View Poll Results: your towing speed
55mph 167 13.11%
60mph 480 37.68%
65mph 450 35.32%
70mph 144 11.30%
75 mph or faster 33 2.59%
Voters: 1274. You may not vote on this poll

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Old 06-04-2007, 03:02 PM   #99
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Quote:
Originally Posted by Minnie's Mate
Thanks Jack. I haven't checked Illinois yet............I do seem to remember someone mentioning that Illinois is strict on speeding for trailers & semis, though.
The state troopers are more than happy to remind anyone towing going faster. In Illinois, on I-57 below I-64 and on I-24 the troopers run in packs and are pretty brutal in their enforcement. I am not sure what happens above I-64 though.
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Old 06-04-2007, 03:30 PM   #100
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Quote:
Originally Posted by jcanavera
But like anything else there is a limit, and once you start doing 75mph to keep up with the flow of the traffic, your ability to deal with an emergency situation or one that requires quick reaction is extremely limited....
Trueish. But the reality of this kind of interstate driving is that I'm sitting behind a truck going 65-75MPH and behind me is either another truck or a parade of cars zipping by to pass. I upgraded to discs so I can easily outstop the truck ahead of me. My real worry is the truck behind me failing to stop or the car behind me doing something stupid because of impatience.
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Originally Posted by jcanavera
You are now creating a situation where you have with no doubt exceeded the speed rating of the tires, thus fostering a potential problem.
Nope. My tires are rated at 75MPH for the load I carry at 65 PSI. Actually, I upgraded my tires so that they are rated at 75MPH for about 42% more than the load I carry on them (3200lbs) - 4540lbs at 75MPH and 5080lbs at 65MPH.
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Old 06-04-2007, 03:42 PM   #101
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Originally Posted by ljmiii
Many of the 'near misses' I see on long drives are cars dodging around big rigs trying to avoid a Winnebago puttering down the road at 50 MPH.
Quote:
Originally Posted by Gen Disarray
Using this logic, the speeders are in the right and the law abiding drivers are in the wrong and unsafe. I'm not buying.
First, on many of these roads the truck/trailer speed limit is 75MPH.

Second, even when the truck/trailer limit is 65 I have never, ever seen anyone pulled over for traveling with the flow of traffic in the slow lane of a crowded Interstate.

Third, I'm not looking to be right - I'm looking to be safe. Vehicles traveling at a speed different from the traffic flow cause accidents - be it weaving through traffic at 25MPH when everyone else is stuck at 5MPH, zipping along at 90MPH when everyone else is going 75MPH, or puttering along the slow lane of an interstate at 50MPH when the big rig traffic is going 75MPH.
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Old 06-04-2007, 04:07 PM   #102
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From the Goodyear web site about RV tires.
On The Wings of Goodyear | RV Tires - Tire Care: Proper Tire Inflation
Click the inflation table to get the data.
Note the max speed for their ST metric tires is 65 mph. While there may be other brands* that will go higher in max speed this is the word from Goodyear.

Attached is a state by state towing regulations. Gives speeds for the states too.

*I believe Cooper may offer thires rated for speeds faster than 65

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Attached Files
File Type: pdf State by state towing regs.pdf (1.72 MB, 69 views)
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Old 06-04-2007, 04:10 PM   #103
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Quote:
Originally Posted by ljmiii
Second, even when the truck/trailer limit is 65 I have never, ever seen anyone pulled over for traveling with the flow of traffic in the slow lane of a crowded Interstate.
They will in California. I have the cancelled check to prove it from 1998.

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Old 06-04-2007, 04:30 PM   #104
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Quote:
Originally Posted by Action
From the Goodyear web site about RV tires.
On The Wings of Goodyear | RV Tires - Tire Care: Proper Tire Inflation
Click the inflation table to get the data.
Note the max speed for their ST metric tires is 65 mph.
Goodyear's Recreational Vehicle Tire and Care Guide show the max speed as 75MPH

http://www.goodyear.com/rv/pdf/rvbrochure.pdf

Middle of Pg 9 in tan box -

IMPORTANT OPERATING INFORMATION
Industry standards dictate that tires with the ST (Special Trailer) designation are speed restricted to 65 mph under normal inflation and load conditions, unless a different speed restriction is indicated on the sidewall of the tire.

Based on industry standards, if tires with the ST designation are used at speeds between 66 and 75 mph, it is necessary to increase the cold inflation pressures by 10 PSI above the recommended pressure for the load.

* Do not exceed the maximum pressure for the wheel.
* If the maximum pressure for the wheel prohibits the increase of air pressure, then the maximum speed must be restricted to 65 MPH.
* The cold inflation pressure must not exceed 10 PSI beyond the inflation specified for the maximum load of the tire.

