GP Suspension Cartridge System for 18+ Softail


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GP Suspension 25MM Cartridge System for 18+ Softail

GP Suspension Cartridge kits include a spring set, specifically selected by a master setup technician based on the riding information you choose. Kits are built to order per your order specifications. Lead time is only about 4-5 weeks.

*Please leave your approx weight in the order notes at checkout. This is important information needed when building your specific kit.


  • 18 FatBob
  • 19+ FatBob
  • 18+ Lowrider
  • 20+ LowriderS

“After ordering a Well-known brand name competitor’s product to fix our Dyna, we understood why riders aren’t buying cartridges for their Harleys; they’re cheap-o versions of their race kits that offer marginally better performance over stock with limited to no adjustment at a premium price. It was wasted money. When we sold the kit, we got a fraction of what we paid and laid it off on some poor sucker. So, we did what anyone with their own suspension manufacturing company would do: we adapted our Premium Championship Road Race cartridge “25” to our own Dyna. On our first test ride, we knew we were cooking. Fast forward one year and view the video of our Harley test rider at Chuckwalla raceway on his Dyna with GP Suspension forks and shocks. We found Zach sending it 10 miles from our facility on the world-famous Mullholland Highway on a stock Dyna and amazing (scaring) the hell out of us, but also almost crashing in every corner due to that typically horrible Harley Suspension. Zach has mad skills, but now with his Dyna on GP Suspension, he has the most performance and adjustability in any front fork kit product for a Dyna (or any cruiser type, for that matter).

We understand wanting to spend money first on a slightly faster ET and nice HP dyno chart, but that concept brings us back to one of our favorite classic cars: the 1987 Buick Grand National. The fastest production car of 1987 was a beast at local drag strips and street races. However, when that beast hit its first corner at the maddening speed it created in its engine bay, it also hit its first tree. See, the Grand National is hell in a straight line, but it handles horribly stock, a 1987 MR2 was better around the track and in the canyons. This is the typical Harley conundrum: slightly faster in a straight line and horrible at even minimum cornering, or awesome cornering and slightly slower off the showroom floor? We know what we’d do, and we did…we took videos of it and we took track times at our favorite road course with it. Then, we went hunting sport bikes with it and sent them packing too. All the while, we laughed and laughed at how fast we could ride this bike and how much fun it was to ride. Best money ever spent on our bikes, bar none. We guarantee you’ll agree on yours. Trust us with your ride. We won’t ever steer your wrong. If you don’t agree, send us the kit within 30 days and we’ll send you your very own numbered bills back along with an autographed picture of Ulysses S Grant.”


How to adjust your GP Suspension 25mm Cartridge kit

Adjustments can be broken down in the following way:

Preload: This is the spring adjustment for your kit, by turning the 14mm dial on your fork cap clockwise you are adding preload to the springs in your forks. This is going to result in a more supported ride. Preload is counted in full rotations. To set your preload you will back the 14mm all the way out(counterclockwise) and count rotations as you spin the 14mm nut in(clockwise).

Six turns of preload is a good place to baseline your suspension.

Your kit will have come with a travel indicator and you can use this to measure how much travel you are using. Keep in mind that the casting is not typically the bottom of your travel. Feel free to call us and we will let you know how far above the casting your model bottoms out at. Measuring how much travel you are using is a good way to fine tune your preload.

Compression & Rebound: These are the hydraulic adjustments for your bike. They will be the 3mm brass allen adjusters found in the middle of your preload adjusters and/or at the bottom of your fork leg. They control the hydraulic bleeds for the up and down damping on your bike. The compression adjustment will adjust the rate at which the fork is able to compress when the front is loaded. The rebound adjustment will adjust the rate at which the fork is able to extend back as the front end is unloaded. The more you close the rebound and compression off by clicking the adjusters in (clockwise) the slower your fork will compress and rebound. The more you open the bleeds up by clicking the adjusters out (counterclockwise) The faster your bike will compress and rebound. Rebound and compression adjustments are counted in clicks. To set your rebound or compression click your adjusters fully closed (All the way clockwise), and then count clicks as you turn them out (counterclockwise).
14 clicks on your rebound and compression is a good place to baseline your suspension.


Additional information

Weight 10 lbs
Dimensions 25 × 4 × 4 in

18 FatBob, 19+ FatBob, 18+ Lowrider, 20+ LowriderS


Stock, +2" Overstock

Riding Style

Casual Road Riding, Cross Country Touring, Aggressive Street Riding/Canyons

Preload Adjuster Color

Blue, Red, Black


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