H. G. Muller wrote on Wed, Sep 14, 2016 06:25 PM UTC:
I once measured the effect of restricting promotion to a minor for one side in Spartan Chess, to see if this was a good way to tune the balance. (After all, players have 8 Pawns there, so even if it only very slightly affects the value of a Pawn, it counts for a lot in the strength of the army.) But I could not measure any effect of it. I guess that in practice promotions can almost always be prevented by sacrificing a minor for the Pawn, and that where they can not, they would be decisive whatever you promote to.
Based on that observation it should not even matter much for the Pawn value if promotion was restricted to Rook everywhere. In which case you would of course always promote to Rook on the 8th, as nothing is to be gained by postponing it. So promoting to Rook must be a viable strategy, and the opponent must defend against that. So most of the time he would sacrifice a minor for the passer even before it reaches 8th rank, or he would make sure he can capture it when it reaches 8th rank, not to give you a free Rook. The only reason not to promote to Rook would then be that you can see you can force it to the 10th, in which case the opponent would also sac a minor for it when it reaches the 8th as a Pawn.
In the end-game, in the case of a promotion race, you cannot afford to delay promotion until you reach the 10th, as the opponent would then promote to Rook on his 8th, and a Rook would be enough to stop your passer completely. So promotion on the 10th becomes mostly theoretical, only occurring in cases that were one side is already completely lost. So the only factor effecting Pawn value is that promotion is shifted up to the opponent Pawn rank, rather than a rank behind it as in orthodox Chess. This should increase the Pawn value. Also because KPK now always is a win.
I once measured the effect of restricting promotion to a minor for one side in Spartan Chess, to see if this was a good way to tune the balance. (After all, players have 8 Pawns there, so even if it only very slightly affects the value of a Pawn, it counts for a lot in the strength of the army.) But I could not measure any effect of it. I guess that in practice promotions can almost always be prevented by sacrificing a minor for the Pawn, and that where they can not, they would be decisive whatever you promote to.
Based on that observation it should not even matter much for the Pawn value if promotion was restricted to Rook everywhere. In which case you would of course always promote to Rook on the 8th, as nothing is to be gained by postponing it. So promoting to Rook must be a viable strategy, and the opponent must defend against that. So most of the time he would sacrifice a minor for the passer even before it reaches 8th rank, or he would make sure he can capture it when it reaches 8th rank, not to give you a free Rook. The only reason not to promote to Rook would then be that you can see you can force it to the 10th, in which case the opponent would also sac a minor for it when it reaches the 8th as a Pawn.
In the end-game, in the case of a promotion race, you cannot afford to delay promotion until you reach the 10th, as the opponent would then promote to Rook on his 8th, and a Rook would be enough to stop your passer completely. So promotion on the 10th becomes mostly theoretical, only occurring in cases that were one side is already completely lost. So the only factor effecting Pawn value is that promotion is shifted up to the opponent Pawn rank, rather than a rank behind it as in orthodox Chess. This should increase the Pawn value. Also because KPK now always is a win.