Tires: Section Width versus Tread width (1 Viewer)

[JohnPW]

I am planning to replace my worn Dunlops with Michelin Defender LTX M/S, and have gone back and forth on size between 285/60R18 and 275/65r18. I will not be buying the LT version of any tire, as it isn't needed for my uses. On the Tire Rack website, I notice Tread width is wider for P rated tires versus XL or LT rated tires of the same section width. Examples:

P275/65r18 sec width 11" tread width 9"
LT275/65r18 sec width 11" tread width 8.6"

Each Defender tire size for which there is a P and an LT version has a more narrow tread width on the LT version, by 2 to 4 tenths of an inch.

285/60r18XL sec width 11.5" tread width 8.9"....a narrower tread on the 11.5" tire versus the 11" 275 width tire.

Questions:
1.) why would tread be more narrow on heavier load tires?
2.) For on road use, wouldn't the tread width be the important measurement, versus section width? (I understand the higher load capacity and tougher construction of the heavier load tires, I'm asking about on road performance like braking, cornering, etc.)
3.) Is there any on road performance advantage (beyond load carrying) of the 285/60r18XL with a 8.9" tread, versus the 275/65r18 with a 9" tread?
4.) The stock Dunlops are listed as 11.5" sec width, 8.6" tread width. The 275/65r18 Defenders have a wider tread (9") in spite of a 0.5" narrower section width. This surprised me. Any thoughts?

Thanks for your perspectives.

 

[Sandroad]

I’m running the Defender 275/65R18. I wanted the slightly higher profile compared to stock and measured the tread wider than the stock Dunlop 285/60-18 tires, so I gained tread width despite the lower section width of the Defender. They have served me extremely well for 50,000 miles and have lots of tread left.

 

[Madtiger]

Me personally, IF P-metric Defender is what i want, then i go with 285/60/18 because of higher load rating (for same tire weight)...our LC is a heavy SUV.

275/65/18 P-metric load rating is same as stock Dunlops...so, it is fine choice too...but b/w the two, i rather go with 285/60/18 XL due to stronger carcass design (per Michelin rep i spoke to).

The beauty of XL is that you get a (slightly) stronger tire with no weight penalty.

 

[gaijin]

I am planning to replace my worn Dunlops with Michelin Defender LTX M/S, and have gone back and forth on size between 285/60R18 and 275/65r18. I will not be buying the LT version of any tire, as it isn't needed for my uses. On the Tire Rack website, I notice Tread width is wider for P rated tires versus XL or LT rated tires of the same section width. Examples:

P275/65r18 sec width 11" tread width 9"
LT275/65r18 sec width 11" tread width 8.6"

Each Defender tire size for which there is a P and an LT version has a more narrow tread width on the LT version, by 2 to 4 tenths of an inch.

285/60r18XL sec width 11.5" tread width 8.9"....a narrower tread on the 11.5" tire versus the 11" 275 width tire.

Questions:
1.) why would tread be more narrow on heavier load tires?
2.) For on road use, wouldn't the tread width be the important measurement, versus section width? (I understand the higher load capacity and tougher construction of the heavier load tires, I'm asking about on road performance like braking, cornering, etc.)
3.) Is there any on road performance advantage (beyond load carrying) of the 285/60r18XL with a 8.9" tread, versus the 275/65r18 with a 9" tread?
4.) The stock Dunlops are listed as 11.5" sec width, 8.6" tread width. The 275/65r18 Defenders have a wider tread (9") in spite of a 0.5" narrower section width. This surprised me. Any thoughts?

Thanks for your perspectives.

I think the way that Tire Rack measures tread width accounts for a lot of the variation you are seeing (Find Tire Rack procedure here: Tread Width Measuring)

The takeaway is that Tire Rack tread width measurements can only be compared to other Tire Rack measurements because they do not use the same method as tire manufacturers. Also, tread design, e.g. street tire vs. All-Terrain tire, due to Tire Rack's measurement procedure, will be dramatically different. This means that it is really only meaningful to compare Tire Rack tread widths for tires with similarly designed tread designs.

HTH

For the click averse - from the Tire Rack site:


Unfortunately there isn't an industry standard that establishes a single procedure for how to measure tire tread widths. And since tire manufacturers can use different methods, their published tread widths would only be meaningful when compared to other tires measured the exact same way.

This makes it challenging to compare tread widths of one tire brand to another, and most tire manufacturers have simply chosen to eliminate tread width dimensions from their brochures and websites.

Because tread width is still a dimension of interest to our customers, Tire Rack has established a common measurement method to address this issue.

The Tire Rack tread width measurement tool helps us define how much of a rounded shoulder's over-the-horizon tread width should be included in the measurement. We use a 20" long tool made with square tube featuring a 30° bend in the middle. Centering this tool on top of the tread design helps us approximate how much of the tread will be in contact with the road when in service.

Measuring the tread width of rounded-shouldered tires is defined by centering our tool on top of the tread and measuring the distance from the outboard to inboard contact.
Once we know the points of contact, we then use a flexible flat steel ruler to measure between those two points. This tool can be used on tires with rounded shoulders, as well as those with square shoulders.

While Tire Rack tread width dimensions may differ slightly from those published by the few remaining tire manufacturers that still offer them, it will be applied universally.

 

[JohnPW]

Thanks for the replies. I looked at a few more tires and found some interesting results (while recognizing this is all minutia that may not mean much). There seems to be a consistently narrower tread on LT rated Michelins, using Tire Rack's measurement method as described by gaijin above...for the Michelin AT2, the P275/65r18 has a 11" sec width and a 9" tread width like the Defenders do. But the AT2 in LT275/65r18 shows a 11" sec width with a tread width dropping to 8.4", more than a half inch narrower than the P rated version.

I looked at the Continental TerrainContacts, and tread width on LT rated versions are either the same as P rated, or 1/10 of an inch narrower.

But looking at the Yokohama Geolander GO15's, the measurements are kind of all over the place..some LT's have wider tread, some have the same...but unlike michelin or continental, the Geolanders have diameter differences between the P and LT versions of the same tire as well. The section widths also vary between the P and LT version of the same tire in same spec.

I get that Tire Rack's measurements aren't precise, and may not be comparable between tire brands. But I'm surprised at the differences between the P and LT versions of the same tire. I can see inflation pressures making a tenth of an inch or so of difference alone, but 0.4" to 0.6" of tread width difference between the P and LT versions seems significant to me, at least in terms of on road use. That's the same as the difference in width of a lower sized tire.