Tire Pressures, speeds, and load range

[thecriscokid]

This is a multi part question all pertaining to tire loads and pressures.

1. What is a safe driving speed at lowered pressures? 20lb=? 15lb=?
Is there a general safe speed guidline? or is it tire by tire

2. What classifies a load range?
I have a Yokohama IT GO 72 Snow tire in 285/75/16 load C. The website says max load of 2755@50lb. Then I also have a BFG KM2 305/70/16 load D = 2680@50lbs. Just to through another example in there the BFG AT 285/75/16D = 3305@65lbs
That part has me confused the Yoko has a lower letter of C but is stated to take a slightly higher load???


Thanks again!

 

[Bandicoot]

For Michelin tyres, their load/pressure/speed recommendations are here:
http://www.michelintransport.com/ple/front/affich.jsp?codeRubrique=53&lang=EN
Others are probably similar
Bandicoot

 

[Overdrive]

As far as "what is a safe speed at lower pressures", there are just too many variables to give a definitive answer.

Some examples of the variables include: vehicle weight, max anticipated speed, dynamic cornering (turning at speed), tire's tread agressivness, surface driving upon. You need enough pressure to hold the tire on the wheel in dynamic situations--will the tire stick to the ground and then peel off the rim due to being pushed sideways by the wheel, or will it slide along the ground and not peel off?

A sandrail running the tires you have would probably be "safe" on sand at 8 psi. A full size pickup, maybe not. A rock crawling rig would run --what?--5psi?

Assuming you'll be running fire-road type situations as opposed to rock crawling, I generally go 20 psi. But I have a heavy vehicle.

 

[charlieaarons]

1. What is a safe driving speed at lowered pressures? 20lb=? 15lb=?
Is there a general safe speed guidline? or is it tire by tire

!

http://www4.mercedes-benz.com/e/unimog/unimog_ugn405/betriebsanleitung/vertiefen/N232D6.html#N23470

Look at the bottom of the above-referenced page. It gives recommended pressures as a % of highway pressure for different (large Unimog-sized) tires. But I think the percentages given related to the aspect ratio of the tire (on a 235/85R16, 85 is the "aspect ratio") might be useful. Note these are probably conservative numbers given by a major mfg.
A letter load range is a mfg. rating of the load capacity of the tire for that particular nominal size. A far more useful rating is the load rating/speed rating. Some tires have a dual rating which Michelin calls "singular point". For example 395/85R20 XZLs are 168G/161J which is 12350 lb @ 90 kph or 10200 lb @ 100 kph.
Comparing your 2 tires is "like apples and oranges". Even though the BFG is a bit wider it is shorter and probably has a smaller air chamber that heats up quicker. Like I said above the load/speed rating is far more useful. It is printed on the sidewall of all tires that are DOT rated.

Charlie

 

[thecriscokid]

Still having a hard time finding anything in my range. 285/75/16 or 305/70/16 with a 6000lb GVW vehicle. I was hoping there were some better guidelines out there. I feel like I encounter some short, 15 mile stretches of paved road in between dirt trails fairly often.

Here is another way of asking the same question:
How fast do you think is safe at 20psi?

 

[78Bronco]

Google search brought me to this in two seconds

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55



No one is going to tell you how fast to drive at 20psi because we don't have all the information. Remember all the Firestone tires that were blowing out and killing people because the vehicle was overloaded and tires under inflated? It's common sense, how fast do you want to drive with 20psi in the tires? Would you do 80mph at 20psi with a fully loaded vehicle?:Wow1:

6000lb GVW vehicle is basically a 1/2ton, load range C is more than adequate. Just two of those yokohamas at 50psi can support 5500 lbs. I think you should visit a retailer to discuss your tire requirements and expectations.

 

[thecriscokid]

Google search brought me to this in two seconds

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55



No one is going to tell you how fast to drive at 20psi because we don't have all the information. Remember all the Firestone tires that were blowing out and killing people because the vehicle was overloaded and tires under inflated? It's common sense, how fast do you want to drive with 20psi in the tires? Would you do 80mph at 20psi with a fully loaded vehicle?:Wow1:

6000lb GVW vehicle is basically a 1/2ton, load range C is more than adequate. Just two of those yokohamas at 50psi can support 5500 lbs. I think you should visit a retailer to discuss your tire requirements and expectations.

Don't get me wrong... I'm not trying to go 80 with flat tires
Is 40mh for 30minute legit?

 

[charlieaarons]

I'd recommend you buy an infrared laser-pointed thermometer and start taking tire sidewall temperatures. That should help answer your questions.

Charlie

 

[thecriscokid]

I'd recommend you buy an infrared laser-pointed thermometer and start taking tire sidewall temperatures. That should help answer your questions.

Charlie

Good call!