Runflats for Military and Off Road Vehicles
- Date: 26th May 2020
- Company: Tyron Runflat Limited
Rubber has three particularly significant advantages.
Firstly, rubber absorbs shock from impact resulting from curb strikes, potholes and operating in hostile environments. Rubber drastically reduces the vibration and stresses transmitted through the runflat to the wheels, axles, and drive shafts with little change to the handling of the vehicle whilst retaining a degree of comfort for the driver and passengers.
Rubber is a compliant material and prevents the damage caused to the tyre from impingement between the runflat and the inside of the tyre.
The third less obvious reason for using rubber rather than composite and probably the most important is the need for ‘Beadlock’.
Without adequate compression of the tyre beads against the flanges of the wheels (Beadlock) the vehicles are going nowhere. With only the ‘drag’ from the deflated tyres, the wheels will slip inside the tyres and that is on level ground, let alone trying to negotiate any obstacles or hills to complete its mission.
So why not use composite or hard material for Beadlock? The answer is in the manufacturing tolerances of the wheels and tyres. Each of these components has a manufacturing tolerance which, when stacked to a maximum combined value, could be a difference of 20mm in the inside measurement between the tyre beads.
Composite or Plastic runflats are manufactured by machining solid moulded blanks. They must be machined to the minimum anticipated measurement between the tyre beads for them to be able to fit, therefore they do not give consistent tyre bead compression and cannot guarantee beadlock. Consequently, the wheels in the deflated tyres may spin freely incapacitating the vehicle, even on a flat surface.
Rubber is then, the only logical option.
The width of the rubber runflat however is over manufactured to allow for these tolerances and during the installation, the rubber will flex and compress the tyre beads against the flanges of the wheels guaranteeing the beadlock, as in figure 2.
In 2008 Tyron invented the world’s first ever multi piece rubber All Terrain Rubber (ATR) Runflat insert which can be fitted in the field, without special tools, giving excellent off road capabilities. The Tyron ATR Runflat systems have been ballistically and endurance tested to demonstrate that the vehicle can keep moving for more than 100km at speed and achieve Finabel standards.
Why Multi Piece? Multi Piece runflats make handling much easier for maintenance and engineering crews in the field or workshop. Even large tyres, such as 14.00R20 and 16.00R20 can be done by two people easily.
Critical cost saving? With constant pressure on budgets the Tyron ATR runflats enable the vehicle engineers to replace or repair the tyre without special tools in the field. Not only does this minimise vehicle down time, it offers massive savings in logistics costs as they negate the need for the return of the wheels and tyres, or whole vehicle to a rear workshop or even by air back to a home base, saving many thousands of Pounds.
But where is the future?
A critical element of the design of 8x8s is a need to reduce the unsprung weight on an axle. At the heart of the patented Tyron ATR runflat is a core which gives the system its strength. Historically this has been steel, however Tyron have developed a carbon core which reduces unsprung weight on an 8x8 fitted with 16.00r20 tyre by around 40kg per runflat, or 240kg per vehicle.
Why Carbon? Carbon’s properties give it the strength of steel but at considerably reduced weight. For AFVs any opportunity to reduce weight is a real benefit, especially if it is unsprung, and gives the user or vehicle designer the opportunity to add to the carrying capacity, armouring, protection or firepower.
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