Speed Limits ... just a suggestion

[phillyg]

Originally Posted by Chalkie

That's funny! In 30+ years of owning RVs and other trailers I never once found an ST tire rated for 65 miles per hour......

That's funny, until the last couple of years I never once found an ST tire rated above 65mph.

[glkids2]

Closer to cities I usually go about 60-65 depending on traffic. Sometimes a little slower. But in the more open road where traffic lightens up. I have push up to 66-67 in the more desolate parts of the country

[masterdrago]

The posted speed limit along our neck of the woods (north of Houston) is 65. We generally run a tad under 80 and very, very frequently get blown by as other drivers seem to need to be running 90+. We are still waiting on our new ordered truck and have chosen a new camper that comes with Goodyear Endurance tires. Best I've been able to find is a speed rating of "N" = 87mph on one of the Goodyear pages for ST tires.

[CaptnJohn]

Originally Posted by phillyg

Drivers in SWFL have lost their minds. What bothers me more than 10-15mph over, is the weaving, tailgating, and other aggressiveness shown by many. The worst is pulling out of a side street or turning left in front of you. If I have to brake for those idiots, they were in the wrong.

You have just mentioned the #1 reason my wife said no more! We have wintered in swfl for years, not this coming winter or ever again.
In addition to your examples how about passing on the bike lane at 80 or motorcycles running between 2 vehicle going the same direction. If my mirrors had been out for towing it would have slapped him.

[laverdur]

Some folks just don't learn.

[bcrvman]

Originally Posted by Donjamin

Last month we spent 3 weeks in Utah camping at Arches, Bryce Canyon And Zion National Parks. Being from California where the trailer towing speed limit is 55, it was a bit unsettling to see an 80 MPH internet speed limit and having travel trailers and 5’ers zooming past us at the posted limit. I felt staying 65 saved fuel and felt comfortable. I guess to each his own.

Don

55mph or 90kph is my ideal speed when moving 30,000 lbs down the road. Maybe it would help people understand if it was expressed in more familiar terms like feet per second. 55mph is 81 feet per second. How many seconds do you think it takes to get your foot from the gas to the brake pedal, then how many more to get you slowed to anything near a speed that will not kill, maim, or cause 10's of thousands in damages. Remember 80mph is 120ft/sec or 50% more than 55.

[laverdur]

ST tires are speed rated at 65 mph. I frequently see people towing at 70+ mph. I suppose they could have changed to LT tires which would allow those speeds but speed is only one aspect of towing. Stopping is the other. I won't get into the fuel economy loss at higher speeds. Although my G614s are rated for more than 65 mph, I enjoy knowing that there is a safety margin if I don't exceed 65 mph.

[Greyghost]

I too tow our Monty at 65, to much is at risk to travel higher than that. Funny thing regarding speeders, when living in West Texss, Tucson, or now northern Florida, It seems to be the same, a complete disregard for the law. You will see driving patterns change around labor day.

[kowbra]

A few thoughts to respond to some of the comments on this thread...

---
ST tires have had speed ratings for decades; IIRC it was the early 90s when the current system of ratings was implemented. It seems that a speed rating "L" is very common, which as others mentioned is 75mph.

---
Fuel mileage and speeds? Here are my experiences from a long trip a few weeks ago; I wanted to gather some data on this particular topic, so all data is based on a single fill up, hand filled to the very top each time:

-lowest mileage on trip, 7.4mpg. Conditions were little wind, but lots of curves, lots of elevation changes; speeds averaged ~60-65mph (kept with traffic on 2 lane highway)
-highest mileage on trip, 10.1mpg. Conditions were calm, straight interstate, little elevation changes; speeds averaged 70mph to keep up with most of the trucks
-second worst mileage (8.1mpg) was ~65mph and facing a quartering headwind. Straight headwinds seem to matter less.
-other mileages were from about 8.5 to 9.5mpg. Speeds ranged mostly from 65 to 70mph.