Pg 16 has the load/inflation chart that specifies maximum load for a given inflation pressure

For ST225/75R15s load rated "C" tires 40 PSI is 1880lbs and 50 PSI (max) is 2150lbs
For ST225/75R15s load rated "D" tires 55 PSI is 2270lbs and 65 PSI (max) is 2540lbs

Thus, you can run Cs at 50 PSI at max load 2150 lbs at up to 65 MPH or max load 1880lbs at up to 75MPH

And you can run Ds at 65 PSI at max load 2540 lbs at up to 65 MPH or max load 2270lbs at up to 75MPH

Obviously no matter what tire or speed you choose, being at a solid percentage less than 'max load' is a good thing.
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Old 06-04-2007, 05:15 PM   #105
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Quote:
Originally Posted by ljmiii
And you can run Ds at 65 PSI at max load 2540 lbs at up to 65 MPH or max load 2270lbs at up to 75MPH

Obviously no matter what tire or speed you choose, being at a solid percentage less than 'max load' is a good thing.
Some how I'm missing where you are getting the 2270 lb max at 75 mph. Everything I'm looking at with an ST rating shows ratings up to 65. All the other tires on page 16 where there are speeds up to 75 are not ST's.

While I see that Goodyear does have a blessing for 75mph with a 10 lb increase in pressure, the overwhelming issue I see is that's still awfully fast to be traveling and I dare say that while I'm not going to be poking along at 50, I'll take my chances at 60-65 in traffic. No matter what kind of brakes you have on that trailer, it just stands to reason that you would be better able to handle an emergency situation at that speed rather than at 75. The Insurance Institue for Highway Safety reported in March of 2007 that in a study that a loaded tractor trailer requires 1/3 more distance to stop at 75 than at 65 mph. While I'm not driving a tractor trailer I probably can use this as a rule of thumb since I'm not using air brakes and brakes the size of a semi.

I can give you tons of examples of a particularly deadly stretch of I-44 just southwest of St. Louis that has killed 17 folks in the last 5 years. Most of these involving trucks traveling too fast and unable to react to suddenly slowing traffic. The latest two weeks ago when a lady was flattened by a semi who flattened her Ford. Maybe if he had been traveling 10 mph slower, he may have had the margin needed to stop or at least do a controlled avoidance.

While I have enough to worry about what's coming up behind me, I want the ability to at least stop and maneuver if something happens.

Jack
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Old 06-04-2007, 06:09 PM   #106
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Quote:
Originally Posted by ljmiii
Originally Posted by ljmiii
Third, I'm not looking to be right - I'm looking to be safe. Vehicles traveling at a speed different from the traffic flow cause accidents - be it weaving through traffic at 25MPH when everyone else is stuck at 5MPH, zipping along at 90MPH when everyone else is going 75MPH, or puttering along the slow lane of an interstate at 50MPH when the big rig traffic is going 75MPH.
I have no idea if your rig is safe at 75 towing, that is not my issue. This is: an operator of a motor vehicle has the responsibility to be able to stop without hitting the vehicle in front. If anything is stoped in your lane you better be able to stop. Period. It is not the responsibility of every driver to increase speed untill reaching that of the fastest driver out on the road that day. To try and place blame in these circumstances on the law abiding driver is at best bad logic. When I am on the road, I can not control how others are operating their vehicles, I can only control how I operate mine. While I was a firefighter/medic I worked enough accidents to fear tail gaiters, speeders, drunks, and cell phone users. I recall one incident in particular in which a semi over-drove a car up to the motor compartment (from the rear) and this was on a two lane, not an interstate. It is not, as you have stated, people driving at different speeds than the flow that is dangerous; it is people operating their vehicles beyond the safety magins of speed and stoping distance, often while not attending to driving that is a the root of the vast majority of accidents. I hope these coments do not sound preachy as I hate that as much as the next person; having said that I would be remiss to allow the "slower driver is dangerous" myth to go unchallenged. *climbs off soapbox*
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Old 06-04-2007, 06:28 PM   #107
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Look the bottom line is the ST tires with the correct load and pressure can do 75Mph and that is supported by the tire manufactures site.

Clear as a bell!

But if the tire can do 75 doesn't mean every driver can handle it without white knuckles.

There are drivers and there are good drivers, proceed at your own pace.

