rtbain
Expert Class
old, fat and slow
Posts: 244
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posted August 08, 2009 04:30 AM
LSR and mile suspension questions
Why not drag racing? Simple, I have tried it and completely suck, absolutely no consistency. In my youth I was a decent club level roadracer so I can pilot a motorbike. It is a good place to work on my launches for the mile.
Might as well start with what I think I know.
- Lowering the bike reduces drag.
- Lengthening the swingarm reduces the tendency to wheelie, allows for a harder launch.
- I think it would add stability at speed with the trade off of slower steering and greater turning radius.
I have taken the engine as far as I want to go before working on handling, brakes and aerodynamics. The bike is a 2007 ZX14, PCIII, Brock Alien head pipe, K&N air filter, Speedo Healer, Shift light, Muzzy air shifter and Innovate data logging system. It made 161bhp (corrected) rear wheel on a Factory Pro EC997a dyno. Base line on stone stock engine was 148bhp (corrected) rear wheel. The easy horsepower has been found.
I am lucky to have found a 200mph wind tunnel that will accept a motorcycle and rider. My plan is to get a base line coefficient of drag before starting modifications.
Longer swingarm. How long? Extensions make me nervous. Long swingarms without any underbracing make me cringe. But both seem to be common practice in this new experience so maybe it’s just the old roadracer in me being hard headed.
Rear links. Now my ignorance shines. There seems to be great debate over which one is best but I can’t understand why one would be substantially different than another. But then again I haven’t a clue. An explanation of the pros and cons of different style links would be greatly appreciated.
Rear shock. It seems to me valving, travel and sring rate would be affected by changing the rear link lenght. In general, what direction should I go?
Front end. Straps and suspension modifications both seem to accomplish the same task, lowering the front. Why not just drop the tubes in the trees?
Thanks in advance to the kind souls who take pity on this clueless old guy and explain why two plus two equals four.
____________
Randy
   
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wrongway
Pro
Posts: 1078
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posted August 08, 2009 05:07 AM
most of the folks you want to talk to are on landracing.com. I could tell you what I think , but the real racers just laugh at me :-(
Roy
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Shane661
Needs a life
Posts: 11494
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posted August 08, 2009 05:36 AM
Leave it stock length. The "launch" is for drag racing, it is really not of great consequence in LSR. Take off briskly and short shift it into second and pin it.
Get some threaded links to lower the bike precisely where you want it. Either internally lower the forks, or use a front strap, or both. Try to avoid sliding the tubes because the bike will bottom out before you reach the limits of suspension travel.
Stock shock will be fine, don't even adjust it until you test it. If you leave it stock wheelbase, the effects will be minimized.
Save your money when it comes to the wind tunnel. Most of your aero gains will be found by studying the tuck of other fast guys. But to be honest, you need seat time at the track more than anything else.
Shane
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BobC
Pro
Posts: 1736
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posted August 08, 2009 05:51 AM
 Edited By: BobC on 8 Aug 2009 13:56
You are where I was a few years back. I'd done sprinting for years and was looking for something more. I joined a club with access to a 2 mile runway which is used for top speed runs. They also do quarters and I found that the sprinting experience was very useful. You have to launch very hard to get the best out of a bike with less than 200bhp, just like a quarter only you keep going.
I run in a class that does not allow engine mods beyond pipe and power commander, unopened engine as they call it. The bike also has to run stock wheebase and use foot shifting. A Speedo Healer and gearing is obviously allowed, as are aerodynamic changes. We have several other classes from showroom stock right through to 500bhp monsters.
I have found that lowering the bike (both ends) not only reduces drag, as you say but also allows a harder launch as there's less tendency to wheelie. I'm getting into the "nines" in the quarter even geared up 17/40 and that makes for a higher speed at the mile. Dropping the tubes in the trees is limited, eventually the front fender will contact the underside of the fairing, by strapping you compress the suspension and avoid contact. Actually I have dropped mine by one centimeter and strap the rest, this still allows some suspension movement for damping and prevents the bike bouncing along on the front tire. If money is no object then rebuilding the forks would be better.
I have done all the basic aerodynamic things such as removing mirrors and tail section, I tried a couple of different screens too. I would be very interested in anything you find out from wind tunnel testing. The ZX-14 fairing is quite small and shoulders, elbows and feet do increase drag by sticking out. I have given some thought to this and have even considered cutting down the seat and fuel tank to get my chest lower and my torso further back.
Edit:
You cannot underestimate the importance of a good fast start and low drag in the mile. Last year a friend of mine ran his ZX-14 in an identical state of tune to mine but was not lowered. Mine was 11mph faster at 203 to his 192. It convinced me.
____________
Candy Thunder Blue 2006 ZZR1400
Stock wheelbase
Max: 205.4 mph in 1.25 miles
2012 ZZR1400 in Golden Blazed Green
Brock CT Full System. etc
Max: 203.1 in 1 mile (so far)
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Shane661
Needs a life
Posts: 11494
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posted August 08, 2009 06:50 AM
Edited By: Shane661 on 8 Aug 2009 15:39
quote:
Edit:
You cannot underestimate the importance of a good fast start and low drag in the mile. Last year a friend of mine ran his ZX-14 in an identical state of tune to mine but was not lowered. Mine was 11mph faster at 203 to his 192. It convinced me.
If you have spent a lot of time at the dragstrip, then you know that the bike will often pull more mph if you bog it off the line. So what does that tell you? If we had a track that was prepped and could handle hard launches, then sure, I would go for it. But most of the time you will either wheelie or spin the tire. Short wheelbase=wheelie, long wheelbase=wheelspin at these venues. Constant acceleration is what is most important. Nobody is measuring your 60 ft. time.
I am sure that there was more to those speed differences that the ride height. Did you ride his bike under the same conditions, and vice-versa? 2" of ride height will not equate to 11 mph. There were definitely other factors at play.
The low drag part I would agree with, and it pretty much goes without saying. But there are way more important things for a new racer to be concerned about than getting every .3 mph out of the machine. For quite some time the limitation will be the rider. I would be more focused the safety gear for both rider and machine.
Randle, I highly suggest that you go to http://www.landracing.com. If you are serious about getting into LSR, plenty of people will be glad to assist you. Or you can email me: shane at warp 12 racing dot com.
BobC can you tell me more about your 1 mile venue? I race at Maxton, but also just did a 1.5 mile course in Loring, ME. Great winds and long distance led to 211.97 mph. I think that may be the fastest ever pass for a stock motor 14 here in the states. We don't often get good wind at our backs over here. Email me if you'd like. I'd love to correspond and compare notes.
Shane
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BobC
Pro
Posts: 1736
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posted August 08, 2009 09:54 AM
quote:
I am sure that there was more to those speed differences that the ride height. Did you ride his bike under the same conditions, and vice-versa? 2" of ride height will not equate to 11 mph. There were definitely other factors at play.
Luckily there was a sideways on photo of both bikes going through the speed trap and you are correct, there is more to it and it's the rider. The other guy's tuck was not as low but it wasn't up to me to suggest I was a better rider. Everything was in my favour, a more aggressive launch and better aerodynamics, he was never going to beat me. Same day and same conditions.
____________
Candy Thunder Blue 2006 ZZR1400
Stock wheelbase
Max: 205.4 mph in 1.25 miles
2012 ZZR1400 in Golden Blazed Green
Brock CT Full System. etc
Max: 203.1 in 1 mile (so far)
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