Montana Tire Ratings and Tow Speed - Page 2 - Montana Owners Club

Cat320 · 03-25-2007, 01:10 PM

Quote:

quote:Originally posted by sreigle

For our 2007 3400RL with the alloy rims the setting is 120 lb/ft.

Same here...book says 110 ft/lbs to 120 ft/lbs.

tollmann · 03-28-2007, 05:04 PM

We try to hold our speed at 65 or under when pulling. My MPG doesn't vary much between 55 & 65 but my old Ford with 3.73 gears seems happier at the higher speed. I blew two rear tires on the Ford on my return trip from Florida. Checked the pressure belore leaving and it was at 80 lbs. We wound up putting the Montys spare on a Ford rim and ran the last 200 miles that way. We held the speed down to 50-55 and everything handled well. We put the trailer tire on the right front and had no problems whatever. Had to do it because no tire store was open and they probably would not have had "E" range tires anyway. Goodyear is replacing under warranty after running all the numbers including weights and tire pressure in remaining tires.

tollmann · 03-29-2007, 01:35 PM

I just came back from my Goodyear dealer. He said that all tires, ST & LT included, have a speed rating of 112 mph unless otherwise noted on the tire. He told me that is the federal standard.

skypilot · 03-30-2007, 11:44 AM

I (politely) request you give your Goodyear this URL off their corporate web site http://www.goodyear.com/rv/pdf/rv_inflation.pdf. It plainly shows the ST tires rated for only 65 miles per hour!!!

dsprik · 03-30-2007, 01:24 PM

Skypilot, I did find that paragragh on your web site:
-------------
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.
--------------
I read this that 75 mph seems to be the max recommend speed on an ST. Over 65 mph, just increase cold inflation press by 10 psi. Unless your wheel/rim is not rated for this increased press...

*On Edit~ I have a question... What if you were expecting to run 70 mph on an Interstate, so you run your press up 10 psi over the stamped in press rating, then discovered most of your day was UNDER 65 towing. What kind of damage will occur is you run over inflated tires at these lower speeds for the remainder of the day???

*2nd Edit~ Just went outside to look at my tires. Mission ST 235-80-16 (TC108) Load Range E. This tire is not listed in Goodyear's chart. There are no Load Range E tires listed there at all. Are Mission tires made differently than Goodyear makes theirs? Also could not even see a press rating stamped on my tire - I know they are 80 #, though.

ols1932 · 03-30-2007, 01:47 PM

I'm convinced that I shouldn't increase the cold pressure in my tires above the manufacturer's recommendation regardless of the speed I am running. Anyway, I run at 60 mph on the flat surfaces and sometimes 70 down hill.

Orv

Cat320 · 03-30-2007, 02:41 PM

This sounds like typical legaleeze mumbo jumbo...

- "Industry standards dictate that tires with the ST (Special Trailer) designation are speed restricted to 65 mph under normal inflation and load conditions." That means the max speed is 65.

- "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." That means if I want to ignore the first paragraph and go faster, it's okay...as long as I increase the TP 10 psi OVER the stated maximum.

I think I'll keep it at 63 and be safe.

Montana Sky · 03-30-2007, 02:53 PM

I keep mine at 80 psi cold and leave it. My towing speed is 65 to 68 mph unless the speed limit is posted lower or I am in the mountains. What works for some, won't work for others.

Post script~ I run LT tires on all my trailers. Have had horrible luck with ST tires on the boat trailer in years past.

jhamlin164 · 03-30-2007, 05:03 PM

Hi Guys,

There's been some pretty "spirited conversation" on this one for sure; I tend to agree with dsprik on this one; 65 mph is the max speed for ST rated tires. I have also read that you can increase cold psi by 10 if you plan to tow between 66 & 75 mph. The overwhelming majority of problems come from OVER-loaded, UNDER-inflated tires. Don't think you'd get into too much trouble if you were overinflated by 10 psi driving at or below 65 mph.

In the event that some of you really like to drive at 70-75, I understand that Goodyear makes a Unisteel G614 RST that is actually an LT rated tire that is specially adapted for trailer applications .............it has a speed rating of 75 mph. The tire also has a weight capacity of about 3750 lbs. The only catch is that one must have special steel wheels that have high pressure tire valves & can support the heavier loads. These tires run pressures of 100-110 psi. The current steel wheels that come stock on our Montanas may already be strong enough to handle the Unisteels....................can't be certain, though. Think I'll give the good folks at Keystone a call tomorrow and see what they have to say. Just my .02s worth.

Jerry

LonnieB · 03-31-2007, 07:16 AM

This might get a little long winded, but I will try to keep it as short as possible.

Almost every tire manufactured today has an International Load and Speed rateing molded into the sidewall. It will be a one to three digit number followed by a letter, or for tires that can be dualled, there may be two, three digit numbers seperated by a slash, followed by a letter. For example, LT265/75R16 BRIDGESTONE DUELER A/T REVO 123/120R. 123/120 is the International Load Index Number, 123 = 3420 lbs. for single, and 120 = 3080 lbs. for duals. The speed rateing of R = 106 mph. max.

ANY tire that does not have this load and speed rateing molded onto it, should be treated as a NON SPEED RATED TIRE, meaning 65 mph. max. This includes ST rated tires.

