8 June 2001

Traction for the big boys

HIGH levels of traction and low inflation capability in a practical package – that was the aim of Michelin designers when it came to producing a tyre to bridge the gap between the XM27/XM28 heavy duty traction tyres and the ultra high volume Megaxbib in the French manufacturers range.

The resulting Mach X Bib is currently available in just one very low profile rear wheel size – 900/50R42 – with a matching 710/55R30 size for the front axles of four-wheel-drive tractors. Other sizes will follow, including narrower but taller versions for in-furrow work.

"The 900/50R42 is clearly a tyre for out-of-furrow operations, such as cultivations and seeding, using tractors in the class up to 240hp," says Benoit Puel of Michelin.

"But it is also a very practical tyre because on most tractors it does not exceed an overall width of 3m, allowing easier transportation on the road."

Although it looks much like a narrower but slightly taller version of the Megaxbib, the newcomer is quite different in both tread design and carcass structure.

While the Megaxbibs emphasis is on carrying capacity and low ground pressure with good traction capability, the Mach X Bibs emphasis is firmly on traction with high draft loads, coupled with low inflation and high load-carrying capabilities.

Similarly, the new tyre is significantly different from the tough XM27/XM28s commonly used in single and dual formation on high horsepower rigid chassis tractors. The tread pattern is more akin to the XM108 and Megaxbib, for one thing, with rounded outer lug ends, slightly wider lug spacing and squared off shoulders. Lug height is 57mm.

Inside, the new tyre gets three layers of textile in the sidewall and another three in the top of the carcass to stabilise the tread and give it more durability. But this structure also allows a lot of sidewall flexibility, enabling the tyre to spread its tread at low pressures.

In terms of performance, the Mach X Bibs outright load-carrying capacity is not quite up with the biggest size in the XM28 line-up (the newly added 710/70R42), but it does hold the advantage at very low inflation pressures and beats the carrying capacity of all smaller sizes in the XM27/XM28 line-up.

Also, its more supple carcass helps it produce a bigger contact patch which, in turn, is converted into reduced soil compaction and improved traction for a given load and tyre inflation pressure.

A summary of comparative test results gathered while developing the new tyre shows the newcomer giving 5% more traction than a 710/70R38 tyre, while reducing soil compaction, measured as wheeling depth, by 18%, says Mr Puel.

"Compared with a bias belted tyre of the type commonly used for high horsepower applications, the Mach X Bib raised traction levels by 15% while cutting wheeling depth by 12%."

In essence, like the Goodyear and Firestone newcomers of this size, the Mach X Bib is a new alternative to the commonly used 710/70R38 tyre on 200hp-plus tractors, for more efficient conversion of power into traction without the practical limitations of a wider, more specialist design. &#42

Specifications and load capacity

Mach X Bib XM28

Size 900/50R42 710/70R38

Volume 923 litres 776 litres

Width 886mm 716mm

Load – 0.6bar (9psi) 3900kg 3690kg

– 1.0bar (14psi) 4740kg 4480kg

– 1.4bar (19psi) 5570kg 5270kg

– 1.6bar (23psi) 5990kg 5670kg

Notes: Section width measured across sidewalls to ETRTO standard. Loads quoted for 30kph maximum speed; tyres rated to 50kph carrying less weight.

The 900/50R42 Michelin Mach X Bib is designed for tractors in the big horsepower league for operators wanting best carrying capacity, traction and low ground pressure without making tractors more than 3m wide.