# shim question

#### georgieboy

Member
I have been reading this great info site of shimprogramm and was wondering about one part of it.
It was the part were the shimstack is altered to gain lowspeed without affecting the highspeed.
The deal was to take 2x 40.2 out and put 1x 40.3 back in to accomplish this task.
My point is: how can there be an increas of lowspeed of 25% and it won't affect the highspeed?
When shims bend they bend non-linear. When the force is already 25% up at the beginning how can it decrease later on?
The rest of the stack was not altered. Only above shims.

#### marcusgunby

Because the shim deflection is now low with a 0.3mm shim-so it doesnt get the large shim deflection it would with a 0.2mm shim, therefore the high speed isnt increased, as the shim doesnt bend enough to get to the part where it really gets stiff.

#### georgieboy

Member
In the programm it reaches the same deflection stock stack compared to the altered stack. So it start with 25% plus and then when deflection increases tapers of again to approx 0 %. It wld mean bending one 0.3 shim intially is tougher than 2x 0.2 shim, i can agree with that. But bending it more and the 2x 0.2 shims are harder to bend. It this the idea??

#### marcusgunby

Its the other way around, two smaller shims bending with big deflections wont produce the resistance a thicker shim does.Not sure on his program , i dont understand alot of the things it produces, i guess you either believe its answers or not.

#### terry hay

Member
Come guys
The stiffness of a shim is relative to the cube of its thickness.
1x1x1 = 1
2x2x2 = 8
3x3x3 = 27
Therefore it takes 8 x 0.1s to equal 1 x 0.2
Marcus, never just believe.
The stiffness of the lowspeed affects all velocities. By increasing low speed you add to the total damping co-efficient.
Terry

#### Jeff Howe

Member
It's suspensions version of the Magic 8 Ball.

#### georgieboy

Member
So can we conclude that it is not possible?

Member
We ha

#### Jeff Howe

Member
That was an unfinished reply hit send button by accident. I love the edit feature.

#### Jeff Howe

Member
My opinion agrees 110% with Terry's. Can we move on to "Kevin says" now.

#### svi

Member
Georgie,
It all depends on what lift you class as high speed.
I personally don't look at any figures above 0.020 lift and really concentrate on figures up to 0.0120 lift. I don't think that the stacks are lifting up to 0.0420 which is the range available, but the shaft speeds I use it for are a lot slower than Marcus posted.

#### georgieboy

Member
When you looking at deflections being so little, lowspeed and highspeed will also influence each other in my opinion. I wld say the only way to go is altering the seperator shim.
Any other way will affect the whole stack.

#### marcusgunby

How do you know the deflections unless we factor in the port size and types etc.

#### MSracer

Kevin is now measuring actual deflections to tie things in with the program , dyno and data recorders. The way he is going about it should give accurate measurments of deflections.

#### svi

Member
Marcus,
I use the program as a "guide" only to relative shim stack stiffnesses on what from experience and knowledge from other sources I expect the lifts to be.
The figures it produces do not really mean anything by themselves, there are no magic answers contained with in them. It's like a lot like data logging it's a usefull guide but it won't give you any answers by itself.

#### georgieboy

Member
Offcourse it all comes to riding the bike on the track, but for me it is important to know the theory behind what i do. When i change shims that i some how know what will be the outcome.
My feeling is to increase lowspeed with for example an extra shim I can only keep the highspeed the same by altering the transition shim.

#### MSracer

For the sake of argument....

How does anyone know that the percentage of increase for a .2 is the same as a .3 through the range of deflection? Do they both increase in strength at the same rate or does one thickness have a different curve than the other?

If say the .2 has a higher percentage of increase than the .3 then why couldn`t the increase or decrease in strength be at one end of the deflection range or the other?

#### georgieboy

Member
Msracer, i just revd some info regarding this topic.
It seems that different shims all progress at a different rate. Thick shims start stiffer initially and get proportionately less stiff as the deflections increase.
If this is true my question is answered.

#### terry hay

Member
George
Thicker shims don't get less stiff as they bend. They simply don't store accumulative energy at the same rate as thinner ones.
Terry

#### georgieboy

Member
Oke, let me put this in my words. Comparing a 0.1 against an 0.2 shim. starting 8 times stiffer but at the end with same deflection let us say 7 times stiffer?

#### MSracer

Goergieboy ,

That is the what I was suggesting. If you graphed out .1 and .3 thickness shims the percentage of increase through the range of deflection would not be the same for both thickness shims.

The only way I know to get an exact answer on the two stacks is to actually measure the pounds of force needed to deflect the stacks a given amount.

I didn`t think you were not saying that thicker shims get softer as they bend , only less of a percentage of increase than the thinner shims.

There is a shim that does get softer after a certain point of deflection though. Any guess??

#### KTM-Lew

Member
This just makes NO sense to me! How can a thicker shim be LESS "effective" at higher deflections than a thinner one? I'm not getting it!

#### MSracer

Not less effective , just a smaller percentage of increase in strength for the thicker shims as they go through the deflection range.

I`m not any good at explaining this , if I think of a good way I will post.

#### terry hay

Member
KTM Lew
The spring action of a shim is derived fron the stretching of the top surface and the compression of the underside. The material in the middle serves to resist both of these actions. Not only does this reduce the rate of energy accumulation but it also lends itself to permanent distortion. Thinner shims are therefore also more durable.
Another reason the stack consisting of thinner shims appears to have greater accumulative affect than a single thicker one is the radiated pivot diameter. If we have a single 24mm x 0.2mm shim pivoting on a 12mm shim. That shim bends at the 12mm point.
Now if we 8 x 24mm x 0.1mm shims pivoting on a 12 shim only the first one bends at the 12mm point. The upper surface of the first shim now presents a slightly larger diameter to the next one and then the one after that. The final shim could now be pivoting effectively on a 13.5 mm diameter and at a much more gentle radius.
Terry Hay

#### KTM-Lew

Member
Terry.....excellant explanation! So in a large stack of thin shims (.10) the clamp is effectively "cone" shaped. Actual size on the shim it touchs and progressively larger the more shims in the stack. Guess that explains why the Yamaha mid-valves were destroying shims. They were using the wrong shims for the application and weren't supporting them correctly. Result=shim failure.

Thanks for the help!

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