All You Need To Know About Rims
Today I open a series of posts about car rims. I’m going to explain the general rules of the rim marking and all the indexes in the names of the rims, give a short FAQ on the topic, the history of MOMO Company, speak about the latest technologies in the area (NanoTec, LiteTec), speak about the advantages of a forged rim, AEZ nanotechnology rims and much more.
Let’s start with the marking of rims.
The article will help you understand how the rims are marked and what are the basic parameters of the rims.
All the rims have the standard parameter marking no matter if it is a light alloy or a steel one.
For example: 6.5Jx15 H2 5х100 ET45 d54.1
15 – the diameter of the rim in inches (D)
6.5 – the width of the rims in inches (B)
J and H2 – the symbols for the specialists. J means the construction of the rim outboard flange (can be JJ, JK, K and L). H2 – the hump construction code (can be H, FH, AH etc.).
Average hump:
Truncated Hump:
Humps are the ring ledges along the rim outboard flange made for tubeless tires. The basic purpose of humps is the firm fixation of the tire in turns in order not allow the depressurizing of the tire. If a rim has one hump along the outer side the marking has a single H index. A lot of rim models have the hump of the inner edge, which is marked H2. Double hump increase the reliability of the tire fixation on the rim, but produce difficulties while assembling.
5×100 – the number of bolts (or screws) in our case it is 5. The diameter in which the bolts are placed is called PCD (Pitch Circle Diameter) and in our case it is 100 mm. If needed PCD can be calculated measuring the distance (A) between the centers of the opposite bolt apertures (it can be done with a simple ruler).
For PCD for the rims with 5 bolts (or screws) distance A must be multiplied by 1.701. PCD=Ax1.701
For the rims with 4 bolts: PCD=Ax1.414
ET45 – the outreach. The distance between the flatness of the rim, (the flatness with contacts with the centre boss) and centre of the rim width. ET is measured in mm and in our case it is 45 mm.
Most frequently user symbols: OFFSET, ET and DEPORT. In case of the negative outreach, the length is marked with “-“ symbol. For instance: ET – 15. The outreach for the wheels is calculated by every car manufacturer. The maintenance of the parameter is one of the key factors when choosing a rim. Moreover, the difference between the real and calculated value creates some sort of power affecting the suspension and braking systems. As a result may come a dangerous deflection from the course. The admission makes around 5.7 mm. It is not recommended to equip a car with the rims with supernumerary outreach. A significant reduction of the outreach makes the track wider. Although it slightly increases the stability of the car in turns and makes the car look a little sportier, it incredible overloads suspension. As a rule the increase of the outreach is practically not possible as the rims might touch braking system elements.
Rim outreach formula:
ET=a – b/2 where
a – the distance between the flatness of the rim and the inner edge.
b – the width of the rim
d54.1 – the diameter of the central aperture which is measured from the side of the rim flatness. DIA is measured in mm and in our case it is 54.1 mm.
Many light alloy rim manufacturers make DIA of a big diameter and for the centering on the boss use centering rings which fix the rim firmly excluding the possibility of vibration.
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- All About Rims: FAQ. Part 1
