Plus Sizing Guides

One of the most common questions for anyone in the tire or wheel business is "what size tire fits on..." or "if I put 18's on my car what size tire will fit?" Experienced salespeople certainly know many fitments right off the top of their heads and its easy to learn to calculate ones you don't know.

But if you're selling lots of tires and wheels, you really need a plus-sizing guide. These handy books have all of the calculations done for you already--it just takes you a couple of seconds to look up a vehicle and see the proper plus 1, 2, 3 or 4 fitment information.

I use two guides on a daily basis. They are (in alphabetical order):

Plus Sizing Guide ($36.95 http://www.tireguides.com/)

The Ultimate Wheel & Tire Plus Sizing Guide ($39.00 http://www.plussizingguide.com/)

I know that similar information can be found online, but I prefer hard copies--I don't have to worry about power failures, slow Internet connections, etc.

Both books offer the same type of data, but there are some differences.

The Plus Sizing Guide is large--507 pages--and covers ten years worth of cars and light trucks. As with other publications by this company, cars are listed first then light trucks in a separate section. For each car model and option, the guide lists the OEM rim diameter and width, tire size, load index, offset and hub diameter. This is followed by plus 0, 1, 2 and 3 sizing options. The format is "landscape" style, you have to turn the book sideways with the long side parallel to you.

This guide includes 37 introductory pages which include acceptable rim width charts for P-metric, Euro-metric and LT tires; RMA replacement guidelines for passenger and light truck tires; and load and inflation tables for LT, Euro-metric and P-metric tires.

The Ultimate Tire & Wheel Plus Sizing Guide is 174 pages. Years of coverage varies by model. The Ford Mustang entry, for example, goes back to 1964. The Honda Civic entry starts in 1980. This guide lists bolt pattern, hub size, offset ranges (low, med, HPO, etc), and thread pitch. Plus sizes are listed with tire OD, section width and sidewall heights.

Also included are 15 pages of reference material. You will find a handy list of tire dimensions sorted by both tire idea and section width. So its easy to see a 245/45R17 tire is 25.7" tall. And if you need to find a 22" tire that is 28" tall, its easy to find that it is a 255/30R22.

Which book is better? Its tough to say. I have both on my desk and use both daily. The Ultimate guide is in my catalog rack and I often go to it first just because of its smaller size--its easy to handle. I use the tire OD charts quite a bit too. I like that it shows the OD of the plus size fitments it recommends too.

The larger Plus Sizing Guide has helped me to solve some fitment issues. I like that it shows me the factory offset instead of just a range. The load and inflation tables get frequent use also.

I recommend having both if you possibly can. But please remember these are only guides. You are responsible for checking clearances on all installs you do.

Finally, one area that is easily overlooked is that neither guide tells you if a particular fitment needs an air pressure adjustment. You can run into this when plus sizing, especially if you are going from a P-metric size to a Euro-metric size tire. Many times you will need to run the new tire at a higher air pressure to maintain the needed load carrying capacity.

I currently use the 2008 editions of both books, but the 2009 editions are available now. If you seriously want to sell wheels, buy them!