Hundreds Of Products Ready Today. Dispatch/Collection T45 Or CDS Roll Cage Steel: Which One To Buy, And What Each Costs
Custom Cages tube steel, decoded
Once someone has picked a Custom Cages kit, the steel is usually the next thing they ring about. The short answer is that neither the FIA nor Motorsport UK names T45 anywhere in their rulebooks, so picking it is a strength and budget decision, not a legality one.
For most club rally, sprint, autotest and track day builds, CDS built to the published specification is a legal cage that has been proving itself for years, and the money you save goes straight into seats, harnesses and pads. T45 earns its place once you are chasing weight on a homologated or certified design, or the kit you have set your heart on only comes in it.
- 639 Custom Cages kits in the range: 396 in T45, 243 in CDS
- T45 appears in neither the FIA nor the Motorsport UK rulebook, checked by full text search
- Custom Cages quote T45 at a minimum 620 N/mm² yield against 370 N/mm² for their high spec CDS
- Minimum tube dimensions are identical for both steels
- Typical gap on a like for like kit is about £377
The two steels, in short
CDS
Cold drawn seamless is the manufacturing process, not a material on its own, and every cage on this page is cold drawn seamless whichever steel it is in. Both rulebooks specify it, so an ERW welded tube is not an option either way. The material behind Custom Cages’ standard grade is an unalloyed carbon steel built to a minimum 370 N/mm² yield and 510 N/mm² tensile, well clear of the regulation floor.
T45
A British tube specification, BS4 T45, made from a carbon manganese steel rather than a chrome moly one, worth having straight if you are reading a spec sheet. Custom Cages quote a minimum 620 N/mm² yield and 700 N/mm² tensile, roughly double the standard grade, which is the whole reason it costs more.
That is the short version. For the full metallurgy, the elongation figures and how each behaves under welding, our CDS versus T45 explainer goes further. This page is about which one to buy and what the range costs.
The strength numbers, side by side
The steel is where the real difference sits, so here it is drawn to scale instead of left as two numbers in a sentence.
Minimum strength, Custom Cages own published figures
Custom Cages’ own minimums for their T45 and their high spec E355 CDS. The FIA table asks for a minimum tensile strength of 350 N/mm², Motorsport UK asks for a minimum yield strength of 350 N/mm², two different measurements from two different rulebooks, and both steels clear either figure with room to spare.
What the regulations actually require
This is where most of the confusion sits. We searched the full text of FIA Appendix J Article 253 in its 2026, 2020 and 2016 editions, and the Motorsport UK National Competition Rules 2026 Edition 3. T45 does not appear once in either.
What both bodies specify instead is the material and the minimum size. Cold drawn seamless unalloyed carbon steel, maximum 0.3% carbon, and: 45 x 2.5mm or 50 x 2.0mm for the main rollbar, 38 x 2.5mm or 40 x 2.0mm for the other members. Those minimum dimensions are the same whatever the tube is made of.
Motorsport UK’s Appendix 3 is written as one baseline, build to their published specification and drawings, plus an exception that opens a Motorsport UK (ASN) ROPS Certificate route, with FIA homologated cages recognised throughout. The FIA text sets out three options for cars homologated between 2017 and 2020: fabricate to the published spec, gain ASN homologation or certification, or run an FIA homologated cage. For cars homologated from 1 January 2021, the FIA dropped the fabricate to spec route entirely. Those cars need a cage that is FIA homologated, or homologated or certified by an ASN, full stop.
Read your own championship regulations before you order either steel. A series is free to set a stricter rule than the national one, and the only way to know for certain is the paperwork for your class. Send Cameron the car and the championship name and he will check it with you before anything gets ordered.
Which one to buy
Buy CDS if
You are doing club rally, sprint, autotest or track day work. You have not committed to a specific championship yet. Or you would rather put the difference into seats, harnesses and pads than into tube you do not need.
Buy T45 if
You are chasing weight, because the extra strength margin is what allows a lighter homologated design. Your championship, or the specific kit you have your eye on, is only offered in T45. Or you are building once and want the strongest tube on the shelf.
What the range costs
All 639 Custom Cages kits we hold, counted and priced with VAT on 13 August 2026.
What the range costs, VAT included
Every Custom Cages kit we hold, counted and priced with VAT on 13 August 2026. Typical is the middle of each range. The gap between the two typical figures is about £377, which is also roughly a decent harness, or the mounting hardware to fit one properly.
| Steel | Kits in stock | From | Typical | To |
|---|---|---|---|---|
| CDS | 243 | £492.00 | £1,380.00 | £2,400.00 |
| T45 | 396 | £1,092.00 | £1,757.02 | £3,256.10 |
Prices include VAT. Typical is the middle of each range, and it is the number worth weighing against the rest of the build.
CDS kits worth a look
A spread across the CDS range, not the whole 243, from a rear half DIY kit to a full multipoint cage. Custom Cages put the steel in every product name, so it is there to check before it goes in the basket.
T45 kits worth a look
Same idea, in T45, from a rear half bolt in kit up to a factory style multipoint cage.
Every kit above is one Custom Cages actually build, but the steel that suits you depends on the class you are entering and which tube your design is offered in as much as it depends on budget. Send Cameron the make, the model and the championship name, and we will tell you which kits fit, in which steel, and what they come to.
Common questions about T45 and CDS
Do the regulations require a T45 cage?
No. We checked the full text of FIA Appendix J Article 253 in its 2026, 2020 and 2016 editions, and the Motorsport UK National Competition Rules 2026, and T45 does not appear in either. Both specify a minimum strength and a minimum tube size, and a CDS cage built to that specification is just as legal.
Is a CDS cage weaker than a T45 one?
Weaker than T45, yes, by design. Weaker than the regulations require, no. Custom Cages’ own high spec CDS clears the 350 N/mm² regulation floor by a wide margin at 370 N/mm² yield and 510 N/mm² tensile. T45 clears the same floor by more.
Does T45 let me run a thinner tube?
Only where that specific cage design is FIA homologated or holds a Motorsport UK ROPS Certificate. On a cage built to the published specification, the minimum tube sizes are identical for both steels.
Why does T45 cost more?
Roughly double the yield and tensile strength of standard CDS. It is a British spec carbon manganese steel, not a plain carbon one, and that is real material cost before Custom Cages have cut a single tube.
Can I tell which steel a kit is before I buy?
Yes. Custom Cages put it straight in the product name on every listing, CDS or T45, so it is there to check before you add anything to the basket.
I have not settled on a championship yet, which should I buy?
CDS. It is the cheaper route into a legal cage and it keeps you clear of paying for a strength margin you might not need yet. If you step up a class in a year or two, fit the cage you will want then instead of pulling out one you have only just put in.
Where this leads
Two make specific guides are live so far, and both stock kits in either steel: Custom Cages BMW E30 and E36 roll cages and Custom Cages Renault roll cages. More makes are being added to the programme regularly.
For what fitting adds on top of the kit price, our roll cage fitting cost guide covers that side of it, and the full Custom Cages range is worth a browse if your car is not one of the two above yet.
If your car and championship are not covered anywhere on this page, ring 0115 9893488 with both and Cameron will check what Custom Cages offer and what it comes to, in either steel.