20,000, that's a load per tire of 5000 lbs.

Thoughts appreciated. Seeking tires and brands.

Details:

42', two axle, four wheel total FR Cardinal. Looking to upgrade to tires capable of a shared load of 20,812 lbs - that's Load Index 138 which is 5203 lbs each multiplied by 4.

Balance: In the front of the 5th wheel, is a diesel generator with 32 Gal diesel tank and at the rear is a Swivel wheel platform hauling an electric golf cart. The weight difference between front weight and rear tongue is fairly neutral with a difference of just 200lbs but collectively with tongue weight from the platform and the generator + fuel the weight goes up. Each end of the rig has been strengthened: the front with heavy steel box section L rails bolted across the I beams and box section inside, and the rear hitch assembly bolted between the I beams.

Thoughts appreciated.

Thanks
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Old 08-29-2015, 03:16 PM   #2
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What Cardinal do you have? All the ones on the web site max at just over 16000 lbs.
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Old 08-29-2015, 03:42 PM   #3
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Try Continental HTL2ECO 235/75R17.5 6,000 lbs @ 125 psi. or Michelin, Goodyear G114, Sailun's 215/75R/17.5 @ 4,805 @ 125 psi. I don't think you will find a 16" tire in the 5,000 lb range. Talk at Scott at trailertiresandwheels.com.
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Old 08-29-2015, 03:45 PM   #4
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I have a 3875FB, GVWR 16314 lbs. Have had each end of the chassis strengthened.


Let me explain the weight distribution though, as I've been re-doing my weight distribution calcs.


The first post did not factor where the pin weight goes. MFG says pin weight loaded is 2634 fully loaded. I calculate about 5,175 pin weight taking steer and drive axle and deducting known weights including cargo, truck etc. This seems high though, but I did add a big generator and 30 Gals of fuel up front total 840 lbs inc chassis steel.


Yesterday I weighed on a 3 section truck scale at 29,960 with truck and rig and tow behind swivel wheel trailer with golf cart loaded.


The truck steer axle was 5700 lb, the drive axle was 8100 lb so assuming that the truck+pin weight = 13,800 lbs. The "Trailer Axle" (includes tow behing swivel wheel) recorded 16,160 lbs, so I deducted 2000 lbs for the swivel wheel, golf cart and bikes, leaving a net weight on both axles of 14160 lbs or 7080 per axle. I know that the present trailer is probably 65/35 weight distribution giving tongue weight of an extra 700 lbs which reduce to 100lbs when I add a balanced Idaho tote trailer, so I'm not counting it.


The axles are rated at 7,000 lbs and I'm assuming have a little bit of wiggle room.


I conclude that if I get tires rated at 4,000 lb each that should be plenty and the final load distribution will be:


Truck inc. pin weight with extra 40 gal tank and other acces = 13,939
New tow behind platform & cargo = 3,000
5th Wheel combined axle weight (assumed) 14,500 (existing 14160 + extra 340 from tow behind tongue weight and any extra cargo)


Total towing weight (not axle weight) inc. truck = 31,300
Axle weight 14,500 - or approx. 3625 per wheel.


Maybe add 10% wiggle room and spec 4,000 lbs tires?



Thoughts?
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Old 08-29-2015, 07:58 PM   #5
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Quote:
Originally Posted by btritschler1437 View Post
Try Continental HTL2ECO 235/75R17.5 6,000 lbs @ 125 psi. or Michelin, Goodyear G114, Sailun's 215/75R/17.5 @ 4,805 @ 125 psi. I don't think you will find a 16" tire in the 5,000 lb range. Talk at Scott at trailertiresandwheels.com.

I think the Continentals are 4,900 lbs. at that size and pressure. It's what I just installed.
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Old 08-29-2015, 08:43 PM   #6
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thanks for this. Looks.like.I would.need 17.5" rims. Continental Corporation*-Low Platform, High Load Capacity Trailer Tire from Continental

tomorrow's task is a re-weigh to establish the exact pin weight, and weight on each axle to validate the calcs I have.

after all the known calcs, I'll make a.tire decision and probably pull the trigger Monday.

regards

shayne
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Old 08-30-2015, 01:00 PM   #7
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Originally Posted by Shayne View Post
I have a 3875FB, GVWR 16314 lbs. Have had each end of the chassis strengthened.

