Progress on the bmw1602.com car ...** UPDATED 09/16/24 *

[bmw1602.com]

Thanks! I get similar inspiration from other build blogs as well....not to mention ideas!

Almost no metal yard stocks DOM tubing. But most yards can order it for you. Usually available in 18' sections.

I get mine from the closest metal yard to my house. Beware prices can vary ALOT from one place to the next so definately do your research!!!!!!!

[bmw1602.com]

Welded the plates in and completed the subframe connector tubes....incredibly I have never seen another '02 with this done to it. I've seen people weld tubes to the area but never actually do it like all the e30 and e36 guys do.

My "comrade" Dimitri, none of this would of been possible without his chain smokin' helping hand.

We are using a Harbor Freight tube notcher in case you where wondering.

Next we tacked in the subframe down bar.

[bmw1602.com]

I have to smile when I remember the funky ass positions you have to get in when welding a cage!

here I am welding the first tube connecting the subframe tubes to the rear tube node.

I can't stress this enough.... when welding ANYTHING get as comfortable as you can get. The more comfortable, the better you can see the cleaner the material is the better your welds will be.....mine are not perfect but it's amazing how much better they are when I happen to be in a more comfy position. Supporting your mig gun with your other hand can be tricky at times when welding in weird positions, but is vital to use you second hand to stabilize the nozzle to give you most control over what you are doing as possible.....

Much like many others I initially planed on Tig'ing the cage but in the interest of saving time I opted for the MIG. After welding some of these tubes I have a hard time imagining doing some of these beads in weird positions with a TIG.... having to manage the filler rod and the pedal would of really been a challenge! not to mention just fitting the tig torch in some of these tight confines.....

in any case he is me after I found a "comfortable position allowing me the best view of what I was welding.

the result I must say almost brings a tear to my eye....hehe

Personally I never seen this design done on any 2002 or e30. I think it's elegant and make perfect sense "engineering wise" and much better than other "subframe connector tube" designs. I just looked at it and this is the design that made the most sense.

[bmw1602.com]

All the "black" tubes are the new tubes in case you did figure that out already.

here is a closer shot of the finished subframe tube

like I said not perfect.....but not bad either....

[bmw1602.com]

Decided to add a horizontal tube across the main hoop legs and stitch it to the transmission tunnel. This tube should help considerable if the car gets t-boned right around the main hoop/door area. It should help keep the cage from collapsing inward. Basiaclly should help support the mid-section of the cage in a side impact.

It's safe to say after my new (coming soon) door bars and all the new tubes the car should be much safer.

It was trickier to fit than I thought as we had to cut a diagonal notch for the diagonal bar from the main hoop.....

The driver side weld came out nice.

Then I welded the tube to the transmission tunnel, should help integrate the cage in one more location to the unibody (there are many others)

[TobyB]

Wow- that's a LOT of tube!

Having a few years (and a couple of wrecks) in these cars, I'm not sure I

would continue the cage structure ahead of the front struts.

Reason being, when you bin it, you want something as a crumple zone

so that you're not stopping instantly. Also, it'll save the rest of the car.

It's easy to replace the fronts of the inner fenders, it's harder to replace

your neck!

Personally, my car's caged so that the whole inner fender's a crumple zone.

Potentially more damage in a wreck, but the inner fender structure's quite

stiff on its own- and if it's well- connected to the cage, the car's very solid.

Looks good! Keep at it...

t

[Colin]

Wow- that's a LOT of tube!

Having a few years (and a couple of wrecks) in these cars, I'm not sure I

would continue the cage structure ahead of the front struts.

Reason being, when you bin it, you want something as a crumple zone

so that you're not stopping instantly. Also, it'll save the rest of the car.

It's easy to replace the fronts of the inner fenders, it's harder to replace

your neck!

Personally, my car's caged so that the whole inner fender's a crumple zone.

Potentially more damage in a wreck, but the inner fender structure's quite

stiff on its own- and if it's well- connected to the cage, the car's very solid.

