Easy WP fork tweaks (all models)

[rayivers]

In the ongoing process of converting my AER to simple air pressure (SAP), I realized some of the mods can be done with the fork & caps in place, for very little work or $. Either or both bleeder screws can be replaced with air valves (plus a reducer for the RH valve if used), a small amount of oil is squirted thru the OEM AER air valve and the fork compressed a few times, compressed air is put in, and for best results, more oil is put into the fork legs thru the new valves. That's it! As long as the M4 reducer adaptor below clears the adjusters, the air valves should also work on the Xplor / 4CS / SM forks. NOTE: These tweaks are intended only for OEM Alta components (fork caps, TCs, bar mounts, etc.); they may also work on aftermarket stuff, or they may not.

The results are
1) reduced AER stiction (imo why many riders don't like it), especially with the pressures recommended below
2) two combined spring curves (one like a coil spring, the other quite different), each individually adjustable in the AER
3) tunable anti-bottoming (mild to fairly strong) using oil level + air pressure, which is much more effective than oil alone

SAP works differently than coil or WP twin-chamber-air (TCA) springs. Instead of always quickly returning the fork back to the race-sag point after compression, SAP has more of a 'dynamic sag' that changes according to the average of up/down forces at any given time. SAP springing is also less position-sensitive, giving roughly-similar downforce on identical impacts over a wide range of travel (coil/TCA springs apply significantly more downforce at more compression/longer travel). I've found SAP works well for braking bumps, rough corners/downhills, and many other situations too. Successfully switching to SAP-only takes a fair amount of effort & expense, but SAP is easy to combine with existing springs & adds a lot of adjustability with little or no downside. If your coil-spring Alta fork is correct or too stiff, SAP + more oil can help mainly with bottoming & brake dive, but SAP can also be used to soften up the AER or firm up any of the forks & make a night-and-day difference in overall springing performance, saving a bunch of time & money too.

The AER fork's weak link is the TCA spring's lack of oil-bath lubrication. Instead of this nearly-universal & excellent low-maint. method, WP uses 11cc of grease, to be repacked after the initial 10 hours & every 40 hrs thereafter. This is a real pain, even if you already have the required 37mm tube clamp/vise and don't melt the top-out spring holder with the torch. Grease works great in rolling-element bearings, less so in high-speed bidirectional sliding applications where it's rapidly pushed out into the end spaces. The air-spring cartridge could've been designed to use a small oil bath - the center shaft is hollow with two small thru-holes under the piston, looks like they thought about it - but WP went with hand-greasing instead, probably for cost reasons. So... instead of reinventing this wheel, just lubricate the pump thru the air valve (way better than the @ zero grease remaining after 30+ hrs), reduce piston seal-to-cartridge pressure/stiction by dropping the main-air psi, and add a slick-sliding air spring or two to fine-tune. If it doesn't work out, just put everything back to stock.

Here's the new Schrader air valve; it fits the M8x1.0 AER LH bleeder hole as-is & can be combined w/reducer below for use in the AER RH & other Alta forks:




Here's the M8-to-M4 reducer needed for the smaller-diameter bleeder holes.

Once the new LH air valve's in, put 30-35 psi pressure in it and let all the air out of the main AER valve, then remove it or its valve core. Compress the forks a bit and squirt in 10-15cc of low-friction lubricant, push the fork way down and halfway up a few times to distribute it, then put the valve or core back in & pressurize as below. The lube will eventually end up in the bottom air chamber where it might splash-lubricate the piston bottom a bit depending on how hard the bike's ridden, but at least it will improve things for a while.

Here's the lubricant (Finish Line Stanchion Lube) I'd use for the AER air spring (the whole bottle).

Air Pressure / Oil Level: In AER forks, I'd try removing 30-40 psi from the main air spring combined w/20 psi (LH leg only) or 10 + 10 psi in both legs to start, and you can use up to 650cc oil in either/both legs to increase anti-bottoming force. In non-AER WP forks, do the same except skip the -30-40 psi and use 630cc max oil to be safe (I don't know the coil spring volume). I've used 40 psi and 690cc in the LH leg only w/no problems, so these numbers are pretty conservative. More oil improves the way the new air pressure works, and adds a lot more anti-bottoming effect than the stock 200cc.

For adding oil, this syringe setup works well w/no valve-core removal needed (female Schrader fitting on hose end, they come in 100ml & smaller sizes too):

 

[Philip]

Very cool, Ray! I really like creative ideas like this!!!

