Das Beast: My E30 track / street build

[dvallis]

You're welcome. I could only find 100 kg (220 lb) planar load cells so three wouldn't be enough per plate. Could have made them but it's just one more thing to do. 4 x 220 lb gives me enough capacity. Even then, these won't be "drive on" as two load cells won't take full corner weight. Will have to jack each wheel and slide them under. Not a big deal.

[ForcedFirebird]

Thanks for posting this public!! Hopefully it's uploaded to r3v database and kept.

Why not use 3x 220kg per pad for 660 per corner? Based on simple geometry, three points create a plane, four adds a variance. Pretty sure this is why the tire balance machines have 3x pads. Personally, I was cursing yesterday since the tire balance machine has 3x contacts, and the one leg just had to land on the concrete expansions joint, no matter how many times the stupid thing was moved back-n-forth 6". Grrr

[dvallis]

Finished the scale design. Pretty simple really.



And now we build it. I had all the parts laying around. LCD first, just to get "proof Of Life"



I'l save you the gory details of the MCU code. First power up ..... It lives! Swoosh. Nothing but net.



Going to work on more suspension tomorrow.

[citizen_insane]

I found this one on Amazon. You could check eBay too. Most important thing is load rating. They need to be at least 100 kg (220 lb) rated so four under a plate will have enough capacity. Most you'll find are only rated for 50 kg.

You can also just buy full bridge strain gauges from Omega and laminate them to your own metal load cells. Probably better quality but you need to know how much strain your cell will experience under load.

Awesome, thanks. I haven't put on strain gauges since college, not sure I fully trust myself to do it if there are relatively cheap off the shelf options.

[dvallis]

I found this one on Amazon. You could check eBay too. Most important thing is load rating. They need to be at least 100 kg (220 lb) rated so four under a plate will have enough capacity. Most you'll find are only rated for 50 kg.

You can also just buy full bridge strain gauges from Omega and laminate them to your own metal load cells. Probably better quality but you need to know how much strain your cell will experience under load.

[citizen_insane]

This is VERY relevant to my interests. I've thought about doing the same a few times, but never bothered to actually look up where to get the hardware. Where are you sourcing your load cells?

[dvallis]

This thing is a $9 load cell. It's a piece of steel with a full bridge strain gauge laminated to a location that bends .. slightly. I used similar strain gauges in the Navy to measure deflection of F18 wing beams under a 10,000 lb computer controlled hydraulic press. THAT was fun to write code for. :-) This one happens to be rated for 220 lbs. Put 4 under a metal pate with associated electronics and you've got an 880 lb scale. One of those under each wheel and we're done.



IT'S ALIVE. Volt meter sees 1.2 mV out of the load cell as I lean on it with my thumb. Using a 24 bit ADC we can resolve ~0.6 uV per count over a 5V range. That 1.2 mV would look like 2000 ADC counts. No problem.



Now I know that works, we'll design the scale plate.

[dvallis]

Thanks for the feedback. My rates & height are close to Spec30 so we should be good for now. Getting more into setup.

Working on building a set of 3500 lb digital corner weight scales for $100 next. Proper scales, not bathroom scale ghetto lever hack. Requires some electronics knowledge, coding skill and a bit of soldering.

Stay tuned.

[MrScuba]

I have an e30 track car, with the Spec e30 suspension. It was a huge improvement in responsiveness over the mutt track/street suspension that was on it. The only criticism I am aware of is from a friend who has a problem with the car hitting the bump stops. I think his car is too low.

[dvallis]

Finished our ride height and toe tools today. Top string is on the frame attached to the car. Bottom string is on jack stands, checking the floor with an attached level.



Surprisingly, our floor is completely level, front to back and left to right. Now we know for setup the string attached to the frame will give us accurate ride heights for corner balancing.

[Digitalwave]

I would not worry about spring rates and such until after you have a bit of seat time in the car. Then adjust as needed.

That is a street setup for the most part, but it shouldn't hold you back for a while.

[dvallis]

Revisiting the spring rates while doing alignment research. Back in 2018, Spec30 adopted a Ground Control kit with 535 lb/in front and 700 lb/in rear. We're currently running 400 lb/in front, 650 lb/in rear. Slightly softer but we did a lot of weight reduction. They might be right for this car.

Spec30 fronts are maked with a custom "Ground Control part number. GC150.64.92

My stock Eibachs are marked as "0600.250.0400" ( 6" length, 2.5" ID, 400 lb/in)

Any racers care to comment on spring rates for an M20 powered E30?

[dvallis]

That is some good suspension porn. Didn't realize E30 M3 struts were an option. Hmmmmm .......

[Digitalwave]

I don't have any direct experience. I run E30 M3 struts and knuckles where the steering arm is separate from the strut tube, so I just have a block of aluminum between the two pieces that helps correct the roll center.



My spacers are only 13m thick; they still work with 16" wheels. Usually you can run up to 25mm/1" thick if you are only going to use 17" wheels.

I have seen guys with BBK's even with stock roll centers on E30 M3s grind down the tip of the control arm for clearance against the rotor. However, I don't think you can really tell anything about the clearance from the angle of that photo unfortunately. It might be plenty, or it might take some creative grinding.

[dvallis]

Digitalwave said: Check out MRT Engineering, they have the nicest E30 bump steer kit I have seen, with real engineering behind it. Second choice would probably be SLR Racing here in Florida. I wouldn't buy anything from Garagistic; they just copy other's designs and sell them for bottom dollar. They typically get a lot of complaints for poor fit and finish.

I talked to the MRT guy on eBay, His kit fits stock struts with the Z3 rack. Also found this thread that shows the MRT kit installed. It puts the knuckle really close to the Stoptech rotors he's using. My rotors are also way thicker than stock.(11.75" x 1.25" Hawk DTC) Not feeling grinding the knuckle for clearance. Any comments?