Many years ago the American engineer Edgar Pickard published a ground-breaking paper in the February 1971 issue of HOOF BEATS on the characteristics of the horse/sulky/driver combination. It is reviewed at the site <www.rjwalsh.com.au/i_faster.htm>.

The particular purpose of this paper is to address a pernicious myth that has been put about by the ignorant, but possibly well-meaning, ever since the advent of the Weber high-uplift sulky in 1968.

Their argument goes like this: “When you take the weight off the front legs with uplift, it has to go somewhere, so it is added to the horse’s rear legs, where it can cause lameness.”

While that argument may sound reasonable to many, it is utterly and completely false. If you put a horse on four scales, one under each hoof, you will find that a horse typically carries 78 per cent of his weight on the front legs and 22 per cent on the rear legs. For an engineer it is an easy matter to calculate how much the weight on front and rear legs varies with various amounts of uplift applied at various points between the points of contact of the front and rear legs. But the point at which the uplift is ordinarily applied is the girth strap which should be under the horse’s center of gravity, which is usually about 15 cm behind the elbows of his front legs.

So then, suppose we stand the horse on 2 scales, one under the two front feet, and one under the two rear feet, and we attach a sulky such that it exerts no lift on the horse’s chest beneath the girth strap. We also sit the sulky on a third scale so that it reads the total weight on the wheels, then we place a 80 kg weight on the seat to simulate a driver. At this stage the scale under the wheels reads 103 kgs if it is an Australian sulky, 113 kgs if it is a north american type. We then adjust the sulky to give us a net uplift of 10 kg on the horse’s chest beneath the girth.

The reading on the front scale will have moved from 312 kg down to 304.2 kg. The reading on the rear scale will have moved from 88 Kg DOWN to 85.80 Kg, while the reading on the sulky scale will have moved UP from 103 Kgs (Aust. sulky) to 113 Kgs. So then, the combined weights on front and rear scales have moved DOWN by 10 kg while the weight on the Sulky scale moved UP by 10 kg.

At this stage it should be obvious that the weight we take from the horse’s legs goes directly to the wheels of the sulky, and that there is a REDUCTION in load on the horse’s rear feet and thus no possibility of increased rear leg lameness due to an increased share of the horse’s weight.

So then, assume we have transferred a certain load from the horse’s feet to the wheels of the sulky; what is the point? Just this: a wheel is a vastly more efficient device for carrying a load than is a leg, and any horse’s energetic cost of locomotion is proportional to the weight on his feet. So, we are transferring load from inefficient legs to highly efficient wheels, and by so doing we reduce the net energy the horse must exert to move at any velocity above zero. In simple language, we let the animal go faster for the same effort.

 

Copyright James S. Walsh