Problem with new tires in second gear only, no problem when I switch to winter tires
 

Ive gt a 2006 x5 4.4 sport, 17" non staggered snows and 19" staggered brand new conti extreme contact dws. 255/50-19 and 275/45-19.

These tires are 1 week old and the excelled shop, euro tire in NJ tells me they will take them back within 30 days if the trouble persists and I want other tires...

The problem ONLY happens in second gear, first is great, then in second under light or medium throttle , don't know about heavy, you just can't feel it.....there is a massive rhythmic clunk, you can almost picture it as one revelation of a wheel, or the driveshaft, clunk, clunk, clunk....then it shifts to Third gear and the problem goes away.....

Really, only in second gear, but under a variety of throttle inputs.....much like a flat spot but again, only in second gear.

Anyone experience anything like this.....I've been so impressed with the tires otherwise.....please help.

Your rear tires are the wrong size. Should be 285/45/19.

yes, but the diameter difference is very small, fractions of an inch, 3 or 4 tenths of an inch, no different than having worn tires on rear and new ones up front.

problem solved with new subframe bushings