Guide To 2025 FSAE Frame Rule Changes
Keep these resources open during your team’s entire frame design process:
2025 FSAE Rulebook
2025 FSAE Structural Equivalency Spreadsheet (SES)
2024 FSAE Tech Inspection sheet
2025 suspension subteam geometry and loads
2025 ergo subteam packaging
2025 drivetrain subteam packaging
The Guide To 2024 Frame Rule Changes has details about even more rules. (Though some obviously change year to year.)
Per GR.4.5, teams need to follow the intent of the rules. The vast majority of rules are about safety, and we are not playing games. We try to write rules with no gray area. (This is impossible.) We try to write rules that everyone will understand perfectly. (This is impossible.) This year, we completely took apart and reassembled a couple of rules sections to try to make them easier to understand, even though the requirements are basically the same. Still, when all you have is the words, how are you supposed to know the intent? Think like an engineer.
How To Interpret Rules (As If There Are 100 Wildly Different Cars To Inspect)
Rule Changes Affecting All Teams
Ride Height And IA Height
These changes enforce height overlap between Impact Attenuators and impact structures.
V.1.4.2
Ride height from the ground to the lowest point of the Side Impact Structure must be <=90mm.
Ride height from the ground to the lowest point of the Side Impact Structure should be <75mm.
This rule is only about that point, not about other parts of the car.
This will affect about 10% of teams.
V.1.4.2.a
In tech inspection, with the tires on the ground, your team needs to be able to clearly, visibly measure ride height to the designated point on the chassis in about 30 seconds and +/-1mm ish. That is what we ultimately care about. Tape measure and/or calipers will be used. The minimum diameter for a top view opening is 5mm; no more than 25mm from the designated point on a non-level surface. If we can simply reach and see the measurement easily from the side or back, great. Access panels, permanent holes, plugs, etc are acceptable, maybe even a quick sidepod off, maybe another creative idea. But not sitting there for minutes while the floor comes off. We do not want to have to zoom in with a phone camera. T.5.5.4, which drains fluid to the ground, might or might not be able to serve a dual purpose here.
F.8.5.6
The bottom leading edge of the Impact Attenuator must be <=150mm above the lowest point of the lower Side Impact tube, measured from its TOP surface. So the functional limit above the location where ride height is measured is 150mm + 25mm (min lower tube allowance, even for monocoques) = 175mm. This will affect about 50% of teams. Flipping a standard foam IA from horizontal to vertical can make this really easy.
These numbers were established using two years of V.1.4.2 ride height measurement for every car in tech inspection. IA requirement must be lower than SIS requirement to account for the possible 0-90mm range of ride heights. We chose this approach, rather than measuring IA height from the ground, to avoid the edge case where a team with a ground scraping ride height and a max height IA (measured from ground) raises the car to accidentally make their IA height dangerous and illegal.
F.6.4.4.b
Upper SIS height is unchanged, but the measurement method is changed to the top edge:
Now the measurement works for tube frames, monocoques, rear impact
Gives the same height range to minimum and large diameter Upper Side Impact tubes.
The window no longer gets tighter for bent Upper SIde Impact tubes.
Triangulation For All Roll Hoop Bends
F.5.6.3
Triangulation is required for every bend below where the Hoop braces are attached, not just the bends below the Upper Side Impact. If a roll hoop is not straight between its brace and the Upper Side Impact, then structural tubes must be added in side view to reach the bends in between. The structural tubes may be on only one side of the roll hoop. And triangulation, per F.1.17, requires all structural tubes below that bend to form triangular openings.
The simplest approach, if there is only one roll hoop bend between the braces and the Upper Side Impact (or MHBS, or FBHS) is to run a tube from the bend to the nearest node on top of that other structure. A shoulder harness bar and shoulder harness braces do not accomplish this. The procedure is the same as 2024 F.5.6.3, now applied to all roll hoop bends.
T.2.4.5-6 Clipping Harnesses To Eyes
We really want you to wrap your shoulder harness. Wrapping anti-subs can also be a good solution on a straight-across Size B tube, as long as the floor is under the belt to protect from abrasion. Both of those approaches need to have lateral spacing controlled, typically with clamps or welded stops.
More harnesses are being supplied with clip ends. Clipping through sheet metal tabs is not appropriate. Eyebolts are typically supplied with the harness, or a bigger welded pad-eye would be an appropriate solution.
