The max for the tires is 7psi, stock specs in the manual are 5psi. I tried running 3.5 like my old quad and it felt like I was bottoming out the tire on a rock too much. I keep it at 5psi now.

I just replaced the stock tires with Maxxis BigHorns last week and am running those at 5psi also.

 

My 550 XP did the same thing. With the front springs on softest setting and at a slower (15-20 mph) speed, a "Harmonic" bounce sets up. Tightened springs one notch cured it.

 

Did you tighten both front and rear springs? If so, what tool do I need to tighten the springs easily?

 

the xp and the regular sportsmans are differnt. the rear springs have a collar that chan be rotated to adjust the spring preload. so say use a channel locks to rotate the collar. iv been trying to find the preload adjuster wrench.

 

yeh there is an actual tool to adjust the springs, but most just use channel locks, I haven't ever messed with my shocks, minus the front spring spacers

Back to your original question, I keep mine right around 5 PSI, and they do slightly wander and vibrate on the road, but not really any noticeable bouncing, I doubt your tires are flat spotted, unless perhaps they sat in the crate flat or something goofy like that, but just by them sitting at your place they wouldn't do anything

 

Tightened fronts only with tool supplied by Po.

 

This is a well-known phenomenon!
Dont get worried of it.
Make sure you ware around 5psi. 4.5-5.5 !
After few minutes of riding the tires will warm up , and the ride will smooth.