2017/18 Preliminary Rules

[Mitchell]

http://www.fsaeonline.com/page.aspx?pageid=a9aedcb6-c965-4c34-a02f-625a6ec5c89f

The 2017/18 rules were released a little while ago for comment. Comments were closed on April 24th. Some interesting proposals with the main points:

- Engine capacity increased to 710cc

- Points restructured:
Static Events:
Presentation 75
Engineering Design 200 (+50)
Cost Analysis 100
Dynamic Events
Acceleration 100 (+25)
Skid-Pad 75 (+25)
Autocross 125 (-25)
Efficiency 100
Endurance 225 (-75)
Total Points 1,000

-Footwell Template tweaked slightly (325x300 instead of 350x350)

Maybe some other minor changes, SAE didn't bother giving a summary at the start of the document.

[Mitchell]

My thoughts are, none of these are game changers. A few more engines become appealing but power stays the same (why not remove the redundant capacity limit completely?).

More points for skid/accel as dynamic events are great, taking the focus off incredible drivers. More points for design, not so great as it's fairly subjective.

How/if these changes will be adopted globally will be interesting to see.

[Z]

- Points restructured:
...
Engineering Design 200 (+50)
...
Endurance 225 (-75)
...

-Footwell Template tweaked slightly (325x300 instead of 350x350)...

I foresee an explosion in the numbers of "Mini-F1" cars turning up, that are incapable of "...driving 30 kms at average speed of 55 kph...".

And many frustrated students, who build a cracker of a fast and reliable car, but are heavily penalised because of the subjective (and often bizarre!) biases of the DJs.

These points-changes are clearly for the benefit of the DJs, NOT for the better education of the students.
~o0o~

Footwell template should be TWO x ~350 mm x 150 mm templates, one for each foot. That would enable a very effective Front-Engine-Front-Drive car!!! :D

Picture a 4WD ATV/Quad-bike, with the rear-drive removed, driver sitting much lower, with engine between their legs and feet on front-axle-line. Big, fat, slicks on front, skinnies on rear, and extremely simple rear-end. With MASSIVELY EFFECTIVE AERO-DF possible, given current Rules.

And much useful learning to be had, given vast majority of production cars nowadays are FEFD.

Z

[mech5496]

Relatively small changes. Engine capacity increase is a good thing, opens up options. Marginally smaller template could free up some more space for front wings. +25 points for accel will most likely push more e-teams to 4WD...maybe.

[Will M]

I agree, no major impact.
Though the smaller template will reduce some headaches.
And having the option to run the engine out of something like a Honda TRX700XX is nice (686cc, factory EFI and drysump).


@Z

Funny you would mention a front engine design.
Several years ago we mocked up a Front-Engine-Rear-Drive car.
Our goal was to experiment to find designs with more rear weight distribution.
(the idea may have been one big rear wing, but this is 5+ years ago)
Anyway, we found that a FERD set up could have much more rear bias than our 'traditional' mid engine set up.
This was because our drivers fully suited up are often heavier than our engine (most of our drivers were over 6 feet tall)
And the engine needed to be fully in front of the rear axle while the driver conceptually could sit right on it or even slightly behind it!

The thought experiment did not get an farther, but it would be interesting to see a broader range of designs.

-William

[Dunk Mckay]

Smaller foot-well template is probably most significant change, as far as car design is concerned.

Agree with Mitchell that engine size limit is redundant, but it's a step in the right direction, especially for those teams in locations that struggle to get smaller engines.

More points focus on skid pad and acceleration is good, although some competitions have already elected to make changes like these themselves. I'd like to see this accompanied by the allowance of a third driver, or additional runs to further minimise the effect of driver skill and chance, to focus purely on the car. With a fast track queue for team's doing their first, and after half time second runs, this could work well.

Moving points to design event is only worth doing if they also overhaul the scoring system used, to make it less subjective.
Back in 2011 we went from 114 at one competition (FSUK) to 50 at another 3 weeks later (FSG). Scaled up to the new proposal that's over 85 points purely down to DJ subjectivity! You could consistently score 10% better in all dynamic events than another team, and still lose to them because a judge decided they liked their car more than yours, even though yours consistently proved itself to be better.
I know this has been discussed to death, and nothing said on here is going to change anything. But I think a bit of transparency as to how teams are scored in design judging would go a long way. If the rulebook included a fixed template for the points breakdown, and the completed forms had to be made available (digitally at least) when the event scores are published. At least to give an explanation. Mark downs should be due to: "they made the wrong engineering decision based on their objectives because XYZ"; and not "I didn't like their design, it wasn't as pretty as other teams, so there."

