Bump Stops and Limit Straps: Setting Up Both Ends of Your Travel

September 10, 2026

Diagram of prerunner suspension travel showing limit strap at full droop and bump stop at full compression

The short answer: bump stops control the end of compression; limit straps control the end of extension. Between them they decide what happens at the two moments your suspension runs out of travel — and if you skip them, your shocks become the crash structure. A coilover that bottoms metal-to-metal or tops out at full droop is a shock you are about to rebuild.

First, a naming thing: “air bumps” and “hydraulic bumps” are the same part

You will hear both terms used as if they were rival technologies. They are not. An air bump and a hydraulic bump stop are the same component — a small nitrogen-charged, oil-filled damper that looks like a miniature shock. The real distinction is against the rubber or urethane bump stop your truck left the factory with, which is a solid lump with no damping at all.

Factory rubber is fine for a speed bump. On a truck being driven the way a prerunner is meant to be driven, it packs down, tears up and does nothing to control the energy of a hard hit.

How a hydraulic bump stop actually works

Inside is shock oil and a nitrogen charge, and the stroke does three different jobs as it compresses:

First third — soft. The shaft compresses the nitrogen, which behaves like a spring with an exponentially increasing rate. Initial contact is gentle rather than a hit.
Middle third — ramping up. Pressure climbs steeply and the bump starts doing real work.
Final third — the save. The piston is forced through oil, and this is where most of the energy actually goes.

Proper units also carry rebound valving, so the bump does not fire the suspension back at you after it has absorbed the hit. That is the difference between a controlled catch and a pogo.

Sizing: body diameter first, then stroke

Body diameter sets how much energy the bump can absorb:

2.0" — suits solid-axle vehicles around 5,000 lb or less. The common choice on lighter trucks.
2.5" — absorbs significantly more energy. For heavier trucks, or where the suspension geometry leverages the bump hard.

Stroke sets when it engages and how long it has to work. This is where prerunners differ from crawlers:

Desert trucks with big travel want 4" of bump travel. More runway to absorb a fast, heavy hit.
A-arm (IFS) vehicles generally run 2–3", because the arm geometry multiplies wheel movement at the bump and there is rarely room for more.
On low ride heights (4–5" of uptravel), 3" stroke if it fits, 2" if you are tight for space. Above 6–7", go to the full 4".

The trade-off nobody mentions: a shorter bump stop has to run higher internal pressure to do the same job in less distance — which means a harder impact. If you can package a longer bump, it will ride better. Fitment, not preference, is usually what decides this.

Brands and mounting

King and ADS use full-size pistons with compression and rebound shims and high-pressure seals, and mount via precision-machined sleeves rather than a traditional pinch-style can. Fox uses smaller internals and is mass-produced — the budget-friendly option, and genuinely fine for most builds. Bilstein’s is close to Fox but substitutes a rebound spring for the shaft spacer, which quiets the clicking. SPC’s Jounce Shock uses externally adjustable needle valves instead of shims — very compact, but difficult to service.

Useful practical note: Fox and King hydraulic bumps share mounting can dimensions, so you can generally swap between them without re-fabricating the mount.

Setting bump stops up

The mount has to be square to the strike plate and strong enough to take the full hit — a bump stop tears out a weak tab rather than absorbing anything. Then tune:

Start around 350–400 psi of nitrogen and work downward. Too much pressure and the bump feels like a wall; too little and you blow straight through it.
Use the o-ring trick. Slide the o-rings on the shaft all the way up before you go out. Drive the truck the way you actually drive it, then look at how far down the shaft the o-rings have been pushed. That is your real-world usage, not a guess.
Target: the bump cycles almost all the way, leaving roughly 1/4" unused as insurance. Using the full stroke means you are one bigger hit away from bottoming; barely touching it means you are carrying a part that is not working.

You will need a nitrogen fill kit — regulator, hose and chuck — available from any welding supply.

Limit straps: the other end of the travel

A limit strap stops the suspension drooping further than you want. Without one, three things end up doing that job instead, and all three are expensive:

The shock itself, topping out on its internal stop every cycle.
The CV axles, running to an angle they were never meant to see.
Ball joints, heims and the arms themselves, taking the full weight of the assembly at the end of its arc.

On a leaf-sprung rear, the strap also keeps the axle’s weight from hanging off the shocks entirely.

Sizing a limit strap — the actual method

This is where most builds get it wrong. Work through it in order:

Get the truck to full droop on a lift or stands, wheels hanging completely unloaded.
Check the CVs before you measure anything. With long travel, the shock will often let the wheel droop further than the CV can tolerate. Cycle it, look for bind, and keep raising the limit until the CV is happy. On an IFS prerunner, the CV angle — not the shock — frequently sets your droop limit.
Measure centre-to-centre between the upper and lower strap mounting holes at that position.
Stay 1–2" shorter than the shock’s fully extended length, so the strap limits travel and the shock never becomes the stop.
Subtract for stretch: about 1" for every 12" of strap. A 24" strap can stretch a full 2" over its life. This is the step almost everyone skips, and it is why a strap that was set correctly last season is letting the suspension hang too far this season.

To fit: bolt the top end on first, compress the suspension an inch or two off full droop, then attach the bottom. Check the strap clears brake lines and everything that moves through the full cycle, and zip-tie any excess so it is not flapping. PRP, Wide Open Design and Bull Strap all sell straps in roughly 6–44" lengths with chromoly ends.

The mistakes that cost parts

Letting the shock be the limiter at either end. Coilovers are damping devices, not travel stops. This is the single most expensive error on this page.
Fitting bumps and never tuning pressure. An untuned bump is a guess. Use the o-rings.
Ignoring strap stretch. Straps are consumables. Re-measure them periodically, not once.
Weak mounting tabs. Both parts concentrate enormous force into a small bracket. Gusset them.
Setting droop without checking CV angle. You will find out at speed, and the repair is not cheap.

Bump stop and limit strap FAQ

What is the difference between an air bump and a hydraulic bump stop?

Nothing — they are two names for the same nitrogen-charged, oil-filled part. The meaningful comparison is against a factory rubber or urethane bump stop, which has no damping and packs down under hard use.

What size bump stop does a prerunner need?

Desert trucks running big travel generally want 4" of bump stroke; independent A-arm front ends usually run 2–3" because of packaging and the leverage of the arm. A 2.0" body suits lighter trucks, 2.5" where there is more weight or more leverage.

How long should my limit straps be?

Short enough that the shock never tops out — typically 1–2" less than the shock’s extended length — and short enough that the CVs never bind. Then take off about 1" per 12" of strap to allow for stretch.

Do I need both, or will bump stops alone do?

Both. They solve opposite problems. Bump stops protect the truck at full compression; limit straps protect it at full extension. Fitting one and not the other just moves where the damage happens.

How do I know my bump stops are set right?

Put the o-rings at the top of the shaft, drive the truck properly, then read where they ended up. You want almost the whole stroke used with roughly a quarter inch left over.

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Categorized in: Prerunner Builds