QuestionQUESTION: Hi Barry,
My question is does the load rating have anything else to do with the ability of the tire to withstand torque? I realize that you cannot recommend putting a lighter load capacity tire onto a vehicle, but just want to understand more about what the load rating really represents. For instance, I have a 2006 Chevy Duramax Ext. Cab with a sticker of 9200 max weight. Factory tires were rated 3042 lbs and I changed the diameter and width of the rims and therefore had to change my tire to a lower rating (2601). I do not haul any weight in the pickup, but I tow a trailer, with a weight of 7000 lbs, tongue weight of 750 lbs. I've recently had a problem with a severe pull to the right caused by the tire that was on the right rear and I am wondering if the torque of the engine could play into this problem by damaging the tire (sidewall, etc.). The tire has only a 2 ply rating sidewall and a 4 ply tread, so wondering if that plays any role as well, or maybe I just had a defective tire. The tire went 10,000 miles without a problem, now I have about 15,000 and problems. There is no visible defect in the sidewall or tread deviation. Mostly just curious about the load rating and what plays into that, again no looking for you to recommend a lighter rating. Thanks.
ANSWER: Lonnie,
You've asked quite a few questions.
But I am really concerned about the 440 # (times 4, that's 1760 # less load capacity)
Towing a trailer requires that you need the load capacity.
Plus - did you factor in that P metric tires are reduced 10% in load capacity when used in the light truck usage?
So I guess what I need to answer your question is:
1) What does the placard say is supposed to be the tire size and the proper inflation pressure for that size. The placard on a GM truck is located on the driver's doorpost.
2) What tire size are you using now?
Please be sure to include that letters in the tire size.
---------- FOLLOW-UP ----------
QUESTION: Thanks for the quick response.
1) Placard says LT245/75/R16; 80PSI rear; 53PSI front
2) 285/60/R17 (noted SUV Tire) 51PSI max
Max load capacity of the truck is 9200 lbs, and with my current tires they total 10,404 lbs...that is the basis of my question--how does this all work together and are there other factors?
ANSWER: Lonnie,
You have a very serious problem. You are using tires that don't have enough load carrying capacity.
First, the tires you currently have on the vehicle are not LT tires, and because they are being used in a light truck application, the load rating is reduced 10%. That means the maximum load carrying capacity is reduced to 2365 # - and that occurs at 36 psi.
Here's how this works:
Load carrying capacities on tires are specified for IDEAL conditions - meaning little cornering, smooth roads, low ambient temperature, etc.
We've learned over the years that oversizing the tires reduces the probability of tire failure from outside influences - impact damage, cut, etc.
We've also learned that oversizing tires helps with high ambient temperatures and high speeds.
So the vehicle manufacturers specify tire sizes and inflation pressures such that there is some reserve capacity to account for the less that ideal conditions plus the things that have been learned.
So let's take a look at what GM specified. I should point out that my book - Tire Guides - doesn't show the combination you've indicated, and because of that it would be wise to check the placard again. The book has been known to be wrong - and in your case, the book identifies the vehicles differently and I can't be sure which vehicle I should be looking for.
But assuming the information you gave me is correct:
Front: LT245/75R16 at 53 psi. That's a load carrying capacity of 2283 #
Rear: LT245/75R16 at 80 psi = 3042 #
If you sum that up you get 10,650. The GVW (Gross Vehicle Weight) of the vehicle is 9200, which means there is a 16% reserve capacity. Just so we are on the same page: GVW is the maximum weight the vehicle was designed to weigh. This includes external loading such as the weight from a towing hitch.
BTW, the GAWR (Gross Axle Weight Rating) that is listed on the vehicle placard would be very helpful in understanding what is going on. The GAWR is the maximum load that axle is designed to carry. So while you are verifying the info you gave me, record the GAWR's as well.
If you were to add the GAWR's up, they would be more than the GVW - because the GVW is based on a symmetrically load truck, and clearly that isn't always the case. The net effect is that the sum of the GAWR's is ALWAYS larger than the GVW.
But I think you should notice that the GWAR's are different front to rear. This means that your truck is designed to carry most of the load in the rear - well, duh, when you put stuff in the bed of the truck, the front tires hardly feel that weight, but the rears sure do!!!
Working backwards: I am going to guess the rear GAWR is in the 5300 # range.
So the tires you have on there now only have a capacity of 4700# - and this doesn't count in the extra capacity that GM feels is needed for their truck to work properly.
Let me tell you this is a dangerous situation and needs to be remedied. An overloaded tire failure can have tragic consequences.
