TCMB's Quest for Better AER48 performance - DIY Valving


Philip

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I wonder if I could achieve that higher low-speed damping with just the clickers. I will definitely try it once the tracks open around here. What does your Restackor model say about the clickers?

Right now my both the front and the rear wheel appear to be a bit too busy in places when they could stay calm, which distracts me and makes me wait for them to calm down, which in turn costs me time.
 

TCMB371

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I've reached the conclusion that TCMB Mod Stack 2 is too stiff on slow speed. It causes a very vague feeling in the front end and causes me to have less confidence in front end traction. It's time to soften up the super slow speed damping to regain traction.

Did some reading and it looks like "traction" velocities are down in the 0-8in/s range. We need to soften up the damping curve in those areas but ramp back up after that. To achieve that damping profile, we need to add float. Here's what 0.1mm of float looks like. Yellow is the stock compression stack, blue is this test stack
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Looks like this would be a great candidate for the preload spring on the face shim to gain back digressiveness. I'm assuming adding a ring shim to the stack would be counter intuitive with a bleed shim infront of the face shim. So how will we accomplish this? At the base valve!

Let's add a ring shim to the base valve to preload the base valve stack. Here, i added 0.1mm of preload to the 6 face shims. This can be seen in Restackor as the different between the "c" (centering) shim and the "r" (ring) shim. 0.2-0.1 = 0.1.
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Check out that drastic difference! The preload on the base valve delays the opening of the face shims, as shown by the rapid increase in damping between 30in/s and 120in/sec. I'm afraid that will be a bit too much high speed damping force, so let's remove some face shims so that the overall stack height matches the original overall stack height.

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Getting closer! Now lets take a look at the raw force comparisons to get a sense of the % difference at various velocities, which should give us an idea how this might "feel" compared to the stock valving.

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I'm thinking 20 in/s is near the fork velocity you'd see landing a soft jump on a nice downslope, so it being 40% softer at that point isn't good. We need to start the ramp up sooner than after 20in/s. Lets try a smaller float on the midvalve. Here's 0.05mm:

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That looks way better for traction. 41% softer than stock at 1in/sec, 20% softer at 8in/sec, about the same by 25in/sec. Upwards of 40% stiffer in speeds above 100in/sec. I'm thinking that might be too stiff, so let's try to target roughly the same low speed profile but have about 25% more damping above 100in/sec. Easiest way to reduce overall damping is to reduce the clamping shim diameter. We'll change the clamp shim on the base valve from 22mm to 20mm.

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Now that looks perfect! 40% softer at 1in/s, ~22% softer at 8in/sec, identical at 25in/sec, then ramps up to 25% stiffer above 50in/sec.

I think i may try this setup next.
 

Philip

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It's really interesting what you are doing. You must be learning a ton.

Have you done anything with the rebound yet? If you soften the compression but leave the front rebound and the rear shock as-is, the front suspension will be packing up more and you may actually lose some front end traction. You may be able to regain it if you back out the front rebound clickers and let the wheel get back on the ground faster.

I'm thinking 20 in/s is near the fork velocity you'd see landing a soft jump on a nice downslope

In Physics they say that mgh = mv^2 / 2. If my calculations are correct, if you flatland a 10-foot drop, you get a 302 in/sec vertical suspension compression speed at the moment when you touch down. To get a 20 in/sec speed you only need a 0.5 inch drop, assuming an incompressible tire. Weird, I know, but this is what the math says.
 

TCMB371

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Have you done anything with the rebound yet? If you soften the compression but leave the front rebound and the rear shock as-is, the front suspension will be packing up more and you may actually lose some front end traction. You may be able to regain it if you back out the front rebound clickers and let the wheel get back on the ground faster.

Rebound damping depends heavily on the spring rate, since no other forces are acting to extend the suspension. The maximum rebound velocity the fork sees will be at the point of bottoming, since the spring force at that point is the highest. Stiffer spring rates require more rebound damping to get the same feel, and softer spring rates require less rebound damping. Typically the best place to start is a rebound setting where the suspension slightly overextends past its sag point after compression but recovers quickly after that. So the goal is to tailor a rebound damping curve for a given spring rate that slightly overextends past sag in a majority of the terrain you encounter. As you can imagine, that depends on the type of terrain you are riding, how fast you are riding, etc. You don't want the suspension to extend so fast that it upsets the chassis, which in term transmits upward force to the rider, but you also don't want it to extend too slowly so that there isn't enough travel to soak up terrain after that.

In Physics they say that mgh = mv^2 / 2. If my calculations are correct, if you flatland a 10-foot drop, you get a 302 in/sec vertical suspension compression speed at the moment when you touch down. To get a 20 in/sec speed you only need a 0.5 inch drop, assuming an incompressible tire. Weird, I know, but this is what the math says.

I did the same exercise when trying to determine velocities, but that freefall equation only accounts for a straight vertical drop to a flat surface. Landing on a downslope from 10 feet up would produce much lower velocities than landing on a flat surface from 10 feet up.

We are objects in motion, so we have to consider the force vector. If the impact force is vectored ahead of the line perpendicular to the surface (a down slope), less net downward force is experienced. If the impact force is vectored behind the line perpendicular to the surface (IE, you case a jump really bad, or you slam into a sharp breaking bump), the impact force is greater because now lateral deceleration forces are being applied. So without having actual suspension telemetry to record the velocities encountered for your riding type, its tough to know for sure exactly what velocities your suspension is experiencing for the type of riding you are doing. Instead, we have to rely on either data that's already out there or using our best educated guess.

