REP Knuckle For 2015.5-Up KTM Shock

As the hours keep ticking away on the 2020.5 KTM 450 SX-F Factory Edition test machine, I have been going through test parts like crazy. I have been testing the REP (Research Engineering Performance) re-valved WP XACT Pro Components and have good things to say about Mark’s work, but I wanted to get a little more comfort for the shock, so he offered up his knuckle and pull rods to me. I explained to him that I felt the KTM was low in the rear, so I would rather not use the pull rods, but I was willing to use the knuckle in corporation with the WP XACT Pro Component shock.

So what is the purpose of the REP knuckle? The reason for designing this linkage system was to help or eliminate a common issue Mark has witnessed with the KTM/Husqvarna. A rider comment that he has repeatedly heard is a lock out sensation in the shock resulting in harshness and unwanted weight transfer. Immediately REP started testing shock settings after shock setting, which helped, but did not fix the issue entirely. This is when REP’s investigation began into the leverage ratios to decipher if this was truly a shock character issue or if the chassis needed some changes. 

The linkage put into the Austrian production has a very "stiff" ratio when compared to other brands, which is why the bikes come with such a soft rear spring. REP feels this is the right direction for the beginning to mid stroke, but the progression at the end of the stroke was slightly too aggressive causing unwanted weight transfer and harshness from the rear of the bike

The REP linkage system makes a more linear progression for models 2015.5 to current. Many of the other companies producing linkages for these bikes result in a softer ratio all the way through the stroke, which is why they also require a stiffer rear spring. The REP system does not stray far from the production ratio for the majority of the shock stroke, but simply tapers off from mid to end. This change does not require a spring change because the ratio from full extension to rider sag point is very similar, but once active on the track the rider will see the digression in the ratio to be quite apparent.

The knuckle can be used with the standard pull rod (like what I did) or the longer REP version. If only the knuckle is used the rear seat height will be raised 1.9mm, but if the entire REP linkage package is used the rear will be lowered 2.1mm when compared to stock. Keep in mind if the entire package is used, it not only lowers the rear, but also exaggerates the flatter ratio that the knuckle is producing. REP recommends the knuckle to all his riders, but Mark decides if the customer needs the pull rod based on the rider's preference and comments.

A couple positives to the knuckle that I noticed right away was comfort on acceleration through deep/choppy ruts and the KTM felt less active on de-cel bumps coming down hills. Without the REP knuckle the KTM kicked me in the butt more than other Japanese bikes do when braking hard on de-cel bumps, but with the REP knuckle the rear of the KTM stayed planted better and gave me a calmer feeling when pushing deeper into rough corners. I managed to get a bone stock 2020 KTM 450 SX-F, (without XACT Pro Components) installed the REP knuckle on the WP shock and it gave me the same feelings in those two areas of the track. I appreciate that I didn’t have to drop a spring rate and basically could just bolt this on and feel an improvement. For $249.95 for the knuckle (with bearings installed), I really like the way the KTM can be pushed harder later in the day when the track gets hammered. I used to shy away from the KTM in the afternoon hours, because it would beat me up a little. Now by adding this REP knuckle to our KTM Factory Edition, it has made this a more comfortable machine to ride when everyone else is packing up to go home. 

Note… Not all aftermarket knuckle/linkage systems work on every brand of motorcycle. Some manufacturer R&D teams get their linkage ratios correct for the masses upon production, but it’s refreshing to see Mark at REP sell a suspension piece for the KTM that actually is noticeably better when riding it back to back with the stock piece. 

FAQ: 

Kris, how do I know if I need a knuckle and not just a re-valve on my shock?  

If you are experiencing a firm feeling coming out of corners and seem to lose traction, this knuckle can help. If you are coming into braking bumps and notice that the KTM has a nice plush feel on the first bump, but then gives you a rear end kick when unloading upon the second touch, this knuckle can help that. These are the two areas that most weekend warrior riders would feel the REP knuckle is better. 

Kris, how do I know if I want the REP pull rods to go along with the knuckle? 

If you want your KTM to feel a little lower in the rear and want more rear steering, then you should look into the REP pull rods as well. I am a big front end steering rider so having the rear end a little higher for me fits my riding style. 

Attached is a graph from REP. The red line is the REP vs the black line Production.

Pro Circuit Link Arm (2020 Yamaha YZ450F)

I have tried links in the past on previous generation YZ450F’s with less than stellar results, but since Yamaha changed the frame on the 2020 machine, I thought I would revisit a link to see if it helps improves the Yamaha’s feel around the track. 

Pro Circuit's linkage arms are CNC-machined from billet aluminum and are designed to stiffen up the initial linkage curve in order to try and improve the geometry of the YZ450F’s chassis, in order to try and make the bike more stable in certain areas of the track. The linkage arms includes all of the required bearings and seals and is ready to bolt up. I wanted to see how it worked with the stock YZ450F suspension valving, so since Pro Circuit is backordered on them for a while, I purchased the Pro Circuit linkage arm at rockymountainatvmc.com for $189.95 . Once I received the PC link, I went to a few tracks to try the it and the stock link, back to back , to see if the Pro Circuit link is a benefit to the average rider. 

One thing that I want from the stock 2020 Yamaha YZ450F is less movement from the rear end under acceleration. With the stock link, the rear end can squat  too much at times (under throttle) and give me the feeling of less connection to the rear wheel under load. I do think the new 2020 frame and suspension valving has helped de-cel pitching, but once the fork is broke in, it can dive a little too much under hard braking. 

