Race Tech ST1300 Kit

[Rob Hephner]

I'm so confused.. Why would set the fork preload at 39mm or 1/3 of travel. In my little mind I would think you would want it right in the middle to take advantage of all the travel for rebound and compression, yes??

mitch

You set Static SAG at 1/3 of the travel so that Dynamic SAG is at 50% of the travel.

You want to be at 50% of travel in the middle of the corner and the additional forces that come into play will put you there when you have your suspensions Static SAG set at 1/3.

 

[mitch96]

ROB,
Thanks. How does a static sag of 1/3 = 1/2 the suspension travel? Point me to a web site or book. Can't know too much about motor-sicles....

mitch

 

[dduelin]

Static sag is usually or often recommended as percentage of range of available suspension travel. This range is in the neighborhood of 25 to 33% of travel and varies as to the type of bike and intended use. There is no magic number that fits all riders and all bikes. As Rob says however, you want the bike to sit at some amount of sag with you on it while sitting still that equates to when the bike is ridden the suspension is working somewhere in the middle third of its travel. In this middle 1/3 you have 1/3 suspension travel left to absorb repetitive bumps, dips, or hard braking without bottoming and still have the upper 1/3 left to keep the suspension from topping out or hitting the full extended length when the forks extend when the road drops away from the front wheel as when it travels across a sharp dip or flies off a rise or bump. The basic idea is we want the wheels to remain on the road when rolling over bumps and dips no matter what speed or lean angle. If the wheel partially unweights or unloads when it rebounds it loses traction. If the suspension cannot keep the wheel on the road then it loses all traction and our connection to the road is lost.

Lee Park's book Total Control has a easily understood and used method to measure static sag. Sport Rider magazine SportRider.com has a link that explains it well.

This is a good basic tutorial then there is much more info in the external links at the bottom:

http://www.statemaster.com/encyclopedia/Suspension-(motorcycle)

 

[mitch96]

DD,
Thanks. I'll do some homework..

Going to FLSTOC??

mitch

 

[dduelin]

DD,
Thanks. I'll do some homework..

Going to FLSTOC??

mitch

Yes Mitch. I am planning on riding down on Friday and spending the night at the Whale Watcher Motel. How about you?

 

[mitch96]

Yup, If I can get the time off from work..

mitch

 

[Pete McCrary]

Matt from RaceTech said that around 45 to 47 mm was good on the rear of the ST13. They set up my shock for 19 mm. Asked Matt what they mean and he said, if I understand them correctly, from fully unloaded turn in the preload till you compress the spring 19 mm.....

I'm so confused.. Why would set the fork preload at 39mm or 1/3 of travel. In my little mind I would think you would want it right in the middle to take advantage of all the travel for rebound and compression, yes??

mitch

The amount of preload and the amount of sag are two different things. They are related yes, but they are two different animals entirely.

You don't set it in the middle because gravity works in only one direction - down. You want more shock/fork travel in a downward state.

My preference (per Andrew Trevitt's Sportbike Suspension Tuning Handbook) is 5-10 mm static sag for the rear (static is with you off the bike) and then 30 mm dynamic sag (you on the bike). These are the numbers you shoot for to determine if you have the correct spring or not on a bike.

35 mm dynamic sag on the forks.

I think getting the correct springs on a bike should be the first priority. It amazes me how all of the suspension "gurus" gloss over the tuning of a bike's suspension when it comes to spring rates. Sag and correct spring rates go hand in hand. That should be the first thing done before twisting damping knobs. Sad but true, a lot of finding the correct spring is trial and error. I have a whole shelf full of springs for my three bikes. Luckily my VFR and ST both use the same size spring. Keep in mind, even on a bike as heavy as an ST, you represent 20-25% of the total bike/rider weight. The spring that works for one person will not be the correct one for someone else. 100# difference in one spring to another can make a big difference in handling.

Keep in mind when you start getting extreme suspension travel you start getting relatively extreme changes in the geometry of the bike. I firmly believe 99% of an ST head shake is related to too soft a rear spring and too high a windshield. The front end of bike becomes "unloaded" in a sense.

Just my 2?.

