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?
Wheels are unsprung weight...damping, whether compression or rebound only affect sprung weight.
I didn't change my 996 when I went to mags. :-\
Ok so my initial thinking on rebound is correct. Just started to over think things in my typical fashion.
The only time the suspension will behave differently with a lighter wheel is when that wheel is off the ground.
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.
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.
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
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.
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.
Displace where?
Through the asphalt? :P
Displace as in move
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.
I'll dig it up later
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.
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."
Could it be the lighter wheels simply uncovered less than optimal settings?
On the average, the front or rear suspension is holding up ~300 lbs.
A change of even 3 pounds on a wheel is going to make a *very* small change on how much the tire squashes on a bump.
Until the tire comes off the ground, no detectable change IMO.
Quote from: Speeddog on October 03, 2012, 08:27:25 PM
On the average, the front or rear suspension is holding up ~300 lbs.
A change of even 3 pounds on a wheel is going to make a *very* small change on how much the tire squashes on a bump.
Until the tire comes off the ground, no detectable change IMO.
+1
Most people including racers don't need to make any extraordinary changes to suspension with lighter wheels.
BST does not recomend any. Nor does OZ.
-M
Quote from: Slide Panda on 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."
His premise is the 5 lb wheel moves up as opposed to the 450 lb bike moving down it seems. That doesn't work physically.
The wheel stays on the road...no?
While they may have needed changes on that particular bike I'm gonna stick with my original thinking.
On a bump, the wheel goes up and it does so with slightly less mass to accelerate.
However, the suspension is set to dampen the bike + rider upon braking, so the need for additional compression because of a lighter wheel must be very minor.
I think the difference would be easiest to detect coming out of a corner. Then one might 'need' a tad more compression. The theory is clear enough, but I'm not sure we're even talking about one click and at those kinds of adjustments it's almost impossible to know what's what with ambient/hydraulic oil/tire temperature and track surface conditions.
Hey Moto if you want to donate a set of BSTs (Fitment for an 08 Duke please) I'd be HAPPY to test this all out. ;D