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Old 06-07-2008, 09:01 PM   #1
maxgs
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Suspension question

Folks,
I'd like to tinker with the bike to reduce push after the apex. From a suspension fundamentals perspective, what are the tweeks that should be considered?

Thanks for the time.

-Curt
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Old 06-07-2008, 09:22 PM   #2
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Quote:
Originally Posted by maxgs View Post
Folks,
I'd like to tinker with the bike to reduce push after the apex. From a suspension fundamentals perspective, what are the tweeks that should be considered?

Thanks for the time.

-Curt
It could be handled one of a few ways. If I'm reading your issue correctly, it could be handled with a reduced compression on the rear shock (to make it squat more), raise the rear shock height to help you finish the turn better, and probably reduce the spring preload too.

My guess is that any one of the three may help there. I'm sure Patrick would have his own ideas (that are more educated than mine).

IMHO, the front end is not the issue because it's fully extended when you're exiting the apex under acceleration.
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Old 06-07-2008, 09:36 PM   #3
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Wouldn't reducing rear shock compression and/or reducing preload on the rear effectively soften the rear shock thus increasing squat? If squat is increased does the fork angle increase as well thus inducing more push?

I thought that when a bike accelerates the rear end actually rises. If that's the case, then I'd want it to rise more slowly or perhaps rise less. To decrease how quickly a shock returns to it's natural ride height, would I increase rebound??

Lot's of questions, just trying to get info from people who know more than me

Last edited by maxgs; 06-07-2008 at 09:40 PM.
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Old 06-07-2008, 09:48 PM   #4
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Hey, I found this on trackbikes.co.uk - http://trackbikes.co.uk/rear-shock-adjustment

Rear shock adjustment

Shock: Lack of Rebound

Symptoms:
* The ride will feel soft or vague and as speed increases, the rear end will want to wallow and/or weave over bumpy surfaces and traction suffers.
* Loss of traction will cause rear end to pogo or chatter due to shock returning too fast on exiting a corner.

Solution: Insufficient rebound - Increase rebound until wallowing and weaving disappears and control and traction are optimized.

Shock: Too Much Rebound

Symptoms:

* Ride is harsh, suspension control is limited and traction is lost.
* Rear end will pack in, forcing the bike wide in corners, due to rear squat. It will slow steering because front end is riding high.
* When rear end packs in, tires generally will overheat and will skip over bumps.
* When chopping throttle, rear end will tend to skip or hop on entries.

Solution: Too much rebound. Decrease rebound "gradually" until harsh ride is gone and traction is regained. Decrease rebound to keep rear end from packing.

Shock: Lack of Compression

Symptoms:

* The bike will not turn in entering a turn.
* With bottoming, control and traction are lost.
* With excessive rear end squat, when accelerating out of corners, the bike will tend to steer wide.

Solution: Insufficient compression. Increase compression "gradually until traction and control is optimized and/or excessive rear end squat is gone.

Shock: Too Much Compression

Symptoms:

* Ride is harsh, but not as bad as too much rebound. As speed increases, so does harshness.
* There is very little rear end squat. This will cause loss of traction/sliding. Tire will overheat.
* Rear end will want to kick when going over medium to large bumps.

Solution: Decrease compression until harshness is gone. Decrease compression until sliding stops and traction is regained.
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Old 06-07-2008, 09:53 PM   #5
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And for completeness sake, here is his opinion on front fork setup diagnostics.

http://trackbikes.co.uk/front-forks-setup

Adjustment Locations on Forks

Rebound adjustment (if applicable) is located near the top of the fork. Compression adjustment (if applicable) is located near the bottom of the fork. Spring preload adjustment (if applicable) is generally hex style and located at the top of the fork.

TroubleShooting

Lack of Rebound

Symptoms:

* Forks are plush, but increasing speed causes loss of control and traction
* The motorcycle wallows and tends to run wide exiting the turn causing fading traction and loss of control.
* When taking a corner a speed, you experience front-end chatter, loss of traction and control.
* Aggressive input at speed lessons control and chassis attitude suffers.
* Front end fails to recover after aggressive input over bumpy surfaces.

Solution: Insufficient rebound. Increase rebound "gradually" until control and traction are optimized and chatter is gone.

Too Much Rebound

Symptoms:

* Front end feels locked up resulting in harsh ride.
* Suspension packs in and fails to return, giving a harsh ride. Typically after the first bump, the bike will skip over subsequent bumps and want to tuck the front.
* With acceleration, the front end will tank slap or shake violently due to lack of front wheel tire contact.

Solution: Too much rebound. Decrease rebound "gradually" until control and traction are optimized.

