Shuddering front end...

[Triathlete]

I have 2 sets of tires...does the exact same thing with both.

[etlsport]

it could be a bearing, but you should feel that while doing a shakedown of the front end. you would also probably hear something

any play in the front propeller shaft?

also check the brakes. if you have a stuck caliper, a warped rotor would give you that vibration/pulling under moderate speed, but once the brakes are applied or you are going fast enough, become less noticable