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Thread: air pressure for 17's ?
12-22-2011, 10:41 PM #1
air pressure for 17's ?
I'm new to the 17" tires. sidewall says max of 44 psi.... Whats everyone running them at ? My new 11' had 28 psi and so far the fuel mileage is less than impressive.... I put 40 in them. Thoughts ?
2011 Silverado 4WD, EC,
4.8L, 4L-60, manual everything !!
so far... Delta Box, Extang Toolbox Tonneau
12-23-2011, 12:30 AM #2
In my 315/70R17 Nitto Trail Grapplers I run 38psi up front and 35psi in the rear for street use. These are D-rated tires; I specifically avoided E-rated TG's to keep ride quality decent, as I don't tow much.
12-25-2011, 09:53 PM #3
I run my 285/70/17 bfgs at 38psi and they ride smooth. Honestly the best way to find ur sweet spot and avoid irregular wear, is by doing the chalk test. Take some chalk, draw a line on each tire, then drive a little (preferablly on straight flat stretch of pavement). If the chalk is visible on the outter parts of the tire and no so much the center, then u need more air. If the chalk is more visible in the center then u have to much air. If the chalk line seems to have worn evenly then ur good at that psi! Hope that helps2010 Silverado Z71 Crew Cab2" Rancho Quick LevelLine-X Bedliner
Rancho 9000XL Shocks
Black Housing HeadlightsGibson dual split exhaust
Hypertech max energy tune285/70/17 bfg km2 with atx slot wheels
12-26-2011, 02:35 PM #4
- Join Date
- Dec 2011
- Monterey, CA
The chalk test is not going to produce usable results. It would take an extreme difference in tire pressure to have only the center section of chalk removed and the sides be scrubbed clean and a very smooth section of polished concrete on which to perform the test. This is truly a pennywise and pound foolish approach to take with your tires, your truck, and your passengers.
The TRA produces a book every year with the tire load ratings at different tire pressures for all the manufacturer's tires which sells for $90. A little more effort is required to track down the information on the manufacturers' websites, in particular Firestone which has at least three different websites with information on its SUV/Light Truck tires and only one with tire psi and load ratings for the tires that came on my 2011 2500HD Silverado.
Firestone rates the load limits for the LT245/75R17 tires at 35psi for a load of 1770 lbs. per tire. My truck has the factory tire psi recommendation of 65 front and 80 for the rear tires and yet according to the Firestone chart with no load (in the bed or passengers) the truck's front tires should be at 45 and my rear tires at 35. With a 1000 lb. load and two 200 lb. passengers the front tires should be at 50 and the rear tires at 40. It is only with a 3,000 lb. load in the bed and with 4 passengers and a driver that my tire pressure should be at the factory recommended 65 and 80 psi for the truck.
So I am back to doing what I have done with every truck I have owned over the past 40 years and have the front and rear tires at 55psi and after 3-4K miles will see how the tires are wearing. If there is more tread wear in the center then I will reduce the pressure by 5psi and if there is more tread wear along the edges, especially the inner edges, then I will add 5psi.
When I load the bed with a camper I will add pressure to the tires beforehand to compensate for the extra wet load as calculated and later confirmed at a local CAT scale. I took my truck when new to a CAT scale and paid the $9.25 to get the exact load on my front and rear axles with no driver, passengers, or load in the truck. At that point in time it was 4380 at the front axle and 2797 at the rear axle. Based solely on those weights the tire pressures recommended by the factory should be reversed unless there is a significant load in the bed or a cab full of adult passengers.
With my stock tires at the factory psi the front tires will support a weight of 5500 lbs and my rear tires will support a maximum load of 6400 lbs. which needs to include the dry weight of the truck on the front and rear axles. With my truck that would enable adding 1100 lbs. to front axle and adding 3600 lbs. to the bed of the truck (based solely on the load rating of the tires and not other components). It is clear that GM has decided to err on the side of gross over inflation of the truck's tires believing that this is a safer approach in general and they are probably right.
At freeway speeds it is better to have the tires overinflated to reduce the risk of their overheating and failing completely. In wet weather or with snow, tires that are overinflated provide less traction and side control and handling control which is another factor to consider. I am more concerned about tire failure from under inflation which is why I chose to add 5psi to the values in the Firestone load limit chart as a starting point with my truck's tires. I can have two passengers and a 1600 lb. load in the bed with no worries at these settings.
12-26-2011, 02:56 PM #5
The chalk test is by no means a precise measure of proper psi, no. But it does help in finding a suitable psi range to operate in that will yield you regular wear. if you plaster the chalk on then sure, itll take a while to show any wear signs. but if you lightly color a line, it doesnt take but a few yards of driving to see where your tires are making contact with the pavement. if youre getting a nice even smear of chalk then your tires have a good even contact patch on the ground. its really not that difficult to notice at all, and only speeds up what he'll end up seeing without chalk if hes running under or over inflated tires anyway...irregular wear.
Ive used this technique along with many people i know to great success. Obviously if you have the time, means, and desire get what you can to be as precise as youd like. but for daily driving, and whatever the cost of a stick of chalk is, this works just fine. but like elkhornsun said, do be aware that over inflated tires in the cold stuff will give u less traction, but if ur towing or hauling alot make sure you air up. Just my 2 cents tho
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