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Tow-Bar Mounted Bike Racks
Modular 1-4 bike racks manufactured in Australia for cars, SUVs, 4WDs and utes.
Caravan Bike Racks · Tow Ball Weight
How the iSi system reduced tow ball weight by 19kg.
A customer came to us recently because his existing rack pushed him over his legal tow ball limit. He needed to shave at least 15kg off to be compliant. His options were limited. Leave bikes behind, or find a rack that could carry the same load with less impact on the tow ball.
We replaced his rack with the iSi system and took 19kg off his tow ball, with the same four bikes (56.5kg combined) on the same caravan. Compliant. With margin to spare. All four bikes loaded.
Tow ball reduction
19kg
Less tow ball weight than a competitor with the same four bikes on the same caravan.
Closer to the axle
383mm
Shorter lever arm. Less force translated through to the tow ball.
Lower load height
200mm
Lower centre of mass. Easier to load bikes. More stable on the road.
01 — Side-by-side
Same caravan. Same bikes. Different result.
Both racks were tested on the same caravan, carrying the same four bikes (56.5kg combined). The difference isn't in what they carry. It's in where the load sits.
Other rack
Flat. Forward. High.
All four bikes lined up at the same height, hanging well forward of the van. Higher centre of mass, longer lever arm, and harder access to individual bikes.
iSi system
Staggered. Tight. Low.
Each bike at a different height, sitting close to the van body. Easy access to every bike, lower centre of mass, and 19kg less on your tow ball.
02 — The physics
It's not just the weight.
Tow ball weight is one of the most misunderstood numbers in caravanning. The weight of the rack and bikes matters. But it's only half the story. Where that weight sits, and how far it sits from your caravan axle, decides how much of it actually lands on the tow ball.
Hold a 5kg dumbbell against your chest. Now hold it out at arm's length. The weight hasn't changed. The load on your shoulder has multiplied. That's leverage. The same physics is at play between a bike rack and your tow ball.
A rack mounted 400mm forward of the van puts the bikes at the end of a long lever arm. The further out they sit, the more downward force they apply to the tow ball, well beyond their actual mass. The iSi system mounts within 25mm of the van front. Bikes sit tight to the body. Close to the axle. Short lever arm. Less leverage. Less load on the tow ball, without changing the rack weight at all.
03 — Bike rack comparison
The difference, side-by-side.
A direct comparison of the two systems carrying the same four bikes. Static rack weight, positioning and towing dynamics.
| Other rack | iSi system | |
|---|---|---|
| Static rack weight | 40.50kg (excl. drawbar mount) | 39.82kg (incl. drawbar mount) |
| Distance from van front | 408mm | 25mm (383mm closer) |
| First bike height | 870mm | 670mm (200mm lower) |
| Tow ball impact (4 bikes) | Higher | 19kg less |
| Centre of mass | High and forward of van | Low and back toward the axle |
| Towing dynamics | Long lever arm increases sway potential | Compact load improves stability |
Comparison based on side-by-side testing of both racks on the same caravan, carrying the same four bikes (56.5kg combined). Static rack weight figures are manufacturer specifications. Tow ball weight reduction is a measured outcome of rack positioning and centre-of-mass placement, not a difference in static rack mass. Results may vary depending on caravan, drawbar configuration and existing setup.
04 — Towing stability
The stability margin you can't feel.
Tow ball weight is only half the story. The other half is what happens to your caravan's centre of mass when bikes get loaded onto it. A rack that sits high and forward of the van raises that centre of mass and shifts it away from the caravan axle. Both work in the same direction. They reduce the stability margin your rig has when something happens at speed.
You won't notice it on a flat highway. At 90km/h in clean air, a poorly positioned rack feels identical to a well positioned one. The caravan tracks straight. The handling feels normal. Nothing tells you the rig is closer to the edge than it should be.
Then a crosswind hits. A truck overtakes you. You hit a long descent at 110km/h. The caravan starts to yaw, and a rig that was sitting on a comfortable stability margin is suddenly past it. Engineering research confirms what experienced caravanners already know. Once sway builds beyond a critical point, it stops self-correcting and starts amplifying. By the time you feel it through the steering wheel, you're correcting a problem that's already running ahead of you.
A rack that places the bikes lower and closer to the caravan axle leaves more margin in the system. Lower centre of mass means less leverage when the caravan starts to yaw. Closer to the axle means less mass acting through the long lever arm that drives sway in the first place. It's the kind of stability you can't feel directly. It's just the absence of a problem.
Watch · Tow ball weight in action
See how rack positioning translates into real tow ball load.
The hidden risk
The danger isn't that a poorly positioned rack feels unstable on a normal day. It's that it feels completely fine right up until the moment it doesn't. Centre of mass and tow ball positioning don't show themselves on the highway in calm conditions. They show themselves at speed in a crosswind, on a descent, or when a B-double passes you on a country road. By then, the time to fix it has passed.
05 — Engineered, not assembled
Configured for your van. Not off the shelf.
The 19kg result wasn't an accident. It happened because the system was configured to mount tight to that customer's specific van, instead of forced into a generic position. No two caravans are the same. Drawbar lengths vary. Tool boxes sit at different heights. Jockey wheels mount in different positions. Expander caravans have bed end articulation that needs clearance. Gas bottle locations differ. Spare wheel mounts get in the way.
An off-the-shelf bike rack will always compromise on at least one of those measurements. The iSi system is manufactured from hundreds of modular components and configured by our team to suit your specific caravan geometry. Post heights, beam lengths, mount types, pivot configurations and drawbar mount specifications are all selected for your van. That's the only way you get a result like 19kg off the tow ball, instead of a one-size-fits-most rack with a generic adapter and a long lever arm.
Drawbar geometry
Tool boxes & gas bottles
Mount specifications selected to clear tool box openings and gas bottle locations specific to your van.
Hardware clearance
Jockey wheel & hand brake
Drawbar mounts engineered around your jockey wheel position and hand brake operation.
Expander caravans
Bed end articulation
Pivot configurations that allow front bed deployment without unloading the bikes.
Bike configuration
Number, weight & type
Post heights and beam length selected for your bike count, including e-bikes up to 32kg per bike.
Tow vehicle
Departure angle
System height configured to clear the rear of your tow vehicle when articulating into camp.
Weight distribution
WDH compatibility
Compatible with most weight distribution hitches, stone guards, storage boxes and existing drawbar fitments.
06 — Why tow ball weight matters
Your tow ball has a legal limit.
Every caravan and tow vehicle has a maximum allowable tow ball download. Typically 8 to 10 percent of ATM, or as specified by the manufacturer. A bike rack and four bikes can add 40kg or more directly to that number, especially when mounted on a long lever arm forward of the van.
Exceed your tow ball limit and you're outside compliance. You're also increasing the risk of trailer sway, uneven tyre wear, and reduced steering feel on your tow vehicle. It's the kind of thing that's invisible on flat highway, and very obvious the first time you hit a long descent, a crosswind, or a corrugated dirt road.
The iSi system is engineered so that its position does the work, keeping tow ball load in check without forcing you to choose between bikes and compliance. If you're not sure where your current setup sits, get in touch with our team.
Ready to configure
Engineered for your van.
Every iSi caravan bike rack is configured specifically for your drawbar, your bikes, and the way you tour. Build yours in minutes, or speak to our sales team.