What a bump stop does, why off-road trucks run hydraulic bump stops, when a bump stop spacer makes sense, and which kit fits your Raptor, TRX, RHO, Bronco, Bronco Raptor or Ranger Raptor.
The Short Answer
A bump stop is the part that stops your suspension at full compression. When the axle or control arm reaches the top of its travel, the bump stop is what it hits instead of the frame. On an off-road truck the better version is a hydraulic bump stop: a short, oil-filled shock that the suspension contacts in the last few inches of travel. Instead of the hit arriving all at once, the hydraulic bump stop builds resistance as it compresses and slows the suspension down, so a big hit turns into a squeeze. A bump stop kit is the mount, the strike plate and the hardware that put a hydraulic bump stop in the right place on your truck. On most trucks the rear kit bolts on. The front kit bolts to the factory lower arm, and its bump stop mount welds to the frame.
What a Bump Stop Does
Every suspension needs something to stop it at both ends of its travel. At full droop that job belongs to the shock or, better, a limit strap. At full compression it belongs to the bump stop. Most hard-driven off-road trucks want both.
1. Protects the Mounts
Without a proper bump stop, a full-compression hit goes straight into the shock mount, the frame and the link or arm mounts. The bump stop takes that load instead.
2. Turns a Hit Into a Squeeze
A hydraulic bump stop starts working before the suspension is out of travel and builds resistance the further it compresses, so the axle slows down over the last few inches instead of arriving all at once.
3. Keeps the Truck Settled
When the hardest hits are controlled, the truck stays composed through rough sections and big whoops, and you keep your speed instead of backing off.
4. Matters More With More Travel
The more wheel travel you add, the more energy is in the system when the suspension reaches the end of its stroke. On a long travel truck a bump stop kit is not optional.
Hydraulic Bump Stops vs. Rubber Stops and Spacers
There are three ways owners end up dealing with full compression: the factory bump stop as it came, a spacer under the factory bump stop, or a hydraulic bump stop kit. They do different jobs.
| What you care about | Hydraulic bump stop kit | Spacer under the stock bump stop | Factory bump stop as-is |
|---|---|---|---|
| What it is | Oil-filled bump stop in its own mount | Moves the stock stop's contact point | Whatever the truck came with, or nothing |
| How it stops the suspension | Builds resistance through its stroke | Same as the stock stop, just sooner | Same as stock |
| Effect on wheel travel | Designed around the suspension cycle | Can take away travel if done wrong | Unchanged |
| Works with long travel | Yes | No | No |
| Bump stop size | 2.5" or 2.0" diameter, by platform | n/a | n/a |
When a Bump Stop Spacer Makes Sense
There is one case where a spacer under the stock rubber bump stop is the right call, and it is specific to the leaf-spring Gen 1 and Gen 2 Ford Raptor (2010–2014 and 2017–2020).
On those trucks the factory rear spring pack has a 1.5" riser block built into the assembly. In stock trim, that riser block is what contacts the bump stop. When you change to an aftermarket leaf spring, the riser block goes away, and so does the part the bump stop was set up to hit. At that point you have two options: put a spacer under the stock bump stop to make up the difference, or swap to a hydraulic aftermarket bump stop kit.
Outside of that case, we do not recommend spacing the stock bump stop down. A spacer that moves the bump stop down can take away wheel travel when it is not done properly, and it does nothing to change how the truck handles a full-compression hit.
Does a Bump Stop Kit Replace the Factory Bump Stop?
It depends on the truck, and on which end of it. Here is how each FMI kit works with what the factory installed.
| Truck | Rear kit | Front kit (stock lower arm) |
|---|---|---|
| Ford F-150 Raptor, Gen 1, Gen 2 and Gen 3 | Adds a hydraulic bump stop. The stock rear bump stop can stay installed, but it is not necessary. | Adds a front bump stop. There is no factory front bump stop to speak of. |
| Ram TRX and Ram RHO | Replaces the factory rear bump stop. | Adds a front bump stop. |
| Ford Bronco Raptor | Replaces the factory rear bump stop. | The Bronco Raptor has a factory front bump stop. The kit for the stock lower arm can be used together with it. |
| Ford Ranger Raptor | Replaces the factory rear bump stop. | Adds a front bump stop. |
| Ford Bronco (non-Raptor) | Adds a bump stop. The stock Bronco has no factory rear bump stop to replace. | Adds a front bump stop. |
Rear Bump Stop Kits by Truck
The rear is where most owners start. The Raptor, Bronco, Bronco Raptor and Ranger Raptor rear kits bolt on, and the Ram TRX and RHO cans install in the factory rear spring buckets with minimal modifications.
Ford F-150 Raptor
2.5" diameter bump stops with 2.5" of travel. Bolt-on, no drilling. Works on a stock truck and on long travel rear suspension.
Running the Gen 1 to Gen 3 or Gen 2 to Gen 3 Conversion?
A Gen 1 Raptor or 2009–2014 F-150 that has been converted to 5-link rear suspension uses the Gen 1 to Gen 3 conversion rear bump stop kit. It only works with the conversion and will not fit a leaf-sprung truck. A converted Gen 2 uses the Gen 3 rear kit. See how to convert a Gen 2 Raptor or F-150 to Gen 3 suspension.
Ram TRX and Ram RHO
2.5" diameter hydraulic bump stops with 2.5" of travel. The cans install in the factory rear spring buckets with minimal modifications.
Ford Bronco, Bronco Raptor and Ranger Raptor
Bolt-on at the frame. No frame welding.
