How fast can you drive with 19.5 tires? - 19.5 tires and speed ratings

[GShail]

I think I have developed another concern over these 19. 5 tires , and that is speed ratings. It seems they are only rated at 75 mph. The 235/80/17 Pirelli Scorpion ATR for example are rated at R - 106 mph.



Is the speed rating on these 19. 5 tires artificially low because they are primarily used in commercial applications, and thus possibly not a true reflection of their capabilities? Can you not safely exceed 75 mph? I don't personally tow fast or drive fast but I am concerned about my employees, we live in some wide open country and sometimes I feel they may push the speed limit. I do not want to have a safety issue creep up because of speed.



How fast can you go with 19. 5's

 

[jelag]

I often drive my 05 3500 at the 75-80 mph range, one of my drivers ran our F550 for 500k miles at those speeds and he now runs our 08 5500 at those speeds when he doesn't get caught...

We don't do those speeds pulling trailers except in those states were its legal...

I guess we have close to 800K miles of track record on Bandag caps on the rear and either Michelin or Bridgestone tires on the front with no problems... besides a few nails. .

 

[GShail]

I am not worried about 8o mph, it's my young employees and their exceeding 80 mph out in open country. I appreciate your input Jelag. What do ambulances use? Many of them must run 19. 5's?

 

[kenny61]

I've done over a hundred (closed course of course) for short periods of time and never had any issues

 

[GShail]

Short closed course . . . . . I believe that . . . but I am worried about employees doing like 87 or so over looooong empty streches in the middle of nowhere.

 

[FordCummins]

The tires are rated at the "lower" speed of 75mph because that speed rating is calculated when the tire is at its maximum payload. I cant remember offhand what the max payload of one of my 245/70R19. 5s is, but I think its in the 5500 to 6000 lbs range. I am assuming your tires will never see that kind of weight in total, and therefore the heat generated will be nowhere near what the tires have been designed to sustain.

The only downside to running at higher speeds with the 19. 5s for long periods of time is faster tire wear.....

 

[GShail]

Excellent reply FordCummins. I feel that the ratings are artificial in some way, light ratings maybe because of a Big Brother/DOT type influence. Across the board, regardless of brand, they are all rated L - 75 mph. Just doesn't make sense.

 

[GShail]

Ok, what about centrifugal forces? I can see that the tire would never see maximum payload and wouldn't get hot. However, would centrifugal forces have an effect on the harder compounds of the 19. 5 tires. Will faster revolutions/higher mph result in the tire flying apart from something other than heat?

 

[TAbbott]

None of the heavy duty, real truck tires are rated at more than 75mph. Even 11R24. 5's are only rated at 75 mph.



These are the tires that are run on the largest over the road trucks that carry the heaviest loads. They'll run at maximum load all day long at 75 mph.



Back before the fuel prices went crazy, how many trucks did you see running along I-40 or I-10 or even I-80 and I-84 at fairly significant speeds with no tire problems at all?



The key is proper inflation.



The "alligators" that are seen, primarily in hot weather, are the result of improperly maintained, underinflated and overheated tires failing. On properly inflated virgin rubber (no caps) I've seen speeds well into triple digits with (thankfully) no tire issues.

 

[jelag]

GShail.....

I hope your people pay for their own speeding tickets the way my people pay for theirs..... If they get more than 1 in a 2 year period they no longer can drive... My insurance company checks all employees 2x's a year... .

TAbbott ... you've got an excellent point, yet out on the long straight stretches in those states were the max truck speed is 75, you see them driving faster... and your right... . Keep them inflated...

We do see a harder ride on the 19. 5 when we have a light load... but we don't run down the pressure...

 

[GShail]

Let me tell you they still run some pretty significant speeds in some of those big trucks. I've seen expedited types rolling near triple digits myself plenty of times. I think my guys will be safe if they are pushing speed with these 19. 5's even though they are 75 mph speed rated.





Since we have been talking a bit about inflation, what kinds of pressures are people running in their 19. 5's, towing or not towing. I certainly cant imagine maxing them up to 110. I'm thinking around 80 lbs on say a 225/70/19. 5 for towing?

 

[Cattletrkr]

My sumitomo 225's are only rated for 65mph. I have no idea why. They have seen many miles of 70mph+ with no issues at all.

19. 5's are most likely rated in the 4-5K range, not 5-6K. Maybe some of the 265 or bigger, but my 245 Mich's were only rated at 4800 and change. The Sumi's are slightly under 4K.

I used to run my Mich's at about 75psi. Made for nice tire wear. Towards the end I tried upping the psi a little to see if mileage would go up. I don't think it did. I run the Sumi's within 5psi of their max of 95psi. BTW, the Mich's were stamed 125psi max.

 

[TAbbott]

Cattletrkr said: "My sumitomo 225's are only rated for 65mph. I have no idea why. "



Are they ST tires? All of the ST tires seem to be rated at 65 mph.

 

[Cattletrkr]

Are they ST tires? All of the ST tires seem to be rated at 65 mph.

Yep. Here's a link.

Sumitomo Tire Line: ST 918

They wear about as good as the Mich's. I should get 120K easily.

 

[jelag]

"""Since we have been talking a bit about inflation, what kinds of pressures are people running in their 19. 5's, towing or not towing. I certainly cant imagine maxing them up to 110. I'm thinking around 80 lbs on say a 225/70/19. 5 for towing?"""

Don't under inflate these tires... . doing so will cause excessive side wall flex and they will over heat... we never run any of them under 90 psi... I'm not trying to say 80 is to low, I'd just hate for you to have a problem...

Like I mentioned above, when the truck is empty it is a harsh ride over the 17" tires. .

 

[TAbbott]

The lowest operating pressure shown on the Goodyear chart for 225/70R19. 5's is 70psi. They are rated to carry 2895 lbs single or 2720 dual at that pressure. With that said, I run my 265's somewhat lower than that when unladen. 60 psi in the rears on an empty p/u seems to work fine. I check them with a laser heat gun and find no excess temparature anywhere -- tread, sidewall, or bead chafer area.



Jelag is right, though, about running them underinflated. The carcass of a 19. 5 is very stiff and heavy -- it has to be to contain the higher pressures enabling the heavy weights they are capable of carrying. They don't like to flex like a P rated or even a LT rated tire will. Running too low of a pressure forces them to over-flex, generating excessive heat which destroys them in short order.

 

[brods]

If you're really concerned, then why not get something like the MADS SL (speed limiter) and set it to 75 or 80? Problem solved, though you may have some unhappy employees.

 

[AABEN]

All ST tires are rated at 65 and are not to be used as a driver tire. So I would not run them on my truck!

 

[Cattletrkr]

All ST tires are rated at 65 and are not to be used as a driver tire. So I would not run them on my truck!

Take a look at the link I posted above. Sumitomo's "ST" is not what you're thinking.

 

[GShail]

Just got back in from the weekly California run. In San Diego I found some Michelin XDE M&S 's for $277 per tire.



Not too worried about a harsh unladen ride, truck turned 340,000 today and I'd bet at least 325,000 have all been towing.