Hey fellas. I've got too much sag on the front end of my '94 (R) model CBR. The springs are original, and a bit tired. Do you guys think I should go for progressive, tri-rate, or single rate but a bit heavier guage? I'm about 95 Kilos with all my gear on. Do all your bikes dive badly under even moderate braking? The springs should help with this, but have any of you re-valved yours and if so what with?
Thanks, Dave.

 

Here are some basic information originating from Traxxion Dynamics:

SPRINGS

Springs are the most important part of the suspension system, other than the tires. They are what holds the bike up, support it under braking and accelerating, and pushes the wheels into dips in the road. Without proper spring selection, the system will not work correctly, no matter what adjustments are made. Oil height is part of the spring component.

Spring rate determines how the bike responds to varying loads. Prolonged braking, acceleration and cornering g's are examples of changing loads. Under severe braking, the fork springs (assisted by the air spring component created by compressing the volume of air above the oil) have to be able to support the total mass of bike and rider (less front end unsprung mass) while still having some travel available for traction. The rear spring needs to support the whole bike and rider (less rear unsprung mass) during strong acceleration while still having some travel available for traction. During cornering, the two ends need to be sufficiently balanced so that one end doesn't compress dramatically more than the other. Given any change in load, the system seeks a new equilibrium position where it can come to rest. Note: that I am referring to the equilibrium position and not the dynamic motion of the system. Spring tuning is not used to address issues of the motion of the system, but rather how a system comes to rest under different loads.

The correct spring is the softest spring available, that is able to support the bike and rider under the hardest of braking/accelerating while still leaving some room for the system to travel if a bumb is encountered in this state.

Springs are rated in three ways, based on the amount of force or mass it takes to compress the spring a given amount:

Pounds per inch - or kg/mm * 55.88 or N/mm * 5.71
Kilograms per mm - or lb/in / 55.88 or N/mm / 9.79
Newtons per mm - or lb/in / 5.71 or kg/mm * 9.79
Only three ways of determining the correct spring rate exist.

Mathmatical modeling and calculations - This would be done by the factories or engineers of top teams. It would be good for getting things in the right ballpark, but all of the variables are impossible to consider.
Data Acquision - This is done by most top level race teams. The actual position of the system will be known for any track position or condition. This is really the best way of knowing what is happening.
Test Rider - A very knowlagable, very experienced rider, with a high degree of skill, will be able to determine if the springs are correct. This is really the point where theory and style will part ways. The stopwatch is the metric.
Most of us are not able to use any of these tools. Worse yet, as good as one person may be at test riding a bike, they can never be a true substitute for the actuall end rider. Due to this, we fall back on some rules of thumb to get us in the ballpark. By using the delta of rider and free sag we can estimate how close our springs are. These are not hard rules, and are open to exception at any time. Remember, also, that sag is a geometry attribute and has almost nothing to due with the suspension system other than changing the extention/compression available at any given point, or in other words, bump and droop distribution.

We can use the concept of "Free Sag" to use the geometry attribute of sag to predict and tune the suspension attribute of spring r

 

dave, Good Q... Blackbirds are to stay away from progesive spinging,I've never heard to stay away for us 1000f people. seems the dive is universal for us... I don't think progr. spings would help that. race tech(US) makes single rate wound,w/ tech to help w/ selection. I have them on my 82 gsx1100, but haven't rode it yet... they were the heaviest rate availeble(i'm 265lb)itermediate to fast rider, street.
"dad" wrote a great post about 1000f suspension, should be in archives. he talked about a 1/2-3/4"spacer up front. I am going to start w/ the spacer solution, then off to racetech for single rate springs. Racetech also makes a "gold valvekit"... cartridge emulator kit, about 150$. I'l bet there as good as they say. I think someone on this forum said they were good too.
One of my concerns, is that w/ linked brakes... changing to realy heavy spings, may upset the "balance" of the link action on bringing the fore/aft suspension reaction. some delink... but i've rode farely fast and not had to wierd of a time. Altho... modulating frnt/ rear brake balance, would be best. I't was pretty wierd to have the front dive w/ the rear brakes !!!!!!!!!!!!! Hope some of this helps, and dosen't open up a bad case of cerebrial intercourse. Clean and free, Ripp'n

 

Here is some more information originating from Wilbers Suspension. I'll go for progressive springs on the Blackbird since there are a number of references to that specific bike. It may be a bad choice for Hurricanes according to Trips experiences and linear springs with the correct rating can never be wrong. To increase the confusion, modern high performance sport bikes do normally have progressive springs stock.