Looks good! Keep at it...

t

Interesting. Looking at these pics, I was starting to wonder where the point of diminishing returns begins. Some crumple zones are obviously desirable and can really save you, and the rest of your car, and furthermore, some body flex can actually help tremendously with traction in situations where there isn't that much grip (typical asphalt). More tubes means more weight, reduced visibility, and the chance of getting shaken up pretty badly. I wonder if there are any engineers that can weigh in on this stuff as I am researching building my own cage and want to know what the most effective minimums are.

[bmw1602.com]

-I'm not planing on going ahead of the shock towers with the cage. Would be a waste of tubing. and yes I'd like to keep the "nose" easily replaceable.

-Like I explained in previous posts......My race class (C-Sedan) has a 2000lb min. weight limit. I was underweight before as were many of my competitors. most just added lead weights to meet the required weight. I figured I'd rather increase the safety and stiffness of my car instead. So in my case weight is not so much an issue. Plus most of the tube is1.5"x0.095 wall tubing.....pretty light compared to what heavier cars (like a e36m3) are required to run. In the end I believe the increase in weight is worth the benefits.

some body flex can actually help tremendously with traction in situations where there isn't that much grip (typical asphalt). More tubes means more weight, reduced visibility, and the chance of getting shaken up pretty badly. I wonder if there are any engineers that can weigh in on this stuff as I am researching building my own cage and want to know what the most effective minimums are.

Let me tackle your comments....

1- since when asphalt a low grip situation? I think you got that one confused.

In any case you want a production sedan race car chassis to be as stiff as possible. Don't confuse chassis flex with body roll. You need the chassis to be a stiff as possible and leave all the work to the suspension. That's the golden rule! Just look at a nascar chassis or a grand am GT chassis or any car on a scca gt3 grid.

Why? you can control the suspension to do what you want. Chassis flex can be unpredictable and most important of all it actually can alter your suspension geometry during cornering!

Maintaining proper suspension geometry is VITAL. As it will induce understeer or oversteer during cornering. The first part of maintaining this geometry is maintaining the suspension attachment points completely static in all spacial directions. Up, down, left right.....they need to not move in relation to one another. Then the next step in maintaining positioning of the suspension parts.

For example, take the front shock towers. say you have sticky slicks on and 500+lbs springs (race setup) and you pitch the car decisively into a corner. If the shock towers flex inward or out ward you get a sudden change in camber which will immediately also affect your toe. Effectively this will either steer the car more or less into the corner than you are imputing and it might help induce understeer or oversteer. Most of all it will make the car a bit unpredictable due to the varying amount of flex and resulting geometry change.

This is exactly why strut braces can be beneficial.

This is also why when it comes to the suspension components the perfect RACE setup is a fully solidly mount suspension (NO Rubber or poly or even delrin) all the bushings get replaced with heim joints or spherical bearings of some sort. Even going from rubber to polyurethane bushings is an attempt at limiting the amount of "deflection" of the suspension parts. Solid (bearings) being the best option.

Take again your front control arm bushings. Under heavy breaking the front wheels are usually trying to resist forces trying to pull the front of the wheels outwards (toe-out). If you had stock rubber bushings you would observe the arms actually moving from their intended positions in high load conditions.......thus altering the suspension geometry....bad. The extra toe out might make the car darty/unstable during braking.

If all the moving parts are solidly mounted via bearings instead of busings all the suspension parts (strut, control arm, radius arm etc...) maintain perfect alignment and provide you with consistent, repeatable suspension setup and feel. That you can then adjust and improve.

look at any race suspension (DTM, WTCC FIA GT) you will almost never see "bushings" just bearings.

In the rear it is the same thing. Have you ever placed a jack stand on you rear subframe and lowered the car onto it? have you seen how much the subframe moves? imagine under heavy load the whole rear subframe will actually move around! This once again will drastically alter your rear suspension geometry and usually induce sudden oversteer.... This is why ireland eng. sells the rear subframe mount poly inserts...to limit this movement.......as before the more of a race setup to aspire to the stiffer you get ......rubber>poly>delrin>solid. Ireland also sells solid rear subframe bushings for this reason.

Which brings us full circle. If now you have increased the spring rate from stock (thus transmitting more force to the car and absorbing less in the spring) if you have also increase the stiffness of the subframe mount bushing or made it solid (like me) then where is ALL that force going to go?

