Jump to content

shock rebound speed

Recommended Posts

shock: 09 KX450F,

rebound stack with 26 .1 bleed shim right after the face shim

I have ridden the shock with the clicker at 3 clicks out.

preloaded spring length: 247mm

shock movement:

rebound_KX450_09_bleed-shim.jpg

initial rod speed:

reb2.jpg

at the red window the rod speed is approx. 2.3m/s

Share this post


Link to post
Share on other sites

due to the amazing reply - to be honest, I don't know what the dyno should tell me, apart from just being interesting - here I add the speed-stroke curve

reb_vel.jpg

Share this post


Link to post
Share on other sites

thats why i didnt reply, dont know what to say LOL.Waiting on clever people...

Share this post


Link to post
Share on other sites

well, kawamaha, i scrolled tru yr latest messages and cld not see any news about yr idea to this set-up.

What were yr thoughts trying this set-up?

Yr rebound stack is like this:

1x faceshim

1x26.1 crossover

the rest of the faceshims?

an other crossover?

tapered stack

Share this post


Link to post
Share on other sites

What were yr thoughts trying this set-up?

the reb stack is stock except the bleed shim. the idea

is to increase the LS compression by closing the reb. clicker. of course I don't want such a stiff rebound, so I inserted a bleed shim to compensate:

http://www.thumpertalk.com/forum/showthread.php?t=855212&page=4

but this is not what I want to show in this dyno, I was just too lazy to go back to stock...

Share this post


Link to post
Share on other sites

wont the shock heat up real fast with very little bleed on the comp side?

Share this post


Link to post
Share on other sites
wont the shock heat up real fast with very little bleed on the comp side?

you have to ask a fast guy that hammers it for 30minutes :thumbsup:

but I think the stack opens at every compression stroke, so I guess it doesn't matter that much...

Share this post


Link to post
Share on other sites

well it might, i know a rider who tried to run the reb at 3 clicks and it really heated the shock up in 18 mins...free bleed is important IMO for controlling shock temps.

You might be able to test heat build up using the dyno?

Share this post


Link to post
Share on other sites
well it might, i know a rider who tried to run the reb at 3 clicks and it really heated the shock up in 18 mins...free bleed is important IMO for controlling shock temps.

You might be able to test heat build up using the dyno?

damping is converting energy into heat. so if he runs a stock stack with only 3 cklicks he has much more rebound - which creates much more heat than only an increased LS compression damping

I could do a test, but not with the actual rebound speed, so I think there's no sense...

Share this post


Link to post
Share on other sites

Imo, with stiffer comp the reb runs cooler and inversely

the overall energie will be the same.

i am surprised how the clicker works, overall stiffer or softer, not only at low-speed??

Share this post


Link to post
Share on other sites

Just to ask the dumb question - the shock was compressed with a spring installed - then released....correct?

That is what I think we are looking at (almost obviously) - and it's quite clear that (as in drag racing - launch and 60ft is everything) what is gained early in the stroke is magnified much later in the stroke - so the very small difference early on in return is magnified at the end quite a bit

Also shows exactly what active was talking about (if memory serves me correctly on those posts) that the peak velocity occurs early on in the return process.

Peak acceleration - by combining all the graphs posted say from initial release to peak velocity is giving me from 0m/s to 2.3m/s in .01 second of 230m/s^2 acceleration

23 G's worth.

On rebound.

Nice.

Now - add inertia effects and the weight of the wheel and swing arm - and things begin to lag quite a bit.

Regarding heat - energy is conserved. If you damp more out - you build more heat! Turning in the clicker on an existing set up will build more heat - no two things about it. However the less heat put into the system on rebound probably balances it out.

Pro's have it twice as bad - more damping AND longer motos!

Share this post


Link to post
Share on other sites
Just to ask the dumb question - the shock was compressed with a spring installed - then released....correct?

exactly :thumbsup:

Also shows exactly what active was talking about (if memory serves me correctly on those posts) that the peak velocity occurs early on in the return process.

yes, but the rate at the rear wheel would be not that intense due to the linkage.

eg. the max. wheel speed is approx. 5.3m/s and 2.8m/s at 40mm rod position.

so at 40mm rod position the rear wheel speed is 53% from maximum, while at the shock its only 40%

Share this post


Link to post
Share on other sites
exactly :thumbsup:

yes, but the rate at the rear wheel would be not that intense due to the linkage.

eg. the max. wheel speed is approx. 5.3m/s and 2.8m/s at 40mm rod position.

so at 40mm rod position the rear wheel speed is 53% from maximum, while at the shock its only 40%

I am a little lost with the last statement can you walk me through it?

Wheel speed would be higher than shaft speed due to linkage - no doubt. But we are neglecting wheel and swing arm inertia for the above graphs - which play a huge role in the entire picture.

Share this post


Link to post
Share on other sites

well, I know, lots of numbers...

oh, I see I made a mistake, but lets start.

hitting a jump face, the shock is almost completely collapsed

after lift off the shock rebounds after the acceleration with the maximum speed of 2.3m/s.

when the rear wheel is reaching approx. sag position, the shock is at 35mm (0mm = completely extended) it has approx. 0.8m/s, thats 35% of 2.3m/s

so if we would have no linkage, like a PDS, the maximum speed at the rear wheel would be 5.5m/s, and at sag position the speed would be 35% or 1.93m/s.

now that we have a linkage, the rear wheel/shock ratio changes through the stroke. so at sag position the rear wheel speed is 2.32m/s, thats 42% of the max. speed.

I took the jump face as example because you know, everything is completely different with bike/rider weight on it...

Share this post


Link to post
Share on other sites

I get what your saying now - you made a jump from 5+ m/s to almost none - and I didn't see what you meant.

So your saying at the wheel at or near full extension (if it were a jump it WOULD extend all the way) the velocity is very small.

Sounds good.

Share this post


Link to post
Share on other sites

Very interesting setup indeed.

Question is, what how does it compare with a rebound-setup that has less lowspeed shims and closed clickers settings?

Share this post


Link to post
Share on other sites
Very interesting setup indeed.

Question is, what how does it compare with a rebound-setup that has less lowspeed shims and closed clickers settings?

what do you mean with less lowspeed shims?

I really can't say anything about stock setup and my current setup because I can't compare a setup to another one with two weeks time lag and a different track condition :thumbsup:

Share this post


Link to post
Share on other sites
Have you ever tried a shaft jet????

me? no, I don't spend money on stuff I can achieve by other ways.

and, I don't have much complaints about the rear, I was just curious...

Share this post


Link to post
Share on other sites

You want to run yr rebound-clickers as close as possible.

Close the clickers by 10, loose one faceshim.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×