Drag launch howto? - K-Bikes.com - Excellence in Motion
 
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post #1 of 9 (permalink) Old Mar 31st, 2006, 12:29 am Thread Starter
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Drag launch howto?

I'm thinking of taking my K1200RS to the local 1/8 mile drags, just for fun. Any suggestions on how to launch, tire pressure, etc? Problems with the dry clutch? Excess rotation about the pitch, roll, or yaw axis is not desired.

KeS
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post #2 of 9 (permalink) Old Mar 31st, 2006, 8:47 am
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Geeezz... My suggestion is you re-think drag racing an RS.... You are kidding, right?

Jerry D. Finley ("Danger" is my middle name)
"I speed, therefore I am. "

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post #3 of 9 (permalink) Old Mar 31st, 2006, 9:37 am
 
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I've only been racing for a couple of years, SEMDRA and Prostar, but that was on a Yamaha Warrior and not the K1200R I just purchased.
From past experiences, I drop the tire pressure to around 12#s and launch at about 2700rpms. This gives me the most grunt without pulling the front-end up. I see a ton of people smoke their tire down to the cords but I just barely warm mine up and let the track do the rest. Typically, it's sticky enough even for street tires.
Have you raced any other bike before or is this just a fun afternoon?
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post #4 of 9 (permalink) Old Mar 31st, 2006, 9:58 am
 
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Quote:
Originally Posted by kevin_stevens
I'm thinking of taking my K1200RS to the local 1/8 mile drags, just for fun. Any suggestions on how to launch, tire pressure, etc? Problems with the dry clutch? Excess rotation about the pitch, roll, or yaw axis is not desired.

KeS
That's a good way to void the warranty if it still has one. The clutch ain't up to it either,
2 or 3 runs is all it will last. BMW doesn't make any good drag racing bikes. Their
bikes suit real world riding.
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post #5 of 9 (permalink) Old Mar 31st, 2006, 11:47 am
 
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As others have said, I"d really think twice about drag racing any of the BMW bikes that have a dry clutch. You could easily ruin the clutch in one afternoon

If you want to do it anyway, just for fun you might try this. Launch from the line just like you're leaving a traffic light, RPM at 2,000 or less, and as soon as the clutch hooks up, open up the throttle. You'll likely loose half a second, or more, on the launch, but at least you would likely have enough clutch left for the ride home.

Unless they have motorcycle "bracket" racing, expect to get eating alive by 600 cc sport bikes :o

However, if they do have "bracket" racing, pick a conservative bracket so you don't have to abuse you bike. Consistency is the name of the game here, mostly on the launch. Depending on your reaction time, I'd launch when the last yellow just lit, or if you're pretty relaxed, when the first yellow lights. Of course, if you're bracket racing, you can wait for the green, if you like, depending on where you are in the bracket. You don't want to break out or red light, either is which is an automatic loss.

Personally, if I were going to try it, I'd suggest that you see if a friend will loan you a 600 sport bike for the afternoon. Those things are tough, and if you did break something, much cheaper to fix than our BMW's.

Have fun, safely
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post #6 of 9 (permalink) Old Mar 31st, 2006, 2:07 pm Thread Starter
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Oh, all right then...

If the clutch isn't up to it, I'll take the TL1000 instead - though I'm much more likely to hurt myself with it. Thanks for the info; didn't know the clutch was a weak point. This is just a for-fun event.

Great - I've got an Evo 8 and a RS, I'm not a big drag guy, but it would be nice to have something with a bulletproof clutch!

KeS
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post #7 of 9 (permalink) Old Mar 31st, 2006, 3:18 pm
 
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Quote:
Originally Posted by kevin_stevens
If the clutch isn't up to it, I'll take the TL1000 instead - though I'm much more likely to hurt myself with it. Thanks for the info; didn't know the clutch was a weak point. This is just a for-fun event.

Great - I've got an Evo 8 and a RS, I'm not a big drag guy, but it would be nice to have something with a bulletproof clutch!

KeS
Suzuki TL1000, good choice! The clutch may rattle a bit, but it's pretty tough. I'd have reasonably fresh oil in the engine when I went to the race, and change it no later than the next day. Other than that, you should be good to go, except for maybe reducing tire pressure in the rear tire a couple of PSI if you get tire spin off the line.

For launch, you can use one of these methods:
1. At the line, hold RPM to about 8,000 and dump the clutch just as the last yellow lights. Control resulting wheel spin with air pressure adjustments. Keep weight well forward to keep the front end down.
2. At the line, hold RPM to about 5,000, just as the last yellow lights, open the throttle all the way, and slip the clutch until fully released at 7k-8k. This is harder to do, and abuses the clutch a bit, but can result in really hard launches without wheelies or wheel spin. Highly modified engines will quickly vaporize a stock clutch, but if you're only running a power commander and pipe, the clutch should probably take it OK.

In either case, I'd wind to red line in the first two gears, and short shift about 500 RPM after that. That TL1000 is a torque monster, it should be quicker that way.

Don't be in too big of a hurry to get tucked in. If you're tucked by the the time you hit third, that should be soon enough. Control is important. You want to strive for minimal wheel spin, and keep the front wheel mostly on the ground. On un-faired bikes I like to tuck in so tight that I use my hand to shift (after either second or third gear, depending on the bike), without clutching, but that shouldn't be necessary on the TL, and that tactic is potentially hard on drive train components.

Some TL1000's were reputed to suffer from headshake problems at high speed if the front end got light. If yours in one of them, you might consider a steering damper.

Once you get the launch technique down to your satisfaction, most of your time improvements are going to come from reading the lights vs reaction time. It's a never ending battle to get better, but can be a ball, and is probably some of the safest racing there is. Have fun
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post #8 of 9 (permalink) Old Mar 31st, 2006, 3:25 pm
 
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OOPs, I just noticed that you're talking about eighth mile drags, not quarter mile. :o

You'll probably hardly need to tuck in eight mile drags, and will probably not get beyond third, or maybe fourth gear, which makes the launch off the line even more important. If you get to liking eighth mile drags, the first modification I'd consider is a large rear sprocket, allowing you to use more gears with the resulting torque multiplication.
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post #9 of 9 (permalink) Old Mar 31st, 2006, 5:15 pm Thread Starter
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Thanks...

I'll stow the large rear sprocket in one of the saddlebags to improve weight distribution.

Actually, for autocross purposes, people have been caught filling the spare tire of Camaros with water - the spare sits right above the right rear wheel, and the improvement in limited slip performance outweighs (literally) the cost of the added mass.

KeS
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