Krooztune KTM WP AER 48 Testing and development

Krooztune KTM WP AER 48 Testing and development

Krooztune KTM WP AER 48 Testing and development – With the prompt arrival of KTM’s much anticipated WP AER 48 Air Fork we decided to hit this hard and fast to find out the good, the bad, and the ugly straight, up from KTM’s latest offering. After the last few years with the 4CS system we were hoping for a good improvement with the bike in stock trim.  

After initial testing it was evident that the ‘AER48 AIR Fork’ equipped KTM range was a vast improvement over last years bikes with the 4CS setup. The Air is adjusted in one valve on top of the Air fork leg and self regulates/balances out inside the fork.  A huge tick to KTM for this as from experience in working with riders from both motocross and enduro we know they can’t be bothered messing about with too much adjustment and simply can not understand clearly the ‘three way air valve system’ that comes stock on the Showa TAC system found on the 2016 KXF450,RMZ450 and CRF250’s.  The downside is you lose the adjustability that the Showa TAC system has, but its easie, a lot easier to adjust and understand. Pump it up, it’s harder. Let some air out, it gets softer, simple.

Krooztune KTM WP AER 48 Testing and development

Test 1 / Stock setup

WP engineers have clearly worked hard to get the stiction out of this Air fork. It is nowhere near as sticky and dead as its competitors.  You can feel the rebound and fork action without the sticky feel messing with the forks action.  It held up on the big hits as expected and seemed to work great in most conditions.

We adjusted the clickers and worked through some simple adjustments and found out this fork is somewhat tunable through the basic external adjusters.  We adjusted the fork rebound quite a lot as we felt this was the only adjustment we had to control the forks ride height.

The biggest negative from the stock bike is that it rides high in the fork stroke. It seems to be choppered out, high in the front and making it feel low in the rear.

We adjusted the bike to suit but was near a band aid fix, it simply worked good where it was but gave us all a front end high feel.

In the sand this front high feel was ok, it kept it high and ploughed through the sand with relative plushness.

On hardpack though we were adjusting it quickly to try to get some good turn in and stability into the ruts. We softened the air pressure to lower the fork ( 154PSI down to 148PSI) but lost the feel on the small chatter. Overall  the fork works well once moving but seemed to take too much of a push to get it going into its action.

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Krooztune KTM WP AER 48 Testing and development

Test 2 / Krooztune Mid Valve Piston and Valve Setting

Upon strip down of this fork previously back at the workshop we found the Stock OEM Rebound/Mid-valve piston to be manufactured from plastic. After several WTF’s and the usual whys and hows, we agreed straight up that this was the achilles heel of the AER 48 Air fork in both durability and performance. We decided to make a trick high grade, hard anodised alloy piston as an upgrade right off the bat.  The Shim stack on the mid-vlave Compression has zero ‘float’ and seems to be hard to tune. This is definitely the reluctance for this fork to move easily into the stroke and work smoother for a Slower rider.

We were almost hesitant to tension the clamp nut back up on this plastic piston in fear of squashing it!  We know we need to make this fork work for Veteran C grade riders right  through to low A grade riders as a priority as well as the durability factor.

After fitting this kit to our RHS damping leg, we found straight away the fork worked easier into the stroke.

It took us several laps to tune the exact rebound clicker to the stock air pressure resulting in a much easier bike to ride into a sharp rut or turn. This fork is now super plush, plusher than any Air fork we have worked with. This is highly due to the lack of stiction allowing the AER 48 Air fork to work and be tuned like a normal spring fork would.

We still find it riding high in the stroke , so we settled on 150PSI with the rebound clicker set to match. We spent several hours working on the final internal valve setting for this new piston gaining data for us to tune it to a C grade guy right through to fast A grade rider on this bike.  The fork action was more instantaneous, plusher and endlessly tunable by adjusting the shim stack.  We modified the main compression shim stack slightly to match this setup better during the day.

