Two Giro helmets with the same rotational protection and a different approach to fit. The honest difference is sizing and ventilation, not safety, and one of those decides it before you order.
Buy the Isode MIPS II for a first helmet, and the Agilis MIPS only if you already know your head circumference and ride in heat. Both carry MIPS, both are from the same bike-specific brand, and neither listing publishes a vent count or a weight. The real difference is fit: the Isode is a universal adult shell with a dial, so it adjusts to your head after it arrives. The Agilis is sized, which fits better when you get the size right and is a return when you do not.
The ventilation gap is real but it is a comfort gap, not a safety gap. Every bike helmet sold in the United States has to meet the federal standard the CPSC enforces, which is why “which of these is safer” is the wrong question and “which of these will you actually wear” is the right one. If budget is the whole constraint, the Bell Revolution MIPS is the floor worth standing on.
How this is funded: we earn a commission if you buy through our links, at no extra cost to you. It never changes which bike we recommend, and we will tell you plainly when we would skip one. Full disclosure.
Quick picks
Ranked on published specs, what the listing does and does not tell you, and who each one actually suits. Select a row to jump to the full write-up. We have not ridden these — here is exactly what we do instead.
#
Bike or gear
Best for
Price
1
Giro Isode MIPS II
The default first helmet: a real cycling brand, MIPS rotational protection, and a universal-fit dial that means you do not have to guess your head size before you buy.
A proper road helmet in real sizes rather than universal fit — cooler, lighter-feeling and better shaped than the Isode, for a meaningful step up in price.
The cheapest MIPS helmet from a major bike brand. If budget is the constraint, this is where the line is — below this, you are giving up rotational protection to save very little.
The default first helmet: a real cycling brand, MIPS rotational protection, and a universal-fit dial that means you do not have to guess your head size before you buy.
Who it is for: Your first helmet, if you want one decision made properly and then forgotten.
What is good
+MIPS — a slip layer inside the helmet designed to reduce rotational force in an angled impact
+Universal adult fit with a dial, so it adjusts rather than needing a size guess
+Giro is a bike-specific brand, not a generic sporting-goods label
What you give up
−Fewer vents than Giro's more expensive road helmets, so it runs warmer in summer
−Universal sizing is a compromise; very small or very large heads fit better in a sized helmet
Skip this if. Skip this if you ride mostly in hot weather or plan to do long, hard climbs. Ventilation is the thing you notice at low speed going uphill, and the Agilis is meaningfully better at it.
Published specifications for the Giro Isode MIPS II
Rotational protection
MIPS
Sizing
Universal adult
Vents
Not published
Weight
Not published
Safety certification
Not published
Specifications read from the retailer listing on July 23, 2026. “Not published” means the listing does not state that figure — we do not estimate it.
#2Best for heat and long rides
Giro Agilis MIPS
A proper road helmet in real sizes rather than universal fit — cooler, lighter-feeling and better shaped than the Isode, for a meaningful step up in price.
Who it is for: Hot weather, long rides, or a head that universal sizing does not suit.
What is good
+Sized (Medium here) rather than universal, which fits better and moves less
+Designed as a road helmet, so ventilation is the priority
+MIPS rotational protection, same as the Isode
What you give up
−Costs roughly half again as much as the Isode
−You need to know your head circumference before ordering
−Stock in any given size and color runs thin
Skip this if. Skip this if you are buying a first helmet and do not yet know your head measurement. A universal-fit Isode you can actually adjust beats a sized helmet in the wrong size, every time.
Published specifications for the Giro Agilis MIPS
Rotational protection
MIPS
Sizing
Medium (sized, not universal)
Vents
Not published
Weight
Not published
Safety certification
Not published
Specifications read from the retailer listing on July 23, 2026. “Not published” means the listing does not state that figure — we do not estimate it.
#3Smallest sensible spend
Bell Revolution MIPS
The cheapest MIPS helmet from a major bike brand. If budget is the constraint, this is where the line is — below this, you are giving up rotational protection to save very little.
Who it is for: The smallest sensible spend on a helmet.
What is good
+MIPS at roughly a third the price of a mid-range road helmet
+Bell is one of the oldest names in bike helmets, not a generic label
+Adult sizing covers most heads
What you give up
−Heavier and warmer than a dedicated road helmet
−No published weight or vent count
−Styling is recreational rather than road
Skip this if. Skip this if you will be riding in summer heat for hours at a time. It is a perfectly good helmet; it is just built for commuting and short rides, and you will feel that on a long climb in July.
Published specifications for the Bell Revolution MIPS
Rotational protection
MIPS
Sizing
Adult (14+ years)
Vents
Not published
Weight
Not published
Safety certification
Not published
Specifications read from the retailer listing on July 23, 2026. “Not published” means the listing does not state that figure — we do not estimate it.
The three helmets, from the listings
Read straight from the listings recorded in each product’s entry above. The bottom three rows are the honest part: not one of these listings publishes a vent count, a weight or the certification it meets, and those are the three figures a buyer comparing helmets would most like to have.
Giro Isode MIPS II
Giro Agilis MIPS
Bell Revolution MIPS
Rotational protection
MIPS
MIPS
MIPS
Sizing
Universal adult, dial adjuster
Sized (Medium on this listing)
Adult (14+ years)
Designed as
Everyday road and recreational
Road helmet, ventilation first
Recreational and commuting
Do you need your head measurement?