By Wilbers:

Linear:
Linear fork springs are THE alternative to progressive springs which are perfect for road use. Because on the race track what counts is effective adaptation and fast adjustment, undisputedly more simple with linear fork springs. Their repertoire might be smaller compared to progressive springs but in comparison to a bumpy country road, a racetrack is totally flat.


Progressive:
With progressive fork springs of Wilbers-Racing-Suspension bottoming out forks and sulky reaction are going to be history. Due to their construction they manage to take small road damages as easy as deep potholes or brutal braking manoeuvres. That is the result of our critical testing- and development procedures. We permanently test our bikes on racetracks like the "Nürburgring" or on the German autobahn. This provides us with the necessary experience of creating the ideal progressive fork spring. Not before all skilled test drivers are satisfied, a product is offered to the market. Wilbers progressive fork springs are resistant to wear off. They have a lifetime guarantee and a detailed installation manual. Together with the best fork oil and a precise air cushioning you can expect perfect results and unforgettable riding experiences.

 

Anyone try the Race tech gold fork valve kit and/or the Race tech fork springs? these together are over $250 - anyone have an opinion wether the difference in handling/ride is worth it?

 

I have only heard well about them and would give them a try if the fork were too soft. A good rear shock is also important since it will have an impact on the front. Both the front and rear suspension must work in harmony to help the bike to flow smoothly over mean bumps.

 

Thanks for all your help fellas. I'll have to take my measurements again and get my head around the data.
You raise some interesting points, such as the need for both front and back to be one kind or another. That's more dollars than I can justify (my wife is pretty tolerant, but it's not a good idea to push your luck.....too far anyway!), and I'm pretty happy with the back.
I wonder what brand new standard, genuine springs would do and how long they would take to tire. Any of you guys had your bike from new?
I've checked out dad's post on the subject and it might be a cheaper temporary fix for me too (thanks dad) while I go through all the other info and decide which way to go.
My first thought (and advice from local bike shop) was progressive, but after picking your brains I think linear might be the go if I can work out the right guage to use. Some of the road I use every day are really crap.
Anyway thanks for the info. Some of you guys really know your stuff!
p.s. This site is a bloody great recource!
Dave.

 

The other problem with progressive suspension is dampening.

The shim stack in your suspension should be matched to your spring rate. That way the re-bound and compression work as they are supposed to.

But you will never have the correct amount of compression and re-bound dampening with progressives as there isn't a single spring rate. If you set the rebound and compression in the middle then in the 1st part of the spring movement it will be over-damped then when in the middle the dampening will be righ then when the spring is in the very bottom of its movement it will be under damped.

So you will never have the correct amount of dampening for the spring.


Also you need to do the rear as well. The sping rate increase on the front must match the increase on the rear. If you just do the front you may find the bike wanting to understeer.

Finally the best way to make your front handle is to re-spring & re-valeve the rear. It will be the single best improvment to handling.

 

I have no adjustment on my front damping (one of the few shortcomings of an otherwise great bike), but the more I read, the more I'm going off the progressive spring idea.
I would still like to know what you think about new standard springs as sometimes Mr. Honda knows best, and I still feel that the back end is doing it's job. The front just droops a bit so first I'll try shimming.
Trips: On another topic I finally got the V&H sounding good. I went from a 60mm baffle tube down to 45mm, and threw out the sound tube (about 35mm diameter) from the centre. The extra thickness of the packing, which I didn't pack too tightly this time, has taken the tinny sound away totally and now it sounds real nice. It was a lot of mucking around, but well worth the effort, and a lot cheaper than another can!
Thanks, Dave.

 

Sounds good.

As for the suspension remember Honda wanted something that was comfortable. I am very aggressive with the bike in cornering and I'm a big bastard as well. Unfortunately the suspension on the Honda was built to a price. The non-adjustability of Honda suspension in general is one of the things I really hate.

I would really love to have fully adjustable suspension as the slow speed compression and re-bound is purposly left soft on these bikes.

I forgot you were in Australia. The cost of aftermarket suspension is fscked here isn't it?