Can anyone enlighten me on the pros and cons of the sliding cheek pelham v a fixed cheek pelham, and also a mullen mouth over a cambridge or port mouth?
I stand corrected as i've just seen one on a google image search- though have nearly 30 pelhams in bit box here and not one sliding!
I think it comes down to the horses preferance, mine likes a sliding cheek weymouth in his double and also schools in a loose ring - but my old mare seemed to be more consistent in the contact in a fixed cheek weymouth - trial and error!
If the cheek of a pelham slides, then it's not acting as a pelham at all, but a gag, where the bit slides upwards against teeth / roof of mouth etc, making it much more severe.
IMO pelham is a much maligned piece of equipment. Relatively mild, and lots of horses go very happily in them. Gags, on the other hand, are used far more often than they are needed. I don't like them at all.