Into the chassis!

So the stiffer the springs and "bushings" or lack of them the more you "work the chassis", This usually result is a twisting in a front to back relationship. THis further can alter the geometry of the car or alignment front to rear and create handling issues.

So in recap. In a perfect chassis you want the chassis to be able to maintain proper suspension attachment points at all times. This allows the suspension to work properly and most of all CONSISTENTLY. This enable you to compare apples to apples when working on your setup and make improvements.

I THINK what you are eluding to in a low traction situation is....

Wet asfault? Rain...In that situation you want to increase the weight transfer on the car and in a sense "soften" or slow down the weight transfer. You want to do this via suspension tuning and not rely on "chasis flex". Generally you'd want adjust the sway bars (smaller or remove them completely) and reduce the spring rates. This is the correct way to deal with this situation. The problem with using "chassis flex" to achive this result is the "spring effect" . For example take a kitchen sponge. imagine this is your car, take each end and twist them in opposite directions. Now let go! What happened? It violently snaps back into it's original shape. Your car is the same way. Imagine your going thru a series of S curves (chicane) once you chassis is loaded in one direction and have taken a set (flexed in one direction) then you have to suddenly change the cars direction it does the same thing the sponge did in your hand and snaps back.....this usually results in a snap oversteer or sudden spin... It's basically like a big spring. Except you can't dampen it with shocks! So the goal then is to eliminate flex and allow the suspension to control the car. Your basically removing variables from the equation.

hope this makes sense....

As far as Reduced visibility?

Not sure what your referring to exactly? This is a race car not a street car. pretty much every race car out there has the standard "x" across the down tubes. I'm not doing anything that different here. Also I have 17" longacre panoramic rear view mirror and it is surprisingly effective. So basically my car is no less visible than any other race car on the grid.

As far as cage design I rule of thumb is that while taking suspension pickup points and load inputs into the chassis into account, you want to think about "load paths" of the forces inputed into the chassis. Where they are coming from and where they are going. You want to shoot for TRIANGLES. Proper triangulation of your tubes is key.

So it's really important to keep the front strut towers exactly where they supposed to be. It's important to keep the rear subframe static. Then it's important they do not move in relation to one another. This is the reason behind integrating the rear subframe mounting points into th cage.

The first people to do this was BMW Motorsport with thier DTM e30M3's

here is a few other examples of this in '02 race cars. But it doesn look like either is sunken into the chassis like the DTM cars did. I just copied what DTM cars were doing.

look closely at these race car subframe location....it's all been done before! I just had a different design about what to do with the loads or tubes.

In my personal opinion the cage in any production race car should be as extensive as the rules allow........ when you see pictures of what some WTCC, ETCC, BTCC and DTM cars have done with the cages in the production chassis you will be amazed at the complexity of thier cages. Especially AUDI's

[Colin]

1- since when asphalt a low grip situation? I think you got that one confused.

Some asphalt isn't that great. I should have written "relatively low grip situations."

In any case you want a production sedan race car chassis to be as stiff as possible. Don't confuse chassis flex with body roll. You need the chassis to be a stiff as possible and leave all the work to the suspension. That's the golden rule!

I wasn't referring to body roll at all. The whole "stiff has possible" concept is actually somewhat debated now. Some highly respected engineers are now working on chassis designs that actually flex, or better yet, have controllable amounts of flex. Research has shown that a degree of flex can help dramatically in less than optimal traction situations (like many of the circuits where club races are held) and actually a chassis with a certain degree of flex can allow the engineer or driver to run a suspension setup which performs better than one could with a "perfectly stiff" chassis. I'm not pretending to be an engineer, so I was asking for comments with the hope that a race engineer may be reading this thread.

The other issue that arises is the "crumple zone" problem which another poster alluded to. If the whole car, including the front end, is tied together so heavily and you hit something, its going to hurt. Nearly the entire G force of the impact will be transferred into the cabin. Ouch!

I know in F1 they very carefully engineer in flex into certain points of the chassis and the suspension. This is all very high level engineering and really far beyond my knowledge so sadly I can't really provide more insight, but I was just looking at pictures of your cage and thinking about all the work that you've put into it and thought maybe you'd be interested.

