What speed is the R129 approval side-impact, according to Which??

Which?'s June 2026 test-method page records the R129 regulation side-impact at 15 mph, on top of the frontal and rear tests it also lists for R44/04. That figure is the UN minimum Which? is describing, not Which?'s own lab speed.

Why is Which?'s own side test so much faster?

Which? says its consumer tests are designed to be more demanding than the regulation minimum and closer to real-world crashes (it cites Euro NCAP-style scenarios). A seat can pass R129 at 15 mph and then score poorly, or well, in Which?'s faster side test.

Does an R44 seat that Which? once side-crash-tested count as 'side-impact approved'?

No. A Which? result is a consumer-test score. The UN R44 label still did not require a side-impact pass. Keep the sticker and the magazine test on separate lines.

Is this why people say i-Size is safer than R44?

Many explainers cite the mandatory side-impact as one reason R129 is a stricter approval. This page records that test difference. It does not grade a named R44 seat against a named R129 seat, and it does not tell you to bin a still-approved R44 seat you already own.

Guides · Car seats · Approval tests

Does R129 require a side impact test that R44 does not?

Updated 10 September 2026 · Checked 10 September 2026 · By MayTally research desk — Checked against official UK sources

What does each UN regulation require in the approval test?

Which?'s how we test page, updated 8 June 2026, sets out the legal minimums the two labels imply:

Swipe sideways for the full table

UN approval tests named by Which? for each label
On the orange label	Frontal impact	Rear impact	Other UN tests Which? lists	Mandatory side-impact?
ECE R44/04	Yes — Which? records 32 mph	Yes — Which? records 18 mph	Roll-over simulation	No
R129	Same frontal and rear tests Which? lists for R44/04	Same rear test Which? lists for R44/04	The R44 set, plus a side-impact test	Yes — Which? records 15 mph

Speeds and the 'no mandatory side-impact on R44' line are from Which? 'How we test baby and child car seats', checked 10 September 2026. They describe the UN approval minimum, not Which?'s own consumer crash programme.

The same split appears in Which?'s weight and height groups article: R44/04 has frontal and rear tests but no side-impact tests; R129 has front, rear and side-impact tests. Beds, Luton and Milton Keynes children's health pages describe i-Size / R129 seats as tested for front, rear and side impacts.

Is a Which? side-crash score the same as the R129 approval test?

No. Keep the two labs apart.

UN approval (the orange label): the minimum a manufacturer must pass to print R44/04 or R129. Which? records no mandatory side-impact on R44, and a 15 mph side-impact on R129.
Which? consumer tests: every reviewed seat, whatever the label, goes through Which?'s own front test (about 31 mph offset) and side test (about 37 mph, described elsewhere on that page as around 30 mph impact speed). Which? says those tests are more demanding than the regulation minimum.
A high Which? score on an R44 seat does not rewrite the UN rule. That seat still did not have to pass a UN side-impact to get its R44 label.
A low Which? score on an R129 seat does not remove the R129 label. The seat passed the UN side-impact; Which? then ran a different test.

When a parent asks "does R129 require a side-impact test that R44 does not?", the answer is about the UN approval rule. Which? star ratings are extra information, not the regulation.

What else does R129 change in the approval test, besides side impact?

Side impact is the difference parents ask about first. Which? and NHS-adjacent pages also record other R129 approval rules that R44 does not share:

Rear-facing minimum: GOV.UK and Which? both say height-based / R129 seats stay rear-facing until the child is over 15 months. Which?'s comparison table records R44's older rearward-facing line as 9 kg (about 10 months).
How the child is measured: R129 labels use height; R44 labels use GOV.UK weight groups.
Dummies: manufacturer explainers for R129 (including Joie's i-Size page) describe Q-series dummies with more sensors than the older P-series used under R44. That is a test-tool change, not a parent-facing safety verdict.

Those extra differences do not cancel the side-impact fact. They also do not turn an approved R44 seat into an illegal seat. Which? still records R44.03 / R44.04 as legal to use in the UK.

Does 'no mandatory side-impact' mean an R44 seat has no side protection?

It means the approval test did not require a side-impact pass. It does not mean the plastic shell has no side wings, and it does not mean Which? has crash-tested that model from the side. Some makers say they ran their own side tests on R44 seats; those private tests are not the UN R44 rule.

Beds, Luton and Milton Keynes children's health wording is that i-Size seats "provide better protection from side impact crashes" because of the crash tests they face. That is their clinical-page summary of the regulation, not a MayTally verdict that a particular R44 seat will fail a side collision.

If R44 skips a side-impact test, is it still legal to use?

Yes, if the label is an approved one. GOV.UK still lists approved ECE R44 weight-based seats for use. RoSPA still accepts R44.03 / R44.04 or R129. The side-impact gap is a fact about the approval test, not a hidden use-ban.

Which? has stopped testing new R44 seats and prefers to review R129 models. That is a consumer-test policy, not a change to GOV.UK's label list.

In short

In shortUN R129 includes a mandatory side-impact approval test. Which? records no such mandatory test on ECE R44. Which?'s own 37 mph-class side crash is a separate consumer programme run on whichever seats it reviews. The test difference is not a MayTally safe / not-safe verdict on any named seat.

Questions parents ask

What speed is the R129 approval side-impact, according to Which??: Which?'s June 2026 test-method page records the R129 regulation side-impact at 15 mph, on top of the frontal and rear tests it also lists for R44/04. That figure is the UN minimum Which? is describing, not Which?'s own lab speed.
Why is Which?'s own side test so much faster?: Which? says its consumer tests are designed to be more demanding than the regulation minimum and closer to real-world crashes (it cites Euro NCAP-style scenarios). A seat can pass R129 at 15 mph and then score poorly, or well, in Which?'s faster side test.
Does an R44 seat that Which? once side-crash-tested count as 'side-impact approved'?: No. A Which? result is a consumer-test score. The UN R44 label still did not require a side-impact pass. Keep the sticker and the magazine test on separate lines.
Is this why people say i-Size is safer than R44?: Many explainers cite the mandatory side-impact as one reason R129 is a stricter approval. This page records that test difference. It does not grade a named R44 seat against a named R129 seat, and it does not tell you to bin a still-approved R44 seat you already own.

Sources

Official pages first. If this page and the official page disagree, the official page wins.

Which? — How we test baby and child car seats — checked 10 September 2026
Which? — Car seat weight groups and height groups explained — checked 10 September 2026
Beds, Luton and Milton Keynes children's health — Car seat safety — checked 10 September 2026
GOV.UK — Child car seats: the rules — checked 10 September 2026
Which? — Child car seat laws in the UK — checked 10 September 2026

This is information, not a guarantee of any payment, and not medical, legal or product-safety advice for your home. Prices and rules change; figures carry the date they were checked. Recall status comes from official records only — a product we cannot find is not a safety all-clear. Tell us if we got a fact wrong.