I was looking for an equivalent for a Michelin XVS 225VR15 tyre, and I realzed that it is not the usual format for tyre size.  The 225 is the tire width, the VR is for V speeds  (149 MPH) and R means  radial, and 15 is the wheel diameter.  Do tyres like these have an aspect ratio, as  in 225/70-15?  Is that even an American tyre size?  European size designations are entirely different.

Internet searches  reveal nothing about it, only the usual metric tyre size that you see on most tyres.

Edited November 10, 20168 yr by TomoHawk

225VR15 means its an 80% hight tire, but they leave the 80 away, you could say its: 225/80VR15  width is 225mm, at 80% the hight is .8 x 225 = 180mm

A 225vr15 that would have a huge sidewall height. Around 28" O.D.

Nice for Tractor tires but not on a Z. The XVS is also an ancient tire, Produced in early 70's. What are you using this on? A big Jag or something?

Edited November 12, 20168 yr by Chickenman

The Michelin XWX tyre is the current version of the XVS tyre, and is an excellent touring or racing tire, especially on classic cars.  It is a development of the XAS racing tyre used on many cars in the 1970s. It is the equivalent of a 225-70-15 tyre which is what I was using before and is also the recommended size for the Zed.  I just can't find any facts that the aspect ratio is 70%  or 80%.

Even at 70 aspect ratio that would be a large tire.  225/70R15 would be about 27.4" OD and a stock tire for our cars would be under 25" OD.

On a '77 280Z from the FSM the stock tire is a 195/70HR14 which has an OD of 24.75".

Edited November 11, 20168 yr by CanTechZ

We are not debating the correct tyre size for a Zed.  The question is: what is the equivalent modern tyre size for a period tyre of 225VR15.  It appears the aspect ratio is 70%, but there hasn't been a consensus so far, nor any official literature or trusted Internet information to refer to.

Sorry for the confusion, I just found this link with a bit of information that may help:

http://www.michelinclassic.com/en/Classic-Tyre-range/XVS

It list dimensions for an XVS 185 VR 15 and shows an OD of 675mm (26.6") that would be the equivalent of an 80% aspect ratio as was suggested by @Martzedcars above.

I'm assuming that the XVS 225 VR 15 would use the same aspect ratio.

Also here is a link with 225/70 VR 15's:

http://www.michelinclassic.com/en/Classic-Tyre-range/XWX

HTH

Mike

Edited November 11, 20168 yr by CanTechZ

I found the same page long ago.  It's too bad there was no consistency or sense with the tyre information of long ago, like there is now.

Thgis is a little off-topic, but what size tyre would you put on a 15 x 4 inch wheel?  105/70-15 maybe?

165 HR 15 OD = 646mm (25.4") = 80% aspect ratio

http://www.michelinclassic.com/en/Classic-Tyre-range/XAS

That is a popular tyre size for that size wheel.

Edited November 11, 20168 yr by TomoHawk

Back to your original question, I found this explanation of Euro-Metric tires on ModernTireDealer.com. They note that If the aspect ratio is not stated in the tire size then it is 82 by default:

From Modern Tire Dealer:

Three sizing systems are employed today for passenger tires: P-metric, European metric and alpha-numeric.

The most common system is P-metric. The size designation indicates cross section in millimeters, aspect ratio, type of construction and appropriate rim diameter. For example, a P235/50R16 describes a tire that is intended for passenger use (P), and features a cross section width of 235mm, an aspect ratio of 50 and radial construction (R). It needs to be mounted to a 16-inch diameter wheel.

European metric, also called metric, is similar. No letter "P" is used as a prefix. The three-digit number at the beginning indicates cross section in millimeters. If the aspect ratio is lower than 82, the aspect ratio number will follow the section width number. If not, then no aspect ratio number will appear.

The next letter indicates the speed rating (sometimes the speed rating is included in a P-metric size after the aspect ratio). The R again refers to radial construction, and the final two-digit number indicates rim diameter in inches.

One example of a European metric tire size (with an 82 aspect ratio) is 155SR13, which indicates a 155mm section width, an S speed rating, radial construction, and a 13-inch wheel.

Here is a link to the full article:

http://www.moderntiredealer.com/article/311243/understanding-tire-dimensions

Here is another link that lists 225R15 as a Euro-Metric "82" series tire:

http://www.tirerack.com/tires/tiretech/45_conversionchart.jsp

HTH

Mike