[bmw1602.com]

I hear you on engineered flex it is widely used in many applications.

I come from the motorcycle world and it is a integral part of designing a motorcycle frame. This was exactly the challenge in created aluminum moto-X frames. Honda's first attempt was too stiff and it took them a few years to perfect thier aluminum perimeter frame on their moto-x bikes. Now almost every manufacturer has a aluminum perimeter frame on their moto-x bikes. They had to engineer the cro-moly like flex of the steel frame into the stiff alum. frame by varying the wall thickness and other tricks. On 2 wheels this has alot of advantages.But 4 wheels and a unibody are different animal completely. Especially a 30+ year old rusty design like the '02.

F1 doesn't really translate very well as they are dealing with alot of rules restrictions and very, very little suspension travel. They same way alot of bicycle road bike frames have "flex" designed into them to aid in bump absorption or ride quality, so do F1 cars rely on some of the materials themselves to aid in bump energy absorption.

Also they are dealing with Carbon fiber chassis and suspension compnents. Engineers can use computer analysis/design to "engineer flex" in only 1 axis by layering the fibers in certain directions. You you might have a suspension arm or a chassis part that may deflect in a X-axis but be stiff in a Y axis. So this way engineers can really control the flex in each CF part. By varying the angles of the thread and thickness and most of all CF constructing almost any 3d shape can be made to engineer flex and adjust the damping of flex components. Carbon fiber and 3d design and construction opens all kinds of possibilities!

Controlling flex with steel chassis is harder because it will flex in every direction. It get's difficult/expensive to extrude shapes with varying thicknesses with steel. Steel is more limited for 3d design.

I would say lets compare apples to apples.

look at top level roll cage deign in world sports car(production based) racing.... (I have attached a few examples) What I am doing is just a small sample of what lengths team will go to increase the chassis strength. The bigger the budget or if the rules allow the car become close and closer to full tube framed race cars like a nascar or a grand-am Riley chassis or a scca GT3 car.

Look at the pics below of the PTG M3 on the rotisserie, you can really see how complex the tube structures are towards the rear of the car. Also look and how reinforced the front tubes to the shock towers are. Like I said it is vital to maintain spacial/3d locations of all suspension mounting points. These pictures demonstrate this. PTG was factory back by BMW Motorsport and had factory help

Look at how they reinforced the whole strut tower area and ran additional tubes and bracing...

[bmw1602.com]

As far as "crumple zones".

The idea is to slow down the rate of deceleration by dissipating the most amount of energy possible, decreasing the rate of deceleration of the occupant.

The problem with this is that "crumple zones" are designed to work best at a specific impact speed.

The ideal energy dissipation/absorption rate of crumple zone on a modern sedan let's suppose might be anywhere from 45mph-60mph at the max. The "crumple zone" on a modern f1 car or indy car for that matter is designed to work best at speeds anywhere from 120-150mph.

Any slower and they will not deform and any faster than they will disintegrate rapidly. Just ask BMW F1 driver Robert Kubica last year in Canada GP as when his car stopped his feet where left dangling outside the cockpit.

So where a production car's crumple zone might save you at 50mph it will not be ideal at 120mph.

Take a stock 3 series for example. Say we are on the track and we slide on the exit of a corner into a concrete wall. Like this scenario at buttonwillow.

(very common accident there and this is why they put tires against that wall)

If you in a stock unmodified 3 series, lets say you hit the wall at 50mph. Your crumple zones will deform your airbags will deploy and your body will decelerate at a much more reduced rate thereby protecting you.

If you take the same car but a full race version.....slicks, suspension, increased HP etc....

You most likely because of the cars increased speed capability will be hitting the same wall instead of 50 at maybe 80mph! This will be above the crumple zones ideal range and the zone will simple collapse, the engine will intrude into the cockpit etc....and injury will sure follow.

Take the same race car with a extensive racing cage impacting the wall at the same speed and the cage will help prevent the catastrophic failure of the structure. The dash bar/foot protection tubes will prevent the engine and wheels from intruding into the driver footwell etc...