As far as adding 10 psi to your ST tires to operate at speeds up to 75 mph goes, there are a couple of reasons why you shouldn't. First and foremost is the pressure rating on the wheel. The steel Montana wheels are rated for 80 psi max. The Mission ST235/85R16E tires are rated for 80 psi max. 10 psi more will put you over max on both counts. The second reason is that travel trailers have special rules to follow, according to Bridgestone/Firestone. " Tire size and inflation pressure will depend on the type and size of trailer and type of hitch utilized. However, in no case may the inflation pressure exceed the maximum cold inflation pressure molded on the tire sidewall."

I have speed rateing and load index charts that I will try to get posted, but may be later today. I still have to work for a living

, and today is inventory day so I better get 'er done. Hope this has answered more questions than it has created.

ols1932 · 03-31-2007, 07:55 AM

Lonnie, you always seem to come through at the right time.

Cat320 · 03-31-2007, 08:22 AM

Good information, Lonnie.

LonnieB · 03-31-2007, 12:31 PM

Here are a couple of partial lists. The International Load Index is way too long to put on here, it starts with #1, and ends with #199, so I have only listed the ones I think will apply to our situation. The speed rating list is below the load index list.

LOAD INDEX

100 - 1760 lbs. 116 - 2760 lbs.
101 - 1820 lbs. 117 - 2830 lbs.
102 - 1870 lbs. 118 - 2910 lbs.
103 - 1930 lbs. 119 - 3000 lbs.
104 - 1980 lbs. 120 - 3080 lbs.
105 - 2040 lbs. 121 - 3200 lbs.
106 - 2090 lbs. 122 - 3300 lbs.
107 - 2150 lbs. 123 - 3420 lbs.
108 - 2200 lbs. 124 - 3520 lbs.
109 - 2270 lbs. 125 - 3640 lbs.
110 - 2340 lbs. 126 - 3740 lbs.
111 - 2400 lbs. 127 - 3860 lbs.
112 - 2470 lbs. 128 - 3960 lbs.
113 - 2540 lbs. 129 - 4080 lbs.
114 - 2600 lbs. 130 - 4180 lbs.
115 - 2680 lbs. 131 - 4300 lbs.

SPEED RATING

M - 81 MPH
N - 87 MPH
P - 93 MPH
Q - 99 MPH
R - 106 MPH
S - 112 MPH
T - 118 MPH
U - 124 MPH
H - 130 MPH
V* (VR) - 149 MPH
W** (ZR) - 168 MPH
Y** (ZR) - 186 MPH
(Y)*** - >186 MPH

* Current tire speed rating markings include the use of the service description to identify the tire's speed capability (P215/65R15 95V - maximum speed 149 mph). Previous customs included the speed symbol in the size designation only (P215/65VR15) and the speed capability was listed as "above 130 mph."

** Any tire with a speed capability above 149 mph can, at the tire manufacturers option, include a "ZR" in the size designation (P275/40ZR17). If a service description IS NOT included, the tire manufacturer must be consulted for the maximum speed capability (P275/40ZR17 - speed capability is > 149 mph). If a service description IS included with the size description, the speed capability is limited by the speed symbol in the service description (P275/40ZR17 93W = maximum speed of 168 mph).

*** Capable of speeds over 186 mph. The tire manufacturer must be consulted for the maximum speed capability.

Sorry, I got a little carried away thinking about all that speed, lol.

dsprik · 03-31-2007, 02:37 PM

Well, I should be fine. My Mission tires will be left at 80#. My back tires on my GMC 2500 are at, and will remain at 80#. My front tires will be at 55#, as per the door post sticker. I will drive right at 62 mph, as I have been doing ever since I started towing this 3400 last summer.

How can I go wrong???

haslcs · 03-31-2007, 02:57 PM

Lonnie B glad you posted this info. it is very informative for us all.

skypilot · 03-31-2007, 04:04 PM

Lonnie B: My thanks as well. By the way, Glad everything and everyone there is safe!. Have to travel to ABQ in 2 weeks; hope weather cooperates.

tollmann · 04-04-2007, 10:40 AM

After checking the Goodyear web site I am going to have words with the manager at my Goodyear store. Not that I would drive my TV that fast but 112mph sounded a little high. I can't imagine the Feds wanting us to go that fast anyway. I remember the 55mph Fed speed limit all too well. Beside that we need all of the tax payers alive and paying their taxes.

sreigle · 04-04-2007, 04:21 PM

The tires on my F250 are LT265/70R17E 221/218R, so they are rated for 3200 lbs single and 2910 dual. Or 6400 lbs for the axle, single.

I realize a dually is not going to carry as much weight per tire as would a SRW carrying the same overall weight. But what is the rationale behind the tire having a lower rating when used as dual?

Lonnie, thanks for the info. That's good info to have at hand and I've saved your info on my system.

LonnieB · 04-05-2007, 02:28 AM

Steve,

That's a good question. My understanding for the lower load rating on dual wheels, is so they don't touch each other. On some vehicles, the duals are very close together, especially if the OEM tires have been replaced with wider ones. The heavier they are loaded, the more they distort where they meet the road, and the closer together they get.

Glenn may know other reasons as he was in this business much longer than I have been.

sreigle · 04-07-2007, 07:41 AM

Interesting. Thanks. I wonder if that could happen with low tire pressure, too. I guess that wouldn't be enough to squat the tires enough to be a problem unless maybe they were way too low.

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