Tire load index: How closely to you pay attention to it?

[Eug]

I noticed that few people here ever talk about tire load index. I didn't pay much attention to it when I was looking for snow tires. I ended up spec'ing the Michelin X-Ice Xi3 for our RAV4 Limited AWD Hybrid, with a load index of 99. However, I just realized the stock tires are 100, and that's what's written in the manual too.

Shouldn't make much of a difference in this case, but had I paid attention to that, I might have just gone with another tire. That said, I will note that the 2014 model of the car (gas version) had a load rating of 99, while the 2015 model, which is the same generation with the exact same weight has a load rating of 100. Strange. Both cars weigh 3610 lbs, and both cars have a gross vehicle weight rating of 4600 lbs. They are of the same generation with the same body and same engine specs. So, I am at a loss as to why the load index would go from 99 to 100 between those two model years.

How closely do you pay attention to load index? I'm thinking it's good to pay attention and you should match the load index or go higher, but then again if you're off by 1, it probably isn't going to matter too much.

 

[skyking]

Look at the actual load rating in pounds or kilos. if it is close don't sweat the small stuff.
It is far more critical in trucks, where for example I could put load range "D" tires on my 3500 truck, and it would be nearly overloaded on the front axle just sitting there without a load in it

 

[Eug]

Curb weight of the car is 3950 lbs, and gross vehicle weight rating is 4950 lbs (curb weight plus 1000 lbs).

99 rating is 1708.6 lbs x 4 or 6834 lbs.
100 rating is 1763.7 lbs x 4 or 7055 lbs.

So the GVWR is not even in the same ballpark as the load indices.

However, if we were to assume a 60/40 split, then the front of the car might be in the worst case scenario 2970 lbs. That would mean 1485 lbs per tire. That means the 99 rating is still overspec'd and the 100 rating is even more overspec'd.

For the Hybrid though I'm guessing it's more like 55/45 at most, since the batteries are all in the back, as is all the storage space. In that case the front is 2723 lbs, with the back being 2228 lbs. That means the 99 rating is overspec'd by almost 350 lbs per tire, and in the back it's overspec'd by almost 600 lbs per tire.

 

[Subyman]

In my experience the load rating has always been way higher than what I could possible put on the vehicle.

 

[Railgun]

How much weight is on the front tires while braking? How about turning?

Read: it's not just static weight you need to take into account.

 

[Eug]

Ok but it still doesn't explain to me why the rating went from 99 to 100 in the 2014 to 2015 model years, despite the fact they had the same body design, curb weight, GVWR, and AFAIK, the same suspension.

The other thing I've noticed is that the higher end model (mine) comes with 18" wheels and a load rating of 100, whereas the mid end model comes with 17" wheels (albeit of a similar overall diameter due to a slightly higher sidewall height) with a load rating of 102. Even more interesting is that the car with the 102 spec is actually a bit lighter since it is missing some of the higher end options.

So I started looking around and it seems most tires that fit that specific 18" size are spec'd at 100 whereas most tires that fit that specific 17" size are spec'd at 102. This is even true across different tire manufacturers, so it seems that the tire manufacturers are kind of standardizing tire sizes and load ratings for certain specific tire sizes that happen to be commonly used.

So it makes me wonder if part of the OEM spec actually depends on tire availability.

 

[jlee]

Ok but it still doesn't explain to me why the rating went from 99 to 100 in the 2014 to 2015 model years, despite the fact they had the same body design, curb weight, GVWR, and AFAIK, the same suspension.

The other thing I've noticed is that the higher end model (mine) comes with 18" wheels and a load rating of 100, whereas the mid end model comes with 17" wheels (albeit of a similar overall diameter due to a slightly higher sidewall height) with a load rating of 102. Even more interesting is that the car with the 102 spec is actually a bit lighter since it is missing some of the higher end options.

So I started looking around and it seems most tires that fit that specific 18" size are spec'd at 100 whereas most tires that fit that specific 17" size are spec'd at 102. This is even true across different tire manufacturers, so it seems that the tire manufacturers are kind of standardizing tire sizes and load ratings for certain specific tire sizes that happen to be commonly used.

So it makes me wonder if part of the OEM spec actually depends on tire availability.

That's quite likely.

 

[skyking]

That's quite likely.

and cheap is the deciding factor there, without a doubt.

 

[Eug]

Interesting. The 2014 Toyota Sienna SE minivan has a curb weight of around 4400 lbs. The GVWR is close to 6000 lbs, considering it seats eight. (The 2016 has a GVWR of 5995. Not sure what the 2014 is.)

The tires it comes with are 235/50R19, which have a load index of 99.

The LE with 18" tires have the exact same size as my RAV4 tires, at 235/55R18, and again the load index is 99.

