Sit Down and Show Off

Update by Per Schroeder to the LeGrand Mk 18 project car
Oct 4, 2011

It looks fast sitting still—even if it's in a showroom.
That's a two-part foam kit from BSCI and 68 pounds of steel. That'll be one heavy seat insert.

The seat (and extra weight) will be exactly where it needs to be for us to meet our minimums and keep our cornerweights in line.

With Nationals in our rearview mirror (if we had one), we’re looking forward to 2012 for another strong showing. Our car is on display in the GRM HQ office here in Holly Hill, Florida, and we’ve already started a list of things we want to accomplish during the offseason.

First item: a seat insert for Kim, our tech editor’s wife. Kim weighs about 80 pounds less than Per on a good day, and that means it will be very hard for her (and the car) to meet the 1020-pound minimum weight. We could add a bunch of ballast between runs. However, that would make the corner weights odd, as we couldn’t add them in the driver’s seat area—or could we?

Our solution is to mold a new seat insert for Kim that has been supplemented with about 70 pounds of steel plate. A plate measuring 12x15x1.25 inches weighs a staggering 68 pounds. This will be placed inside the molding bag before the two-part foam is poured in and expands around our svelte co-driver. The seat (and extra weight) will be exactly where it needs to be for us to meet our minimums and keep our cornerweights in line.

Look for a full how-to on this in a month or so.

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View comments on the GRM forums
Ransom GRM+ Memberand PowerDork
10/4/11 4:22 p.m.

I guess this will be in the writeup, but that's heavy enough that I'm guessing it'll need to be fastened to the car and not just held in place by the driver? I wouldn't want my lower legs trying to stop a 68-lb plate attempting to leave the lower seat edgewise in a hard stop...

Per Schroeder
Per Schroeder PowerDork
10/4/11 4:54 p.m.

It's positioned in the car so that it's essentially strapped to your back--and the harnesses are keeping you/it in place. Wouldn't do it for a road racing car, but typical for autocross mod cars.

ThePhranc Dork
10/5/11 8:47 a.m.

Would lead not be better? Heavier and can be set lower.

10/5/11 8:52 a.m.

Since the weight is so critical i only mention the slight error in your weight of the plate, Pro-Engineer comes up with 63.675lbs for that size plate with sharp corners.

12x16x1.25 = 67.9 12x16.125x1.25 = 68.45

I don't know the exact envelope that you have to work with... So i just threw that size in there.

10/5/11 8:57 a.m.


12x12.375x1.25 68.49lbs

Per Schroeder
Per Schroeder PowerDork
10/5/11 9:15 a.m.

You're right, it's more like 16" tall. Weighed 68 pounds on our big postal scale.


10/5/11 9:37 a.m.

Good deal!

I also don't like the idea of the weight "being strapped to your back" in the worse case an accident. Her chest would compress (just break ribs in the best case) So i offer a "simple suggestion" I would take some 90° angle steel and make a slide in plate retainer welded to the chassis (behind the seat?), with a bolt on top to retain it again for the worse case.

Good luck! :)

Per Schroeder
Per Schroeder PowerDork
10/5/11 10:10 a.m.

Good idea--I'll see if I can work that in.

BanzaiBeast New Reader
10/11/11 12:26 p.m.

This idea probably won't work for your application, but it is another avenue: ballast tank to fill/drain to give the correct weight.

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