Front Bump Stops and Limit Straps
At the front, FMI builds the bump stop into a limit strap and bump stop kit that works with the factory lower control arm. It handles both ends of the travel: the limit strap stops top-out before the shock does, and the bump stop handles full compression.
The lower bracket bolts to the factory cast aluminum lower arm. The bump stop mount welds to the frame, so this kit should be installed by a qualified welder or fabricator. Check your shock package on the product page before ordering, since some aftermarket front shocks and hose setups need to be confirmed for clearance.
| Front kit for the stock lower arm | Bump stop size |
|---|---|
| Gen 1 Raptor, 2010–2014 | 2.5" diameter, 2.5" travel |
| Gen 2 Raptor, 2017–2020 | 2.5" diameter, 2.5" travel |
| Gen 3 Raptor and Raptor R, 2021–2026 | 2.5" diameter, 2.5" travel |
| Ram TRX, 2021–2024 | 2.5" diameter, 2.5" travel |
| Ram TRX, 2027 | 2.5" diameter, 2.5" travel |
| Ram RHO, 2025+ | 2.5" diameter, 2.5" travel |
| Bronco Raptor, 2022+ | 2.5" diameter, 2.5" travel |
| Bronco, 2021+ | 2.0" diameter, 2.0" travel |
| Ranger Raptor, 2024+ | 2.0" diameter, 2.0" travel |
Running FMI fabricated lower control arms? Those arms have a bump pad built in, and the matching weld-on front bump stop can mounts to the frame above it. Kits are available for the Gen 1, Gen 2 and Gen 3 Raptor, the 2021–2024 TRX and the 2027 TRX.
Which Hydraulic Bump Stop Fits Your Kit
2.5" Kits
Raptor, TRX, RHO and Bronco Raptor kits take a 2.5" diameter bump stop with 2.5" of travel. Fox, King and ADS 2.5" bump stops fit, and some kits also list Carbon. The FOX Factory Race 2.5 x 2.45 fits the FMI 2.5" kits for the Gen 1, Gen 2 and Gen 3 Raptor, Bronco Raptor and 2021+ Ram TRX.
2.0" Kits
Bronco front and rear kits and the Ranger Raptor front kit take a 2.0" diameter bump stop with 2.0" of travel. The FOX 2.5 Factory Race bump stop will not fit FMI Bronco kits.
Most kits let you pick the bump stop brand at checkout, or order the mounts only if you already have bump stops.
Where to Start
If you are adding lift, read Lift Collars vs. Top Spacers for why we control both ends of the travel with parts designed to be travel stops.
Bump Stop FAQ
What is a bump stop on a truck?
A bump stop is the part that stops the suspension at full compression, so the axle or control arm hits it instead of the frame. Off-road trucks often use hydraulic bump stops, which are short oil-filled shocks that slow the suspension down over the last few inches of travel.
What does a hydraulic bump stop do?
It controls the last part of the suspension travel. Instead of the suspension slamming into a hard stop, the hydraulic bump stop builds resistance as it compresses, which softens big hits and protects the shock mounts, frame and link or arm mounts.
Do I need bump stops on a stock truck?
If you drive it hard off-road, yes. FMI rear bump stop kits work on stock trucks, and on most platforms the rear kit bolts on, which makes it one of the easiest suspension upgrades to start with.
Does a bump stop kit replace the factory bump stop?
On the Ram TRX, Ram RHO, Bronco Raptor and Ranger Raptor, the rear kit replaces the factory rear bump stop. On the F-150 Raptor, the stock rear bump stop can stay installed but it is not necessary. The stock Bronco has no factory rear bump stop, so that kit adds one. At the front, only the Bronco Raptor has a factory bump stop, and the FMI kit for the stock lower arm can be used together with it.
Should I use a bump stop spacer?
Only in one case: a leaf-spring Gen 1 or Gen 2 Ford Raptor that has switched to aftermarket springs. The stock spring pack has a 1.5" riser block that contacts the bump stop, and aftermarket springs remove it, so you either put a spacer under the stock bump stop or switch to a hydraulic bump stop kit. Otherwise we do not recommend it, because a spacer that moves the stock bump stop down can take away wheel travel when it is not done properly.
Are FMI bump stop kits bolt-on?
The Raptor, Bronco, Bronco Raptor and Ranger Raptor rear kits bolt on. The Ram TRX and RHO cans install in the factory rear spring buckets with minimal modifications, and the Bronco Raptor kit requires removing a couple of small factory wire-management brackets from the rear axle. The front limit strap and bump stop kits bolt to the factory lower arm, but the bump stop mount welds to the frame and should be installed by a qualified welder or fabricator.
What size bump stop do I need?
Raptor, TRX, RHO and Bronco Raptor kits use a 2.5" diameter bump stop with 2.5" of travel. Bronco kits and the Ranger Raptor front kit use a 2.0" diameter bump stop with 2.0" of travel.
What is the difference between a bump stop and a limit strap?
They work at opposite ends of the travel. The bump stop stops the suspension at full compression. The limit strap stops it at full droop so the shock does not have to. The FMI front kits include both.
Can I add a bump stop kit with a long travel kit?
Yes, and you should. The Gen 1, Gen 2 and Gen 3 Raptor rear kits all work with long travel rear suspension, including FMI long travel kits. The more travel the truck has, the more the bump stop matters.
Can I add rear lift with the TRX or RHO bump stop kit?
Yes. The rear spring spacer plates stack with the bump stop cans in .75" and 1" thicknesses, and it makes sense to do both at once since the spring bucket is apart either way.
See every kit in one place in the FMI bump stop kit collection, or call the shop and tell us what you are building.