Take the eyebolt from the manufacturer, or one rated for the T.2.4.3.a load, and thread it into a welded insert that is perpendicular to the tube. Square tube: The insert can go straight in the side or the top depending on your belt spacing needs. Round tube: Even better if you can try to get it in plane with the belt. The belt will stop the eyebolt from unthreading, meeting T.8.3, but you still need to shim eyebolts so they are tight and aligned. Use some serious threadlocker too.
T.2.4.3-4 Bolting Harnesses To Tabs
With welded tabs assigned welded steel properties from the rules, you should generally expect that these will be thicker than what is probably high grade steel in the harness ends. Choose thicker rather than taller to keep the tab from rubbing on the belt, keeping offset to a practical minimum. It is also acceptable to through bolt harness ends through a welded insert, or blind thread them into welded inserts as with eyebolts above. Though a positive locking mechanism will need to be added in this case.
F.5.11 External Items
This revised section is only a little bit tougher than in the past. Everything but wings in this area has been the source of stress. We are aiming for clarity.
If something is attached on the side or the back of the car, below the height of the Upper Side Impact or other triangulated structure, we have to make sure it is not fuel or battery or HV or compressed gas. And we have to consider the effects on a corner worker or on another impacting car. But it is generally not a big deal. Even the bottom parts of the Main Hoop are not areas of much concern, though mounting at a node will avoid the concern entirely.
When something is attached above the rest of the chassis to the Main Hoop or Main Hoop braces, we freak out. These are the most important tubes on the chassis. They have one very hard job: Protect the driver in a rollover. NOTHING on the Main Hoop or Main Hoop Braces is how I want you to think.
I do not have the clout to enforce NOTHING mounted on the Main Hoop or Main Hoop Braces. I can’t even get rid of “just fail the fastener in shear and put a random brace under it,” F.5.11.2.b. Which helps the unfortunate team that has to weld at competition because they put their wing mounts or rockers in the middle of the Main Hoop Braces. Do not put suspension on the upper portions of the Main Hoop or Main Hoop Braces. Node, YES. Span, NO.
We accept that wings are going to be mounted to Main Hoop Braces and F.7.8 Main Hoop Brace Attachments. Wing mounting expectations are unchanged from 2020-present. When a mount has a single fastener at a Main Hoop Brace node, F.5.11.2.a, great, that is the best solution. That applies to any external item on the Main Hoop or Main Hoop Braces, so start designing your external camera mounts to go next to wing mounts right now.
Like the shoulder harness bar (which has one very hard job, F.6.5.3: 2024 “should”, 2025 “must”), there are a few things that are reasonable or permitted by other rules to attach to the Main Hoop and Main Hoop Braces without meeting F.5.11.2, like the head restraint, bodywork, lightweight intake manifolds, manual service disconnect, shutdown buttons.
Items inside the tubes, and you have zip ties or hose clamps holding them on? No problem. Some big pillow block? You will have to take it off. Your F.5.11.2 or .3 legal item: Don't put it up against the tube. Your throttle body and shutoff buttons? F.5.11.5 Move it away from the tube forward or rearward so it can’t get driven into the tube wall from the side view or the top. F.5.11.5 offset is not about the shadows from wings. Wings and endplates seem to be ~200+mm away from the tubes, which is plenty of offset of a different nature.
Motor and accumulator mounts are internal, yes, but work on running those mounts to nodes or other tubes. (F.5.11.4: 2025 “should”, 2026 “must”.)
Existing Policies Spelled Out
T.8.3.3
When the Positive Locking Mechanism is prevailing torque nuts or nutplates:
a. Locking fasteners must be in as new condition in Tech Inspection.
b. A supply of replacements must be presented in Tech Inspection, including any attachment method.
F.5.14.d
If your external steering protection is removable, just follow mono attachment procedures, including boxing tube mounts.
F.8.6.3.b
We want teams to continue working on moving pedal pivots off the base of the Front Bulkhead to another structure at least 25mm rearwards.
Rule Changes Affecting Monocoque Teams
As always, if you are stuck with legacy monocoque tooling that has issues with rules compliance, get in touch early in the process.
Front Hoop Lamination
We are going to start ramping up enforcement of the encapsulation. This is the laminate that runs from one skin, all the way around the hoop, and back to the original skin on the other side. The encapsulating laminate is the one that should be entered for equivalence.