But that doesn't answer the question that you asked: The pull caused by the RR tire.
How do you know it is the RR that is the problem?
Possible causes?
Assuming it is the RR, it could be the tire is separating and causing more drag.
It could also be that the trailer is out of alignment with the truck, and that's the source of the pull. I'm sure that doesn't make sense to you, but if the trailer is out of alignment, it can cause a sideways force on the hitch - and that will cause the tow vehicle to feel like it has a internally caused pull.
You also asked about the 2 ply sidewall, 4 ply tread. Most passenger and light truck radial tires are built this way. It's the size and the quantity of the materials that is important - not the number of plies.
So I suggest you get tires on the truck that have more capacity. GM spent a lot of time and has years of experience to draw from, so deviating from their specification is not a good idea.
---------- FOLLOW-UP ----------
QUESTION: Since my tires do not have a "P" notation and they were sold as "SUV" tires, I assumed they were not passenger tires, so can you clarify that?
The pull on the truck is without the trailer, so I understand what you mean, but the pull started happening on the truck without the trailer--I do not use the trailer often.
The placard states the rear GAWR is 6084. The payload is 2591; I am assuming the rear of the truck weighs appx. 3015 lbs based on 45% of the total weight (6700)of the vehicle...so my point is the tires I have on the truck surpass the 3015 plus the trailer 750 lbs and your calc shows I have 4730 in the rear, that is what I don't understand. Also, I am confused about your reference to 36psi, since max load and pressure is at 51 psi?
I know it is the RR because I rotated the tire, the pull became more severe, so I cross-rotated the front tire to test my theory and the pull went the other way. So, I rotated the tire back to the rear and the pull lessened.
I am having trouble finding a tire rated high enough that does not exceed my diameter max of 30.5" to fit a 17"x8" rim. Any ideas?
AnswerLonnie,
"......Since my tires do not have a "P" notation and they were sold as "SUV" tires, I assumed they were not passenger tires, so can you clarify that?....."
This is about the way tire sizing is standardized. While the tires were designed for usage on an SUV, the tire size (and the load carrying characteristics) falls under the umbrella of "passenger car" Since there is not a "P" in front of the tire size, these tires are built to either Asian or European tire standards. (BTW I know it is European because the Asian standard doesn't even list this size!)
But there is no question they are incapable of handling 80 psi as specified on the placard.
"......The placard states the rear GAWR is 6084. The payload is 2591; I am assuming the rear of the truck weighs appx. 3015 lbs based on 45% of the total weight (6700)of the vehicle......"
Well I would have taken the rear GAWR (6084) and subtracted the payload (2591) and figured the rear axle weighed 3493 empty. So we are different by 500# and that's cause for concern.
One little wrinkle here is that I assumed the payload would be centered over the rear axle. I don't think that is a bad assumption, but it is an assumption nevertheless.
".....so my point is the tires I have on the truck surpass the 3015 plus the trailer 750 lbs and your calc shows I have 4730 in the rear, that is what I don't understand......"
I am not sure where this is going, but I think you are making an awful lot of assumptions about how much load there is on the tires. For example, the weight of the trailer and the tongue weight, as well as the weight distribution of the empty truck. Don't forget that the payload may not be evenly distributed side to side.
So it might be best if you weighed everything. This would be prudent given that you are trying to re-engineer the tires on the truck.
"... Also, I am confused about your reference to 36psi, since max load and pressure is at 51 psi?...."
Look again. The sidewall of the tire says "Max Load XXXX, Max pressure XX" and not "Max load XXXX at XX pressure". Those 2 items are not connected.
".....I know it is the RR because I rotated the tire, the pull became more severe, so I cross-rotated the front tire to test my theory and the pull went the other way. So, I rotated the tire back to the rear and the pull lessened...."
Couldn't that also point to the front tire?? It's my experience that pull is almost exclusive a front end issue.
Try this: Swap the front tires side to side. If the pull changes direction, it's the front tires. If the pull doesn't change, it's probably the alignment. If the pull goes away, it's a combination of both.
Since you are reporting that the pull descreased, I'm guessing you have both a tire problem AND an alignment problem.
"....... am having trouble finding a tire rated high enough that does not exceed my diameter max of 30.5" to fit a 17"x8" rim. Any ideas?...."
How about an LT245/70R17? 30.6" diameter and 3000# load capacity. These tires will be labeled with a Load Idex as 119/116.
But I am concerned about the rim's load carrying capacity. I don't know this for a fact, but I think GM is very careful about the bolt pattern matching up with the load carrying capacity of the rims. I am not sure the aftermarket is as careful.
