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February 27, 2021, 07:34:07 PM

What constitutes a chassis or monocoque mod. re IVA.

This is a discussion for the topic What constitutes a chassis or monocoque mod. re IVA. on the board Beach Buggy IVA / SVA Help.

Author Topic: What constitutes a chassis or monocoque mod. re IVA.  (Read 751 times)

this user is offline Manxdavid

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Rediscovered on another forum a conversation between Kev Rooney of (the now defunct ACE) and the then VOSA re chassis and monocoque mods. Not strictly VW related I know but worth a read.

"ACE (Association of Car Enthusiasts)

VOSA have provided the following response to your questions;


Q) What is classed as chassis? Is it purely the outer longitudinal rails or are the crossmembers between these also a part of the chassis?

A) Chassis should be taken to include crossmembers.

Q) We know that cutting or shortening a chassis is classed as modification but is this relative to the vehicle wheelbase i.e. the chassis must remain uncut between the 2 axles but anything forward of front or aft of rear suspension mounts can be removed?

A) Chassis includes the full original length of the longitudinal members including to the front of the front axle and to the rear of the rear axle.

Q) Is it acceptable to remove bodymounts, which contribute no strength to the chassis when changing a body to a different style /make?

A) Yes, providing they are additional to and are not an integral part of the chassis structure.

Q) Is it acceptable to strengthen a chassis by the addition of boxing plates a process that involves turning a 3-sided open chassis rail into a fully enclosed 'box' chassis?

A) Yes, providing the original structure remains unchanged.


Q) What is the definition of a monococque ?

A) A design in which body and chassis are all one unit.

Q) Why does cutting into a monococque affect the vehicle identity if it retains the same shape /profile as before.

A) Cutting is considered to be modifying the vehicle from its original specification. Any modification to the chassis/monocoque body is considered to render the vehicle no longer original specification or of original identity.

Q) Is it acceptable to modify a vehicle bulkhead and/or transmission tunnel when performing an engine change or fitting another make?

A) No, Assuming this is in relation to a monocoque structure. This would be considered a modification to the structure.

Q) Is it acceptable to fully weld sections that are spot-welded as part of the original construction methods, to increase the strength of the body?

A) Yes, providing the original structure is retained.

ACE felt that further clarification was needed from VOSA so we sent more questions.

The following responses are from the VOSA Press Office:-

The answers to our chassied vehicle rules queries seem mainly straightforward, However, we have further questions based on the answers supplied.

Q) As chassis strengthening is allowed, are we correct in assuming that additional crossmembers would also be allowed?

A) It is important that the original chassis structure is retained unmodified, and while it is acceptable to strengthen areas and include additional brackets or crossmembers, It would be limited to additions within the existing chassis frame structure. Additional chassis structures, i.e. extending the outward parameters of the original chassis structure would be considered a modification.

Q) It is the monococque rules that need the most clarification.
Your reply states that any cutting of the monococque" is considered to render the vehicle identity no longer original specification or of original identity ". This would suggest that any crash repairs necessitating cutting and removal of panels or chassis sections, or restoration work would call the vehicle's identity into question?

We presume that the point should really be that any cutting... other than in factory designed joining areas...would be the actual criteria?

A) In this respect it is necessary to differentiate between modification and repair. Any repair process that is in line with manufacturer's recommendations and that returns the structure to its original specification would not be considered to be a modification.

Q) Would the modification of wings to allow clearance for larger wheels fall foul of the regulations?

We presume not as the common fitment of sunroofs does not create issues as this is a non stressed item of the monococque, the same as wings?"

A) When considering a monocoque structure, it is necessary to consider what constitutes cosmetic panels that do not significantly add to the structural strength and which panels provide structural integrity. In general front wings modified in this way would not constitute a modification to the monocoque structure.

With reference to the further query, VOSA have advised that they would prefer the following statement:

What constitutes a monocoque is that of how an OEM manufacturer would view it. The chassis or `cage` assembly and all components that form it, less any cosmetic panels or infills that make no structural consideration to the monocoque or its component parts.
However, we must emphasis that this information is given for general guidance and each case will be judged on its merits.

Whilst none of this is definitive, and it contains the usual 'Judged on it's own merits' criteria, it does answer a lot of questions where the modifier has only been able to speculate in the past.

It means we are aware of what we can or cannot do and still retain the 5 points from the start of any modification process.

So, to summarise the above information:


It is acceptable to box original chassis and also to add additional crossmembers but not to alter the existing chassis in any way to allow for their installation.

It is acceptable to remove NON STRUCTURAL body mounts and engine / gearbox mounts.

It is NOT acceptable to shorten, or lengthen the chassis, either in between standard suspension points or fore and aft of these.

Any additional items welded creating a longer overall chassis are classed as modifications. It would however be acceptable to bolt a reasonably sized additional subframe to existing mounting holes.

Any outriggers (as opposed to continuous chassis frame) fore or aft from the chassis would need clarification from VOSA as to their purpose before removal or alteration was accepted. This would be based on their purpose and whether they formed part of the vehicles original Type Approval.


It is NOT acceptable for the bulkhead, or transmission tunnel area, to be modified.

The specification for a monococque will vary with each manufacturer and the decision on what are acceptable modifications will be based on those criteria for each vehicle.

It is acceptable for additional seam welding to be carried out.

Should there be any further questions relating the above information on specific vehicles ACE would be willing to assist in further clarification on an individual basis.

The above information relates to only 5 points (awarded for original unmodified chassis / monococque) of the 8 points system for retaining vehicle identity and we will be clarifying other sections in the future."

I remembered VW floors being mentioned in a following discussion so I asked Kev, his response:

"... seeing as I wrote it I can confirm that a Beetle floorpan needs pans as well to be considered original, a backbone alone is not enough."

I'll have the original correspondence here as well...somewhere.
« Last Edit: July 15, 2018, 05:32:18 PM by Manxdavid »
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