But please don't crawl in the right or worse yet left lanes on an interstate, you could become a pancake.
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Old 06-04-2007, 06:39 PM   #108
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Quote:
Originally Posted by jcanavera
Some how I'm missing where you are getting the 2270 lb max at 75 mph...While I see that Goodyear does have a blessing for 75mph with a 10 lb increase in pressure...
Goodyear does do a poor job of explaining their speed/load/pressure charts. Their tire guide says you can go 75MPH with a 10lb increase in pressure - but that doesn't mean you can put 75PSI in your 65PSI tires and go 75MPH. Instead, you have to read the chart 'backwards' - to use their tires at 75MPH you have to decrease your load to the value in the chart shown at 10 PSI less than you have. In other words, to use your load rated D tires at 75MPH you need to decrease the load to the value shown under 55 PSI (2270lbs) - and then 'increase' the tire pressure back up to 65 PSI.

Quote:
Originally Posted by jcanavera
No matter what kind of brakes you have on that trailer, it just stands to reason that you would be better able to handle an emergency situation at that speed rather than at 75.
No question...and one of the many reasons I go 65 max on the open road or with light traffic on the highway. But on a congested interstate, I'm much less likely to get into an emergency situation if I'm going with the flow of traffic than if I'm forcing the trucks going 70 to fight their way into the truck traffic going 75 which in turn is trying to avoid the traffic in the fast lane going 80 and the cars dipping back into the middle lane because 80 is too slow.
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Old 06-04-2007, 07:39 PM   #109
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Quote:
Originally Posted by ljmiii
Their tire guide says you can go 75MPH with a 10lb increase in pressure - but that doesn't mean you can put 75PSI in your 65PSI tires and go 75MPH. Instead, you have to read the chart 'backwards' - to use their tires at 75MPH you have to decrease your load to the value in the chart shown at 10 PSI less than you have. In other words, to use your load rated D tires at 75MPH you need to decrease the load to the value shown under 55 PSI (2270lbs) - and then 'increase' the tire pressure back up to 65 PSI.
This also assumes your towed load is less than max capacity of the tire(s).* Most trailer manufacturers install tires that are rated just over the total max load of the trailer. It is less expensive to install tires that have little load capacity margin left. So most trailer buyers do not have the option of reducing the load, unless they buy larger capacity tires. This is true for many many trailers of all types out there.

Not so for the typical passenger vehicle. The typical passenger vehicle has lots of load capacity left to take on additional loading. Usually people.


*For this discussion, max is 90% of the rated load.

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Old 06-04-2007, 08:02 PM   #110
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Quote:
Originally Posted by ljmiii
Goodyear does do a poor job of explaining their speed/load/pressure charts. Their tire guide says you can go 75MPH with a 10lb increase in pressure - but that doesn't mean you can put 75PSI in your 65PSI tires and go 75MPH. Instead, you have to read the chart 'backwards' - to use their tires at 75MPH you have to decrease your load to the value in the chart shown at 10 PSI less than you have. In other words, to use your load rated D tires at 75MPH you need to decrease the load to the value shown under 55 PSI (2270lbs) - and then 'increase' the tire pressure back up to 65 PSI.
Correct.

Now let's touch on what the true load on the tires are.

Say you trailer hits the scales at 8,000lbs.

From that you subtract the tongue weight 900 lbs, that's 7100 divided by 4 = 1725.

(I've heard people say you can subtract the weight of the tires and wheels also, but that's getting a bit anal)

Even adding 10% for a safety margin you're well under that 2270.

You may get 75mph at 55 or 60psi.

But if your in that range I would go 65 less rolling resistance.

On wet roads you may want to drop the PSI a little which will give you a greater footprint to grab the road. (you will be going a little slower anyway.)

Get an exact weight on your trailer like at a Cat scale then get the tire chart put it someplace to check when your on the road.
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Old 06-04-2007, 09:11 PM   #111
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Tires

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The Cooper tire is the Custom Trailer Plus:

Cooper Tires - Tire Selector

It carries a Speed Rating of "S", 112MPH:

Cooper Tires - Speed Rating

I would have bought them but no one would order them for me. The Cooper marketing structure is that you have to order tires in large quantities, not oneses and twoses. No one was willing to order $60,000 in tires just to sell me 5 tires.

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Old 06-04-2007, 09:21 PM   #112
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Ok, let's try another angle. Assuming you've reached your cruising speed (and are thus no longer accelerating), the overwhelming majority of the gas you're burning is being used to overcome aerodynamic drag. Drag increases exponentially with speed. To go twice as fast, you have to overcome four times as much aerodynamic resistance.

On our last trip, we got about 12 mpg at 55 mph. That's with a 28' trailer and a 3/4 ton big block gasser pickup. Do any of you with similar rigs who tow at 75 mph have reliable mileage data to compare? I'm curious how big the difference might be.
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