[Kevin Hayward]

With the increase of engine capacity, increase in Accel points, combined with the previous change in charging setup we have seen a pretty dramatic shift in the rules towards engine development. I wouldn't say this is on the same level as what happened when the big wings / sharp trailing edges were allowed, but still notable.

I think this is a great thing for the comp. The earlier increase in economy (then efficiency) broke the fine balance between the small singles and more powerful cars, making it pretty clear what was the best way to go. This change opens up a lot of new engine possibilities that were just outside the 600cc limit, including big singles and twins. This will make it fascinating.

Not a fan of the change to the design points, given the subjectivity involved. I think we really need to see more sharing of what constitutes a good design presentation. Something like how we can all see the best marketing presentations from FS Germany. Release the top 3 design reports from each comp? If we are focused on this as an educational activity then lets share the knowledge a little more.

I think the drop in the Endurance points is going too far. In fact I think the multiplier for TMax should be increased. There should always be a huge bonus to teams that finish that event. Failing to finish 22km is pretty damning of your team's design and there should be no possibility of your car being up amongst the top 10-20% if you are unable to complete the design brief.

Template rule change is a good one. Hopefully if these rules are tweaked a little more we may see some return to teams having to make real decisions involving chassis packaging and ergonomics.

Allowing some of the aero in the exclusion zone needlessly complicates already overly complex rules (with terrible diagrams), for minimal performance change. This shouldn't have been done.

All up I think the increase of design options offered by the engine changes make it interesting enough that I am excited about what we may see over the next few years in increased variety.

I award these rule changes a grade of 67% (a little better than average) ;)

Kev

[Jay Lawrence]

Yeah nuking endurance (100% objective) in favour of design (pretty much 100% subjective) seems like a terrible idea

[apalrd]

Not a fan of the change to the design points, given the subjectivity involved. I think we really need to see more sharing of what constitutes a good design presentation. Something like how we can all see the best marketing presentations from FS Germany. Release the top 3 design reports from each comp? If we are focused on this as an educational activity then lets share the knowledge a little more.


Why don't we release all of the design reports? The SAE Clean Snowmobile Challenge releases all of the team's design reports and PDFs of their powerpoint 'design' presentation online after the competition.

[JulianH]

Why don't we release all of the design reports? The SAE Clean Snowmobile Challenge releases all of the team's design reports and PDFs of their powerpoint 'design' presentation online after the competition.

I think this is a great idea.

The Design Reports I got to read at FS Austria (I still think FSA 2014 was one of the best "fields" ever) were really really bad for a lot of teams (even the ones with great cars).
I think teams can learn a lot from the GFRs, Delfts and Zurichs of writting design reports...

[MCoach]

Having participated in Clean Snowmobile with Andrew, there are some downsides that come from being able to see everyone's reports.

You find some neat tricks within the rules, whether it may be a favorable scoring factor towards engine choice, costing methods, design components, etc. and people can openly analyze your methods....or blatantly copy them.
Every entry becomes an open book. I agree that teams could learn a lot from the top teams, but there is a risk that needs to be managed (preferably by the teams, themselves) of making good/bad decisions and not understanding why these things work or issues to look out for.

We brought a turbo ACE 600 to snowmobile competition in 2013, placing 2nd. The year after that 4 of these concepts were entered into the competition (3 showed up) running the same turbo and components from our design paper and cost documentation and placed 1,3,4 (of gasoline engines). In 2015, the concept went 1,2,3.
All teams had some issues with controlling knock from the engines, some learned how to manage it along with the other quirks that come with boosted, alternative fueled vehicles. The other end of this that one of the vehicle that rounded up the bottom was also a turbo ACE 600s, troubled by engine issues and controls.

Another thing that happened is that ETS found some questionable costing methods that became pretty commonplace by 2016 before the costing judges shut that down. They found something neat and everyone being able to see followed suit pretty quickly.

Just an alternative perspective from a similar world.

[JulianH]

Having participated in Clean Snowmobile with Andrew, there are some downsides that come from being able to see everyone's reports.

