Bike Tuning
- Thread starter Honda_guy
- 29 comments
- 1,660 views
- 125
Honda_guy
Yes it does make a large difference. Especially the preload settings. Lowering the front changes the rake and trail geometry of the front wheel.. this has a HUGE effect (at least in real life) on how the motorcycle handles.
A chopper has alot of rake, and normally, alot of trail. The forks are set out at a large angle (sometimes up to 45 degrees or more). This makes the bike very stable, but slow to turn, and not very responsive. It also makes it difficult for the front suspension to react to bumps in the road.
A sportbike has a very steep rake, and a short trail, this makes the bike very 'twitchy' or quick to respond, and it takes alot less effort to make the bike turn fast. It also makes the front suspension more effective. Modern sportbikes have rake of around 22.5-24 degrees. This is quite radical, and mirrors racing bikes of the last decade.
By lowering the front suspension (softening the preload), you decrease the rake and the trail. This makes the bike respond better. Although, softening the preload too much can make the bike wallow, and you lose ground clearance.. so its a carefull balance. If you are tuning a racebike, then you have alot more flexibility.
Be carefull, however, the steeper the rake becomes, the more unstable the bike is, and the more likely headshake is. Headshake is when you see the bars oscilate back and forth. This is not neccicarily a bad thing, its the bike self-stabilizing. But if it gets out of control, its bad news. Too much headshake can cause the rear wheel to loose contact with the ground. This is a 'tank slapper'.
In real life, the cure for headshake is to ride it out. Keep a loose grip on the bars. If you grip them tightly, the oscillations get transferred directly to the chassis through your arms! This causes it to get worse.. unfortiunatly, the reaction of many novice riders is to grab the bars firmly to try and stop them shaking. Also, getting on the gas can help cure headshake.. There is a famous saying:
"When in doubt, gas it. (It may not fix the problem, but it will end the suspense)"
Its very true, alot of motorcycle issues are cured as soon as you get on the gas.
Unlike a car, the suspension of a motorcycle actually raises up as a reaction to the torque when you get on the gas. This increases your ground clearance.
(you can see this happen in TT)
So, for example, if you are ripping through a corner, on the gas, and you accidentaly scrape your footpeg on the ground... your fine. But if you get scared and chop the throttle (NEVER CHOP THE THROTTLE), the suspension compresses, and you lose that cornering clearance... The bike gets levered up on the footpeg and the tires actually lose contact with the ground.
The damping settings are very touchy on a bike.. scince you arent dealing with alot of wieght.. Best thing to do is experiment. The settings of your suspension should reflect how you ride. If you rely on stopping quickly, turning the bike and nailing it, then you may want to stiffen up your front suspension to make the bike more stable under hard braking. If you use maximum lean and keep corner speed high, you want a balanced setting with a compliant rear shock, this allows you to accellerate harder while leaned over.
Just experiment, you will notice significant changes.
Hope this helps!
- 125
Ducatista
I made a drastic improvement on the street GSX-R 600 but increasing preload on the front just 1 click. I changed some other things as well.. cant remember them offhand.
- 125
My pleasure =-)
Spectre600
I was practicing for the New York race of the Special Machines Series with the Moriwaki CBR1000RR and decided to give the suspension settings a try. I decreased the front preload two clicks and the rear one.
I thought it made a difference; I went half a second faster and the turn-in surely felt quicker. Is there any advantage to increasing the preload, e.g. increasing ground clearance and allowing the bike to lean more?
As for the rear actualy raising during acceleration, that has to do with the tension on the chain correct? The compression of the spring caused by the weight transfer is overcome by the chain pulling pulling under acceleration?
- 125
Ducatista
Yes, (again, in real life... not completely sure about TT yet) increasing the preload will make the bike ride higher, and it will improve your cornering clearance. Allowing you to better approach (or exceed..) the limits of the tires. I found it difficult to start fuddling around with suspension on a racebike. But, if it works, dont knock it!
Ducatista
Thats a good way of thinking about it.. Think about the forces in general. Acceleration is like a big hand pushing on the rear tire. Now think about how the swingarm is angled on a bike. Its hanging down. If you were to place the front tire against a wall, and push on the rear tire, because of the way the swingarm is situated, it would 'push' the bike up. In a way, this is also caused by the chain 'pulling' forward on the rear wheel. You have the right idea.
Now on to your comment about wieght transfer vs. torque effect. This is something thats on the cutting edge of racing technology. The goal is to position the swingarm in such a way, that the torque effect is equal to the wieght transfer, so in effect there is *NO* suspension compression or extension in the rear of the bike. Pretty nifty stuff. Make the angle of the swingarm too 'shallow', and the wieght transfer may overcome the torque effect. Make it too 'steep' and the torque effect may overcome the wieght transfer (this is the preffered 'error').
Thats stuff thats on the minds of the MotoGP tuners.