Was that work certified by Forest River or a certified vehicle modifier or is it a gray area modification?

It's very risky to go over any of the limitations found on the trailer's certification label (except those that are variable, such as tires, which provide reserve load capacity for themselves when increased).
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Old 08-31-2015, 09:38 AM   #8
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the rear hitch was installed by a certified welder familiar with RV's. Chose to custom build the hitch for max strength with a large plate area each side and bolt it on in case we changed anything. That turned out to be a good idea because we are about to swap to an even more capable Idaho Tote trailer (worth a search to see this technology). The platform has hydraulic steering wheels so it will move with the RV, as well as electric brakes. This combination when balanced won't add much load and is a nice counter balance for the generator up front.

The front was strengthened as part of the generator install at the front by a very experienced RV dealer who is also a Cummins generator dealer. I called for strengthening to more than 3G's of force per the Cummins install spec.

For those considering a genset in the Cardinal at the front, it has only a thin plate across the base and even using the specified 5KW Cummins genset (I have a 7.5KW diesel), I would recommend considering strengthening it anyway.

The weigh in yesterday on CAT scales at Pilot was very helpful. FYI, cat can weight both axles as well as a "split axle" weight by positioning each axle on two of the 3 scales. We spent a couple of hours weighing everything. We weighed the truck attached with rig, and without rig to derive the pin weight, as well as the combined axle, split axle, and even our golf cart. We also.did tue split axle weight of the golf cart to establish how much weight differential exists on the GC axles. This is because the GC will be loaded sideways on the towing platform, over the axle and we can counter balance the lighter side with cargo, for an even smooth ride.

I am now satisfied the axle weights are good and each piece of our package has a known weight.

In summary, for the many RV'ers who have not considered their weight dynamics, a trip to a weigh scale at a truck stop may be very valuable, and avoid unpleasant surprises down the road.
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Old 08-31-2015, 11:16 AM   #9
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I think the Continentals are 4,900 lbs. at that size and pressure. It's what I just installed.

I happened to think about this, this morning. 4,805 per the tire.

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Yes, you have to upgrade to 17.5" rims for these tires. There are 2 outfits that I found who do it:
http://www.ricksontruckwheels.com/
http://www.trailertiresandwheels.com/

I liked the woman that I spoke with at Rickson a lot. Very friendly, knowledgeable, and super helpful in answering my newbie questions. BUT- their turn around time was just too long for me, I didn't like the rims, and TT&W ended up being about $400 cheaper.

With going to a 17.5" rim + tire, you end up with the same basic outer diameter of the tire because you have a shorter sidewall. I actually decreased my outer diameter size by about 1/2". Many people only upgrade their 4 wheels and keep their 16" spare as the size is so close. It's what I did, just to save some money for now. I'll get a cheap steel wheel and tire for a spare at some point.

The closest 16" ST tire is going to have a capacity of 3,900 lbs. in the Goodyear G614. Otherwise, ST and LT tires aren't going to have the carrying capacity in a 16" wheel. I was space constrained and ultimately wanted out of a ST tire, so I opted for this.

I only have 300-400 miles on these wheels + tires, so I can't speak to longevity. But, for now- I'm happy with my decision.
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Old 08-31-2015, 12:50 PM   #10
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Originally Posted by Shayne View Post
thanks for this. Looks.like.I would.need 17.5" rims. Continental Corporation*-Low Platform, High Load Capacity Trailer Tire from Continental

tomorrow's task is a re-weigh to establish the exact pin weight, and weight on each axle to validate the calcs I have.

after all the known calcs, I'll make a.tire decision and probably pull the trigger Monday.

regards

shayne
Be sure you understand the MAX operating speed for Low Platform Trailer tires. Many say 62 mph. This is MAX not average speed. Think of it as you would engine red line .
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