I've got a 2000 Sportsman 500, but my friends just bought two 2005 700 EFI's. We went riding last weekend and traded machines for a little while. I was impressed at how easy it was to stear the 700's compared to my "beast", but both of their machines had a really bad shake over 30 mph. We were on a gravel road and as you approached 30 mph, the handlebars started shaking real bad (like a car's stearing wheel when a tire is out of balance or it is out of allignment). The shake didn't get better at higher speeds. They have less than 100 miles on these machines and they have the stock PXT tires. One of my friends said they had their machine up to 60 mph the weekend before and never noticed the shaking. They are calling the dealer they bought them from, but I was curious if anyone had experienced this with their new machines before, or if you had any thoughts on the cause. Made me feel good about my good ol' 500, though!

 

I had the same problem on my 800 that you have, do the 700's have the same rims as the 800? (aluminum) The problem is the tires poor build quality and on mine the rims with no center hole makes it rather difficult to balance them properly. They are not balanced right from Polaris, they only add weight to the inside of the rim and the tires have substantial dynamic inbalance which causes the bars to shake side to side, they need weight on the outside of the rim also to correct the balance issue. I replaced both front tires (warranty) and finally was able to balance them on a spin balancer, I used tape weight on the outside between the wheel spokes so it's not so noticable. One tire took 8 1/4 ounces (6 on the outside) and the other took 5 1/2 (3 on the outside) to make them right, problem corrected

 

The 2006 I think has aluminum wheels, but not the 2005, they are steel. I have the stock PXT's on my steel wheels and they go perfect, no shaking whatsoever...

I put on larger 27" tires with aluminum wheels and they shake some, the mudlites shake pretty good, but not uncontrollable, the 589's not too bad now...

First off, I would take it to the dealer, mine came with balancing weights from the dealer, see if your friends machine has them on. Second, crank the preload up on the rear shocks, this took almost all of the shake away from my 589's...as it keeps more weight on the front end so that it isn't floating while going fast...and that is the problem, when you are cruising 30+ mph, the front end is really light and it will exaggerate the shake...

 

I would say its most likely the tire out of round, i had a bad DU wetland (same) and ITP replaced it free of charge now i have no problem but it did wear out a tie rod end due to the whobble.
Check thiose too.

Jim