# Analysis of TG (Tire Geometry)

The following definitions orient themselves at the possibilities of the TG measuring system "RFP-5" of SEICHTER GmbH

## Bulge

### Standard bulge

Bulges are raised areas of the tire surface, especially in the sidewall. They could be caused by defects in the fabric of the tire that weaken the wall of the tire and thus result in bulging under pressure. The bulge analysis calculates the height of the bulge in a limited patch of a surface, the measuring window. The size of the active measuring range of the capacitve sensors will be considered through the correction factors in the measuring result. The measuring window for the standard bulge is 8.0°. The biggest bulge determined in one rotation is the bulge value of this track.

Simplified one must imagine the analysis in such a way that the connecting line between the outside points of the measuring window is the base for the devia-tion of the middle point. The deviation is the bulge value. This calculation is supported by suitable fixed filters and corrective factors.

### Variable bulge - Spot Measurement

The measuring window of the variable bulge lies in the range of 2° - 40°. This analysis suits especially for the measurement of bulges (spots) on the tire tread. Larger bulges can be caused here through the segments of the tire mold. The largest bulge found in a circumference represents the bulge value of this track. Filters and shoes are available in the area 0° to 40°. The shoe permits the suppression of flashes.

### Dynamic bulge

This procedure examines the dynamic characteristic of bulges at two different tire pressures. By the help of capacitve sensors it doesn’t determine the real bulge height but the change of the bulge height: this is called the dynamic bulge measurement. The recommended test pressure is at first 1 bar and then 4 bar.

The great advance of this measuring method is the complete suppression of let-tering, pins and other contours. The measuring window for the dynamic bulge is 8,0°. The greatest bulge differ-ence established in 2 rotations is the value of the dynamic bulge of this track.

## Depression

### Standard depression

These include depressions and indentations in the tire surface, especially in the sidewall. One possible cause of these is the occurrence of ply overlap during assembly of the belt package, which has the effect of reinforcing the sidewall at this point and increasing resistance to tire pressure there. The tire is limited in its expansion at this point and a depression results. Depression analysis calculates the depth of the depression in a limited area of the surface. The size of the active measuring sensor surface is considered by correction factors in the meas-uring results. This limited area, the measuring window, amounts to 8.0°. The greatest depression different established in one rotation is the value of the depression of this track.

### Variable depression

The measuring window of the variable depression lies in the range of 2° - 40°. The largest depression found in a circumference represents the depression value of this track. Filters and shoes are available in the area 0° to 40°. The shoe permits the suppression of profile gaps.

### Dynamic depression

This procedure examines the dynamic characteristic of depressions at two different tire pressures. By the help of capacitve sensors it doesn’t determine the real depression depth but the change of the depression depth: this is called the dynamic depression measurement.The recommended test pressure is at first 1 bar and then 4 bar.

The great advance of this measuring method is the complete subpression of writing, pins and other contours. The measuring window for the dynamic de-pression is 8,0°. The greatest depres-sion difference established in 2 rotations is the value of the dynamic depression of this track.

### Runout (radial and lateral)

### Please have a look to our Powerpoint Presentation about the correct application of "filter" "Shoe I" and "Shoe II"

The runout is the difference between the greatest and smallest clearance between sensor and sidewall in a circumference (lateral runout) or between the sensor and the tread (radial runout). Filtering over an angle area selectable in advance (at the most 40°) suppresses shortwave irregularities, such as bulges and depressions (on the sidewalls) or tread blocks and gaps between the treads (on the tread surface).

It is additionally possible to define „shoe 1“ and „shoe 2“ in like manner as for skatetype mechanical sensors. The size of these shoes - to be selected in angular degrees - has a crucial influence on test readings. Shoe 1 serves to suppress spew, while 2 makes it possible to bridge gaps in the tread pattern. A smaller shoe tends to detect more irregularities, with the effect that the results are higher. A larger shoe covers larger shares of the tread or sidewall and sees to it that irregularities of a smaller magnitude are ignored.

### Wobble

Wobble offsets the runout progression of one track vis-à-vis that of another. In every case, wobble analysis can, in principle, combine any two measuring tracks. For the calculations it is advisable, however, to use two opposing tracks - with respect to their position on the tire - in the vicinity of the sidewall. One can then think of wobble as the motion of the imagined center of the tire between the tire's side flanks as the tire rotates. Filters and shoes can also be employed in conjunction with wobble.

### Harmonic analysis

This analysis calculates the amount and phase angle of the first 16 harmonics (0. -15.) on the basis of the FFT algorithm.

The Fourier transform opens the way to expressing each periodic function in its components at discrete frequencies and describes the frequency composition (the spectrum) of the function. Any function whatsoever can be composed of different sinusoidal components with different amplitudes and phases.

A FFT algorithm requires a binary block length (= number of breaker points). This is always to be realized through the use of a binary divided shaft encoder, which transmits the tire's rotation. In any case, the implemented interpolation procedure also supports the use of nonbinary divided shaft encoders.

### Radius

The radius measurement records the curvature radius of the tread. The distance values from three sensors are recorded per measuring point. The sensors are positioned at the center and at the two outer sides of the tread. With exact knowledge of the positions of the sensors, conclusions can be drawn as to the curvature radius via a geometric calculation.

### Circumference

The measurement of the tire circumference takes place on the bearing surface. For the circumference a desired value can be given. This is checked for exceeding or falling below. A prerequisite for the circumference measurement is an accurate adjustment of the RFP-5 Positioning-System.

## Measuring accuracy for geometric measurements

**N>10 (Xj = individual value, X = arithmetic mean of all Xj) S max. = 0,05mm S typ. = 0,03mm**