Best Upgrades for a 2021 Softail Slim
Ask five people what to put on a 2021 Softail Slim first and you'll get five different answers, mostly guesses. Here's ours, and it isn't a guess. Every part below is verified to fit this exact bike.
The Softail platform hides its rear suspension inside the frame, so from twenty feet it reads like a hardtail, but every version rides like a modern bike. It's the lineup's most personalized family: Fat Boy, Street Bob, Low Rider S, Breakout, Heritage Classic, and more all share the same bones. Riders take them everywhere from clean OEM+ builds to full club-style customs, and no two end up looking alike.
A full build, every part verified to fit
Generated by the same verified-fitment engine that powers the builder, priced from real listings.
Built for a $5,000 budget: 8 parts, $4,866 total.
Trask Performance Trask Big Papi Air Cleaner - M8 Gen 1
$649.95Air Intake
One of the most common first upgrades on any M8. A freer-breathing intake pairs naturally with an exhaust and a tuner, and with a cam change later.
S&S Cycle S&S Cycle Grand National Slip-Ons for M8 Softail Models, Chrome
$1,231.95Exhaust
The most-heard upgrade on any build: tone, weight savings, and the foundation most performance work builds on.
Zippers Performance ThunderMax with AutoTune for 2021+ Softail
$1,088.95Fuel Tuner
Any breathing or cam change needs fueling to match. A tuner is how the engine actually uses the parts around it.
⚠ Closed-course/race product: confirming legal use for your riding is on you.
Fuel Moto Fuel Moto Chain Drive Conversion - M8 Softail
$299.95Clutch
Clutch upgrades change lever pull and engagement feel, a common pairing with a performance build that's added more power than the stock clutch was sized for.
Arlen Ness Gold & Black 49mm Fork Tubes, M8 Softail
$499.95Front Suspension
Fork upgrades: the front half of ride quality, and the half that matters most under hard braking.
⚙ requires 49mm (non-inverted) front fork legs - excludes Low Rider S/ST which use inverted USD forks
Burly Brand 18" Gorilla Apes
$266.95Handlebars
Bar shape sets your entire riding posture, the biggest single change to how a bike fits you.
Burly Brand M8 Softail Slammer Shock
$527.95Rear Shocks
Stock rear shocks on most H-D models aren't adjustable for load or rebound. An adjustable shock is usually the highest-impact ride-quality upgrade on the bike.
Klock Werks Shelton Handlebar Risers
$299.95Risers
Bar height and reach is a comfort and control issue, not just a style one. Risers change your riding position without needing new bars.
⚙ Requires 1-inch handlebars and 3-1/2 inch center-to-center riser spacing; an alternative gauge mount may be required depending on the model.
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Frequently asked questions
What's the most popular first upgrade for a 2021 Softail Slim?
Exhaust, almost always. Usually paired with an air intake and a tuner so the sound and the breathing change together. See the build above for what that combination actually costs and fits on your 2021 Softail Slim.
Will a part fit my 2021 Softail Slim without anything else changing?
If it's shown in your build above, yes. Every part on this page is checked against your 2021 Softail Slim's exact fitment data before it's ever recommended. And if something needs a companion part to work right, like a tuner with certain cams, that's called out on the item itself, not left for you to find out after it arrives.
How much does a typical first build cost for a 2021 Softail Slim?
It depends on what you're after. The build above is a full build for the budget shown, with every part and the total priced from real listings. Set your own budget and style and it rebuilds around them.