A container chassis carries its load at the back on either two axles (a tandem) or three (a tridem, which most people also call a tri-axle). In British Columbia the difference that matters most isn’t the size of the box. It’s how much weight the law lets that group of axles carry.
We rent 40′ tridem, 20-40-45 tridem, extendable and gooseneck chassis, and dry van trailers, so you can match the chassis to the lane: see container chassis rental for the classes and the containers each one takes, or the Max-Atlas chassis we sell. This guide sets out what the province’s rules say, what a third axle changes, and how to choose for the boxes you actually move.
What BC’s rules say about axle groups
The weights come from the province’s Commercial Transport Regulations (CTR), B.C. Reg. 30/78, which set the size and weight limits for commercial vehicles on BC highways.1 Two definitions in section 1.01 do most of the work:
- A tandem axle is two or more equally spaced consecutive axles with an axle spread of 1.0 m to 1.85 m. The axle spread is the distance between the centres of the outside axles.1
- A tridem axle is three equally spaced consecutive axles with an axle spread of 2.4 m to 3.7 m on semi-trailers and trailers.13
2Tandem
- Axle spread
- 1.0 m to 1.85 m
- Most on the group
- 17,000 kg (37,479 lb)
3Tridem
- Axle spread
- 2.4 m to 3.7 m
- Most on the group
- 24,000 kg (52,911 lb)
- Also
- No two neighbouring axles over 17,000 kg (37,479 lb)
A truck pulling a container chassis is a tractor semi-trailer combination, and Appendix D of the regulation lists the most each axle group of that combination may carry:2
9,100kg
on a single axle (20,062 lb)
17,000kg
on a tandem axle (37,479 lb)
24,000kg
on a tridem axle (52,911 lb)
Section 7.16 adds rules inside the group: no single axle may carry more than 9,100 kg (20,062 lb), neighbouring axles must be within 1,000 kg (2,205 lb) of each other, and on a tridem no two neighbouring axles may carry more than 17,000 kg (37,479 lb) together.1
Other limits can be lower
The appendix figures are maximums. The regulation also caps each axle at the manufacturer’s rated capacity for the axle, its brakes and its suspension (section 7.16), each tire at its rated capacity and at the loads in the appendix (Appendix D lists 3,000 kg a tire, 4,550 kg for a wide-base single), and the licensed gross vehicle weight at 63,500 kg (section 7.13). Appendix D shows the whole combination’s limit as “Maximum GCVW – 57 100 kg (Single Steer with PME)”, and posted highway limits and seasonal axle weight restrictions can apply too.124
One rule that doesn’t apply: the trailer axle track-width rules in section 7.07(1) don’t apply to container chassis used only to carry multimodal shipping containers.1
What the third axle changes
Put simply, the third axle raises the legal ceiling on the chassis’s axle group by 7,000 kg (15,432 lb): from 17,000 kg on a tandem to 24,000 kg on a tridem.2 Whether that matters depends on how heavy your boxes are and how their weight lands on the chassis.
Tandem and tridem container chassis in BC
| Tandem | Tridem | |
|---|---|---|
| Axles in the rear group | 2 | 3 |
| Axle spread (CTR s. 1.01) | 1.0 m to 1.85 m | 2.4 m to 3.7 m |
| Most on the group (CTR Appendix D) | 17,000 kg (37,479 lb) | 24,000 kg (52,911 lb) |
| Most on any one axle (s. 7.16) | 9,100 kg (20,062 lb) | 9,100 kg (20,062 lb) |
| Neighbouring axles within (s. 7.16) | 1,000 kg (2,205 lb) | 1,000 kg (2,205 lb) |
| Two neighbouring axles together (s. 7.16) | — | At most 17,000 kg (37,479 lb) |
| Our rental classes | 40′ gooseneck: 40 ft boxes | 40′ tridem: 20 and 40 ft; 20-40-45 tridem: 20, 40 and 45 ft |
| Max-Atlas models | 40′ gooseneck tandem | 20′-40′-45′ tridem, the 40′-53′ and 40′-60′ tridem extendables |
Weights: Commercial Transport Regulations (B.C. Reg. 30/78), section 1.01, section 7.16 and Appendix D, consolidation current to September 29, 2026; checked October 5, 2026.
Where a tridem earns its keep
- Heavy boxes. When the weight on the chassis’s axle group can pass 17,000 kg, only a tridem keeps it inside the Appendix D maximum, up to 24,000 kg.