Learnings?
-driving 60mph vs 65mph vs 70mph did not prove to impact mileage significantly. As above, the best mileage of the trip was at 70mph and the worst was at 60-65mph.
-conditions such as winds (especially side winds), and/or sudden or significant elevation changes and/or curvy roads had FAR more impact on mileage than did changes in speeds, as above.

Note that this is the observations for my rig, and YMMV - pun intended
My rig: 2020 RAM 3500 Cummins HO with Aisin, and 2021 Montana 3790RD, loaded to max as we live in it about 6 months per year.

A starting point for your rig; for a diesel engine, the peak torque RPM is often the sweet spot for mileage. On my truck peak torque is ~1700rpm and I think that is ~68mph. When I run at 60mph IIRC my RPM is at ~1450-1500 and the truck will sound like it labors on inclines, then may want to downshift earlier. I try to stay at 62-65mph up to 70mph on interstates, which seems to be the sweetspot.

---
Tire temperatures and speeds?
(my experience includes over 1m miles towing, commercial for years)... People can get all caught up with looking at their TPMS readings and temperature readings while driving, but note that tire manufacturers do not specify max "hot" tire pressures, nor do they specify max operating temperature limits.

So, what are the keys to preventing a tire blowout?
First and foremost - PROPER TIRE PRESSURE!!! If you have an L rated tire (like most new Montana's) and you fill it to the proper tire pressure with proper weight loading, your tire will stay within the designed limits for pressures and operating temperatures. Say it another way - driving at 60mph vs 70mph will not likely be the cause of a blowout if you maintain proper loading and proper tire pressure (of course assumes tire is in good condition)

Second, if you have a TPMS, some systems measure tire temperatures as well as pressure (often will warn at 156F). I think the biggest value in a TPMS system is not to stress overmuch on the actual pressures and temperatures, but to monitor for any sudden changes. So, if all of your tires start at 110psi and a couple hours in they are all at 130psi, should you stop and let air out? Of course not; we all know the values are to be measured cold. But if all tires are at 130psi and suddenly one goes down to 110psi, you should suspect a leak and get over to deal with it.
The same with temperature; should you stress if you see tire temperatures of 130 or 140F, but all tires are similar and none changed suddenly? Again, no worries. However, if all tires are at 130F then suddenly one tire goes up to 150F and climbing, that's when you know you need to get over asap to prevent a problem (could be stuck brake, or dry bearing, etc).

My tire experience so far? I now have over 20,000 miles on the truck and at last service it was scheduled for tire rotation; all of the tires were identical in measurements so they didn't even rotate them (14/32 tread depth, 18 new). And, with over 9,000 miles on the trailer tires, they are wearing very evenly and look almost new.

I do hope the above data is helpful to others!
Brad

[kowbra]

Originally Posted by laverdur

ST tires are speed rated at 65 mph. I frequently see people towing at 70+ mph. I suppose they could have changed to LT tires which would allow those speeds but speed is only one aspect of towing. Stopping is the other. I won't get into the fuel economy loss at higher speeds. Although my G614s are rated for more than 65 mph, I enjoy knowing that there is a safety margin if I don't exceed 65 mph.

GY G614 ST tires are speed rating L, which is 75mph. Sailun ST tires are also speed rating L.

See my other post on actual results of mileage at different speeds.

I agree that slower speeds may give a safety advantage in a lot of situations, but one could also argue that on a busy interstate a vehicle traveling at 65mph will pose an increased safety risk if most trucks are traveling at 70mph+ and cars at 80mph+. A study in Montana in the late 80s concluded that the largest safety risk on interstates was not the max speed, but the speed differential between fastest and slowest vehicles. It was what led them to be the first state to remove speed limits on their interstates (they have now set them at 80mph and at 70mph I get passed by almost every vehicle on the road)

My conclusion? It is too arbitrary to say that a slower speed is automatically safer or that it will always guarantee better mileage. Rather, to me, it is more important to have appropriate speeds for the situation based on the road conditions, weather, traffic, weight, etc.

