It is balance, it's to do with resonance, once it falls into a resonance it will shake, high highs and low lows doubling up on itself.
Its like when armies cross bridges they don't march coz the resonance could destroy it.
It doesnt neccicerly mean tire balance either. Youll find that manufactures have tolerances on wheels, on how eliptical they can be, and youll find they usually alow a lot of eliptaclity (dunno if thats an actual word).
You may find going round a gradual corner between 110-120 also changes the vibration if its in 2 wheels because they to fall in and out of resonance with each other.
Best would be to identfy the inbalance, try to correct it but also to put the worst wheels on the back. If there all bad, a regular (5,000-10,000km) tire rotation should minimise the tires getting worn improperly thus worsening the problem.
I've been there an done that with balancing. My dad fitted oversize wheels to 4wd and the balancing was a nightmare, bought new wheels and they were off too. The bigger the wheel and tire, the more pronouced a bad balance is. There is some vibration at 90-100km/h and we consider ourselves lucky.
Bear in mind that a re balance of your wheels may not solve the problem, it might just shift it to a different speed range, if your unlucky it will be below 110!
Adam
