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Originally Posted by Pete Love on Street Luge BBS
There are two (mutually contradictory, of course) theories about double trucks:
Theory a) Double trucks divides the load on your bearings in two, hence reducing rolling resistance on the straight, giving you a higher top speed. This depends on rolling resistance of bearings rising much faster than linearly with applied load, which, even with cheap bearings, probably isn't true. (Note that ABEC ratings are an engineering specification and confer zero information about the actual performance characteristics of your bearings. It would be nice if someone measured drag versus load and rpm across several makes, but there you go.) Also one has to contend with twice the flat tire effect from your wheels, so this is a really bad theory in my opinion.
Theory b) Double trucks `give more traction' in corners. Now, there are two reasons your wheels will slide - they are either not loaded enough, or loaded too much. If you sit up in turns you are unloading the rear truck and loading the front. On a single truck you are probably loading the wheels beyond their sticking point and they will slide, scrubbing speed. Putting another truck in will halve the load on the front wheels and bring them below the point where they start sliding. The front of the luge will then stay hooked up through the turn, and you won't scrub as much speed. This is a good theory and is backed up by my own experience and numerous conversations with and observations of people who regularly kick my ass in corners.
Amusingly, when I went to a double truck setup at hot heels I immediately was able to stay in front of Jerry Gilder, who then changed his setup and sat on the finish line saying `so this is what luging is supposed to be like'. We were then so evenly matched we kept crashing into each other.
So on the basis of theory b) the answers to your questions are:
1) Just enough so one set does not touch on the straights but contacts in turns.
2) Yes. The closer they are the closer the turning circles of the two wheels will be and so the amount that the two trucks `fight' each other is minimized.
3) A longer wheelbase on straights is more stable, so the rear truck in the air means you maximize your wheelbase (and hence stability) on the straight.
4) Here you have to be careful. If you are genuinely running on one truck on the straights then that truck must be tight enough that you don't speed wobble. If you are running the trucks so that you always have the two front trucks equally loaded you can run them looser.
5) Hmmm.... the only guy I know who does this is Darren Lott, about whom there are also two theories:
a) Darren is so far out there in his thinking on luge construction he has a totally separate take on every technical issue. If you could duplicate his kit identically you would fly. Get one tiny technical detail wrong and you'll spin out and crash and you'll DIE.
b) Darren rides the most totally insane setup deliberately to fuck with your head, so your so confused wondering why he has four different kinds of trucks, wheels and a luge carved from whalebone that your technique is totally screwed.
However, given all the above it is important to remember the aphorism that ``In theory, theory and practice are identical, but in practice they are totally different''. Here are the ``in practice'' answers to your questions.
1) Whatever height difference you can get out of the 4 sets of wheels which are all worn to different sizes. If you get 3 out of four wheels on the ground on the flat you've won.
2) See 1)
3) Because that's the hanger they used at big air and they're too mean to spend the $15 for a new RII.
4) Run the trucks at the tightness you put them on at in the hotel at six in the morning with a stinking acidic hangover before the race.
5) If you have one hanger more narrow than the others its because you've put one of Pete Eliots on by mistake, due to aforementioned stinking acidic hangover.
6) Whatever crazy setup you end up with, make up 4 theories (and three new laws of physics) to fuck with everybody's heads before the race. Remember, if you can get them fiddling with their gear there's at least a small chance that they won't tighten something up and spew a wheel so you can pass them. Unless its Pete Eliot in which case he wont even notice you've got his hangars until you're in the airport on the way home. That's if he even makes it off the taxiway at Heathrow.
OK, I'll stop now.