You find some neat tricks within the rules, whether it may be a favorable scoring factor towards engine choice, costing methods, design components, etc. and people can openly analyze your methods....or blatantly copy them.
Every entry becomes an open book. I agree that teams could learn a lot from the top teams, but there is a risk that needs to be managed (preferably by the teams, themselves) of making good/bad decisions and not understanding why these things work or issues to look out for.

We brought a turbo ACE 600 to snowmobile competition in 2013, placing 2nd. The year after that 4 of these concepts were entered into the competition (3 showed up) running the same turbo and components from our design paper and cost documentation and placed 1,3,4 (of gasoline engines). In 2015, the concept went 1,2,3.
All teams had some issues with controlling knock from the engines, some learned how to manage it along with the other quirks that come with boosted, alternative fueled vehicles. The other end of this that one of the vehicle that rounded up the bottom was also a turbo ACE 600s, troubled by engine issues and controls.

Another thing that happened is that ETS found some questionable costing methods that became pretty commonplace by 2016 before the costing judges shut that down. They found something neat and everyone being able to see followed suit pretty quickly.

Just an alternative perspective from a similar world.

You have a point.

Copying is potentially a bigger problem, but I don't know if the Report itself creates that. I mean you can walk to the cars of the other teams and LOOK what they are doing. At most events you can attend other teams design events and photograph their posters (a Chinese team videotaped our design event in 2013 at FSG...), or just talk to people.

If a "cheating" costing method is found, I think this loophole should be fixed from year to year. I have seen Cost reports where the core material of the wings was bought as a block and was not milled or cut so it was super cheap. Nobody noticed.

I don't like the secrecy in FSAE.
A couple of examples:
The tires that GFR uses in Wetpad. They scratched of where they are coming from to prevent others from using them.
The strange differential of Rennteam Stuttgart 2014. When asked they replied with "we decided as a team that we will not discuss it".

Every team of course can decide what they are doing and what they are telling others. I also agree that every team should have some "tricks", be it a special manufacturing process for CFRP parts or whatever, but I think in an environment where everyone should be able to learn as much as possible, QUESTIONS should be answered by the teams, if others ask politely... Maybe that is just my rose-coloured glasses which drove my into management consulting ;)

[MCoach]

Yes, and it's just a simple point. I agree that this information should be openly shared, for the sake of learning.
Secrecy belongs to companies and teams that fiercely fight each other for market share and podiums, shouldn't be that way in FSAE. Unfortunately, a lot of sponsorship money rides on some teams performances. Some are told "You cannot register for other competitions unless you place top 10 at Michigan" by their advisors.

One part of that story is that the ACE itself has become a pretty dominant engine for the competition. So, moving to the engine itself wasn't exactly a difficult choice for anyone in the last few years.
ETS's method for costing for the competition wasn't exactly illegal due to how open the rules are for that competition, but it posed a favorable environment for teams from Canada. Currency wasn't normalized for their rules so any receipts/quotes from a Canadian supplier became 15-25% cheaper.


I've seen GFR use grooved LC0s for wet skidpad and their attempt (engine didn't start) at 2013 FSAE-Michigan in the past few years. The one's I've seen just have the Hoosier "Wet" groove pattern in them. Can't say if this is the same for the European events.

Again, I agree with you. I just wanted to pose a scenario.

[Kevin Hayward]

What is wrong with copying?

Human advancement is built on copying and modifying.

Life itself is built on copying and modifying. Take out the copying and it all stops, take out the modifying and nothing gets better.

The best way to ensure that the field keeps improving is to allow it to copy the best. It is the mutations (sorry I mean modifications) that will lead to the best becoming second rate in a few seasons. The only sadness there is for those that jealously guard information in the hope that they can hold a competitive advantage at the expense of the fitness of the population (sorry I mean competition).

Even for the top teams it is a completely ludicrous position to hold. If we imagine that this information is shared from 500 teams around the world. Not wanting this shared keeps your information from getting out, but it also prevents the information from 499 teams coming in. If it was a two team competition it makes some sense given the information you receive is likely less valuable than what you gave. However even if 99% of the information you get from the 499 teams is not worth receiving you gain more from the 1% you get back than what you gave out.