 

[mitch96]

PETE,
Thanks, good info..
Is there static and dynamic sag for the front??

mitch

 

[dduelin]

My preference (per Andrew Trevitt's Sportbike Suspension Tuning Handbook) is 5-10 mm static sag for the rear (static is with you off the bike) and then 30 mm dynamic sag (you on the bike). These are the numbers you shoot for to determine if you have the correct spring or not on a bike.

35 mm dynamic sag on the forks.

This is the first time I have seen static sag defined as "rider off bike" although a number of references mention 30-35 mm static sag as ball park figures or starting points.

 

[Rob Hephner]

Static SAG is a measurement of the rider ON the bike NOT moving, thus STATIC.

Dynamic SAG would be the SAG of the bike as it is moving down the roadway.

Since you can't run along beside a bike easily and measure it as you ride it, Static SAG is a way to set you bike up with spending the money for a device such as a Shock Clock, which could measure Dynamic SAG.

To get a proper static measurement of a bike, the rider MUST be on the bike. (The 3 measurement process eliminates friction from being a factor.)

Now, it is true you do not want a spring with zero preload, but also true you do not want a spring will all the preload dialed in.

If you have either situation you'll need a spring with a different rate, as yes I agree that a proper spring should be the first step. But, if you are rinding with improper damping settings you could be in more jeopardy, so setting those properly, even with the wrong spring is not a bad idea.

 

[Rob Hephner]

I firmly believe 99% of an ST head shake is related to too soft a rear spring and too high a windshield. The front end of bike becomes "unloaded" in a sense.

Just my 2?.

I agree 99%.

 

[dduelin]

Keep in mind when you start getting extreme suspension travel you start getting relatively extreme changes in the geometry of the bike. I firmly believe 99% of an ST head shake is related to too soft a rear spring and too high a windshield. The front end of bike becomes "unloaded" in a sense.

Just my 2?.

I don't disagree anecdotally but adding rear ride height by cranking up preload ( the stock prescription to eliminate or at least raise the speed the ST weave sets in ) is counterintuitive to what we know about slowing steering and adding stability by way of geometry changes. Raising the rear decreases trail, speeds up steering, and reduces stability. Why do you think cranking up the rear shock works on the ST?

I never ride fast with the shield up more than two inches or so and yet have had no weave on the same road in the morning and had weave on that same road in the afternoon with the shield down and in clear air. I was the only vehicle on a rather remote road capable of handling the top speed of this bike. The only change was a jacket liner doffed and stored in a saddlebag and a slight crosswind in the afternoon when the morning was wind calm. My pet theory is the wind breaking around the rather broad and blunt front of the ST fairing/mirror housings sheds vortices similiar to what makes a flag wave or those created during yaw instability (dutch roll) in airplanes with insufficient area in the vertical stabilizer. A cross wind adds the X factor to start the weave which then is cyclical as the bike alternatively sheds vortices cyclically from side to side. I believe that dirty air from traffic is sufficient to be the X factor that starts the vortice shedding at much lower speeds (80-90 mph) compared to clear clean air (115-120+).

 

[jnsgardner]

Try borrowing a fork brace. It's only four bolts and takes about five minutes. My STeed went from steady to rock steady. Also, since I put it on, I have had not the slightest indication of cupping on the front tire.

John

 

[Pete McCrary]

I don't disagree anecdotally but adding rear ride height by cranking up preload ( the stock prescription to eliminate or at least raise the speed the ST weave sets in ) is counterintuitive to what we know about slowing steering and adding stability by way of geometry changes. Raising the rear decreases trail, speeds up steering, and reduces stability. Why do you think cranking up the rear shock works on the ST?

I never ride fast with the shield up more than two inches or so and yet have had no weave on the same road in the morning and had weave on that same road in the afternoon with the shield down and in clear air. I was the only vehicle on a rather remote road capable of handling the top speed of this bike. The only change was a jacket liner doffed and stored in a saddlebag and a slight crosswind in the afternoon when the morning was wind calm. My pet theory is the wind breaking around the rather broad and blunt front of the ST fairing/mirror housings sheds vortices similiar to what makes a flag wave or those created during yaw instability (dutch roll) in airplanes with insufficient area in the vertical stabilizer. A cross wind adds the X factor to start the weave which then is cyclical as the bike alternatively sheds vortices cyclically from side to side. I believe that dirty air from traffic is sufficient to be the X factor that starts the vortice shedding at much lower speeds (80-90 mph) compared to clear clean air (115-120+).

