3.5 Riding checks

[Borgthar]

If its possible can two people ride a mount simultaneously and both use their ride by attacks and spirited charges to hit the same target and if so what penalties if any occur? We tried this attack on a fire giant and the DM declared we could not do to a rule in the book complete warrior (which I've been unable to find rules on two riders in said book) so he would let us make attack rolls however we would have a -10 because of the two riders and when we got hit we had to make balance checks to stay mounted. I'm not sure if my DM hammered us for cheesing the system and just didn't want to say no or what.

[Allanimal]

If its possible can two people ride a mount simultaneously and both use their ride by attacks and spirited charges to hit the same target and if so what penalties if any occur? We tried this attack on a fire giant and the DM declared we could not do to a rule in the book complete warrior (which I've been unable to find rules on two riders in said book) so he would let us make attack rolls however we would have a -10 because of the two riders and when we got hit we had to make balance checks to stay mounted. I'm not sure if my DM hammered us for cheesing the system and just didn't want to say no or what.

I don’t recall, nor can I web search for, rules on dual riders. If i were DM in this situation, and now rules text was available, i would only allow the primary rider that is, the one controlling the mount, to benefit from the mounted combat feats. The secondary rider could attack normally, but not benefit from feats.

Your DMs ruling seems a bit harsh to me. A -10 is a massive penalty. I could see saying two PCs sharing a mount is equivalent to squeezing and use similar penalties, but -10 is a lot.

Edit: I did find in the rules compendium, p.89

Multiple riders share their mount's space completely as well.
That’s the only mention so far I have found about multiple riders. And there is no indication of mechanical side effects of multiple riders. So the rules acknowledge multiple riders, which to me means that the mounted combat rules apply equally to both riders. Obviously the mount can only do one set of actions (and there is no mention of what happens when both riders give conflicting instructions to the mount...)

[robsworld]

If its possible can two people ride a mount simultaneously and both use their ride by attacks and spirited charges to hit the same target and if so what penalties if any occur? We tried this attack on a fire giant and the DM declared we could not do to a rule in the book complete warrior (which I've been unable to find rules on two riders in said book) so he would let us make attack rolls however we would have a -10 because of the two riders and when we got hit we had to make balance checks to stay mounted. I'm not sure if my DM hammered us for cheesing the system and just didn't want to say no or what.

I like your question. This situation might come up in my game. I'm getting ready to restart a campaign at 1st level, and one of the characters is planning to ride a mount 'at all times'. I can see him sharing the mount with another rider, and both of them might want to attack the same opponent at some point.

I'm not aware of any rule that would prohibit this activity (that doesn't mean there isn't a rule that prohibits the activity. I'll assume you've done some searches, and couldn't find the reference your DM cited. If someone finds a rule regarding this activity, I hope they will cite the reference here.

Without a specific (known) rule, one might ask - Are both riders skilled in 'Ride By' and 'Spirited Charge'? (your message wasn't specific, but I infer that they were (you said: "use their ride by attacks and spirited charges"). If this is the case, I can't see why the DM might rule against this activity or penalize it.

If both character's have the necessary feats, why would they be prohibited from riding the same mount? What if they were both riding on a magical carpet? I would allow the player with the highest Ride skill to guide the mount (using his/her skill and initiative roll for the mount's movement).

Both attacks should be allowed as the character's 'Ride by' the opponent in question. If necessary, they could coordinate their strikes by invoking a 'Readied Action' - When the mount takes them into range for a Charge attack.