And just before I get accused of this encouraging non-competition I want to ensure you nothing could be further from the truth. If we look at the evolutionary process we see the following steps:

1. Start with a population

2. Select the highest performing members of the population

3. Copy the best performing members of the population and modify through mutation (and possibly combination) to create a new population

4. Return to step 2


Take away the competition and there is no improvement. Take away copying and the process stops. Take away new information (i.e. mutation) and all long term improvement is halted. It should be noted that this process works incredibly well both in real life and simulated.

Pretty simple approach to trying to promote the best ultimate solutions are as follows:

- Develop an appropriate selection method / competition
- Promote the sharing of information (copying / combination)
- Promote new information (mutation / innovation)

If you want to know more go and have a good look into the field of evolutionary computation, or speak to a farmer, or start breeding guppies.

Cheers,

Kev

[JulianH]

I've seen GFR use grooved LC0s for wet skidpad and their attempt (engine didn't start) at 2013 FSAE-Michigan in the past few years. The one's I've seen just have the Hoosier "Wet" groove pattern in them. Can't say if this is the same for the European events.

Again, I agree with you. I just wanted to pose a scenario.

They ran 13inch the last 2 years.
http://media.formulastudent.de/FSG15/Hockenheim-2015/Skidpad/i-XzDLwZ6/0/X3/20150731_17-53-32_7802_scheuplein-X3.jpg

Could be a regular R25B 13inch cutted or a WET, don't know. Probably found something good ;)

[JT A.]

Here's an example of how sharing design reports could be used to a positive or negative effect on the competition. Lets say that a team that does very well in design has some engineering approach to selecting spring and damping rates. Maybe it involves collecting track data, doing some FFT analysis to see what frequencies most of your suspension movement is occurring at, using a 1/4 car suspension model to minimize tire load variation. Or maybe it involves some kind of weighted compromise between tire load variation and aerodynamic platform control. So their design report describes the process they used, and they came up with 3.4Hz ride frequencies with 1.1 damping ratio.

If design reports get published, some teams will read that and think "that's an interesting approach, lets try that and see what we come up with, or see if we can test/validate/improve that methodology. Students learn, the competition gets better, sharing design reports has served a good purpose.

Other teams will read the best team's design report and say "Team X runs 3.4hz ride frequency, 1.1 damping ratio, that's what we're going to do too."

The teams that use the published design reports "the right way" to learn more makes it worth doing. Even if some teams use it "the wrong way" and just copy. The teams that are coming up with good designs and design processes will feel like they are losing an advantage by giving that info to other teams. I think it falls on the design judges to sort out who are the good engineers and who are the copy-cats, and score them appropriately. If they can do that fairly and consistently, the teams that do the best engineering still keep some advantage, but the rest of the teams will be stronger and more competitive. Overall a net positive.

[mech5496]

Agree with the open everything concept as well. Speaking of fuel efficiency (mentioned on previous page), I cannot see why a fuel flow limit is not imposed instead of an air restrictor; this would push teams in pursuing more efficiency out of their engines

[Charles Kaneb]

Cole,

Half of the Texas A&M Racing Secrets are in Neil's book, the other half are distributed with Claude's seminar!

-CPK

[Claude Rouelle]

I have seen a few good and even a few excellent cars in FSAE/FS and I have a few good memorizes of the science, logic, and the clarity, the rationality, the objectivity, (and the enthusiasm!) that was used by some students to defend their car design choice, simulation, drawing, assembly, testing and validations phases.
Some of them were able to come back to me with sound counter-arguments when I purposely disagree with them.
A design judge disagreeing can be a bad sign because the car is not so nicely designed or executed or, worse, the students have no validation at all.
Or it can be a good sign because the design judge pushes to know how deep the students’ knowledge is.
When, after having covered the basics, a design judge is asking very detailed and picky questions the students should look at it as a sign they are doing well.

But here is my point: I have seen good car and have listen to good arguments but I never saw a design report that knocked my socks off.

Some reports are really bad (often they come from teams who do not really care), some are average.
Some are good (these are the ones that excites my curiosity, that makes me want to see the car closer and engage in a good engineering conversation)
But I never saw an amazing design report.

I guess one of the reasons of this is that it is difficult to show all your knowledge, know-how and accomplishment in just an 8 page report, let alone several weeks before the competition.