I have once built Schrader valve air bleed hole adapters for my YZ450. I wanted slightly stiffer forks and thought I might achieve better results with air pressures instead of stiffer springs. They worked! But they leaked because I used brazing and epoxy, LOL. Straight adapters like the ones you have shown would have interfered with the handlebars.

Where could I read about the 48AER inner workings? I want to understand how it works without having to take it apart. Then I will probably appreciate your advice a whole lot more.

I have soured quite a it on all WP products, and all things-KTM, after having been burnt a few times with a couple of their bikes. I spent a half a year of my life helping Kreft figure out how to make the 4CS forks usable for motocross. Revalved those forks about 25 times. Hurt my wrists on hard landings multiple time. And then I bolted on stock KYB SSS and they were still better, LOL. After that experience I decided to leave the WP tuning to other people.

 

[TCMB371]

Just trying to make sure i understand what youre doing here.

So essentially youre removing the air from the air spring chamber, adding a little oil into the air spring chamber , compressing so the oil reaches the balance chamber, and then adding back air pressure but a little less since the volume is displaced by the added oil? Lubricating the air piston and making the spring force curve more progressive due to the lower air volume.

 

[rayivers]

So essentially youre removing the air from the air spring chamber, adding a little oil into the air spring chamber , compressing so the oil reaches the balance chamber, and then adding back air pressure but a little less since the volume is displaced by the added oil? Lubricating the air piston and making the spring force curve more progressive due to the lower air volume.

Yes and no ... initially you want to avoid the chamber-balancing pass-thru slot down near the bottom (which opens around full fork extension) so the new oil can distribute in the top positive chamber - that's why I mentioned compressing the forks slightly before putting the oil in (to push the piston up past the slot), then compressing further to spread the oil up the tube. Otherwise, the new oil will instantly vanish through the slot into the bottom chamber (depending on the rotational position of the spring cartridge; if the slot's facing forward/up it will take longer to drain, but I didn't want to complexify things as I have a tendency to do ). This is just the minor AER TCA-lube part; the main thing is to also add air pressure / oil to the tubes to supplement (and/or partially substitute for) the TCA spring, allowing it to be run at lower pressure for less stiction. I calculated 420cc of total TCA positive volume (300cc swept piston volume + 120cc positive chamber, 3.5:1 compression ratio) with a smaller negative chamber - super hard to calculate that volume, it's got all sorts of stuff in it - so the short-term effect (positive chamber only) of the 15cc oil reduction will be negligible, and the small long-term effect (negative chamber only, after it drains through the slot) will mostly be confined to 75-100% extension. The add-back pressure shouldn't be impacted at all, especially since it will be reduced quite a bit anyway to allow the new air pressure to do its thing.

 

[rayivers]

Very cool, Ray! I really like creative ideas like this!!!

Thanks! I like that it's so easy to do. I've been using/loving air-spring-only forks since the 70's.

I have once built Schrader valve air bleed hole adapters for my YZ450... They worked! But they leaked because I used brazing and epoxy, LOL. Straight adapters like the ones you have shown would have interfered with the handlebars.

I think I got lucky with my Goki Schrader unit - the epoxy and crossover tube/fittings never leaked at all. The forks got a little stiffer when it was hot out, but not much. Your post reminded me of something... I'll edit my initial post to specify the mods are for OEM Alta components only (forks/caps, TC's, bar mounts, etc.).

Where could I read about the 48AER inner workings? I want to understand how it works without having to take it apart. Then I will probably appreciate your advice a whole lot more.

Let me get back to you on this. The bicycle guys have excellent design info online, they've been using air forever for its light weight and have it all figured out.

Idk if this is helpful or not, but here goes... the TCA spring is basically a 'stereo air spring', with two air chambers (one on each end) working off each other. The big positive chamber's pressure goes up and the smaller negative chamber's goes down during compression, partially 'cancelling each other out' to achieve a composite spring-force curve as similar as possible to a coil spring's. Making each chamber smaller increases its pressure rise/fall per unit travel, and therefore its effectiveness.

Graphs help a lot in visualizing this. I'll poke around and see what I come up with.

I have soured quite a bit on all WP products

And I thought I was the only one. Idk about the top-end CV and Traxx stuff, but on my bike I see nice-looking exteriors but price-point designs/components when I work on them, and feel pain when I ride on them (my AER is close now, but the WP guts are mostly gone). The WP shock was a lost cause for the woods, had to go Ohlins. The SSS stuff on my '08 YZ was fine, wish I got to ride that bike more.

