It's a subject I was looking at last weekend, and came to a couple of conclusions.
Firstly there's a fixed overhead of weight that it's very hard to avoid, I weighed wheels, motor, tav, rear axle, disc brake, chainwheel, and front axle, and they come in somewhere North of 60kgs. The 'average' US karts seem to be coming in at around 115kgs, (250lbs.)
So the only real scope for weight reduction is to keep the chassis and body somewhere between 30 and 55kgs. So there's not a huge difference if you consider the all up weight of car and driver is around 200kgs.
Secondly there is a probably a greater difference in driver weights, I'm around 80kgs, some of our colonial cousins are 20kgs above that, so there's probably a bigger difference in driver weights than karts.
So I stopped worrying too much about it, kart weight differences can be in the region of 10%, with tuning there can be 20% or 30% difference in engine output while still being under the 10hp guidelines, so you can always tweak the motor or play with gearing if you feel you're not competitive.
I too am watching the pounds, (or kgs), and did a quick audit on my build to date last week that gave the following rough estimates if it's any use, I used bathroom scales, so it's probably a bit flaky at the moment.
Engine 14.6, wheels 22.8, tav brake disc hubs 8, rear axle, chainwheel, hubs 8.6, front axle 5, steering column and wheel 1.8, giving a fixed overhead I can do little about of 60.8kgs
The chassis rails, crossmembers, floors and front spring perch are 19.6, the nosecone and scuttle 4.6, and my indulgence of a reverse box is 3.6
This puts me currently at 88.5 kilos, with side panels, a tail section, bonnet, pedals, brake caliper, chain and probably a battery to complete, so my target of 100kg is likely to be exceeded, but probably only by about 10% I'm not going to stress too much about it, I think it's going to end up somewhere on the middle of the pack weight wise. I'm just hoping that my centre of gravity will be lower than most, - I will get it built first, then worry about where I can drill holes to lighten it later.
Peter
