Bagger wobble exposed!
HDF Community Team
Joined: Nov 2012
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From: USA
Though they do rubber mount the suspension to the chassis. Don't loose track of that. If the suspension were hard mounted, you'd have a lot more road vibration and harshness. Racers will often replace the rubber suspension bushings with urethane, delrin or sometimes even metal (Oilite most commonly). It helps keep the suspension in sharper alignment, at the expense of ride plushness.
Banned
Joined: Apr 2014
Posts: 678
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From: LA
Do you think there is any merit to bracing the frame at all, e.g. the later baggers have a light brace across the front downtubes?
Or do you think the frame is rigid enough to cope? I know your experience is "don't worry about it Graham" and I am sure you are right.
I'm going off to measure the free play on my pivot ... it certainly rattles and I remember Hillside (?) saying they re-machine theirs to a fine tolerance or running fit.
Or do you think the frame is rigid enough to cope? I know your experience is "don't worry about it Graham" and I am sure you are right.
I'm going off to measure the free play on my pivot ... it certainly rattles and I remember Hillside (?) saying they re-machine theirs to a fine tolerance or running fit.
Tourer
Joined: Apr 2014
Posts: 288
Likes: 3
From: UK
There are some interesting theories her but there are some simple laws of physics that you need to apply which is why HD ended up with this design in the first place. If you are going to have go here is what you need to do.
1) Vibration isolation. In order to isolate the motor you need a specific stiffness. This is in all 3 axis, vertical, horizontal and lateral. This is achieved by the mount arrangement that HD use. You cannot cheat on this, too stiff and it will be too harsh. On a Vtwin motor like this it needs to be soft. The formulae are complex but the results are what they are and the RK mount system is good at isolating vibration so they have got the sums right. Its not something you can do by guesswork.
2) Reaction to final drive torque. A 110cu can produce up to 500 ftlbs at the output shaft of the gearbox, that's generating a huge amount of pull on the drive belt trying to drag that side of the transmission back and twisting the front of the motor upward. Use the diameter of the output pulley and output torque to calculate force on the tension side of the belt. Apply the mount stiffness from item 1) above and you will get the movement of the motor due to drive torque. If you are going to mount the swing arm direct to the frame you need to consider this carefully.
3) Tractive effort. On the Harley system the pull on the drive belt equates to rear wheel torque and generates tractive effort. The tractive push from the rear wheel is transmitted through the mounts into the frame. Its possible to generate 1g acceleration so base you calculation of the entire weight of the bike pushing forward on the mounts. Add this to the drive torque above to get the final engine movement under load.
When you have got a handle on all these things and done the math then lets see your design proposal for an alternative mount system.
1) Vibration isolation. In order to isolate the motor you need a specific stiffness. This is in all 3 axis, vertical, horizontal and lateral. This is achieved by the mount arrangement that HD use. You cannot cheat on this, too stiff and it will be too harsh. On a Vtwin motor like this it needs to be soft. The formulae are complex but the results are what they are and the RK mount system is good at isolating vibration so they have got the sums right. Its not something you can do by guesswork.
2) Reaction to final drive torque. A 110cu can produce up to 500 ftlbs at the output shaft of the gearbox, that's generating a huge amount of pull on the drive belt trying to drag that side of the transmission back and twisting the front of the motor upward. Use the diameter of the output pulley and output torque to calculate force on the tension side of the belt. Apply the mount stiffness from item 1) above and you will get the movement of the motor due to drive torque. If you are going to mount the swing arm direct to the frame you need to consider this carefully.
3) Tractive effort. On the Harley system the pull on the drive belt equates to rear wheel torque and generates tractive effort. The tractive push from the rear wheel is transmitted through the mounts into the frame. Its possible to generate 1g acceleration so base you calculation of the entire weight of the bike pushing forward on the mounts. Add this to the drive torque above to get the final engine movement under load.
When you have got a handle on all these things and done the math then lets see your design proposal for an alternative mount system.
Last edited by 4_stroke; Aug 15, 2014 at 03:46 AM.
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Club Member
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From: Bedford UK
DR,
The other weakness of the touring models isn't so much the frame or steering head, as the forks and the top fork tree. That is not to suggest the frame couldn't be better or stiffer, but while the fork legs are so poorly supported at the top tree there is no point looking any further! As you know the CCE kit addresses the forks problem, for those of us determined to sort things out.
The other weakness of the touring models isn't so much the frame or steering head, as the forks and the top fork tree. That is not to suggest the frame couldn't be better or stiffer, but while the fork legs are so poorly supported at the top tree there is no point looking any further! As you know the CCE kit addresses the forks problem, for those of us determined to sort things out.
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Club Member
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From: Bedford UK
That is addressed by the third stabiliser link, which is the subject of much of the discussion above. My 107" Glide and Buell both produce similar torque levels and both have three stabilisers!
Tourer
Joined: Apr 2014
Posts: 288
Likes: 3
From: UK
This is not an issue on the RK because the swing arm and transmission are close coupled. The forces are reacted through the swingarm pivot point on the transmission. It only applies if the back wheel and output shaft on the transmission are separated by a rubber mount. The only reaction is the vertical movement of the front of the motor and corresponding downward force on the back of the transmission.
Last edited by 4_stroke; Aug 15, 2014 at 04:32 AM.
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Club Member
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From: Bedford UK
This is not an issue on the RK because the swing arm and transmission are close coupled. The forces are reacted through the swingarm pivot point on the transmission. It only applies if the back wheel and output shaft on the transmission are separated by a rubber mount. The only reaction is the vertical movement of the front of the motor and corresponding downward force on the back of the transmission.
Last edited by grbrown; Aug 15, 2014 at 05:03 AM. Reason: Spelling!
Tourer
Joined: Apr 2014
Posts: 288
Likes: 3
From: UK
There's study and there's understand. There is noting wrong with the Harley system apart from the fact that it was designed in the shovel head era and has not been upscaled to suit later heavier bikes with better tyres. Plus the FXR frame was a lot stiffer than the RKs
3 links work if correctly positioned and the frame is stiff enough to take the side loads. These loads are not predominantly due to final drive torque as such but the yawing effect which can be induced during a turn when there is side loads on the frame.
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Club Member
Joined: Jun 2007
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From: Bedford UK
A suitable third link, as exhaustively discussed above, will provide substantial and worthwhile improvements to ride quality and handling in a stock bike, whether early or latest style. The design has proved remarkably adaptable, despite it's age!
Tourer
Joined: Apr 2014
Posts: 288
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From: UK
FFS...... I am not arguing with you, I am trying to agree.
What I AM saying is this subject has been done to death on a lot of other forums and there are lots of folk who think that they can do a better job of it. If that's the case then show us the math behind it.
Last edited by 4_stroke; Aug 15, 2014 at 05:21 AM.