So here is an idea.
In the same spirit as the business review, why don’t we have each of the top 3 design finalists going on stage for let’s say 50 minutes.
25 minutes to make a power point presentation with video, graphs whatever, simulation, data analysis, whatever they need (but it must remain an engineering presentation, it can’t be a long marketing video)
of the how / why/ how much of their design choices and test validation and 25 minutes of Q&A from the students.

Maybe the questions should be only asked by students of any other teams.
The design judges would attend but would not ask any question.
The design judges would afterwards use their appreciation of how each team did defend their car design and how they were able to defend their choice in public during the Q&A as one of the criteria (but not the only one - the usual design judging process will still go on) to determine who the design winner is.

[turtle]

So here is an idea.
In the same spirit as the business review, why don’t we have each of the top 3 design finalists going on stage for let’s say 50 minutes.
25 minutes to make a power point presentation with video, graphs whatever, simulation, data analysis, whatever they need (but it must remain an engineering presentation, it can’t be a long marketing video)
of the how / why/ how much of their design choices and test validation and 25 minutes of Q&A from the students.


This is a fresh idea that I think is worth entertaining. Taking the top 3 design finalists represents 2.5% of the total number of entrants at Michigan, but lets start somewhere. Here are some reasons why I think this might be an interesting change.

The design review is not very informative. The design review at the end of the competition is supposed to explain to students why a team won the event, but the message gets condensed to the simulate/test/validate motto. After several years of hearing this, I am sure there are frustrated students who just are not figuring out exactly what this means. Instead of telling the students why they won design, just show them why!
Technical communication is a design consideration. The industry is filled with engineers of all disciplines, and lets not forget that other professions exist as well. The ability to communicate and justify decisions to a wider audience is a life skill. Students must show that they can not only demonstrate depth, but breadth of knowledge and the ability to convey it to others. Design finalists will have incentive to present their best content if some points are allocated for the presentation.
Students can be leaders in the competition. Presenting as a design finalist sets the benchmark for everyone and reduces the mystery of the design event. Students will show students what makes a good FSAE car. The design event is no longer about pleasing an impossible design judge but rather improving and learning as a student.

Hopefully you end up with three unique presentations highlighting three different concepts. The goal here is to open the design event for students to see. What might be satisfactory for a design judge might be the biggest revelation for a student.

OK this doesn't address the concerns about subjectivity in the design judging or the copying problem, but lets start somewhere.

Using Kevin Hayward's notion of the genetic algorithm, lets consider FSAE as a search problem. Some questions to ask when considering a rule changes: Is the competition in a minima and is this global minima? Do we want to encourage or discourage the use of greedy algorithms? Is there sufficient diversity within the population? How will the change influence the search?

[Kevin Hayward]

Turtle,

It is nice to see some of the right questions being asked when approaching this as an optimisation problem.

I would posit that the changing environment (i.e. rules and condition changes between comps) rules out a static location of minima.

An argument could also be made that the selection process is not deterministic, the fittest x team/cars are not always the top x team/cars at comp.

I also think that our human idea of randomness (usually a uniform distribution) is not what we should expect. It doesn't matter if large proportion of a population are incredibly similar, and we should expect this. At any given time the FS field should have a lot of common traits, and we would expect when new successful information enters the population that other teams will absorb it quite rapidly. What would help in the long run is some ability to encourage the creation of new information. There are plenty of ways to achieve this algorithmically, and good ways to do it in practice in FS, especially given that points can be directly given for innovation.

...

Claude,

I wouldn't expect to see an amazing design report any time soon. I have been involved in FS since 2001, both as a student and as a Faculty advisor (Including 4 design event wins, and a number of placings). In that time there has been almost no feedback given to the teams I have been involved with as to the structure and quality of the design report. There have been exceptions including from you in Oz 2012, and Pat's advice to improve drawings (given to all teams).

Without a decent feedback mechanism there is little possibility for teams to significantly improve their reports.

I know of a few teams trying to share some information here, including the team I advise. On ECU's facebook page the team has released 3 past design reports, the most recent being 2012 (A report you provided some feedback on). These posts have been the amongst the best viewed posts the team has put up.

Our students would love to have a better insight into the processes other teams use in the design of their vehicles. However apart from a few teams that release good reports, or are quite willing to share (i.e. GFR, Monash, UQ, and others). This seems like such a small amount of available information for decades of work conducted largely at the expense of publicly funded institutions.