Here's where things get interesting. Freefall equations account for an object falling until it impacts a surface. But we can use the same concept to determine how quickly a wheel needs to "move out of the way" of a bump. If the front wheel can't move out of the way quick enough, that translates upward force to the chassis. If the fork is so soft that the wheel can move out of the way quickly, then almost 0 force (outside of momentum forces of the unsprung weight) are applied to the chassis, and you essentially plow through bumps without feeling them.

The kicker is the fork velocities when hitting a square edged bump may be identical to the fork velocities you'd see when flat landing. So a damping curve that would allow you to plow through those square edged bumps would likely be way too little to support you on an overjump, and this is precisely why there is no one shim stack configuration that rains supreme. Suspension is a compromise, and the goal would be to feel the best in "most" scenarios you encounter during your riding.

For a 21" tire, hitting a 3" square edge bump at 50mph is the same 300in/s initial velocity you'd experience at impact of a 10ft freefall to flat! With the same valving for those two scenarios, the chassis should "feel" roughly the same in both scenarios on initial impact. You always hear in motocross how pros have super stiff suspension compared to us mortals, but it makes sense. Hitting a 3" square bump at 30mph produces roughly 2/3 the fork velocity as hitting that same 3" square edge bump at 50mph, so more damping force is needed to get the same feeling in the chassis!
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Philip

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One cool think I learned from Bob Bell of Precision Concepts is that the high-speed compression damping may be made almost flat at the limit. He says at some point there is just no need for this ultra-high high-speed compression damping. This is I think is the philosophy that he used for the square edge damping tuning.

The good news for motocross riders is that square edges are almost never found on prepped tracks. It is more of a consideration for the off-road riders.
 

TCMB371

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The maximum rebound velocity the fork sees will be at the point of bottoming, since the spring force at that point is the highest.

I just wanted to clarify, because what i said here is wrong. The spring is indeed producing its maximum force at bottoming, but the maximum velocity can't be at bottoming. The spring has to accelerate from a fully compressed state (0in/s) to its terminal velocity (depends on the spring rate).

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When you hit a bump, the fork doesnt just snap to a max velocity instantly. It has to accelerate from 0 to get to that max velocity. This means your "low speed" damping has a little bit of an effect on the bigger, faster hits too! And the same can be said for rebound.
 

TCMB371

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I decided to ditch the DIY valving effort temporarily and go with a set of RaceTech Gold Valves. I went with a Expert skill level setting and WOW! This suspension is amazing now!

I sort of have a RaceTech sponsorship deal, so i've been asked not to share my exact valve stacks. But I'll try to describe the strategies used.

Fork:
They have me running 170psi in the air fork coupled with 0.4mm of float on the midvalve compression stack. So the theory of "less" damping and higher spring rate applies here, as i was suspecting earlier in this thread. This, combined with a pretty heavy base valve and midvalve compression stack, allows the fork to move very easily in slow velocity situations, but ramp up quickly to soak up everything else, including intentional flat landing! It almost feels like a coil spring fork now! I have so much more traction in the front end and so much more confidence. The base valve and midvalve compression stacks are single stage, meaning they provide a relatively linear damping curve. The rebound stack on the midvalve uses a two stage stack with a 0.10mm crossover (really tiny), meaning it provides a progressive damping curve. I'm guessing the thought there is to allow the fork to quickly extend over small chop, but not pogo after a huge compression event. And it fricken works awesome!

Shock:
I had previously been running a 6.4kg/mm shock spring (10% stiffer than stock rate) due to the lack of damping in the stock shock, even after increasing the damping about 15-20% with some DIY valving. Racetech had me go back down to the stock 6.0kg/mm spring. I have a check valve nut on the end of the shock shaft that separates the rebound circuit from the compression circuit, which means adjustments to the rebound clicker no longer effect the compression circuit. Both the compression and rebound stacks are two stage using a thin 0.10mm crossover. This allows the shock to move a bit more free under slow velocities but quickly ramps up on bigger hits and larger braking bumps.

Interestingly enough, the new shock configuration has increased my battery range! I'm guessing my previous configuration was too stiff and packed too much allowing the rear tire to spin a lot, wasting energy. The shock now seems to stick to the ground, meaning I get less wheel spin!
 

Philip

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have so much more traction in the front end and so much more confidence.
This is truly awesome! All the revalves that I tried, I could live with the WP suspension ride properties, but I never quite felt like the front wheel was sticking to the ground enough. This is exciting to hear!!!

RaceTech sells these as DYI kits, don't they? Could you please post the part number and the price? I might want to try it.
 

TCMB371

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This is truly awesome! All the revalves that I tried, I could live with the WP suspension ride properties, but I never quite felt like the front wheel was sticking to the ground enough. This is exciting to hear!!!

RaceTech sells these as DYI kits, don't they? Could you please post the part number and the price? I might want to try it.

Yeah, you can install it yourself if you know how to dissemble the forks properly. You also need to have very small drill bits to drill 1 or 2 bleed holes, depending on your setup. Mine called for 1.3mm bleed and 1.6mm bleed in two separate spots. 1.3mm is basically a 3/64 drill bit, smaller than a 1/16. You'll also need accurate feeler gauges to measure the float properly.

Fork kit : FMGV 343406C
Shock kit : SMGV5003
Rebound Separator Valve: SMRS 1210000
 

TCMB371

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Yup, about that! + a few hours of your time and suspension oil all over you and your garage :LOL:.

I recommend you get some genuine SKF bushings and seals for the fork, and SKF shock seal as well. I've found that the standard KTM ones that are supposedly SKF have higher stiction than the genuine "green" SKF ones.
 

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