- Weights you can’t predict. If you don’t know a box’s weight until you see its papers, the extra headroom leaves room for the heavy ones.
- 45 ft boxes. Our 20-40-45 tridem takes 20, 40 and 45 ft containers.
Where a tandem is enough
- Boxes that stay well under 17,000 kg on the chassis’s axle group, lane after lane.
- 40 ft boxes on the 40′ gooseneck. It’s a tandem, and it takes 40 ft containers.
Check a box against both limits
Got a scale ticket, or a weight from the box’s papers? Enter the weight on the chassis’s rear axle group (not the whole truck) to see how it sits against each maximum.
Worksheet: your numbers
Legal on a tandem? On a tridem?
Your number stays in your browser.
Your result
Room on a tandem (17,000 kg)
—
Room on a tridem (24,000 kg)
—
Fill in your numbers to see the result.
Axle-group maximums from CTR Appendix D only. Tire, axle and licensed limits, posted and seasonal limits and the combination’s total can be lower. A guide, not a ruling.
Tandem or tridem? Answer two questions
Pick the answers that fit the lane. You’ll get a suggestion, the reasons for it and where to go next.
Decision helper
Which chassis fits this lane?
Worked out in your browser; nothing is saved or sent.
If you answer
- 40 ft only and Always well under 17,000 kg
Our suggestion
A tandem: the 40′ gooseneck
For 40 ft boxes that stay well under a tandem’s maximum, a tandem does the job. Our 40′ gooseneck is a tandem and takes 40 ft containers.
If you answer
- 40 ft only and Sometimes over 17,000 kg
- 40 ft only and I don’t know yet
- 20 ft and 40 ft and Always well under 17,000 kg
- 20 ft and 40 ft and Sometimes over 17,000 kg
- 20 ft and 40 ft and I don’t know yet
Our suggestion
A tridem: the 40′ tridem
It takes 20 and 40 ft containers, and its axle group may carry up to 24,000 kg.
If you answer
- 45 ft as well
Our suggestion
The 20-40-45 tridem
It takes 20, 40 and 45 ft containers on a tridem axle group.
If you answer
- 53 ft domestic boxes
Our suggestion
An extendable: the 40–53
It takes 20, 40 and 53 ft containers.
A starting point, not a ruling: the regulation, CVSE and your permits decide what’s legal on the road.
Is the third axle worth it on this lane?
If a tridem costs you more each month than a tandem, set that against what a box costs you when it’s too heavy for the chassis you sent. Use your own figures: we don’t fill in any prices, and every rental quote is custom.
Worksheet: your numbers
The third axle, in your numbers
Worked out in your browser; nothing is saved or sent.
Your result
What the heavy boxes cost you a month
—
Left after the tridem’s extra cost
—
Heavy boxes a month to break even
—
Fill in your numbers to see the result.
Your own figures only. Not financial advice.
How to choose by lane
List the lane’s boxes
Pull the container lengths and weights for the lane from your own records.
Find the heavy ones
Count the boxes whose weight on the chassis’s axle group could pass 17,000 kg.
Check the lengths
45 ft boxes need the 20-40-45 tridem; 53 ft boxes need an extendable.
Price both
Ask for a quote on each, then run the worksheet above with your own figures.
Decide by lane, not fleet-wide
Tandems where boxes run light, tridems where they run heavy.
Calculator
Compare renting, leasing and buying a container chassis with your own quotes. Enter the figures you were given; we never fill in…
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FAQ
Tandem and tridem questions
Is a tri-axle the same as a tridem?
Yes. Tridem is the word the regulation uses: three equally spaced axles with a spread of 2.4 m to 3.7 m on a semi-trailer (CTR section 1.01). Tri-axle is the everyday name.
Can a tandem chassis carry a 40 ft container?
Yes. Our 40′ gooseneck is a tandem and takes 40 ft containers. What limits a tandem is the weight on its axle group: 17,000 kg (37,479 lb) under CTR Appendix D.
Does a tridem let me carry a heavier container?
It raises the most the chassis’s axle group may carry, from 17,000 kg to 24,000 kg (CTR Appendix D). The other limits still apply: each axle, the tires, the licensed weight, posted and seasonal limits, and the combination’s total.
Where do I check the rules?
In the Commercial Transport Regulations on BC Laws, linked in the sources below. The compliance centre gathers the official sources in one place.
How is a chassis rental priced?
Every quote is custom: it depends on the term, how many chassis and how you’ll use them. How renting works explains what goes into a quote, or ask for one on the chassis rental page.
