I ride a Tandem and the accepted rule is that you go 20psi above the max stated on the sidewall. On Tandems you also do not go to the narrowest tyre around so 1 1/4 tyres should be OK but go 10psi above the max printed on the sidewall. Weight of the Tandem is 400lbs all up so the tyres will take the weight. Someone said it already but get the wheles checked before you ride and keep an eye on spoke tension.