FB chassis

[4wheeldrift]

Does anyone have basic chassis dimensions we could use to start our chassis? We have done a lot of autocad work on our own here and looked a tons of pics we tried to scale and dimension . To start with we are looking for the length from rear rollbar hoop/bulkhead to the front rollhoop bulkhead. We are thinking around 36inches. Then from the front rollhoop to the front bulkhead/footbox. Here we are looking at 24 inches. Planning on centering the front axle at the center of the foot box. This would give us a total of 60 inches for the drivers compartment. We plan on using 1.5" dom tubing and for a bulkhead height and width of 22". We are looking at a wheelbase of 100 inches. Before we start bending and welding we would like to see if we are in the ballpark.

[RobLav]

Most of us here would probably recommend that you not build your own chassis. You can buy a new Citation FB chassis at a very competitive price. The amount of time (plus materials and equipment) you would spend to design and build a new chassis is not worth the 1/7th of the total cost to build a new car. My Citation chassis is about 1/7th of the total cost to build my car, and I'm trying to do this fairly cheaply.

In my view, there is too much risk and opportunity cost in trying to design and build your own chassis.

[Jim Nash]

Before you start bending and welding steel I would suggest making a mock-up with much more forgiving material. Depending on what you have around it shouldn't cost much and you are going to learn a lot about your design.
Jim Nash

[carnut169]

Recently there was a 99 Van Diemen listed for $15k. Might still be available.

You sell the engine, bellhousing, and trans (best guesses- $4500, $500, $2000) now you have suspension, frame, floor, bodywork, wheels, shocks, and LOTS of other bits and pieces (like belts, transponder, bell cranks, fire system...) for $8k. You also have the piece of mind that your car will have value should you decide to sell, and that it works as it was designed and built by a company that has been building race cars for quite some time.

Your going to spend triple that to get something worth half of that. Not smart.

[S Lathrop]

Front bulkhead is 0". Dash 28" back of seat 64" (24" up). My frame is longer than that. 22" inches wide at the drivers elbows is fine. The height is best determined by the drivers seating position and the roll bar height. Check the roll cage rules. 22" might do.

Why 1.5 dia tubing? The rules require 1.375 min and that is fine.

Think very carefully about your roll bar design. One new car has used the alternative structures rule to build something that has not been allowed in SCCA racing since the early '80's. Especially think about where the point of failure of your roll bar will be. Remember that the bar will have to flex under loads.

I had a roll bar structure fail because I had not allowed for sufficient flex. In that design I had the hoop braced front and rear 6" below the top (per the rules). The bar sheered off at the braces. I don't build roll bars that way any more.


The best design, in my opinion is something similar to the Ralt RT 40-41 FA. That structure is not legal in SCCA but should be. That structure will fail from the top down. The hoop has a major increase in structural strength at a point even with the drivers head. From the top to the drivers head the structure just meets the minimum requirements. This is the crush or energy absorbing structure. This reduces the loads transmitted to the main driver cell structure and the driver. It also extends the survival structure to the top of the drivers head.

The Ralt structure is a double hoop with vertical legs for about 6" the the legs splay out to a much larger base. The Spec racer roll bar violates all the rules for roll bar structures in SCCA but maybe it is closer to what we should build. I think that a basic hoop that is even to 2" above the drivers head. Then a second hoop of thinner tubing above the first and the braces at the junction of the 2 hoops. You always have to think about the aerodynamic penalty of the roll bar.

[4wheeldrift]

Thank you for your help so far. A little backround on why we are doing this from scratch. 15k up front is out of the question for us when we can do it for basically free.I am a fully certified welder with every welding proces imaginable and certified to xray quality welds on nuclear pressure vessels and piping on down to structural plate. I have over 30 yrs of experience with welding stainless/titanium/aluminum etc. I have a degree in electronics engineering. I own my own top of the line synchrowave 250 tig welding and mp250 mig welding and fabricating equipment. I work part time for a full cnc machine shop and have full access to any fabricating equpment I may possibly need. So basically my time , the equipment , supplies , measuring gauges etc is all free. We have tons of 1.5" dom tube on hand. I have access to the best mechanical engineers/thermal dynamacists/electrical engineers etc at my full time job that said thay would be happy to analyze our designs. One of the engineers builds carbon fiber ice racing booats so he is totally " on board" with this project.