The downside to this is you do transfer more energy into the occupant/driver.

So in a race car our bodies are much more secure via 6 point 3' harnesses & race seat. The belts in turn are designed to stretch up to 6" or more during a high G impact. This further helps decelerate your body to counteract the larger transfer of force.

In this video you can see the amount belts stretch during an impact.

Which by the way emphasizes the importance of tightening your belts!

This in turn created a problem for your head slowing down as the belts held your body but not your heavy helmet clad head. Luckily Hans (also depicted in the video above) device helped address this. Also the new racing seats with side impact head protection, side nets etc...

Anyway back to the issue, basically road car safety features apply to road car speeds. Some of them just will not work at high impact speeds of a race track and or multiple impacts as sometimes happens in a race situations.

In a race cars since you are dealing with higher speeds, multiple impacts, t-bone impacts etc.... you are forced to increase the protection. This in turns transfers more force and deceleration rates to the driver which in turn has safety devices designed to deal with the increased forces encountered. Which is why you would never see a stock seat, stock belts and non-helmeted driver in a race car.

You increase the impact strength of the vehicle to cope with the increase speeds and potential impacts and thus add features to deal with that increase.

But there in-lies the conundrum. The faster you go the more you have to increase the strength to deal with the speed during driving and during impacts.....or else you get serious failure and injury. So what to do?

The new Nascar chassis worked in cooperation with DOW corporation and developed a special FOAM called IMPAXX. It's a revolutionary way to deal with energy absorption.

It's now commercially available but still expensive. A member on bimmerforums just purchased and fitted it to his e46 race car.

you can see pictures of his installation here.

http://forums.bimmerforums.com/forum/showthread.php?p=12907528&highlight=impaxx#post12907528

But basically the as long as you can keep the drivers body from striking any solid objects inside the vehicle you can survive very high g-forces. Airforce test pilots have survived up to 47g deceleration impacts on rocket sleds while developing aircraft belts. Emerson Fittipaldi's crash recorder a spike of 87G's and Kubica's crash last year recorded 67g spike. The airforce guy on the sled endured his 47 deceleration over a longer distance. So that also has alot to do with it. Sustained high G deceleration will probably kill you above 50g's. We have seen from Kubica's and Emerson's crash data that we can survive very high g-loads if they are momentary.

actually, racing car driver David Purley survived an estimated 179.8 g in 1977 when he decelerated from 173 km/h (108 mph) to rest over a distance of 66 cm (26 inches) after his throttle got stuck wide open and he hit a wall.[2] Indy Car driver Kenny Bräck crashed on lap 188 of the 2003 race at Texas Motor Speedway. Bräck and Tomas Scheckter touched wheels, sending Bräck into the air at 200+ mph, hitting a steel support beam for the catch fencing. According to Bräck's site his car recorded 214 g.

Needless to say the development of the HANS devices has been crucial to surviving higher G impacts.

check out these links for more info

http://www.ejectionsite.com/stapp.htm

http://autospeed.com/cms/A_109806/article.html

So in a race car it's more about designing for the stronger impact and in a street car it's more about designing to protect for slower speeds.

All that said both my front engine bay design and my rear tube designs leave plenty of sheet metal to get crumpled and absorb some lower speed impacts. The way I have the rear if I get rear ended or hit a wall with the rear. I can just go to the junkyard with my sawzall and chop a donor car from the wheel wells forward and weld the clip on.......basically the same thin in the front.

[srfjay]

Wow great info . Thanks for writing it all down.

[bmw1602.com]

Here is an example of the continued improvement that then turns into almost a whole new car......this is a scca gt3 tube frame racecar.

[bmw1602.com]

some more intresting 2002 race car stuff .....for you all entertainment.

[JK]

Great work Pedro. I'd like to know how the car works once you are done. My weight has to be 2200# and I think I'll be substantially underweight when I'm done...I might follow your lead if it comes to bolting on 400# of weight. Have you worked on the oil pan yet? Love your trailing arms and front suspension arms...mass produce them and I'll buy some.

P.S. Industrial Metal in Sun Valley stocks DOM tubing in most sizes.