Bob Drake Catalog

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http://www.bobdrake.com

DETERMINING SIZE OF WHEELS
Picking wheels and tires for your new ride can be the toughest part of the project. Once you have decided on the look
you want, determining size is the next step. What you want and what you can have are often not the same. Follow along
and we’ll give you some tips.

Step 1.
Jack up your car and put jack stands under the suspension (not the frame). This will put your hubs in the fender opening
where they will be when the car is on the ground.

Step 2.
Lay a straight edge vertically across the wheel mounting flange
so that it extends up into the fender. Now measure:

1. From this extension into the body and


2. Towards you to the inside lip of the fender and


3. From the center of the hub up to the top of the fender.

Record these measurements. Now you’re starting to get an idea
of what you can have.

Step 3.
Take the #3 measurement and subtract 3 to 4 inches for
suspension travel, then double it. This will give you the tallest
tire height you can run. Now add up #1 & #2 measurement.
This will give you the widest cross section (not tread
width) that you can run.

Now, we’ll take just a minute to talk about tire size. We won’t go into a whole lot of detail here - just basics. Your friendly
neighborhood tire dealer will have charts showing the various dimensions of different tires. The Coker Tire Co. has good
tables in their catalog.

TIRE SIZE
There are 3 dimensions on a tire that you care about.

1. Side wall diameter or height. This will tell you how tall the tire is.


2. Tread. This tells you how wide just the tread is - “Where the rubber meets the road”.


3. Cross section - This is normally the widest part of the tire. This is the dimension that
   can rub paint off your fenders. This measurement is taken across the tire about half
   way up the sidewall.

Today’s radial tire sizes can seem very confusing, but they are not all that tough if
you do a little math. If a tire size is 225/60R15 it tells us that the cross section is
225 millimeters wide (about 8 7 /8").

Yes it would be a lot simpler if the rest of the world did it our way but we are
in the minority here. The 60 says that the section height or sidewall (from the inside
bead that sits on the wheel to the top of the tread) is 60% of the cross section or
87 /8" x .60 = 5 3 /8". The R means radial and the 15 corresponds to wheel diameter.

So, because the 60 is a percentage ratio it means that as this number goes up (70-75-78) the tire gets taller and has a
narrower tread. Conversely as this number goes down (50-40-35) the tire gets shorter and has a wider tread.

Now that you know all this, you are ready to pick a tire size for your car. Wheels are next.

C

AB

’s

Of Skins & Rims

3. CROSS
   SECTION
   2.
   TREAD


4. SIDE
   WALL

TIRE

RIM

TIRE SIZE

DIMENSION #1

DIMENSION

#2

DIMENSION #3

STEP 2.

FENDER

BRAKE DRUM

AXLE