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Tire load ratings - do they matter?

I have a interesting situation to say the least.

Does the tire load rating matter?

My local Mazda dealership doesn’t think the load rating matters unless I’m driving 140 MPH. I don’t drive my car much as I bike to work all the time, and only drive my vehicle when going on long trips at high speeds (75 to 80 MPH freeway driving.)

I purchased a set of 4 Kumo KH-16 215/50R17 tires with the road hazard plan at my local Mazda dealership on 2/22/2013 with 87,554 miles on my vehicle.

Immediately after I purchased the set of tires on 3/2/2013 at 87,745 miles the rear driver-side tire went flat due to a sidewall puncture

On 3/19/2013 at 90,158 miles (~300 miles later) the other rear tire started a slow leak on a trip from Kansas to Florida and I had air it up every 200 miles. They found a damaged tire and replaced it.

4,300 miles later at 94,451 miles (8/5/2013) on the next trip the front driver tire developed a sidewall bubble and had to be replaced.

At 95,631 miles on 9/24/2013 after that the only other tire that wasn’t replaced had to be replaced due to a leaking TPMS sensor

On 12/21/2013 at 97,848 miles a nail was found and a broken valve stem again in the rear driverside tire, and the tire was patched up.

We made a trip from Kansas to Texas without issue in March.

On a trip to Des Moines yesterday (at 104,154 miles) the rear tire had to be replaced at Tires Plus due to a 3 inch slice in the tire.

Bad luck? Or bad tires? At Tires Plus they stated that the Kumos they put on at Mazda were rated for 90V load rating. They stated that this is illegal and Mazda recommends 93V or higher load rating tires. They put a Bridgestone 95V rated tire on the vehicle, which I immediately note drives a **** load smoother.

I am trying to get some firepower to complain to the manager at the Mazda dealership which put these tires on my car, but they seem to insist that it doesn’t really matter unless I’m driving 140 MPH or higher what load rating the tires are. I need some official documentation to prove them wrong and if I can’t get my way with the dealership, I need some official documentation to provide a lawyer, as this is 6 flats in less than 16 months, and I have only had 1 flat prior to this in the 50,000+ miles I have owned this vehicle - so something is up!

I think load ratings do matter, otherwise they wouldnt even have load ratings for tires. Load ratings arent just for how fast you drive.Turning puts a lot of stress on the sidewalls so I imagine that the manufacturer load ratings take into account the suspension and turning radius of the particular car.

Load ratings do matter. The speed rating is an entirely different rating, not to be confused with the load rating I’ve attached a link that should help you to understand the tire codes.

Thanks for listing that link TSM. I just had a guy ask yesterday about tire codes.

Model year?


2008 Mazda6 i Value Edition. i4 engine.

I just looked at your owner’s manual online, and Tires Plus is correct

You should have P215/50R17 93V tires

Which would mean your Mazda dealer installed tires with an incorrect load rating

So you don’t have to flip through the whole manual, it’s on page 10-7

If you can’t find yours, let me know, and I’ll post the link

Thank you. Found it. Now I just have to talk to management to get a proper set of tires when I get there Monday, as well as a new donut as this saga has caused me to put at least 1,000 miles on it. Higlighted the manual.

While there’s some flexibility on the speed rating, there’s not on the load rating. Ford’s problems with blowouts on the Explorer was at least partly caused by specifying too low of a load rating.

Michelin says this about load rating:

“A tire with a higher load index than that of the Original Equipment tire indicates an increase in load capacity. A tire with a load index equal to that of the Original Equipment tire indicates an equivalent load capacity. A tire with a lower load index than the Original Equipment tire indicates the tire does not equal the load capacity of the original and should not be considered for installation on the vehicle.” (emphasis is mine)

The Mazda dealer never should have installed tires with the lower load rating. If you don’t get satisfaction from the dealer, you should contact Mazda customer service and report this incident. I would go to the Service Manager and complain since the people out front don’t seem to understand the issue.

If the GVWR is under 5300#, the 90 speed rating is adequate. But it is more likely over 5700, and the 93 rating is proper. You should find the GVWR in your owner’s manual somewhere. But since the manual already says that the 93 load rating is correct, that implies that the GVWR is a little over 5700#.

Could the “load index” specification be a marketing ploy? Load range and maximum load have been on tire sidewalls for quite some time. Most tires are capable of carrying half the total weight of the vehicle they are mounted on.

The gross weight for that car is 4279 lbs, so it would be well under the 5300 max for those tires. The curb weight is 3093 lbs.

I don’t know if there needs to be a specific margin between the gross weight and the load index for the tires, but if not, that doesn’t sound like the reason for the problems.

The dealership still should have installed the proper tires, however.

OK, everyone. It’s a bit more complicated than what has been stated.

First, the original tires were Extra Load, but the inflation pressure specified is 32 psi - which means Mazda could have specified Standard Load tires, but for some reason didn’t. So while the Mazda dealer didn’t do exactly as he should have done, what he did isn’t exactly wrong either.

So f00dl3, don’t try to “correct” the dealer. Not only is that a bad idea (they don’t kindly to non-experts), you can’t really point out a technical error on their part.

So, Yes, it was bad luck. It is unfortunate that you were the guy at the short end of the stick.

Tire load ratings, do they matter ? Ahhh, yes !

Load ratings yes, load index??? Load ratings are the old ply ratings, @dagosa. As in 4-ply rated tires which have actually been 2 ply construction for 40+ years. It seems like a lot of razzle dazzle to me.

Not to be confused with puncture and sidewall resistance to damage.

Considering your experience with these tires and the fact that they did not meet OEM requirements, I would demand the dealership install a set of decent, quality tires on your car…perhaps ones that do not say Kumo on the sidewall. If you hit a brick wall there, drive over to COSTCO and have them install a set of Mitchelin’s meeting the specs in your owners manual (or better) and put your tire problems behind you. Have them take a look at the TPM’s too and service that system if required…

I went there and they are going to 1 - replace the full set with a set that meets the requirements listed in the manual, 2 - re-imburse me for the Tires Plus tire, 3 - replace the donut that now has 1000 miles on it, and 4 - provide a rental car until it’s all done. I’m happy for now - spoke with the manager and he saw the error.

Yes…they matter a lot. Case in point…I answered an ad for a set of “new” tires and wheels that were the size I needed. When I got there…the tires and wheels were still mounted on the truck. In the course of our verbal exchange…the owner said that he wrecked on an open road when he lost control and flipped over in a field. When he filed the insurance claim…it was denied. I took a real close look at tires and gave him an answer for the denial. The tires were new but they were light “ST” trailer tires. Legally, in our state anyway, they can’t even be mounted on a motor vehicle. I told him he needed to change the ad but it was still the same a week later. Some people…I think he knew the reason for the insurance claim denial all the time.

Some people....I think he knew the reason for the insurance claim denial all the time.
@missileman, He DID know exactly why! Insurance companies do not deny a claim for no reason. They tell you the exact reason, otherwise they would be in court 24/7 fighting denial of claims battles.