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Old 06-09-2008, 09:19 PM
rhc43 rhc43 is offline
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Towing with OEM Scorpion STR A Tires?

Our family will be taking delivery on a new Travel Trailer very soon. I have an 2007 Expedition EB regular length with HD tow package. The OEM tires are the Pirelli Scorpion STR A size P255/70/18 112 S. Sidewall shows max psi of 44 and max load at 2,469. We expect the TT to be around 7,500 fully loaded.

Does anyone have first hand experience towing similar weight with this tire that you could share?

I'm sure the best move is to replace my tires with LT tires. However, we only have 16,000 miles on current tires and would of course prefer not to have to replace them just yet.

Thanks in advance for your input.
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Old 06-09-2008, 10:44 PM
mjdoyle mjdoyle is offline
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2008 EL with the 18" chrome clad rims, but (I believe) the same tire size. We have a max wt. 7700lb travel trailer that we pul with no issue with these tires. I have pulled with the trailer fully loaded (including water/LP) as well as empty and it does have a "soft" ride, but not uncomfortable.

I agree, a stiffer sidewall would be nice. I am currently looking for a set of OEM 17" rims to use as winter rims/tires, and will probably skin them with LT tires. That way I can use them for towing on our longer trips as well. But, it isn't enough for me to worry about it.

-Mike
2000 Mercury Mountaineer V6
2008 Ford Expedition EL XLT
2001 Keystone Bobcat 280BH
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Old 06-10-2008, 05:35 AM
chuck s chuck s is offline
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Unless you're putting the trailer on the roof, the tire capacity won't influence towing ability. The tires have a capacity of 9876 pounds.

The axle ratings are computed with the tire pressure on the data plate. That's 7800 pounds with the stock tires at 35psi. But tire pressure may not be the critical factor to the axle rating.

May we assume the 7500 pounds is a fully loaded, gross trailer weight and not the fantasy "dry weight". Trailers are 400+ pounds heaver than the "dry weight" as they roll out of the factory and get heavier fast!

A 7500 pound trailer will need at least 750 pounds on the ball and a good weight distribution hitch is mandatory. We're using the Equalizer 1000/10,000 pound unit for our lighter, but tongue heavy trailer.

We're using the Tekonsha P3 electronic brake controller. Either the P3 or Prodigy remain the best controllers on the market and will stop you highway or city without messing with the controls.

I have two rules of thumb for towing weights. The 1000 Pound Rule states you need 1000 pounds more towing capacity than the trailer weight to accound for vehicle loads; the One Ton Rule states you won't be happy towing with less than a ton "excess" capacity.

-- Chuck
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Old 06-10-2008, 02:15 PM
rhc43 rhc43 is offline
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Mike / Chuck - Thanks for the input. Appears that I should be OK with these. the 7,500 for the TT does assume fully loaded and I think it is a conservative estimate. The dry weight is actually listed at only 5,475. Once we do take delivery we will get everything all loaded up and hit a CAT scale which lucky for us is only 15 minutes away. I definitely need to know where we stand with all the weights for my own peace of mind.

We also are going with the P3 and the equalizer 1,000/10,000 set up. I will also be picking up a sherline tongue scale as I know I'll need to carefully manage the tongue weight.

Thanks again.

Bob
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Old 06-10-2008, 02:26 PM
mjdoyle mjdoyle is offline
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Sounds like we are all on the same line with regards to what we are towing. My dry is right around 5800, I too have a P3, and use a 1000/10,000 Equalizer.

Out of curiosity, where are you picking up your tongue scale from? I too was hoping to pick one up, but haven't had the greatest luck finding one mail order.

Thanks!
-Mike
2000 Mercury Mountaineer
2008 Ford Expedtion EL XLT
2001 Keystone Bobcat 280BH
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Old 06-10-2008, 02:45 PM
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ltatkinson ltatkinson is offline
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I just bought a new TT with a dry wieght of 7800 and a hitch weight of right around 1000#. I put my tires up to 44psi, and it pulled and drove great.