Test 3 / Krooztune SFF Air to spring Conversion

After dialling in our stock Air fork and then spending hours on our new Krooztune Mid-valve assembly we couldn’t wait to install our SFF spring conversion kit and see for ourselves what this bike feels like with a spring fork. The install took us no longer than 20mins trackside on our suspension bench.

This kit is only fitted to the WP AER Air leg. Basically you un bolt the stock AER 48 system and slide in our ready to go cartridge and spring as a replacement.

The kit is designed to keep the Air system together and be a near complete replacement giving you the option of easily swapping backwards and forwards from Air to spring if needed. Eg, selling the bike. Most guys will put the stock setup back in and keep the spring setup for there new one.

We started at our base Oil level , the usual 5-6mm spring preload and sent out the test rider to give it a shake down.  Feed back to the rider  was instant.  The feel from Air to spring is obvious.  The action and overall working of the fork seemed strangely similar.


Krooztune KTM WP AER 48 Testing and development

The biggest thing noted was a balanced bike.  No longer running high in the stroke the bike settled easier into the turns and straight from the horses mouth, it was simply easier to hit the marks out on the super rough track.  The rear shock seemed to kick around a lot more with this setup so we softened it off to match the now balanced bike.

It was obvious the bike  is not transferring all the weight rearward to the shock and definitely lightened the load off the back of the bike , in turn making it feel harder in the rear.  Surprisingly 4-5 clicks softer than the stock shock compression setting sorted this out.

The WP shock compression adjuster works well, our kicky rear end was gone.  We were careful not to rush into slowing the rebound on the shock, as this would have been the wrong move.  Always adjust compression before rebound on the rear shock. 80% of the time the kicking action is compression related.

After initial fitment of this kit we tried several spring rates , preloads and took notes.  The harder springs obviously sat up more in the stroke ,  just like the AER48 Air system did but were simply harder.  No big surprises, we just wanted to see what Air pressure related to what spring rate.  We settled with spring rates exactly like normal for rider weight and speed. Nothing unusual learnt today regarding spring rates.

Krooztune KTM WP AER 48 Testing and development

Krooztune KTM WP AER 48 Testing and development

The end result after testing with the Spring conversion.  Its easy to fit, its super balanced, turns smoother, super easy to adjust and it never changes whilst riding.  This has to be a major plus for the Enduro/offroad boys and girls running longer ride times.  It needs less garage time and will obviously last a lot longer between services.

The against – the WP AER 48 system is lighter in overall weight and more adjustable for different riders on the same bike. It’s Cheaper, it comes stock on the bike.

Both setups worked great with the new Krooztune Mid/Rebound Piston although required different clicker settings. We ran 14 clicks out with the AER48 setup and 19 clicks out with the spring matched to our new Krooztune Midvalve/rebound piston.  We also softened the compression adjuster on the fork 2 clicks with the spring for a consistent feel between the two vastly different setups.

Now available online

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Krooztune KTM WP AER 48 Testing and development

Testing Results

Overall a massive day with the all new AER 48 Air fork.  It is night and day above its competitors in many ways but lacks the adjustment of the 3 air valve setup that the Showa TAC fork offers.  These extra adjusters would have cured the high feel to this fork but overall it’s better without the extra adjustment, they are too confusing for the many. We learned a lot and are deep into production of our upgrade parts already.  Krooztune Performance parts will be available fast worldwide and easily purchased from or in store shortly. A huge thanks to Morgan Fogarty for taking the time in this test.  Watch this face

Bike tested

KTMSXF 250 2017 equipped with the new ‘WP AER48 Air fork’.

Tested by

Myself (C level Veteran rider ) and Morgan ( A grade Gun and general MX bandit ).

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$20 Flat Shipping within Australia

Flat wordlwide shipping rate of $45 international DHL shipping Worldwide –  $60 for SFF kits. Most deliveries shipping to USA/Canada/UK in 3 – 4 days.

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