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Discussion Starter · #1 ·
So I'm continuing to progress in my understanding of suspension, so I can better tune all the knobbies and get the bike to behave properly over the bumpy NHMS track.

My bike has AK-20 forks, and a Penske 8987 triple rear shock. My laptimes at NHMS are very low 20's and knocking on the door of teens. That puts me about 3 seconds away from the fast guys.

Here is my latest observation: the suspension is SO MUCH BETTER controlled in the cool New Hampshire mornings, compared to the heat of the afternoon. This is especially noticeable in a GTL (20 minute) race, where the suspension gradually worsens over the course of the race. I would not characterize the difference as "subtle" either-- it's quite different when it's cool, compared to when it's hot.

My Penske shock has whatever oil that GMD computrack puts in it when they rebuild it. And my AK-20 forks have Motul 7.5W oil, which is what Traxxion recommends.

My first thought is that I need to increase damping overall, because as the suspension fluid heats up, damping decreases. And since the bike performs better when the fluid is cool, that must mean that increased damping = better performing.

But the fork's rebound is already quite stiff. I had an earlier thread where I mentioned that I have my AK-20 forks set to only 3/4 turn out from full stiff, which people indicated was more damping than typical. Of course this leaves the compression setting, which could also be allowing too much spring compression. But I can't just change my compression on the AK-20s. So perhaps I should call Traxxion and get some new shims that will increase compression damping?

My rear shock also has quite stiff rebound setting. So I'm thinking about increasing the compression damping there too. I know the slow speed compression is 4 clicks out from full stiff. But the high speed compression is about in the middle of the adjustment range (I forget the actual clicks, but I set it to the "middle" of the range).

What about thicker fork fluid? Stiffer springs? Any other thoughts or advice?

Thanks in advance!
 

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When was everything rebuilt last? At minimum once a year suspension should get done.

I'd ask Traxxion if they could revalve your forks for a lighter oil (5wt). The lighter oil is less affected by temperature. As you stated, I think rebound is most of your problem.

Can you try to describe how the handling changes.
 

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Discussion Starter · #4 ·
When was everything rebuilt last? At minimum once a year suspension should get done.

I'd ask Traxxion if they could revalve your forks for a lighter oil (5wt). The lighter oil is less affected by temperature. As you stated, I think rebound is most of your problem.

Can you try to describe how the handling changes.
Everything was rebuilt this past spring. The way it changes is that it just feels like the suspension travels further, both front and rear. More suspension travel equals the bike feeling like it's all over the place when I hit a bump when leaned over.

I think I will be going for more compression damping in the forks, which means having Traxxion get me new shims, and probably more compression and rebound damping in the rear.
 

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Have you identified yet which end is starting the squirming? I ask because if the shock is heating up over time (could have low nitrogen pressure for instance) and losening up it will affect how the front behaves - I'd run it hard till it gets squirmy then have a helper shove the bike down in hte pits and see if everything is still moving in time front and back before changing anything first personally - on the rebound (not familiar with traxxion ak-20s....yet) I'm assuming by hard you mean full slow - which ya that sounds like a lot, fluid wieght plus setting = front end rebound speed (in general) so the 5w oil Trace was talking about would actually speed up the rebound (akin to turning hte adjuster out or to the fast end) if I'm remembering correctly and reading things right

Just my non-suspension expert suggestions and thoughts - lol
 

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^You read it right Terry. But I suggested getting stiffer valving as well. Light oil viscosity is more consistent through temperature ranges. Ideally, trying to keep the same overall dampening, just with lighter oil so it won't fade after 3-4 really hard laps.
 

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I run the stock forks with Traxxion internals and run 20w oil I never have a problem with the front even when superhot out on track . My problem is with the Penske gettin hot and fading even after fresh rebuild am gonna play with it next month at HPT and see if I can get figured out !
 

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So further educate me here then - I thought AK-20s had one leg running the compression and one running rebound (so I was told at least)

on the original subject - I'm be the rear is getting out of sorts a bit and the front and rear are not in sync is more the issue in this case
 

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Not sure on the oil in rear TSE did the rebuild in march I ran in april it was in the 40s and not really a problem with the 20w and .85 springs !
 
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