My suspension sound bite: "More flow = more options". I think this philosophy is the main reason Race Tech has been so successful. If your piston doesn't flow enough oil, revalving can have only a limited effect - and you can always reduce flow if you want.

 

[Philip]

Graphs help a lot in visualizing this. I'll poke around and see what I come up with.

Thanks, Ray! I think I can visualize the graphs. But I wonder if you have seen any good cross-sectional views or pictures/videos with good explanations. I am sure I would figure it all out if I take the fork apart, but this is exactly what I do not want to do, LOL!

My suspension sound bite: "More flow = more options". I think this philosophy is the main reason Race Tech has been so successful. If your piston doesn't flow enough oil, revalving can have only a limited effect - and you can always reduce flow if you want.

From what I heard, the WP 4CS fork is actually a bad copy of some Ohlins fork. It should have had a more precise low-speed control with more oil flow, but it ended up losing almost all of the high-speed control. And then tuners, including Race Tech, spent years trying to figure it out, not understanding how it should have worked in the first place, LOL. Luckily, that abomination went away. Unluckily, we got it on our Alta EX/MX models.

 

[Philip]

I have a free air fork mod for everybody too. Do not use air in your air forks. Use nitrogen. Auto racers have used nitrogen in tires for decades. We use nitrogen in the rear shock reservoirs. Why would we still use air in the air forks???

 

[rayivers]

Thanks, Ray! I think I can visualize the graphs. But I wonder if you have seen any good cross-sectional views or pictures/videos with good explanations. I am sure I would figure it all out if I take the fork apart, but this is exactly what I do not want to do, LOL!

OK, here's a transparent AER LH fork leg:

Here's close-up of the negative air chamber, with the top-out spring & the stuff the torch melts :

Here's the entire fork in cross-section:


... and here's the best TCA-spring video I've seen yet - if you watch it all you'll know how to design one, on paper at least:

Re the video above - I disagree with it somewhat from 2:40 to 4:20. If you put in a lot of air pressure it's absolutely correct - the fork won't move unless it hits a significant obstacle - but to me that's WAY too much! My SAP setup has 'normal-range' pressure (38 psi one leg, 19 psi x 2) and is extremely compliant to even the smallest bump. I'll be using stiffer top-out springs to simulate a negative air chamber. They arrived last week and are plenty strong, now I need to find time to tear both legs apart (again).

From what I heard, the WP 4CS fork is actually a bad copy of some Ohlins fork. It should have had a more precise low-speed control with more oil flow, but it ended up losing almost all of the high-speed control. And then tuners, including Race Tech, spent years trying to figure it out, not understanding how it should have worked in the first place, LOL.

I have no 4CS experience, but if I had one I'd do the same as my AER - replace both damping pistons with higher-flow ones, then start from there. It's easy for me to say this in 2022, but back in 2014 or whenever there were way fewer options, and a lot less familiarity and experience as well.

I have a free air fork mod for everybody too. Do not use air in your air forks. Use nitrogen. Auto racers have used nitrogen in tires for decades. We use nitrogen in the rear shock reservoirs. Why would we still use air in the air forks???

I think this was brought up in a Science of Supercross episode - it was a temperature thing. The shocks got stinking hot and nitrogen was an absolute must, but even the pro forks were barely getting warm with low air compression. so there was little benefit in using nitrogen. I'm surprised the manufacturers haven't gone to high-pressure nitrogen in the forks anyway - just another "selling feature" intended to lock the home mechanics out of the front end too.

 

[C5tor]

I have a free air fork mod for everybody too. Do not use air in your air forks. Use nitrogen. Auto racers have used nitrogen in tires for decades. We use nitrogen in the rear shock reservoirs. Why would we still use air in the air forks???

I always considered the whole nitrogen thing was pretty gimmicky for most applications. Regular old air is already 78% nitrogen. The only real advantage using 100% nitrogen is there is no moisture, and the water does tend to expand with heat. But otherwise, pure nitrogen just isn’t very practical for the layman that needs to adjust tire or shock pressure in the field.

 

[rayivers]

I always considered the whole nitrogen thing was pretty gimmicky for most applications... pure nitrogen just isn’t very practical for the layman that needs to adjust tire or shock pressure in the field.

I think this is inevitable trickle-down from the OEM racing programs, but imo it's also a guarantee that gas-station pump air thru an old sandblasting hose won't be used. Filtered / dried compressed air would probably work fine for most temperate-zone non-racers, but tropical or desert riders might be another story - maybe the OEM's are just covering all the bases (shocks only, not forks).