Understanding Wheel & Tire Dimension Measurements

[Noel]

Wheel Dis-sected

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch01.gif

Wheel Size

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch02.gif

Offset

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch03.gif

The offset indicates the distance from the center of the wheel to the attaching disk part (unit:m/m). As seen in the attached drawing, the offset is indicated by "+" when the fitting surface extends beyond the central line of the rim and "-" when it is falls within. Caution is required to prevent the tyre from coming into contact with the fender of the vehicle, brake caliper if the offsets are very different or any suspension/braking components.

Pitch Centre Diameter

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch04.gif

The number of bolts used to install a wheel varies from 4 to 6 depending on the vehicle make/model, thus the wheel to be installed should also possess the same number of hub bolt holes. PCD indicates the diameter of the circle in mm connecting the center of each hub bolt. Since the PCD also varies according to the vehicle make/model, make sure a suitable one is selected.

Clearance

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch05.gif

Fender clearance indicates the marginal space between the tyre and the fender or body of the vehicle. Inner clearance indicates the distance between the tire and wheel and the body part which is positioned closest to the tire and wheel. Dimensions for both right and left clearance should be measured on a level surface, and the smaller value is then considered as the inner clearance.

Tyre

http://www.enkei.co.jp/en/images/elem_local_t_know_sketch06.gif

1 - Tyre Width (MM or Inch)
2 - Aspect Ratio
3 - Radial Construction
4 - Rim Diameter
5 - Load Index
6 - Speed Symbol
7 - Tire Outer Diameter (Inch)
8 - Ply Rating


Edit by MemphisRheins:


Wheel Off-Set Calculator (http://www.1010tires.com/WheelOffsetCalculator.asp)

Tire Size Calculator (http://www.1010tires.com/TireSizeCalculator.asp)

[TtSsXx]

thnx for sharing.....update my car knowledge

[-phase-]

thanks for another awesome post noel :)

[stephen8512]

Great post noel
just a question
how do you find the offset on a wheel if ur not told by the wheel manufacturer? is there a way of finding out?

[Noel]

To calculate exact wheel offset, you need to do the following with the tyres not mounted.

A - Obtain wheel backspace.
B - Obtain wheel width.
C - Obtain wheel centreline.

Subtract C from A to get offset.

* The easiest way to measure wheel backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up. Take a straight edge and lay it diagonally across the inside flange of the wheel. Take a measuring tape and calculate the distance from where the straight edge contacts the inside flange to the centre hub.

* If backspace is less than the wheel centerline the offset is negative. While greater backspace than the wheel centerline means the offset is positive.

[stephen8512]

what does the Z (speed symbol) mean?

[Special_Ed]

what does the Z (speed symbol) mean?

Speed rating of the tire; as follows - http://www.discounttire.com/dtcs/infoSpeedRating.dos

[genk-jomblo]

Great post noel
just a question
how do you find the offset on a wheel if ur not told by the wheel manufacturer? is there a way of finding out?
usually the offset is located on the back of the rims. if not stated there then .... hmmm ... maybe you need to PM noel and ask how to .. lolz ..

[vansterdam]

Here are some good calculators:
tire size calculator (http://www.1010tires.com/TireSizeCalculator.asp)
wheel offset calculator (http://www.1010tires.com/WheelOffsetCalculator.asp)

[CACKYWHEELS]

Let's not forget that if your wheel is a "17X8" it really isn't 17" tall and 8" wide,
and that not all tires are really the same size/width!