We would also be able to look at doing work for any other racers that may need a hand with anything they need. We just needed an idea where to start. Thanks again for your help. "Blue chips are happy chips"

[Joefisherff]

Check the rules on your footbox design as well as there is specific wording around how far the drivers feet can extend in the footbox relative to the front wheels.

[4wheeldrift]

Yes we did a wood mock up. Seemed to be a bit tight in the footbox area. We would like to stretch that to 30" so we can keep the mastercylinders in side the chassis. Our mockup started at front bulkhead(footbox) station 0:Front rollhoop bulkhead(dash bulkhead) 24" , Rear rollhoop 60". Chassis outside width 22" with 1.5" dom tube leaves 19" inside width naroowing down from the dash at 22" x 22" to 14" x 14". Our footboox design leaves the soles of the drivers feet in a relaxed position at the front rim as per what we deciphered from the rules. We may go to front bulkhead 0" frontroolhoop 30" rear rollhoop 60" but that seems to make the cockpit /sterring wheel a bit cramped. What we are trying to build is a foremost safe design, erred on the safe side, probably will be a bit heavy, but most importantly crashworthy, utilizing all the engineering aspects of other designs that we can incorporate into ours. We do not want to leave any stone unturned in our quest for safety and survivability for ourselves and others. Our rollbar design seemed to also be designed in the same fashion that some1 else said failed on their design so we will need help in this design also

[Ian Lenhart]

Do you need to look at a few formula fords for a better visual? I'm in Milwuakee. I can also use your help with a project I'm working on.

Ian
414-719-2043

[4wheeldrift]

JEN
Never thought to use the plastic tube for a mock up! Ingeneuos! We sued 2x2 sq wood(1.2 x 1.5) and plywood. Lathrop thank yopu or your measurements. I seems that 36" from front rollhoop(dash bulkhead) to rear rollhoop(rollbar bulkhead) is confirmed by your measurements.We will go with 30" from front bulkhead(staion 0") to front roll hoop and 36" from front rollhoop to rear roll hoop giving us a chassis length of 66"front bulkhead to rear bulkhead. This will put the heaviest lump of mass(the driver) a bit rearward(6"0 further back than we wanted) so we may locate the engine now as far forward as we can within our 100" wheelbase tartget. Ian we definitly will come and look and take measurements when it is convienient for you. Again thank you all for your help in helping us confirm our figures. As an ex motorcycle road racer for 30 yrs this class (FB) is a great opportunity to het the races again

[Lee Stohr]

Usually you start by carefully studying whatever cars are doing the winning. You try and find some area you think you can improve, it might be aero L/D, suspension grip, hp, traction, etc. Then you design your car with the supposed improvement but making sure your car is at least as good in every other area. One mistake anywhere and you will be uncompetitive.
Always try and give yourself one year to design/build, and one year to sort out your new car. Everyone thinks they can do better than that, almost no one ever does.

[4wheeldrift]

Lee we agree with your schedule of 1 yr to design 1 yr to build and 1 yr to sort out . We have spent many hrs examining every F1/F3000/GP2/FA etc rom 1975 to present that we could find on the internet and library and any other source at hand. We are looking at this a hobby( albiet an expensive one) and an opportunity for engineering design/innovation , alternative approaches to a solution . We also hope to be able to bring our car and ideas to high schools to show that scientific excellence has a real world applications.

[Lee Stohr]

Don't spend too long on the drawing board, the learning doesn't even begin until you start racing the thing. After a couple years running your first car you will probably toss it the dumpster and start another one anyway. Also, rules and technology change while you are fiddling in the shop. It's a very challenging sport, have fun and good luck.

[4wheeldrift]

Ian has contacted me to do some trial fitting and measuring on his FF. That should give us a great basis to start out with.

[cparsons]

4wheel, your chassis dimensions are very similar to mine. I would have to check the lengths, but I also have 22" outside width of cockpit (excluding side pods) at the main hoop, 19" inside because I used 1.5" dom on ALL vertical hoops, and I have 4 - main, front, mid and foot. I believe the distance from main hoop to foot hoop is also 60". Forward bracing from main hoop to front hoop is also 1.5" dom. the rest is 1.0" tube and assorted rectangular/square, depending on the purpose.

[4wheeldrift]

CPARSON: thank you for your input and your measurements. Those dimensions seem to confirm what our auto cad layout is. Based on another suggestion as regard to safety We have nodified our roll hoop to a 2 bar type 1 main vertical hoop and 1 roll hoop brace leading back to the rear motor mout bulkhead plus the rquired 2 forward mount braces.