No
Yes, before ordering
No
Vent count
Not published
Not published
Not published
Weight
Not published
Not published
Not published
Certification printed on the listing
Not published
Not published
Not published
The decision is sizing, and it happens before you order
A universal-fit helmet has one shell and a dial that takes up the slack. A sized helmet has a shell shaped for a range of head circumferences, so it sits lower and moves less — when you buy the right size. The Agilis listing here is a Medium, which means you need to have put a tape measure around your head, just above the ears, before you click buy.
That is a two-minute job and our helmet-fitting guide walks through it along with the rest of the fit check: level on the head, two fingers above the eyebrows, straps forming a V under the ears, and a chin strap you can get one finger under and no more. A helmet that fails that check protects you less, regardless of which of these three it is.
Ventilation: the gap that is real and is not published
Giro designed the Agilis as a road helmet, which in manufacturer language means ventilation and low weight are the priorities. The Isode has fewer vents and runs warmer. We can tell you that is the design intent — neither listing publishes a vent count or an airflow figure, so we cannot tell you by how much, and we are not going to invent a number to fill the gap.
Where you feel it is going uphill slowly in summer, because that is when your own speed stops moving air through the shell. If most of your riding is an hour on flat roads in spring and autumn, the difference will not be the thing you notice. If you are climbing in July, it is. Our hot-weather kit page makes the same argument across the rest of the kit list.
Road, commuter or mountain shell?
Manufacturers do split helmets into categories, and Trek publish their own descriptions: road helmets are built as light as possible and prioritize ventilation and aerodynamics, mountain helmets generally add a visor and extend further down the back of the head, and commuter helmets borrow from both. The CPSC publish guidance on matching helmet type to activity for the same reason.
On this page: the Agilis is the road shell, the Isode and the Bell sit in the everyday-and-commuting space. None of that changes the certification each has to meet to be sold. Road versus mountain helmets is the full version of that comparison if you are deciding between shapes rather than between these two models.
What we would buy
First helmet, no measurement taken, wants one decision made and then forgotten: the Isode. It is a real bike brand with MIPS and a dial, and the universal fit removes the one way this purchase goes wrong by post.
Already owns a helmet, rides long in warm weather, knows the measurement: the Agilis, in the right size, accepting that stock in any given size and color runs thin. Tightest possible budget: the Bell Revolution, because below a MIPS helmet from a major brand you are giving up rotational protection to save very little.
One rule that applies to all three: a helmet that has taken a real impact is finished, even if it looks fine. The foam works by crushing, and crushed foam does not come back. Budget for the replacement rather than inspecting it hopefully. The full helmet shortlist covers the cheaper and the sized options either side of these three.
We have not ridden these bikes. Every site in this category says it tested twenty of them. We have not tested any, and we say so. What we did instead: read the manufacturer listings and manuals, compiled the published specs, worked out the real out-the-door cost, and checked live availability and price. Here is exactly how that works.
Questions people actually ask
Is the Giro Agilis worth the extra over the Isode?+
If you know your head measurement and ride in heat or on long climbs, yes — a sized road helmet fits better and ventilates better by design. If this is a first helmet and you have not measured your head, no: a universal-fit Isode you can adjust beats a sized helmet in the wrong size every time.
Is the Isode or Agilis safer?+
Neither listing publishes its certification, but every bike helmet sold in the United States must meet the federal CPSC standard, and both of these carry MIPS. Treat the choice as fit and ventilation rather than protection — and remember a correctly fitted cheaper helmet outperforms an expensive one worn loose.
How do I know what size helmet I need?+
Measure the circumference of your head with a soft tape, roughly an inch above your eyebrows, and compare it to the size chart on the listing. Universal-fit helmets like the Isode and the Bell skip that step, which is the main reason we recommend them for a first purchase.
Does MIPS actually do anything?+
Mips publish the mechanism: a low-friction layer that lets the shell move slightly relative to the head, intended to reduce rotational motion in an angled impact. We have not tested helmets and will not claim a figure. What we will say is that MIPS now costs very little extra, which makes skipping it hard to justify.
How many vents do these helmets have?+
Neither Giro listing publishes a vent count, and nor does the Bell. We report that rather than count the holes in a product photo. What is published is design intent: the Agilis is built as a road helmet, where ventilation is the priority.
When should I replace a bike helmet?+
After any real impact, immediately — the protective foam works by crushing and does not recover. Otherwise, when the straps, buckle or retention dial stop holding it in the position a fit check requires.
Is a more expensive helmet more comfortable?+
Usually it is lighter and better ventilated, which reads as comfort on a long ride in warm weather. On a short commute in cool air, most people cannot tell the difference, which is why we would rather see a beginner spend the gap on shorts or a rear light.
Sources
Specifications come from the manufacturer or the retailer listing, dated. Where a figure is not published, we say so rather than estimating it.
Trek — Types of bike helmets explained — A manufacturer's own category descriptions: mountain bike helmets generally have a visor and extend further down the back of the head; road helmets are as light as possible and prioritize ventilation and aerodynamics; commuter helmets borrow features from both (accessed September 18, 2026)
