RPM7 - excellent

Forklift safety demands that people understand the issues completely.

The degradation in capacity of the forklift tynes (forks) is faster than for the forklift because the formula only considers the distance from the fork heel. A fork rated at 2500 kg @ 600 mm will be rated at 2500 * 600/900 = 1670 kg.

However for a counterbalance forklift with a distance of 400 mm from the centre of the drive axle to the fork face of 400 mm, the formula is 2500 * (600+400)/(900+400) = 1920 kg.

For that reason some forklift manufacturers actually fit forks with a higher rating than the forklift. For example if they fit forks rated at 3000 kg @ 600 mm in the case above, then the fork rating at 900 mm is 3000 * 600/900 = 2000 kg which is close to the forklift rating as a whole.

Finally in regard to the 100 lb/in rule that started this discussion. That rule of thumb only applies to forks with ratings of 3000 - 4000 lb (with an error in the range of up to 20%), or coounterbalance forklift trucks with a distance from the centre of the drive axle to the fork face of 16 inches (400 mm) with ratings of 4000 - 5500 lb (with an error in the range of up to 20%). SO MY RECOMMENDATION IS TO NEVER USE SUCH A RULE.

If you want to be conservative you use the fork strength related rule of "rated load" x "rated distance" / "larger centre of mass distance".

BUT ALWAYS KEEP IN MIND THAT AT FULL HEIGHT, ESPECIALLY FOR LIFT HEIGHTS OVER 4500 mm THE SITUATION MAY BE MORE COMPLEX AND YOU SHOULD CONTACT AND GET ADVICE FROM THE MANUFACTURER/ SUPPLIER.