Lack of Compression

Symptoms:

* Front-end dives severely, sometimes bottoming out over heavy bumps or during aggressive breaking.
* Front feels soft or vague similar to lack of rebound.
* When bottoming, a clunk is heard. This is due to reaching the bottom of fork travel.

Solution: Insufficient compression. Increase "gradually" until control and traction are optimized.

Too Much Compression

Symptom:

* Front end rides high through the corners, causing the bike to steer wide. It should maintain the pre-determined sag, which will allow the steering geometry to remain constant.

Solution: Decrease compression "gradually" until bike neither bottoms or rides high.

Symptom:

* Front end chatters or shakes entering turns. This is due to incorrect oil height and/or too much low speed compression damping.

Solution: First, verify that oil height is correct. If correct, then decrease compression "gradually" until chattering and shaking ceases.

Symptom:

* Bumps and ripples are felt directly in the triple clamps and through the chassis. This causes the front wheel to bounce over bumps.

Solution: Decrease compression "gradually" until control is regained.

Symptom:

* Ride is generally hard, and gets even harder when braking or entering turns.

Solution: Decrease compression "gradually" until control is regained.

Last edited by maxgs; 06-07-2008 at 09:58 PM.
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Old 06-07-2008, 10:01 PM   #6
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Dude, I didn't read any of that...

But to answer what you were asking, yes, it will increase "squat", the front end isn't going to be affected anyway because when you're coming out of the corner finishing the turn, it's fully extended and not really working at all with regard to it's function.

If you got your answer with your research, then there ya go
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Old 06-07-2008, 10:01 PM   #7
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And lastly.... from http://trackbikes.co.uk/suspension-set-up-guide


Suspension Set-up Guide

Correct suspension setup is the key to fast consistent laps. Setting your bike up specifically for the track is necessary if you want to go get the best out of yourself and your bike.

To what extent you change your suspension settings will depend on whether your bike will also have to cope with riding on the road. Tracks are generally smooth and grippy, roads arenít. If you are only going to use the bike on the track you have the luxury of fitting harder springs and modifying internals. If you ride on the road as well as the track you will probably want to keep a certain comfort level and concentrate on just optimising the current equipment

With incorrect suspension setup, tyre wear is increased and handling suffers, which in turn can result in rider fatigue. Lap times can be dramatically slower and in extreme case safety can be compromised. Hopefully the following guide will help you dial in your suspension for faster and safer riding both on and off the track.

Firstly you will need to check the Fork and Shock sag: this is the amount the forks and rear shock settle under load. To measure it do the following: push down on the forks to settle them, then mark the stanchion with a felt pen or put a cable tie where the dust seal is sitting. Next ask some for help to lift on the bars so the front wheel is just off the ground and measure the amount the forks have traveled down. This is the static sag (or unladen sag), changed by adjusting the spring preload (more preload = less sag). Repeat the same process for the rear, this time measuring the distance from the wheel spindle to a fixed point on the tail. Now you are ready to begin setting up your suspension. The key is to do it a little at a time and make notes as you go.

Basic Setup: Check the following

* Forks sag 18-22 mm for dry track, 23-27mm for rain.
* Shock sag 8-10mm for dry track, 10-14mm for rain.
* Check chain alignment. If not correct, bike will crab walk and sprocket wear will be increased.
* Proper tyre balance and pressure, starting with 30psi front and 32psi rear (either dry and wet).
* Steering head bearings and torque specifications - if too loose, there will be head shake at high speeds.
* Front-end alignment. Check wheel alignment with triple clamps. If out of alignment, fork geometry will be incorrect and steering will suffer.
* Crash damage, check for proper frame geometry.

Stock Tuning Limitations

Manufacturers plan on designing a bike that works moderately well for a large section of riders and usages. To accomplish this as economically as possible, they use valving with very small venturis. These are then matched to a very basic shim stack which creates a damping curve for the given suspension component. At slower speeds this design can work moderately well, but at higher speeds, when the suspension must react more quickly, the suspension will not flow enough oil, and will experience hydraulic lock. With hydraulic lock, the fork and/or shock cannot dampen correctly and handling suffers. The solution is to re-valve the active components to gain a proper damping curve. It does not matter what components you have, (Ohlins, Fox, Kayaba, Showa), matching them to your intended use and weight will vastly improve their action. Furthermore, if you can achieve the damping curve that is needed, it does not matter what brand name is on the component. Often with stock components, when you turn the adjusters full in or out, you do not notice a difference. In part, this is due to the fact that the manufacturer has put the damping curve in an area outside of your ideal range. Also, because the valves have such small venturis, the adjuster change makes very little difference. After re-valving, the adjusters will be brought into play, and when you make an adjustment, you will be able to notice that it affects the way the way the fork or shock performs.