If teams are so against releasing the top of a given year how about releasing all reports 2-3 years after a given competition has ended? (Although I like your idea as well)

Heck we could treat it like most information developed at universities, and put it behind a paywall, that in no way benefits the authors. At least the information would be available.

Kev

[Will M]

Out of curiosity did anyone here submit comments?
I learned that the preliminary rules were posted from this thread and the survey was already closed.

-William

[JT A.]

In that time there has been almost no feedback given to the teams I have been involved with as to the structure and quality of the design report.

Kev

In my 4 years of doing FSAE we only got feedback on one of our design reports. One judge said it was the best of the whole competition, another judge didn't like it. Go figure...

[eric922]

So it looks like they decided not to shrink the footwell template in the official rules release? The only change in that section of rules is the exclusion of a line of text.

Correct me if I'm mistaken.

[FrederikWe]

Does somebody have information why the minimum amount of bolts for the IAA attachment will be changed from 4 to 8? Where there any incidents in the past?

[Mitchell]

So it looks like they decided not to shrink the footwell template in the official rules release? The only change in that section of rules is the exclusion of a line of text.

Correct me if I'm mistaken.

It does look like they might have made a mistake there. It mentions Section T4.2 as a "Notable Change" but it seems unchanged.

Besides the removal of the completely redundant 2016 point:
"T4.2.4 Teams whose cars do not comply with T4.1.1 or T4.2.1 will not be given a Technical Inspection Sticker and will NOT be allowed to compete in the dynamic events."


Does somebody have information why the minimum amount of bolts for the IAA attachment will be changed from 4 to 8? Where there any incidents in the past?

This is unlucky for the teams who don't weld the IA plate on. Don't stress though, welding was already the lighter solution when it was 4 bolts.

[FrederikWe]

This is unlucky for the teams who don't weld the IA plate on. Don't stress though, welding was already the lighter solution when it was 4 bolts.

You forget about the monocoque Teams ;)

[jd74914]

Does somebody have information why the minimum amount of bolts for the IAA attachment will be changed from 4 to 8? Where there any incidents in the past?

No official information but...there was a car that crashed at FSAEM in 2014 or 2015 with a bolted on IA plate where the assembly basically pushed into the leg area and crushed the pedals. Seeing that was a little scary.

[Dunk Mckay]

No official information but...there was a car that crashed at FSAEM in 2014 or 2015 with a bolted on IA plate where the assembly basically pushed into the leg area and crushed the pedals. Seeing that was a little scary.

How was this not picked up by the IA testing? Do they not have to mount it representative of what is on the car, and demonstrate less than 1" deflection? Were they using the standard design, and therefore hadn't had to test their bulkhead/chassis arrangement? Is this a shortcoming in the rules? And is adding more bolts to the attachment method really a robust way of solving the problem?

[FrederikWe]

Maybe it was poor welding of the brackets.
Maybe whole assembly got only tested in a quasi-static test and the dynamic forces of the impact were reasonably higher
Maybe the Front Bulkhead was not a square shape but rather a shape were a little movement up and down or sideways allows the AIP to fall into the frame.

Those are only a few assumptions and are not based on knowledge what actually happened.

But regarding the question if this really fixes the problem I think not.
There is another part about the shape of the AIP in this rules section updated which in my opinion addresses the problem in a more effective way.

T3.20.5 “For welded joints the profile must extend at least to the centerline of the Front Bulkhead tubes on all
sides. For bolted joints the profile must match the outside dimensions of the Front Bulkhead around the
entire periphery.“

Just adding more attachment bolts sound to me like: “Last year, we have been slow in endurance, so this year we installed a bigger engine.”

For example for a common Monocoque Front Bulkhead the cutout is often only slightly wider than the minimum width for the impact attenuator.
I hardly disbelief that you will be able to push the AIP into the monocoque before crushing the whole car.
Also each attachment point on a monocoque car must be able to carry 30 KN. Why on earth does the full attachment of an AIP need to be able to carry 240 KN when the maximum allowed deceleration force is 120KN?
And even this 120 KN will never stress the bolts alone, because the force is manly supported through the Front Bulkhead.

Having to attach the AIP with 8 fasteners with positive locking is unnecessary, heavy, disadvantages monocoque cars because they have no option to weld and means more work every time you setup the car after transport (if you have to demount the AIP for it)