Lessons Learned - Chassis

[JerryH]

If you were to build a second car, is there anything that you would do differently that you think that other builders would benefit to learn about. Conversely, is there anything that worked particularly well that you would recommend to others? Please confine this thread to chassis construction.

[Warren Nethercote]

Yeah, design and maybe even build your suspension and then build a chassis to fit the suspension, not the other way around. Ask me how I know.

[turbo_bird]

I'd build the tunnel around the transmission after I had the engine and transmission in place instead of making it fit in a prebuilt tunnel. I would also probably use an aluminum floor and run it across the full width of the car instead of just a piece under each side of the car. I would also probably build the car with a race legal roll cage. I would pay more attention to weight, such as diagonals made from 1/2" or 3/4" round instead of 1" square where possible. A structural braced dash hoop instead of one that's just there to hold the dash would add some stiffness too, and I'd put it further back than the typical locost plans, more like a real lotus.
Kristian

[C10CoryM]

-I'm pretty comfortable saying my style of engine mounts are great. viewtopic.php?f=4&t=11912#p114600 Fast and easy to do, and rock solid. Cheap too.
-don't spend too much time on every single connection. Yes, your frame will be straighter, but you will waste so much time. A millimeter or two isn't going to be noticeable. I wasted a lot of time on my frame and yes, it is very straight.... but not worth the time spent.
-plan swaybar frame mounts while building. I didn't and it's going to suck to install one now.
-level your build table so you can work with levels and plumbs. Makes it easier/faster to be sure things are in the right spot.
-have a block setup to hold the chassis at ride-height when on the build table. Literally just level blocks that you can screw the chassis down to. This way you can build/mount/test your entire suspension while on the build table. Can also mount your engine if it hangs below the rails.

[bob]

The next chassis wont have the same wall thickness tubing throughout, I would definitely use thin gauge tubing on all but the tubes that have chassis suspension lugs, engine mounts, seat belt mounts and roll bars attached I would use 3mm wall thickness. You would only be adding a few pounds.

Bob

[TRX]

I built my first chassis out of hot-rolled tubing. I spent three days de-scaling it with abrasive discs, and it was still smoky to weld. Hey, I didn't know any better...

+1 on the reduced-diameter diagonals. That eliminates the odd overhanging corners when you use square tubing. I'll probably use 3/4" round tubing on the midi chassis.

edit: it's never too early to start shopping for rivets. Sometimes you can find a bargain on eBay. If you get a deal on more rivets than you need, don't worry about it. They're like leftover chassis tubing - they're useful "bench stock" for all sorts of projects.

[davew]

My number one change which wish I had incorporated in the build is a bolt-in transmission crossmember. The design should allow the driveshaft to be engage in the tailstock first, then the trans/driveshaft bolted in place. Dave W

[nick47]

I would echo turbo_bird's comment about building the transmission tunnel around the actual drivetrain.

I'm not sure I'd make the scuttle frame removable next time, but I would definitely make it easy to remove the scuttle sheeting.

During the full welding process, I'd flip the frame over after every 20 welds or so.

I would move the steering wheel and pedals 3/8" to the right.

But that's about it. I really like my frame, and after 20K miles it's as solid as ever. I was careful to follow the book as closely as possible, and maybe that's why I don't have any issues now.

[JerryH]

You can make the build table easy to level, and re-level, by screwing lag bolts into the bottom ends of the table legs and turning them to raise and lower each corner.

[john hennessy]

the distance from the windshield to the drivers head should be no more than 36" so move the scuttle or make it longer, your ears will thank you

[JerryH]

-I'm pretty comfortable saying my style of engine mounts are great. viewtopic.php?f=4&t=11912#p114600 Fast and easy to do, and rock solid. Cheap too.
-don't spend too much time on every single connection. Yes, your frame will be straighter, but you will waste so much time. A millimeter or two isn't going to be noticeable. I wasted a lot of time on my frame and yes, it is very straight.... but not worth the time spent.
-plan swaybar frame mounts while building. I didn't and it's going to suck to install one now.
-level your build table so you can work with levels and plumbs. Makes it easier/faster to be sure things are in the right spot.
-have a block setup to hold the chassis at ride-height when on the build table. Literally just level blocks that you can screw the chassis down to. This way you can build/mount/test your entire suspension while on the build table. Can also mount your engine if it hangs below the rails.

An excellent example of why I wanted to start this thread. I've read through most of the posts at least twice and still missed this.

[Bonjo2]

It's obvious the tube I had added under each seat to the tunnel took the brunt of my accident and saved my life.

-16g 3/4" chromoly not enough for a-arms, esp with sticky tires and v8 power 1" .09 or greater... All of my arms bent or crumpled or tore apart. The shear point should be at the heim or bushing.
-Get passengers closer to center
-Think of tunnel as a crumpled zone in side-impact accident focus is for and aft rigidity and keeping shaft from entering vehicle
-cross bars under front and back of seat stop at tunnel
-side impact bars connect before and after driver, then to floor at angle
-gussets to side, square tube likes to break given weld is flat, vs a round notched tube
-Welding a 1/8" or more thickness suspension or shock mount to 16g tubing bad. Mine simply tore off above and below welds. Having a 1/8" mount that spreads load over 2 times the area better. The tiny 3/8" suspension bolts and mounts all held up fine. The 16g 1 1/4" primary tubes did not.


Seat halo probably would have prevented my head injury.

[Bonjo2]

Rivets and aluminum floor.

even at a 2.5-3" spacing, all but a handful of the rivets holding my floor, trans tunnel and seat panel on sheared completely. The black sikafex held better than the rivets. I used standard hardware store "Ace" brand mild steel and aluminum rivets in 1/8" and 3/16"

[RTz]

Thanks for the insight Bonjo. Structural rivets would hold up better, but probably insignificant in your case?

I made a list of things I would do differently if I were to build another car, most are subtleties, move this a little here, that a little there. One of the more significant items that I would do differently is the scuttle frame. My scuttle is flat across the top and if I had formed a slight upward bow, the scuttle top and hood would be more ridged. I added stiffeners on the bottom of both and am happy with the rigidity, but probably could have avoided the stiffeners altogether.

[Mnot]

There are three major things that I would do differently on my chassis. I made a Haynes chassis that is 2-2-2. I would do a 4-2-2 next time because I have several family and friends that cannot fit in the 16" seats.

On the Haynes, the lower engine tubes narrow toward the center at the front more than the uppers. This is completely unnecessary and limited where I could route things. Additionally, the aluminum skin is unsupported at the bottom edge and more vulnerable to damage. Lastly, this makes my LCA's even longer than my UCA's and now I have more camber gain that I really need. The spindles I used would have close to the right amount of camber gain built into them.

The other major change I would make is to my diff mount section. I made a trapezoid "box" to house my Ford 8.8. I really like this diff because it was affordable, gear options are plentiful, and the LSD works really well but it is big and heavy. I would have made the diff "box" square next time. Because I made the bottom of the trapezoid smaller than the top, it is exhausting to get it into place. My diff is 75lbs and it is a real struggle to get it in or out. Additionally, it also creates longer LCA's and more camber gain than needed. The spindle mounts would make the control arms unequal length and the perfect amount of camber gain in compression but with 2" longer LCA's it is too much now, but not so much that it is worth cutting it and redoing them.