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AER 48 MODS


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Hi guys, 

I wanted to give anyone a heads up on some mods I have tried on the wp AER48 forks. Bike is a 2017 450sxf, I weigh 93kg and race mainly intermediate cross country and some b grade mx.

First thing I did was a revalve. I increased the base valve stack and reduced the mid valve. After some riding I tweaked this abit by going from an 11mm clamp to a 12mm on the mid stack. I then updated the air piston and top out spring to the 2018 parts. 

Next stop was a krooztune mid valve piston to replace my plastic stock one. It took some convincing for them to send me one with out a bleed hole pre drilled in it. I fitted my mid valve stack that I had on the OEM piston which had 0 float, but by the following weekend I had gone back to a 11mm clamp on the mid compression stack to allow for the reduced port edge on the new alloy piston.

Plenty of riding followed 

Then what if?

I got hold of a donor set of AER cartridges from a 2017 350 which I had fitted kyb sss internals into a few years back.

I disassembled the damper cartridge and air cartridge to swap them around. I had a 48mm nylon spacer made to eliminate the top out spring on the air side. I fitted the air piston (old x ring style) and air side seal head into the damper unit body with the bleed hole at the top welded up and caps changed over. This gave me air cartridge with no bypass dimple and independent positive and negative chambers.

I did one track session and a xc race I didn't complete. I knew I was in trouble right at the start of the race but lessons were learned.

Back to the old traditional air chamber with more riding, a 4th in the iron man open class at the Pirini 4 hour and won my intermediate class in the 3 round belray 2 hour series.

More what if?

Ok I thought, best of both worlds. I reduced my nylon spacer to 40mm, 12x18x40 to be exact. Under that I fitted 11x5mm cross section oring. The oring is essentially my bump stop. So we have 2018 u seal style piston with nylon stem, custom spacer and oring then seal head.

Why did I remove the top out spring? Because I wanted to add preload to my air spring to eliminate the vague feeling caused by the fact that for approximately 11mm of stroke (due to the bypass dimple) the air chamber has neutral force.

After doing this I refitted the unit and added a extra valve to the fork cap so I can pressurize the outer chamber. You cant achieve the same thing with the stock setup because you would be working against the top out spring and until you bottomed that out you would still technically have zero preload. FYI I don't run a top out spring in the shock.

So I've done approximately 100km of trail riding with some tinkering. Running 155psi inner and 5psi outer 10 comp 16 rebound 175ml of oil.

Definitely worth the effort, plenty of front end bite, I was looking for holes and it was eating them up. More refining this weekend and I'll get the data logger out again I think.

There is so so so many mis perceptions around suspension function and some of it comes from guys who own big businesses.

If we look at a air spring curve against our desired coil curve we see the issue isn't ramp up but in fact the flat mid stroke support which causes the fork to collapse faster which essentially makes your valving "stiffer". Shim stack A with a 4.4N spring is stiffer than shim stack A with a 5.2N spring if the same force is applied, not because it's "riding in the soft part of the stroke" but because spring rate relates to spring frequency. 

I checked, even with a theoretical 0psi in the outer chamber of a fork at full travel 175ml of oil (had 0psi inner) you get 45psi at the bottom of the stroke on that outer chamber, so for anyone to say coil springs dont ramp up, well they need a slap.

5psi in the outer is 48N of preload this also adds support in the flat mid stroke area. 

Anyway sorry for the long winded post.

 

20200523_105815.jpg

Edited by vince46
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I went a different way ,wp bladder fork on the damper side ,so it's a spring hybrid ,the bladder fork needs to be lengthened 10mm to match an aer air side 

 

You have to use the 2015 small axle euro fork for it to work 

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17 minutes ago, mog said:

I went a different way ,wp bladder fork on the damper side ,so it's a spring hybrid ,the bladder fork needs to be lengthened 10mm to match an aer air side 

 

You have to use the 2015 small axle euro fork for it to work 

Hey Mog, so you are running 1 Bladder fork cartridge with 1 spring on the damper side? then less air? that bladder cartridge only moves 135ml of oil compared to the aer's 272ml which is very similar to the shock volume 

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6 hours ago, Edge316 said:

Great post, very informative and interesting! Vince,  how did your AER mods compare to the kyb conversion? Did you get a chance to ride the 350 with the conversion?

No I haven't ridden the 350. The spring rate is 5n and I would be 5.2n plus the valving is a tad soft but I should take it for a spin some day. They kyb's are set up so you just remove the cartridge and refit the AER with no modification to the axle lugs. If I did it again I would change a couple of things.

I think spring will always be the preference for most as many struggle to check their tyre pressure let alone fork and then taking into account having to accommodate ambient temperature is beyond most.

Most don't even want to understand suspension theory but the industry is to blame for that, I find the faster the rider the less he knows.

People argue its different for everyone and I would say emotionally it is, but in reality something like suspension which is bound by the laws of physics there is only one way to do it. Kyb, showa and Wp all have different ways of thinking but I feel only ones barking up the right tree.

Force=mass×acceleration

Kinetic energy=1/2 mass x velocity squared.

You cant escape these two.

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4 hours ago, vince46 said:

Force=mass×acceleration

Kinetic energy=1/2 mass x velocity squared.

You cant escape these two.

...but, but, but.. what about Q=mC∆T, or Hooke's law (F=-kx)..? lol

Definitely keep up the good work and keep posting your results.  I enjoy reading about it.

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  • 2 weeks later...

So I did the Taupo berm buster trail ride last weekend with the modded fork and started the day at 158psi inner and 5psi outer. 

I really like the positive feel it gives on the front wheel, more grip and more feel.

The ride was extremely rough with big square edge hits and the bike was handling it well. I ended up at 14 clicks compression and 16 rebound. Later in the day I tried 155psi inner and 5 outer but I feel the 158 was better.

I have also stumbled across some cheap bladder forks last week so I have addressed the check valve issue, valved them to my spec no float no bleed holes, and am waiting on some springs to turn up. 

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