Brad

[kowbra]

Originally Posted by bcrvman

55mph or 90kph is my ideal speed when moving 30,000 lbs down the road. Maybe it would help people understand if it was expressed in more familiar terms like feet per second. 55mph is 81 feet per second. How many seconds do you think it takes to get your foot from the gas to the brake pedal, then how many more to get you slowed to anything near a speed that will not kill, maim, or cause 10's of thousands in damages. Remember 80mph is 120ft/sec or 50% more than 55.

I like how you report the speed in ft/sec - it really does help to remember how much speed will impact stopping distance. (the above were calculations that were part of the commercial trucking exams I had to take but that was many decades ago). IIRC, rough math is that doubling the weight doubles the stopping distance, but doubling the speed quadruples the stopping distance.

An observation - our Montana is the first RV trailer I've had with disc brakes. This is the BEST thing to improve stopping distance; period, full stop.

IMHO, anyone concerned with braking needs to look at disc brakes on their trailer. This one change will make more of a difference than SRW vs DRW, more than any 5-10mph difference in speed. The difference is truly amazing, and if any have not tried it, I recommend that they should.

Brad

[Mosnowman]

Psssssst......a secret.....

Trooper Slang:

Under 9 your fine....
Over 9 your mine...

[twindman]

I found an interesting thing with my TPMS temp readouts. Mine said tires between 92 an 100 one day. I got out the infrared thermometer and one of them that I checked was 120 or 130. Apparently TPMS temps not too accurate.

[mlh]

Most TPMS checks the temperature of the valve stem and your infrared thermometer checks the temperature of your tire. Both are probably accurate but checking two different places.
Lynwood

[Bad Moon]

Originally Posted by phillyg

That's funny, until the last couple of years I never once found an ST tire rated above 65mph.

The Goodyear Endurance ST tires on my rig are speed rated to 87mph. But I keep it below that. You know, margin of safety and all. :-)

[Foldbak]

For me the answer is simple. At $6.50 a gallon I'm running at 61 MPH. In good conditions that equates to 10 - 12 MPG.

[kowbra]

Originally Posted by Foldbak

For me the answer is simple. At $6.50 a gallon I'm running at 61 MPH. In good conditions that equates to 10 - 12 MPG.

Yes, it's good to know what speed is ideal for your rig. For ours, 61mph does not seem to get the best mileage; usually 65-68 is the sweet spot. (details in posts above).
Manufacturers know roads have higher speed limits and people drive faster than before, so they are adjusting accordingly. Newer trucks have different fuel delivery algorithms, are more aerodynamic, etc, etc, etc; the ideal speed of a newer rig may be very different than past rigs we may have had.

If any have not experimented with this, they should try varying their speed and checking the results. Of course, it's difficult to do perfect testing, but ideally if you have a "favorite trip" and you can have similar conditions, you could drive the trip at different speeds to get a good idea on your trucks "sweet spot" speed.

Slower may be better, but not always.
(and of course we are not talking about comparing 80mph to 60mph here, even though we've all likely been passed by folks towing 5th wheels at 80mph+; I doubt any rigs today can achieve ideal mileage at those speeds...)

Brad

[JABURKHOLDER]

Originally Posted by Lee-CI

Our Ram shifts into sixth at 57-58.

??????

My F350 shifts into 6th at 35mph.

Anyway, I tow at 58-60mph. Unhitched, what ever I feel like (within reason).

[Lee-CI]

Originally Posted by JABURKHOLDER

??????

My F350 shifts into 6th at 35mph.

Anyway, I tow at 58-60mph. Unhitched, what ever I feel like (within reason).

LOL - betting you have TEN gears in yours! Good one! Well played sir!


Edit: I know DARN good and well that I know / recognize your name! Been what - 30 years?

[JABURKHOLDER]

Originally Posted by Lee-CI

LOL - betting you have TEN gears in yours! Good one! Well played sir!


Edit: I know DARN good and well that I know / recognize your name! Been what - 30 years?

Unless you were in the Navy, in Hawaii, in 1992, I don’t believe we know each other. Too bad. According to my dog at the time, I was a great guy.