After I installed the PC link I re-checked my sag numbers to make sure they were in the spec I desired. I ran 105mm of sag with the stock link and am currently at 105mm of sag with the PC link. With the PC 143.5mm link installed (142.0mm is stock) the Yamaha has a noticeably different feel to it on the track. I immediately noticed that my rear end felt firmer under acceleration, but that feeling wasn't such a positive change. I went back to the van and turned my high speed compression (on the shock) out a quarter turn to help soften up the feeling on acceleration chop. Once I adjusted the high speed compression, I could start to feel the benefits of the Pro Circuit pull rods. 

Off throttle (de-cel) the Yamaha YZ450F felt flatter and less front end heavy, which gave me a YZ450F that now had more control on braking bumps. Corner entry wasn't improved, but I could feel how the Yamaha could lean over better through the middle to end of each corner. With the Pro Circuit link It took slightly less effort for me to continue my lean on the Yamaha, which usually isn't its strong point. Out of the corner (with the softer high speed compression setting) the Yamaha had more rear wheel traction and followed the ground better on acceleration bumps. The rear of the bike was higher in its stroke with the PC rods and gave me more of a plush feel than the stock link. I am able to run a softer high speed compression setting as well as low speed to get more comfort on choppy ruts. 

The overall feeling of the YZ450F with the PC link is a slightly calmer chassis off throttle with a better mid to exit cornering feel. If I had to point out a negative about the PC link it would have to be that once you’re off throttle the Yamaha has a firmer rear end feel. Even though I am gaining control on braking bumps, the YZ450F will feel firmer if the rider isn’t aggressive or pushing the bike. I feel the Pro Circuit linkage arms reward a more aggressive rider, so if you’re the average weekend warrior that likes to cruise his Yamaha YZ450F and is comfortable with your set up, these Pro Circuit linkage arms may not be the best purchasing decision. However, if you’re looking for more control on braking bumps, with a firmer feel and an easier area 2 to 3 (see testing term explanation below)  through corners, then the Pro Circuit linkage arms make a positive difference. 

Cornering Testing Terminology: 

Area 1: Beginning of corner (initial lean, tip in)

Area 2: Middle of corner (weight feel, traction, cornering stability)

Area 3: Exit of corner (rear wheel traction/connection, comfort)

Ride Engineering Performance Link (KTM 125SX)

My son loves riding his 2020 KTM 125SX, but comments all the time on how he feels like the KTM sits taller than his Yamaha YZ125. When I watch him ride I notice that the rear end of his 125SX kicks him in his ass when hitting braking bumps and when that happens, it makes the front end dive too much on corner entry. He only weighs in at around 115 pounds, so going down a spring rate on the shock was a must, but to me, the bike still looked unbalanced on de-cel.

I called up Adrian at Ride Engineering and asked what he had for the KTM 125SX and we both agreed to try a rear link to see if that would help balance out the bike. This Ride Engineering link lowers the back of the KTM 125SX chassis by 7mm to try and improve the ride balance. I set the sag at 103mm with the Ride Engineering link versus the usual 105mm of sag that we were running on Aden’s KTM. Just know that you might have to adjust your air pressure setting on your AER fork to get the right front end feel, since you’re dropping the rear of the bike with the new link (more on that below).

For this test I had two KTM 125SX machines. One was set up for my son, with his softer shock spring and one was just a bone stock KTM 125SX with the sag set for me at 105mm. We started later in the day at a couple tracks on separate days to make sure the track was nice and broke in before we started to make our changes. Doing this ensures that the track doesn't change too much from each change we made to the orange machines. With the Ride Engineering link I noticed better tracking/acceleration coming out of choppy corners and slightly more stability off-throttle. I really liked that the link helped the ride attitude of the KTM when leaning, under throttle, on choppy terrain. I had more trust in the KTM when loading the chassis hard on throttle. I didn't get near as much kicking coming down rough hills and the overall cornering character didn’t suffer. I was worried that this Ride Engineering link would hurt turn in, but to my surprise it didn't affect the KTM’s easy natured turn in character. 

Aden’s comments didn't exactly mimic mine, but one comment that actually made sense was he did like that he felt lower to the ground, when sitting, and that helped him with his starts. When watching him ride the bike was visibly less busy in the rear and didn't give him as much kicking on de-cel. The length of the Ride Engineering pull rods are 1.3mm’s longer than stock and come in at a 149.5mm overall length. Aden doesn't know enough about chassis testing to give me some great feedback, but some of his comments overlapped mine. I more or less watch the bike when he rides and then decide if it’s a good direction or not. We decided to leave the Ride Engineering link on his bike after we both came to an agreement that he looked/felt better on a rough track with it on.

If you do decide to get the Ride Engineering Performance Link just know that you may have to adjust your AER fork pressure, if you’re still on air forks. Now with the Ride Engineering pull rods installed the rear end will ride a little lower, so the front end might seem a little high. Dropping the air pressure anywhere between .2-.5 bar might be needed to get some added front end traction. We dropped Aden’s air pressure from 8.3 bar to 8.1 bar at some tracks and even down to 8 bar at others. Try running your normal AER pressure when you first put on the Ride pull rods and see how your front end feels though corners. If you feel like your front end is tall, your front end is pushing, or have a vague front end feel, just try to drop your air pressure slightly. This will help let the fork use more of its stroke and get that front tire to bite into the ground more. 

The Ride Engineering Performance Link comes complete with bearings and seals and is not that difficult to install. I literally changed the link out at the track on several days. If you’re looking to get a little more stability and rear wheel traction without sacrificing cornering, then you might want to try this link. MSRP is $219.95, but you can use the code Keefer-20 to save 20% if you want to order through ride-engineering.com.