The Effects of Horse Weight

Do you believe that weight is an effective tool for controlling the performance of a horse? Do you think a horse going up 10lbs in the weights has less chance today than last time? Weight is one of the great racing conundrums. How can a few pounds extra on the back of a 1000lb thoroughbred influence its performance?

Weight is used to handicap a horses chance of winning. The more successful the horse, the more weight it carries and the less successful it should be in future races. At the other end poor horses are allowed to carry less weight and should thus better their recent finishing positions.

The handicapper has the task of assigning ratings for every horse that runs at least 3 races. But how accurate are his ratings? Like anyone who compiles weight adjusted ratings the figures are going to be complicated by incorrect going descriptions and different course topologies such as those which favour top weights.

The following tables should shed some light on how much of an effect weight has on a horse. First we will look at the performance of horses carrying more or less weight than their last race, next the performance of the handicapper, and finally the effect on extra weight influences such as overweight, penalties and allowances.

Changes in weight

all turf runners Win%
108,413 carried more weight, 11,083 won 10.22%
113,231 carried less weight, 9,768 won 8.63%
index 1.19

The above table shows the results of 221,644 runners on the turf since 1993. Horses carrying more weight than their last race won 10.22%. Horses carrying less weight than their last race won 8.63%. This means a horse carrying more weight than last time is 1.19 times more likely to win than one that is carrying less.

Obviously, this is looking at all turf races and does not take into account horses going up or down in class which will have a bearing on the allocated weight.

turf runners in same class Win%
38,120 carried more weight, 3,925 won 10.30%
40,950 carried less weight, 3,630 won 8.86%
index 1.16

The figures are pretty much the same as in all races. Horses carrying more weight than in their last race, which was of the same class, won more than those carrying less.

turf runners handicap today, handicap last time Win%
55,031 carried more weight, 5,474 won 9.95%
57,085 carried less weight, 4,217 won 7.39%
index 1.35

The above table examines handicap races where the last race was a handicap too. Although the strike rates are lower, the index is bigger indicating that a horse that is rising in the weights is progressing in the right direction.

turf runners handicap today, handicap last time same class Win%
20,108 carried more weight, 2,092 won 10.40%
22,380 carried less weight, 1,658 won 7.41%
index 1.40

Weight rise handicappers running in the same class have a big advantage.

turf runners in stakes races Win%
36,323 carried more weight, 4,268 won 11.75%
39,751 carried less weight, 4,665 won 11.74%
index 1.00

Weight change in stakes races has no effect.

turf runners handicap today, stakes last time Win%
10,155 carried more weight, 1,035 won 10.19%
11,093 carried less weight, 1,412 won 12.73%
index 0.80

The above table is the only one where it is an advantage to be carrying less weight.

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