Tim
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Old 06-10-2008, 04:22 PM
rhc43 rhc43 is offline
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There's an ebay store selling the 1k, 2k and 5K sherline scales for $104 plus $3 shipping. This was the cheapest I could find. I actually just bought one. Here's a link: Sherline LM2000 Weight Scale - eBay (item 220221745040 end time Jul-06-08 13:26:52 PDT)
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Old 06-10-2008, 07:21 PM
montecarlo31 montecarlo31 is offline
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I've switched my cheap factory tires out with BF Goodrich AT KOs. They are load rated and make a huge difference, there is a lot less sway and wander in the steering, you turn the wheel it does. The stiff sidewall is nice and in my opinion makes for easier towing (I.E. less flex on the side wall in turns and in wind).
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Old 06-10-2008, 07:39 PM
chuck s chuck s is offline
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This is ours without water in the tank. Goes to nearly 800 with water on board.

Click the image to open in full size.


-- Chuck
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Old 06-11-2008, 05:24 PM
montecarlo31 montecarlo31 is offline
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Has anyone noticed how weak the factory welds look on the stcok receive? I know it's off topic but very scary if you add some serious tongue weight. I'm getting ready to take mine off and add gussetts. Anyone else have any input?
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Old 06-11-2008, 07:13 PM
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ltatkinson ltatkinson is offline
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I think the hitch is fine if you stay close to the rating of the truck.


Tim
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Old 06-16-2008, 04:56 PM
montecarlo31 montecarlo31 is offline
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Quote:
Originally Posted by ltatkinson View Post
I think the hitch is fine if you stay close to the rating of the truck.


Tim

920 lbs on two welds that are two inches long. Yeah, that's 460 lbs per weld, or 230 lbs per welded inch. Who knows, maybe it's safe but I'm not sold on it yet.
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Old 06-23-2008, 10:01 AM
rhc43 rhc43 is offline
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Hey chuck s and mjdoyle - I should be picking up our TT in another couple of weeks. Regarding your use of the P3 brake controller, how do you each have your set as far as the power level and boos settings you use. Just looking for a good starting point from which I can fine tune. Thanks.
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Old 06-23-2008, 06:17 PM
mjdoyle mjdoyle is offline
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Quote:
Originally Posted by rhc43 View Post
Regarding your use of the P3 brake controller, how do you each have your set as far as the power level and boos settings you use. Just looking for a good starting point from which I can fine tune. Thanks.
The instructions for the P3 are as follows:


1. Connect trailer to tow vehicle.

2. With engine running set power (with Power
Buttons) to indicate 6.0
3. Drive tow vehicle and trailer on a dry level paved
surface at 25 mph and fully apply Manual Knob.

If trailer brakes lock up:

Turn power down using Power Buttons.

If braking was not sufficient:

Turn power up using Power Buttons.
4. Repeat Step (3) until power has been set to a point
just below wheel lock up or at a sufficient force as
to achieve maximum braking power.
5. Using the brake pedal, make a few low speed
stops to check the power setting. Trailer braking is
initiated and terminated via the stoplight switch.
When the brake pedal is released, trailer braking
will cease.
When I did this for my combination, I got all of the way up to 13 and still had no lockup so I figured I was ok. Then, when doing step 5 it felt like the trailer was stopping me instead of working in tandem with the truck. I ended up going back down to 12 volts and it feels much better. I have been running mine at Boost 1 for the past few trips, and am going to change to boost 0 to see if it makes a difference. This may have been the "trailer stopping me" sensation I was feeling before.

I would recommend you start out the same way as recommended in the instructions. It only takes you one hit of the lever to know if 6 is going to work for you or not...

-Mike
2000 Mercury Mountaineer
2008 Ford Expedition EL XLT
2001 Keystone Bobcat 280BH
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Old 06-24-2008, 05:31 AM
chuck s chuck s is offline
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Use 6.0 as a starting point per the instructions (quoted above). I believe there a pre-step to warm the brakes first before doing the 25 mph and override procedure.

If you have to go all the way to 13 the trailer brakes need adjustment. A new trailer brakes will wear in fairly rapidly so be prepared to repeat the controller adjustment in a few hundred miles and adjust the brakes as you get up toward 13 on the scale.

I do not use Boost in other than rare occasions such as very heavy rain where the early increased brake force helps dry the drums. Boost adds no power, it only applies it earlier. My trailer weighs under 5000 pounds and heavier trailers may benefit from Boost. It adds braking early in the cycle and consequently wears the trailer brakes more.

-- Chuck
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Old 06-24-2008, 05:31 AM
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