Front Suspension Upgrade - FZR

OK for clarification the monroe term rod actually means spring diameter, not the diameter of the wire used to produce the spring - confusing at first

Easier to understand...

http://www.bluecoilspring.com/rate.htm

http://performancetrends.com/Definitions/Spring-Rate.htm

 

After reading half that article i thought tha the compression rate is mostly controlled by the oil flow through the valves in the rod, arent the springs there to return the forks to their uncompressed position?
I can see that they would assist in dampening but the oil does all the work?
It might be a simpler operation to reduce the holes in the rods?
What percentage does each component play in the job ?

 

there's different element all interacting

Spring rate on it's own affects how much weight causes a certain amount of compression - the damping attempts to control the end points of travel to ensure the spring doesn't overshoot and pogo.

Instead reaching the compressed state and recoiling at the desired rate, also the rebound damping controls the return so it doesn't overextend and bounce upwards.

Now that I know what symptoms I'm looking for I will be able to hopefully diagnose what occurring more easily

peace out

Glenn

 

Sorry forgot to mention you may be right on the money about the size of the damper holes as I read elsewhere recently that someone got some forks from Japan and the holes were both larger and there were more of them...

 

Reading the specs for the 400 springs that Brian published - it's simple enough to see where the lowest rate ends in the fork travel - its basically the available space between the coils of the softer section.

Of note, the tighter coils are the lower spring rate.

On my springs - the softer section is ~145mm long - the coil wire diameter is 4mm and there are 18 coils. So ~1/2 of that section is the initial travel.
Making the assumption that the lower rate spring section binds before the higher rate section begins to compress - which is not quite true.

Now 32mm of that is the extension outside the tube - the compression height, some of which is taken up by both the top out spring under the damper tube and some by the main compression spring.

Minus the static sag...

So the dive under braking is at least the remaining softer end of the main spring and the momentum from that soft start carries onto the stiffer section.

This is where I am now forming an opinion against dual rate springs for forks.

When you grab the front brake and the forks begin to compress under braking forces combined with the bike and rider weight, you generate momentum, which is then carried forward into the compression of the higher spring rate section.

If you have spare springs take the softer section (tighter coils) off and extend the spacer to make up for the removed length and see how they go.

 

Interesting, I calculated a spring rate of 0.72 for an 85kg rider on the FZR250 off the Racetek site. The lightest they sell is .85kg/mm.
Whats the suspension like on the FZR400's ? Soft like the 250's or a bit stiffer ?
Whats the hole centres on the rear shock on the 400's ?

 

curious - for the FZR400 spring rate - I get .748km/mm for semi wet weight of 151kgs and rider weight of 85kg

I'm not certain of the actual semi-wet weight and what that term specifies - it's ambiguous at best

 

OK makes sense, but where does that sit between a dry weight of 141kg and a wet weight of 151kg

Their wet weight sounds more like actual semi-wet weight because there isn't a full fuel tank of 14 in a 10kg difference

 

I know if I went back through I might find the answers, but how do the 400's suspension compare to the 250's?
Mean size wise, will the springs fit into the 250's & is the rear the same length?
You know what I'm thinking.
That'll be too easy I suppose.

 

If you go back through the various bike options on the race tech site you'll find the S3234 series springs are for the FZR400 - 600 750 and various others...

Anyway the racetech springs are recommended for the fzr400 forks and the R6 shock for the swinger

 

Guys great read on some things which I've already done, and also some of what I had planned to do

http://www.rgv250.co.uk/forums/index.php?/topic/50707-increased-spring-rate-done-cheaply/

I'm going to finish my second doodad for changing the spring length whilst they are in the forks, so I can test ride it before cutting anything - then I'll do a full write-up

peace out

 

Hmmm - much nicer price

http://www.mikesxs.net/product/27-1086.html

 

well locally available progressive springs with some listed specifically for the
fzr400, the same ones are also listed for the fzr600, fz700, fz750, and Seca II

http://www.ikonsuspension.com/content/application_lists/fork_springs/yamaha_fork_application.shtml

peace out

 

Yes the fork spring specs and prices are a bit of a glaring omission but at least they should be able to answer any questions knowledgeably which is a bonus

Did you check out the mikes damping valves?

http://www.mikesxs.net/product/27-1086.html

~1/3 the price of race tech ones and with any luck will fit our damping rods

I'm going to ask for the dimensions as these seem to get mentioned everywhere for many different makes and models of bikes