Another interesting note: The BMW bikes all have paralever front suspensions (at least in TT, some older and newer BMW models have conventional forks). These are ridgid forks with 2 pivot points and complex geometry that can be tuned for anti or pro dive charitaristics under different forces. They are modelled after a hossack (sp?) type suspension like in F1 race cars. The famous John Britten V1000 racebike had it as well. Google his name up if you want to see a truely revolutionary bike (swingarm and front suspension bolted to the engine via carbon fibre chassis, F1 style hossack front suspension... just loads of cool stuff. And Britten was a dyslexic that built it with 2-3 other guys)
The advantage of a anti-dive front suspension would be increased stability under braking. The advantage of a pro-dive suspension would be faster turn in (under braking, the rake and trail of a bike decreases, making it easier to turn in most cases).
- 8,480
- P_Balance
Spectre600
What about if the bike uses a driveshaft instead of chains?
I hopped on the YSP/Presto R1 to practice some for the next Special Machines Series race, Valencia, and I tried the same thing there. The bike felt more responsive and I went quicker than in stock form. However, when I did the exact opposite -- the front preload up two clicks over stock and the rear up one click -- it did seem like the bike cornered faster in some places.
It almost seems like it's once again a matter between responsiveness versus corner speed. Maybe that's why lowering the preload helped especially in New York, because of the nature of the course. Fun stuff.
How about the brake bias? According to the description, a higher rear brake bias compared to the front makes the bike more prone to oversteering under braking. Is that because of the greater gyroscopic effect of the rear wheel is reduced more this way, and can this be used to make the bike turn in quicker under braking?
It almost seems like it's once again a matter between responsiveness versus corner speed. Maybe that's why lowering the preload helped especially in New York, because of the nature of the course. Fun stuff.
How about the brake bias? According to the description, a higher rear brake bias compared to the front makes the bike more prone to oversteering under braking. Is that because of the greater gyroscopic effect of the rear wheel is reduced more this way, and can this be used to make the bike turn in quicker under braking?
- 845
slo-car
i ditto that. most def. big help
- 125
PERFECT BALANCE
The 'hand of accelleration' is still pushing on the rear tire, regardless of the drivetrain. The bike will still want to raise up on the suspension.
There is one BIG disadvantage to shaft drive bikes. A chain acts as a 'shock obsorber' for the engine to wheel interface. Scince a bike is so much lighter than a car, a heavy hand will make for a REALLY jerky ride. Scince a shaft drive is directly connected to the rear wheel, this effect is pronounced even further and is called 'Shaft-Jacking'.
This is why shaft-drive motorcycles are hardly ever seen in racing applications. For touring, they are fantastic tho. Chains require alot of maintainance. They stretch, they need lubricated weekly. Shafts need re-oiled evry year or so.
Nowadays, shaft drives are getting better at reducing shaft-jacking. BMW in particular has a system that is supposed to be quite good. But still doesent match a chain drive in smoothness.
Ducatista
This is pretty misleading. It seems that TT takes alot of its cues from GT. The use of rear brakes is the only thing I dislike in TT. I find it to be unrealistic.
In real life, racers use 100% front brakes for stopping. Rear brakes are not for slowing down on a racebike. They are for controlling the chassis, and are rarely used. They can help stabilize the bike under hard braking, or help tune the speed. But using them to slow down is a recipie for disaster.. hears why.
Imagine you are flying towards a harpin corner, and you need to slow down quickly. You slowly start to squeeze both the front and rear brakes evenly.
Wieght quickly transfers to the front of the bike. The extra wieght on the front really lets the front tire dig in and is hauling you down from some major speed (fast braking on a bike is far more violent and powerfull than hard accelleration...). All the while, the rear of the bike gets lighter and lighter. Eventually, the back wheel is wieghtless, not off the ground yet, but just as in hard accelleration, you have reached the limit of deceleration. Now, if you simply touched the rear brake, the rear wheel would stop spinning.
What happens when the rear wheel stops spinning? Glad you asked. Now you have lost 60-70% of your gyroscopic stability, and the bike starts to 'step out' to the side. You are also leaving a black strip of rubber behind you.
What do you do now? As an instict, you may hastily release the rear brake. Bad move. Now the rear violently regains traction and the bike *SNAPS* back inline. It snaps so hard, infact, you are thrown over the *high side* of the bike. Worst case, it can slam ontop of you.
What if you know better than to release the brake all at once? You can try and release it slowly and hope you can hold on tight enough to not get thrown.. but now the bike is dangourously unstable (probably headshaking), and your at a hairpin corner. Seems like checkmate again.
Maybe you are a moto-gp GOD and decide to toss it into the corner regardless.. now the rear is quickly sliding out, your knee is down on the ground and you hold the bike up with it.. Gassing it takes all your balls and the bike shakes violently as it reagains traction and the tire spins wildly out of the corner. Good, you survived. Now go change your underwear.