Also, while expanding foam is prohibited for filling in the encapsulation, core splice would be acceptable.
Even after your SES is approved, please add manufacturing photos of your front hoop lamination to the SES and resubmit.
Existing Policy Spelled Out
F.4.3.2.g
Unidirectional plies must be enclosed by balanced plies. Unidirectional plies should not be the nearest plies to core material.
Designing For Adhesive Shear, Not Peel Strength
F.4.3.7.a
More than one smart team asked last year: If we bond one piece on two perpendicular faces, can we just use shear strength instead of peel strength? One plane will always be in shear. And we said yes, that is a great idea!
Insert Material
Per F.7.8.8, bolted attachment points with test loads (roll hoops, accumulator, AIP, removable rear impact, etc.) require either solid inserts or single thickness layup hardpoints with no core. Inserts provide extra local stiffness as a load path to prevent core crush and engage both skins in the pullout load. You can see that if you work through the SES math. Core material alone does not serve this function. Core alone could allow one skin to be loaded and failed in shear before loading the other skin, basically cutting the load rating of the attachment in half. We have done an initial review of materials. We expect all monocoque teams this year to work toward using inserts that are at least 4GPa modulus, 2.5MPa shear, and 12MPa compression strength. These minimums are effectively End Grain Balsa, but not the engineered balsas whose properties are half as much. We will work with teams and assess the information that comes in this year to write a proper rule for 2026.
Rule Changes Affecting IC Teams
Existing Policy Spelled Out
F.9.1.3
Portions of the fuel filler neck (IC.5.4) that are higher than the Upper SIS tube (F.6.4.4) may be outside the primary structure envelope (F.1.11).
We want the whole fuel system to be inside the envelope of the tubes. If sticking the filler neck out can’t be avoided, it is not allowed to exit the chassis until above Upper SIS height (exiting above the Upper MHBS as a functional equivalent is generally accepted.) Preferably with a flexible section to prevent the neck from compromising lower sections of the tank.
Rule Changes Affecting EV Teams
Size B Tubes For Accumulator Attachment
F.3.2.1.m
Not just accumulator protection, also accumulator attachment.
Existing Policy Spelled Out
F.11.4 Accumulator Clearance
Except for where the mounts attach the accumulator to the chassis, the intent is to allow up to 25mm of chassis deformation before contacting the accumulator. The concern is crushing cells inside the accumulator. So any part of the accumulator counts. And anything between the accumulator and chassis is subtracted from that distance.
“Should”: Make a good faith effort, we’ll make a good faith judgment.
HV Protection
HV side and rear protection is the same, just rewritten to match Front Bulkhead and FBHS for consistency. Changes to HV protection from 2024 to 2025 are:
Slight increase to align Rear Impact minimum height requirement, 240mm to 265mm
F.11.3.3 No more passes for upper rear impact way forward of the back of the chassis
More than one smart team asked: “Can we weld in two structural tubes where the diff mounts would be?” and we said “No problem,” and added F.11.3.4.b for everyone in 2025.
A couple of monocoques showed up in 2024 with rear impact perimeters and nothing in the middle. We didn’t have a diagonal rule then, but we do now. There are even more options than front impact for diagonal equivalence.
Important nuance, unchanged: The rear bulkhead does not have to be the rearmost part of the car. It just has to be behind any chassis-side HV components. There may be additional unregulated structure behind the rear bulkhead.
Accumulator Container
The accumulator container section was entirely reorganized for clarity. But the expectations are the same: Each battery segment enclosed in its own six sided box.
The only significant change, F.10.3.2, we really want you to mechanically attach your segments to the container. If those are sturdy enough, you can have way fewer attachments on your lid. And those attachments can be latches. Safety win meets operational win.
Segments
The 2024 SES started enforcing F.10.3.1 to make the segments sturdy. We want the structural cross section of the segments with no container. The segments make the container stiffer, not the other way around. So remove all cells, all non structural (wiring, etc.). Then sweep for the minimum structural cross section in top view (G92) side view (G95) front view (G98). The test load is (number of segments in {direction} * mass of segment * acceleration.) 2024 Comparison: UTS * cross sectional area. 2025 Comparison: We hope to build in some Euler Johnson buckling limits.
The only way to fail in 2024 was to have cells holding apart two unconnected sides of a segment structure. The plan is for 2025 to only be a little more difficult. And we do want the segment structures to play a role in holding each cell in place.
