Suspension Question - Wrist Twisters
 
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post #1 of 5 Old 10-07-2017, 08:03 AM Thread Starter
Milites Gregarius
 
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Suspension Question

This pertains to my DR650 dual sport but it is a general question.

I'm a tall brute and decided to throw on some raising links (shorter dogbones) and it lifted the rear at least 1-2 inches. The rear suspension now seems really form (almost too firm). For context, I still have stock shocks/front springs and they are notoriously soft on this bike. I'm still wrapping my head around rebound vs. compression damping etc etc -- what are the mechanics behind raising the rear of a bike and why that would make the rear shock feel firm?

2002 Honda 919
1999 DR650
1998 GS500 - sold
2014 Ninja 300 - sold
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post #2 of 5 Old 10-07-2017, 09:39 AM
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Quote:
Originally Posted by knicholas View Post
This pertains to my DR650 dual sport but it is a general question.

I'm a tall brute and decided to throw on some raising links (shorter dogbones) and it lifted the rear at least 1-2 inches. The rear suspension now seems really form (almost too firm). For context, I still have stock shocks/front springs and they are notoriously soft on this bike. I'm still wrapping my head around rebound vs. compression damping etc etc -- what are the mechanics behind raising the rear of a bike and why that would make the rear shock feel firm?
I don't know anything about DRs but your post is describing a linked suspension, and that you have changed the length of a link component.
Such length changes will change the leverage, which affects the forces the spring and damper see.
It also affects the ride height, for any given shock length X spring x installed spring height x installed preload.
Depending on which length has been changed, and whether it's been made longer or shorter, the affects can be in either direction.
To put it in perspective, look at it this way.
In conceptual terms, a typical linked swingarm needs about half as much spring rate as an unlinked swingarm, and the damper will need to provide far less hydraulic damping forces.

You might be able to find a XL based calculator somewhere on the web, and play with the inputs to give you some good insight as to what you are observing, and how to change things in a direction you want.

Hopefully the above is of some help.

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post #3 of 5 Old 10-07-2017, 09:52 AM Thread Starter
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Quote:
Originally Posted by mcromo44 View Post
I don't know anything about DRs but your post is describing a linked suspension, and that you have changed the length of a link component.
Such length changes will change the leverage, which affects the forces the spring and damper see.
It also affects the ride height, for any given shock length X spring x installed spring height x installed preload.
Depending on which length has been changed, and whether it's been made longer or shorter, the affects can be in either direction.
To put it in perspective, look at it this way.
In conceptual terms, a typical linked swingarm needs about half as much spring rate as an unlinked swingarm, and the damper will need to provide far less hydraulic damping forces.

You might be able to find a XL based calculator somewhere on the web, and play with the inputs to give you some good insight as to what you are observing, and how to change things in a direction you want.

Hopefully the above is of some help.
Aha - the exact person I was hoping would respond

Unfortunately, bike suspension has always been rocket science to me. I mean I'm a PhD student for goodness sakes, it should not be this hard. At any rate, I appreciate your note! Maybe tonight before bed I'll dissect it and get to the bottom of this rocket science once and for all

2002 Honda 919
1999 DR650
1998 GS500 - sold
2014 Ninja 300 - sold
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post #4 of 5 Old 10-07-2017, 11:52 AM
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Originally Posted by knicholas View Post

Unfortunately, bike suspension has always been rocket science to me.
It's not rocket science, and if it was, I for one would be seriously hooped.
All of it can be reduced to bite sized conceptual basics that can then be built upon.
Aside from hydraulic damping force curves, most can be explained in terms of high school level physics aided by some similar level geometry.
Perhaps some college level stuff re spring theory, but even that can be explained in simple low level terms.
A wee bit of energy conversion understanding, re the damper converting force into heat by friction.
The mistake is trying to grasp the complexities right off the bat.
Get the building blocks established in conceptual terms, relate them, then go from there.
You'll likely blow past us all once you put your mind to it.

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post #5 of 5 Old 10-08-2017, 08:34 AM Thread Starter
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Good tips! I'll look forward to being a resident forum expert in the future

2002 Honda 919
1999 DR650
1998 GS500 - sold
2014 Ninja 300 - sold
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