What they tell you to do in real life, is to keep the rear wheel locked untill you come to a complete stop. You will either just stop, and be fine. Or you will low-side (harmless compared to high-siding).
Anyways, back to TT: I find that if you use just the front brake, you retain the ability to keep your line in the turn, although you cant stop as fast. So I use mainly the front brake, and I use little bits of the rear brake to 'adjust' my speed closer to the apex.
(Most all) Bikes dont have power brakes, and the braking is totally up to the rider. They shouldave left it this way in TT. Maybe integrating it as part of a riding style.. not bike tuning.
- 125
Flattery will get you nowhere... (dont stop)
This is just the real-world knowledge I have aquired through experience and research. Im unsure if it applies to TT. Although most of it seems to work quite nicely.
My advice is helping you understand how bikes work? Is it helping you out in TT? Both? Let me know.
This is just the real-world knowledge I have aquired through experience and research. Im unsure if it applies to TT. Although most of it seems to work quite nicely.
My advice is helping you understand how bikes work? Is it helping you out in TT? Both? Let me know.
- 125
Honda_guy
Awsome!
Maybe it would be worthwile to write a short guide? I have not tried many of the things I know to work in real life in TT.. But maybe a short 'Intro to motorcycle dynamics'.
Would that be helpfull? Does it belong here?
Give me your ideas, let me know.
Yes, that sounds like it would be very helpful, and I am sure many of us would welcome something like that. Right now I'm reading a book by Gaetano Cocco called Motorcycle Technology and Design; it's very interesting, but I think a "condensed version," if you will, and how the dynamics apply to setting up a motorcycle, would be very appropriate here.
- 89
- Whenever GT5 or GoW3 is released
- corn13
I don't know that much about bike but I pick up the game and as I race on Deep Forest. I notice that watching the replay on the front straight right after the starting line right before the hill. My bike keeps lifting off the ground right before I get to the peak of the top of hill, then of course it jumps again after the peak into the first turn.
Is it the preload the reason the bike jumps/lifts off the ground before the hill or is it the bound/rebound? And what needs to be adjust more or less?
I was using the CBR600RR (JP) by the way.
Is it the preload the reason the bike jumps/lifts off the ground before the hill or is it the bound/rebound? And what needs to be adjust more or less?
I was using the CBR600RR (JP) by the way.
- 125
corn13
I am late for work... but ill briefly explain whats probably happening.
I doubt its the preload that causes your bike to jump. More likely, its damping settings that arent compliant enough.
Rebound setting normally mirrors the strenght of your springs.. EI, if you have very stiff springs, you need higher rebound damping to control them when they extend.. otherwise they extend too fast and unload the chassis. If the rebound is TOO high however, the wheel will not be able to follow the backside of a bump, the suspension will stay compressed.
Generally, once you find a good setting for rebound damping (that matches your spring rate), you dont need to mess with it much.
Compression damping is a different story. You normally change compressing damping to suit the type of bumps you encounter. If your on a smooth, high speed circut, you can have higher damping settings, which makes the bike respond better, and feel more stable. However, if you have hard compression settings, and you encounter a bump, the suspension wont be able to comply with the changing terrain and it will bounce your bike into the air (in extreme cases).
If your compression setting is too LOW, then the wheel will get thrown up, without enough damping to slow it down, it will lose contact with the ground. This doesent cause your bike to bounce up in the air, but the wheel does loose contact with the ground and you loose traction.
Most likely whats happening to you is either your compression is too high (Is your bike getting 'jerked' up into the air?), or your rebound is too high (does it feel like you go over bumps ok, but then you 'land' suddenly?)
Setting your preload higher will give you a bit more suspension travel to play with.
Good luck.
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- 3,863
- forever_n00b
- random1self
how do i keep the rear wheel on the ground? specially at places like the last corner of valencia and everywhere at deep forest? i dont even have to get on the front brake hard the rear will come up, step out and i crash as soon as its back on the ground.
at valenicas last corner ive to back off early and gradually apply the brakes. i dont, then the rear end will come up as soon as any front brake is applied.
at valenicas last corner ive to back off early and gradually apply the brakes. i dont, then the rear end will come up as soon as any front brake is applied.
- 125
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Never had problems with this... are you sure you arent pushing forward on the stick *at all*?
Make sure you dont tuck when you brake.. this doesnt cause the rear to come up, but it puts more wieght forward.
- 3,863
- forever_n00b
- random1self
nope, not really. i dont use weight shift like that because the rear always lift when i do. im usually straight side to side. purhapes the negative (forward) seating position is hurting braking?
- 125
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Possible.. A radical suspension setup might cause the rear to bounce when it gets light... other than that, id have to see a replay to diagnose it.
- 3,863
- forever_n00b
- random1self
i dont really tweak the suspesion, just change the tyres depending on the race then ride it.
- 125
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The only way you could be lifting the rear wheel so much is by inadvertantly pushing forward on the stick (or if your controller is screwed up and badly calibrated).
Other than that.. no idea!
