Like most of you, I have several bikes. One bike has me confused. It's a 58cm Specialized Sequoia Elite (2008) and the issue is that whenever I stand while pedaling up a hill. the back wheel loses traction. It feels like the whole back end is twisting. This doesn't happen with my other bikes which include a Large Giant Escape, a large mountain bike and a 56 cm cross bike. This problem has never occurred on any previous bikes I've owned. So my question is, what's up with this one?

Most of the time a quick release with the cam on the side will clamp harder and fix that. Make sure the sirfaces all look right. Flat & parallel. Knurled washers not smooth. No boogers sticking in.

I've had that happen with some tires, mostly inexpensive ones with hard rubber. Try switching to something softer that gives better traction.

Thanks for the comments. I don't think it's a tire issue. I think it's a bike issue. Is this something that might be expected given the wheel length? (the Giant Escape 1 is virtually the same). I don't know and maybe there is nothing I can do to fix it, but I thought I would ask.

That shouldn't be happening. I agree with the comment about the skewer slipping might be the cause. I missed the twisting part first time. The other possibility is the chain slipping.

By "back wheel loses traction" you mean the tire spins against the ground? If it's a smooth tire on dirt, you can expect that. If it's on pavement, maybe you are unweighting the rear wheel when you stand and lean forward?

So I assumed the wheel was slipping out of the dropouts under a power stroke and binding against the chainstay. If that's not what is happening I don't understand your description.

Thanks, but that's not what I mean. The whole back end of the bike wants to twist. It feels to me that there is too much weight in the front vs. the back. My question is, why on this bike but not the others?

Yes, I think you are exactly right. The question I have is why this bike and is there anything I can do about it?

Why that bike? The bike's geometry, the hardness of the tires, etc.

What to do about it? Concentrate on shifting your weight to the back wheel to maintain traction.

If the back wheel is slipping due to less traction you need to shift your weight towards the back of the bike as Trahak just said above. . The easiest way to do this is to stay seated. If you have to stand, don't lead forward as much. Depending on the geometry of the bike, the type of surface you are riding on, the type of tire you are using and of course your style of riding can contribute to this phenomena.

Swap rear wheels with one of the other bikes and see if the problem transfers with the wheel.

I'd check the rear triangle for cracks (seat cluster, BB).