Future Hiro thought that Sylar was the bomb. If he and Peter were such good friends in the future, how come Peter doesn't tell him the truth?

That might be why what Future Hiro told Peter on the train didn't stop the bomb from exploding.

I had this same thought. Following that line of inquiry brings you to the question, what happens when Hiro attacks Sylar, as depicted in Isaac's artwork? Unto itself, it certainly isn't going to stop the explosion.

No, not nessaceraly. Hiro (in episode 20 I belve, Five Years Gone) at the end had a peice of Isaac's artwork which shows Hiro and Sylar, the sword in his chest.

peter didnt want to hurt hiro, the same reason he waited so long to tell niki he was the bomb, Ando died in the explosion and peter was afraid of what hiro would think

This question was asked in another thread to which I responded with the following:

"I suppose the obvious reason is that Sylar was the bomb originally and telling Peter to save the cheerleader changed that. It's possible that the fPeter that fHiro has spoken with before he time jumped to deliver the message to pPeter isn't the same one that we saw. If that's the case, then maybe the fPeter we saw thinks that he's already told fHiro that he was the bomb and, of course, fHiro doesn't remember it because he never experienced that conversation. Under these conditions, the fPeter we saw wouldn't have a reason to tell fHiro if he thought he already knew."

future Hiro did know who the bomb was until he changed the past. Then Peter became the bomb, but Hiro didn't know.

Now, my understanding of events is that Hiro, in whatever connotation you place him thinks Sylar is the bomb. Remember that Hiro now in feudal Japan still thinks Sylar is the bomb, since he never saw Peter blow up. 5YG Hiro believes it and always had. Since he was once present Hiro, then you have to believe that when the bomb went off in his time it was still Peter. I know he says he stabbed Sylar and Sylar exploded, but IIRC, he doesn't say that Sylar exploded right away, right? I mean if that were the case then the future Hiro would be toast, right? So it makes me think that he stabbed Sylar and Peter still exploded later, and convinced the world that Sylar was really the bomb, it was just coincidental that future Hiro already thought this. This also supports the theory that future Hiro's actions didn't change events the way he planned, even though he had a significant role in changing them, it wasn't all about just saving the cheerleader.

some people have been given long winded reasons. Basically i think which has been mentioned previously. Simple Hiro did not know that Peter was the bomb. That is because in the future where Sylar killed Candace he takes nathan's form so everyone assumes Sylar is dead so therefore thinking he was the explosion. Though it was really peter.

I may be wrong on this but didn't Peter say that only Nathan knew he was the bomb and covered it up. If I'm right (correct me if I a wrong) then everyone bar Peter and Nathan who is now Sylar thinks that it was Sylar who was the bomb thus everyone thinks the same.