I guess minivans aren't driven the same way as the RAV4, but it's way heavier, with roughly an additional 1000 lbs for the GVWR, yet it has a slightly lower load index of 99 (vs. 100 for the RAV4).

 

[Eug]

The other thing I've noticed is that even the tire manufacturers are not consistent about this.

If I go to the Michelin site, for my car with a load index of 100, they only will spec tires that are 100 or above.

However, if I go to the Continental site of the Bridgestone site and search for tires for my car, they seem perfectly happy to spec tires that are 99 (but not say 97). Most of the tires are 100, but there are some included in the mix that are 99.

 

[slashbinslashbash]

Maybe just a rounding error?

 

[Eug]

Maybe just a rounding error?

Nah. As mentioned, the Sienna with a gross vehicle weight rating of 5995 lbs specs a tire with a 235/55R18 tire with a load rating of 99.
OTOH, the RAV4 Hybrid with a gross vehicle weight rating of 4950 lbs specs a tire with a 235/55R18 tire with a load rating of 100.
Note that both have the P prefix in the specs: P235/55R18. Toyota does NOT specific LT tires for the RAV4.

So a car that is over 1000 lbs more for GVWR with the exact same tire size gets a slightly lower load rating. It isn't just rounding error.

Interestingly, the ground clearance between the two is not all that different, at least for the high end Sienna, with a clearance of 6.5". It's 7.0" on the RAV4 Hybrid. In contrast, something like a Corolla is only 5.5".

I think again it's the availability issue. If you buy an SUV tire in that size, they're generally 100 or higher. If you buy a passenger car tire in that size, many are 99 (although many are 100 too). The Sienna is always going to be on a paved road (aside from a few gravel roads), but a RAV4 might occasionally go for some light off-roading. However, honestly I don't think of the RAV4 as a real off-road vehicle (even if it's better than a Sienna for that purpose), and in our case we bought it as a mainly city and sometimes highway vehicle.

 

[NutBucket]

You're probably just worrying about it too much. For example, I don't think you can find a 225/40R18 tire that isn't XL rated. An XL rating is hardly necessary for a compact sedan.

"I think again it's the availability issue." -- Exactly!

 

[slashbinslashbash]

Nah. As mentioned, the Sienna with a gross vehicle weight rating of 5995 lbs specs a tire with a 235/55R18 tire with a load rating of 99.
OTOH, the RAV4 Hybrid with a gross vehicle weight rating of 4950 lbs specs a tire with a 235/55R18 tire with a load rating of 100.
Note that both have the P prefix in the specs: P235/55R18. Toyota does NOT specific LT tires for the RAV4.

So a car that is over 1000 lbs more for GVWR with the exact same tire size gets a slightly lower load rating. It isn't just rounding error.

Interestingly, the ground clearance between the two is not all that different, at least for the high end Sienna, with a clearance of 6.5". It's 7.0" on the RAV4 Hybrid. In contrast, something like a Corolla is only 5.5".

I think again it's the availability issue. If you buy an SUV tire in that size, they're generally 100 or higher. If you buy a passenger car tire in that size, many are 99 (although many are 100 too). The Sienna is always going to be on a paved road (aside from a few gravel roads), but a RAV4 might occasionally go for some light off-roading. However, honestly I don't think of the RAV4 as a real off-road vehicle (even if it's better than a Sienna for that purpose), and in our case we bought it as a mainly city and sometimes highway vehicle.

I was really only looking at your original example of the difference between the two different model years of Rav4. Same GVWR but one loading of 99 and the other of 100. Maybe for SUV's they add a safety factor of 50%. 4600x1.5 = 6900, which splits the difference between the 99 and 100.

Maybe they use a different safety factor for minivans.

Or maybe, yeah, commonly available tires tend to cluster around the 100 weight rating.

 

[heymrdj]

When I had my Expedition and I was towing all the time, I always looked at the load rating per tire. It was very easy for the truck's size of tire to come in a P, a PXL, and an LT. To meet the truck's weight capabilities you had to have at least the PXL.

 

[Eug]

Yeah, I'd never put a P tire on a truck that requires LT tires.

However, the vehicles I'm talking about all are spec'd with P (not P XL) tires. Ironically though, I have P 95T XL winter tires on my Prius, even though it only requires P 89S (non-XL) tires. The tire I wanted doesn't come with any other spec in that size for some reason. I like the stiffer tire though actually. Improves handling vs. my existing floppy 89S touring tires.

 

[Midwayman]

Ran into this with my wife's CRV. The tires with the 'right' load rating were like $200 more vs the exact same tire in a lower load. Both were way way way over the GVW. Unless you're carrying a full passenger load + cargo + towing I wouldn't worry too much about undershooting a little bit.