DR650 turned into SM, now has a problem
 

One of my coworkers has a Suzuki DR650 that he turned into a SM. He took off the 21" front wheel and put a 17" front wheel on it. Now he is experiencing what he is calling a "tank slapper" like condition when he gets to about 70mph. He cant figure out why. I'm guessing that by going to the smaller wheel, he essentially lowered the front of the bike 2 inches and has fucked up the steering geometry. Anyone have any thoughts on what is wrong? Forks are bad? Wheel is bent? It doesn't have any problems below 70mph.

sounds like wheel balance issues

A wheel out of balance would cause the tire to rotate out of round(up and down) but he is getting the handle bar to shake side to side. Would off balance tires cause a side to side shake?

how tight are the spokes? they might need adjusted or maintained

It was a brand new rim installed by a Suzuki dealer. Spokes should be tight.

i would check the balance out first, if its off the affects would be magnified by the increased speed, or possibly the bearings in the steering stem could be bad

It's the change in steering geometry, dropping the front takes a lot of rake out of the front, and the closer the front gets to up and down, the more likely it is to shake.

How do you fix that, longer fork tubes? He certainly doesn't have 2" of fork to slide back though the triple tree.

or what he said, lol

he could try dropping the rear shock in the lower position - it's easy to do, free and doesn't take all that long.

No guarantees that it will help thou...