Another problem with stock suspension is the springs that are used. Often they are progressive, increasing the spring rate with increased compression distance. This means that the valving is correct for only one part of the springís travel, all other is compromise. If the factory does install a straight-rate spring, it is rarely the correct rate for the weight of the rider with gear. The solution is to install a straight-rate spring that matches the valving for the combined weight of the bike, rider and gear to the type of riding intended.

Remember!

* Always make small adjustments, more is not always better.
* Always keep notes of what you have done.
* Suspension tuning is an art - be patient
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Old 06-07-2008, 11:32 PM   #8
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Quote:
Originally Posted by tomLSTD View Post
Dude, I didn't read any of that...

But to answer what you were asking, yes, it will increase "squat", the front end isn't going to be affected anyway because when you're coming out of the corner finishing the turn, it's fully extended and not really working at all with regard to it's function.

If you got your answer with your research, then there ya go
What you said regarding this being a shock issue instead of a fork or front end issue really makes sense. I appreciate the help.

-Curt
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Old 06-09-2008, 07:33 PM   #9
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I would drop the front if it is still in the stock position. And, raise the rear.

How much depends on you and how slow/fast you are.

Then it will become a damping/spring issue.
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Old 06-09-2008, 07:34 PM   #10
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Oh, and yes it depends on tires, but only by how much.

Most folks will tell you BS, but if you wanna go fast....................
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Old 06-09-2008, 07:39 PM   #11
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Continuing the thread on suspension adjustment, I found great information in the Penske Racing Shock technical manual.

Ride Height Affects of Rear Shock
Going Longer with the rear shock "eye to eye" will:
1. Raise the rear ride height.

2. Transfer weight from the rear wheel to the front wheel

3. Make the front turn in quicker

4. Reduce chain torque to the rear wheel
Going Shorter with the rear shock "eye to eye" will:
1. Lower the rear ride height

2. Transfer more weight to the rear wheel

3. Make the front turn in slower

4. Increase chain torque to the rear wheel
Road Race Track Tuning of the Rear Shock: Symptoms and Suggestions

A. Change only one adjustment at a time, and send the rider out for evaluation and feedback.

B. Take notes: Keep track of rider comments, lap times, tire conditions, and current weather conditions

C. Be patient, go back to your original settings if you get lost

Symptom: Harsh over bumps
1. Go softer with low speed compression, 2 to 4 clicks at a time (counter clockwise)

2. Go softer with high speed compression, 1 to 2 clicks at a time

3. Increase rear spring sag, -1/2 to 1 turn at a time on spring perch

4. Change to a softer spring rate.

5. Note: too soft compression can bring about a harsh feeling by allowing too much shock travel

Symptom: Excessive wheel spin exiting corners
1. Repeat above steps

2. Rebound can be too fast, allowing the rear to unload and spin the tire. Use caution when changing rebound.

Symptom: Wallowing exiting the corner. Wallowing: to roll oneself about in a lazy, relaxed, or ungainly manner (Webster)
1. Stiffen low speed compression (clockwise)

2. Stiffen high speed compression, 1 to 2 clicks at a time.

3. Decrease rear spring sag.

4. Slow down rebound, 1 to 2 clicks at a time (clockwise).

5. Change to a stiffer spring.

Symptom: Slow turn in
1. Raise for legs in triple clamp.

2. Increase rear eyelet length, 1/2 to 1 turn at a time. Cannot exceed 12mm of thread exposed.

3. Soften fork compression.

4. Increase front fork sag.

5. Speed-up rear rebound.

Symptom: Mid corner push - front:
1. Stiffen rear low speed compression.

2. Slow down fork rebound
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Old 06-09-2008, 07:46 PM   #12
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good stuff Curt...simplifies it for an inexperienced track guy like me
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Old 06-09-2008, 07:48 PM   #13
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Side experience on a heavy bike, very common for busas to drop the front or raise the rear 1" stagger. This causes the crouch on the bike which helps to prevent wheelies initially, and allows a quicker turn in. Plus out of the shot the squat puts the bike fairly even which still allows plenty of control even w the front end beginning to float from acceleration.

I like the dampening to be a little tight and rebound to be a tad softer in the rear so its not springing me back to a stock position. I feel more 'set' when riding. Of course it all changes when you have a passenger(which I frequently have) but the bike can be adjusted to where they don't even seem like they are there using a higher rebound.
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Old 06-09-2008, 07:54 PM   #14
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See my post. lol
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