Can someone explain this to me, I can't seem to wrap my head around it.

'12 SG, owned since new but I've just noticed it yesterday while out for a ride.
When sitting at a stop I get normal shake at idle, if I apply the front brake only the amount of shake 'doubles'. If I apply the rear brake only, almost all shake goes away.

I'm not worried something is wrong, I just can't understand the dynamics

Thanks

 

potential steering stem nut loose. id check that first without hesitation.

 

I don't believe the shake actually doubles, but rather the feeling you get as you have engaged the brakes and it simply sends the vibrations up the forks and handlebars.

 

I've noticed this on the last two bikes I've owned - a Fat Bob and Street Glide. If you watch the front wheel without the brake applied, you will see it roll back and forth a little. With the brake applied, the energy has to go somewhere. You may notice that it isn't as bad if you are using the brake to hold yourself on an incline. I noticed it less on a bike with stock cams.

 

I kinda agree, it's the tensed and stiff arm holding that brake lever that vibrates your head off.

I say kinda, because there does seem to be a slight change in the vibration in the seat and the mirrors as I play with holding the rear brake, rolling against it, as well holding the front brake and rolling against it.

I generally am not happy or comfortable holding the bike with my foot on the brakes, especially when I have to jump feet around to engage 1st when the light turns green. So I hold the bike with my feet on the ground if possible, and put up with the vibration of holding the front brake otherwise. I've also been known to turn the bike off and restart when it's time to go.

 

I've also noticed the idle shake being stronger while stopped with the front brake pulled on my FXDF and now on the SGS. The FXDF seemed to do this more, I wonder if the rake makes it stronger or the weight of the fairing on the SGS dampens it some.

 

You know that every bike I have ever owned has done that for the last 45 yrs. don't worry about it that's just the way it is.

 

when the front brake is not applied, the ability for the front wheel to move (ever so slightly) separately from the rest of the bike absorbs some of the vibration. When you apply the front brake, you've eliminated the "slack" in the front end and it becomes a solid unit therefore the vibration that was previously absorbed / dissipated by the front wheel's separate movement is now transferred up the forks, to the frame and handlebars.

other contributing factor, front motor mount wearing out which transfers more vibration to the frame.

 

Thanks for the replies guys. Like I stated, I'm not worried. I'm just trying to understand why it happens.
I don't understand how clamping a set of break pads on a rotor(s) changes the harmonics (for lack of a better term) of the bike. It's not stiff arm either, i've tried two fingers pulling the lever and thumb on the grip with loose arm....still does it. Also, applying rear brake lessins the 'felt' vibration.
Oh well, I'll think on it some more. For now I'm going for a ride.
Thanks all and Happy Easter!

 

Weavr99
THAT makes sense