I think the stock rear spring is so soft that rear of the bike squats. Yes, raising the rear does quicken the steering, but it also puts more weight on the front end. I don't think you can crank enough pre-load into the stock spring to counter act this.

Keep in mind that the aerodynamic center of force when the windshield is in it's higher positions is above the center of mass/gravity of the bike. In a sense, the wind force is trying to rotate the bike about the CoG of the bike.

 

[Pete McCrary]

Static SAG is a measurement of the rider ON the bike NOT moving, thus STATIC.

Dynamic SAG would be the SAG of the bike as it is moving down the roadway.

Since you can't run along beside a bike easily and measure it as you ride it, Static SAG is a way to set you bike up with spending the money for a device such as a Shock Clock, which could measure Dynamic SAG.

To get a proper static measurement of a bike, the rider MUST be on the bike. (The 3 measurement process eliminates friction from being a factor.)

Now, it is true you do not want a spring with zero preload, but also true you do not want a spring will all the preload dialed in.

If you have either situation you'll need a spring with a different rate, as yes I agree that a proper spring should be the first step. But, if you are rinding with improper damping settings you could be in more jeopardy, so setting those properly, even with the wrong spring is not a bad idea.

Tomatoe, tomato. Every suspension literature I have ever read refers to "static sag" as the sag of the bike without the rider on the bike, "dynamic sag" as the sag with the rider on the bike. I know they are cumbersome semantics - maybe we should refer to them as "empty" or riderless sag and sag with rider.

 

[Rob Hephner]

Tomatoe, tomato. Every suspension literature I have ever read refers to "static sag" as the sag of the bike without the rider on the bike, "dynamic sag" as the sag with the rider on the bike. I know they are cumbersome semantics - maybe we should refer to them as "empty" or riderless sag and sag with rider.

http://www.sportrider.com/tech/146_0006_sag/index.html

As I think I said, you do want some unloaded sag, as a loose spring would not be ideal.

There will be a book out soon that helps really define a lot of these terms and place them in a common architecture.

 

[islandstar]

Anyone know if Race Tech is having trouble filling front fork spring back orders? Been waiting for over 3 weeks now and I can't get a return call back. I discussed with them on taking the bike in for the front fork work to get done in person.

I guess I have to drive over there and ask in person.

I hate to beg someone to take my money

 

[dduelin]

Tomatoe, tomato. Every suspension literature I have ever read refers to "static sag" as the sag of the bike without the rider on the bike, "dynamic sag" as the sag with the rider on the bike. I know they are cumbersome semantics - maybe we should refer to them as "empty" or riderless sag and sag with rider.

I think you mean "free sag" as bike with no rider but whatever. Why I keyed on your attributed definition is that the original Sportbike Suspension Tuning articles were part of a column "Ask A Geek" in Sportbike magazine. The geek was Trevett and if his book uses your definition then he changed his definitions from the original columns and from any number of tuning references out there. If the book is so, they run counter to what terms are commonly used.

 

[mitch96]

Been waiting for over 3 weeks now and I can't get a return call back.

I just ordered gold valves for the front of the ST13. They are there and gladly took my money!! . When it gets a little cooler, gonna throw in the gold valves and replace the head bearings with tapered ones. Then I'll have a mostly Race Tech suspension. I now have sonic 1.2's, Belray 8wt and a racetech rebuild rear shock and racetech/eibach spring. Then I'll try the fork brace again. Matt from racetech thinks they are a good choice if you like the feel of it. Tomatoe/tomato...

mitch
playing in the gray zone

 

[Pete McCrary]

I think you mean "free sag" as bike with no rider but whatever. Why I keyed on your attributed definition is that the original Sportbike Suspension Tuning articles were part of a column "Ask A Geek" in Sportbike magazine. The geek was Trevett and if his book uses your definition then he changed his definitions from the original columns and from any number of tuning references out there. If the book is so, they run counter to what terms are commonly used.

I'll have to dig the book out and see what terms Andrew used when he wrote the book.

The book is at home - I'll make a post this evening when I get home and check.