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Lighter wheels - suspension changes?

Started by Slide Panda, October 02, 2012, 07:31:23 PM

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Slide Panda

October 02, 2012, 07:31:23 PM
So, spent some dollars and a lot more manaul effort on getting the wheels on the KTM to be tubeless and some other light bits. Better part of pound from the front and near 3 from the rear. So that tells me I can expect some more suspension twiddling in my future.

Lighter wheels will mean a need for more compression damping as there's less mass to absorb shocks. Got that...

But I'm not quite sure how this will translate for rebound. Part of me wants to say the rebound should stay as is - as it's really more of a relation between the damping action and the spring returning the system. Part that I'm leaning away from says a bit more rebound as the springs got less unsprung mass to push on the return.

Anyone else been in the lightened wheel camp? How'd you alter suspension?
Andy gurus care to weigh in?

-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

ducpainter

#1
October 02, 2012, 07:36:00 PM
Wheels are unsprung weight...damping, whether compression or rebound only affect sprung weight.

I didn't change my 996 when I went to mags. :-\
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Slide Panda

#2
October 03, 2012, 03:47:47 AM
Ok so my initial thinking on rebound is correct. Just started to over think things in my typical fashion.

-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

Speeddog

#3
October 03, 2012, 08:54:09 AM
The only time the suspension will behave differently with a lighter wheel is when that wheel is off the ground.

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Slide Panda

#4
October 03, 2012, 09:01:47 AM
One of the books I have specifically mentions an instance where they switched to carbon wheels and found a need for more compression damping. Probably not an issue for me as I didn't loose that much... and these KTMs are Waaaay over damped. The manual recommended 'sport' settings were like riding a set of 2x4s with wheels.
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

ducpainter

#5
October 03, 2012, 09:06:25 AM
Quote from: Slide Panda on October 03, 2012, 09:01:47 AM
One of the books I have specifically mentions an instance where they switched to carbon wheels and found a need for more compression damping. Probably not an issue for me as I didn't loose that much... and these KTMs are Waaaay over damped. The manual recommended 'sport' settings were like riding a set of 2x4s with wheels.
I don't understand why.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Slide Panda

#6
October 03, 2012, 09:08:30 AM
Why KTM do it?  ;D
Few things like that I wonder about on this bike... another being the fact that there are a number of (easily) water permitted connectors in the harness, on an offroad bike
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

ducpainter

#7
October 03, 2012, 09:31:29 AM
Quote from: Slide Panda on October 03, 2012, 09:08:30 AM
Why KTM do it?  ;D
Few things like that I wonder about on this bike... another being the fact that there are a number of (easily) water permitted connectors in the harness, on an offroad bike
No

Why suspension changes were necessary.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Slide Panda

#8
October 03, 2012, 09:35:11 AM
I was being a smart ass.

Don't have the book on had to quote from - but the gist was that the lighter wheels were easier to displace, faster when they hit a bump (F=ma).

So the reduction of mass required adjustment to balance the equation - my notion of it.
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

ducpainter

#9
October 03, 2012, 09:52:41 AM
Displace where?

Through the asphalt? :P
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Slide Panda

#10
October 03, 2012, 10:00:50 AM
Displace as in move
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

ducpainter

#11
October 03, 2012, 10:03:25 AM
Quote from: Slide Panda on October 03, 2012, 10:00:50 AM
Displace as in move
Well they do 'move' easier...with the axis of the steering stem.

I just don't understand how damping requirements change.

I'm willing to listen if you can find the quote.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."


Slide Panda

#12
October 03, 2012, 10:08:20 AM
I'll dig it up later
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.

stopintime

#13
October 03, 2012, 10:37:14 AM
I did my share of (over)thinking this when I got my lighter wheels.
Not that I have a conclusive answer....

Compression on the brakes or when the bike rolls into a hole - no difference.

Compression when the wheel is pushed up against the bike - faster/easier compression. This could require more compression damping. ALSO, less tire compression with less following tire pressure 'backfire'. This could allow less compression damping. One positive and one negative means nothing to adjust(?)

If one of the wheels leaves the ground after a road bump, it will return faster. That is a good thing and does not need to be corrected by altering the rebound damping.

When I was done thinking about it, I asked my suspension guy and he said lighter wheels are just going to make suspension better without any need to adjust.
252,000 km/seventeen years - loving it

Slide Panda

#14
October 03, 2012, 07:19:51 PM
From Sportbike Suspension Tuning by Andrew Trevitt on pages 71-72

"... On a magazine project GSX-R 1000, we installed carbon fiber wheels that were several pounds lighter than stock.  To account for the huge drop in unsprung weight we had to increase compression damping. The lighter wheels were deflecting more over bumps and more damping was necessary to better control the lighter wheels."
-Throttle's on the right, so are the brakes.  Good luck.
- '00 M900S with all the farkles
- '08 KTM 690 StupidMoto
- '07 Triumph 675 Track bike.
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