Tyres

Tyres are the only point of contact between the vehicle and the road surface. For MAN and Mercedes trucks, buses and vans, they determine not only traction and braking distance, but also steering precision, axle load capacity, fuel consumption and the service life of wheel bearings, steering components and suspension parts. Operating conditions, axle configuration and permitted weights determine which type of tyre is technically suitable. Tyres for a MAN TGL, TGS, TGX or TGE, for example, differ significantly from versions for a Mercedes Atego, Actros, Arocs, Sprinter, Citaro or Tourismo. Specific requirements also apply to MAN Lion’s City, Lion’s Coach and Neoplan buses regarding load capacity, heat generation and comfort.

Always select tyres based on the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient. The chassis number confirms, among other things, the homologation, rim size, axle loads, brake configuration, drive axle version and any twin-wheel or super-single fitment.

Professional tyres are selected according to nominal size, construction, load index, speed rating, carcass type and axle position. Common sizes include 205/75 R17.5, 215/75 R17.5, 295/80 R22.5, 315/70 R22.5 and 385/65 R22.5. The designation indicates tyre width, aspect ratio, radial carcass construction and rim diameter respectively. The actual overall diameter and dynamic rolling circumference must remain within the tolerance permitted by the manufacturer, especially on driven axles with differential lock, hub reduction or electronic traction control.

Steer tyres generally have a rib tread pattern for precise steering, low rolling resistance and stable water evacuation. Drive tyres use a block or traction tread pattern with larger sipes and open tread grooves for power transmission. Trailer, tag axle and bus tyres are designed for high radial loads, controlled wear and heat dissipation during long journeys. Tread design, carcass reinforcement and rubber compound vary for construction traffic, distribution, international transport and winter use. Also ensure the correct load/speed index, M+S or 3PMSF classification and, where applicable, retreadability.

With twin-wheel fitments, the size, construction, remaining tread depth and rolling circumference of both tyres at each wheel position must be as similar as possible. An excessive difference in diameter causes continuous compensation in the differential, higher tyre temperatures and overloading of axle shafts and planetary hub reductions.

Irregular wear usually provides information about an underlying fault. Wear on one shoulder often indicates incorrect toe, camber or caster settings, worn kingpins, track rod ends or control arm bushes. Sawtooth wear is often caused by incorrect toe adjustment, play in the steering system or frequent tight turns. Local flat spots may result from wheel lock-up during braking, a faulty ABS/EBS system or insufficient brake force distribution. A central wear strip usually indicates excessive tyre pressure; wear on both shoulders is more likely to indicate insufficient pressure, overloading or excessive carcass deformation.

Start the diagnosis with a cold pressure measurement using a calibrated pressure gauge and compare the measured value with the specified pressure for the current axle load. Then check tread depth at several points across the tread width, measure the rolling circumference of tyres on the same axle and inspect the sidewalls for cuts, impact damage, bulges and dry cracks. In the event of vibrations, also check wheel balance, radial and lateral run-out of the tyre and rim, hub fitment, wheel nut tightening torque and wheel bearing play. A temperature difference between tyres on the same axle, measured after loading with an infrared thermometer, may indicate pressure loss, brake drag or internal carcass damage.

Replace tyres immediately in the event of exposed carcass, cord breakage, bulges, structural sidewall damage or tread below the legal and operationally safe limit. On driven axles, preferably replace tyres in pairs or across the complete axle. Correct fitting requires clean rim seats, a suitable tubeless valve combination, checked centring and tightening torques in accordance with vehicle and rim specifications. Thanks to a wide availability of parts and technical support, Braem can help ensure that tyre, rim and axle configurations are correctly matched.