Questions about Fork Oil and Springs

[FZRGarret]

Hey everyone I have been searching the forums all morning trying to find answers to a few questions I have about "stiffening" the front end of my '94 FZR600.

What I am trying to do is fix the front end dive the bike has under heavy acceleration and braking without putting in a ton of money into the suspension on a bike that is just ridden on the streets.

I have been researching and everyone seems to offer different answers...

1) Will replacing the oil seals on the fork and adding heavier fluid i.e. 15wt or 20wt oil alone make a noticeable difference in the front end diving?

2) If not, will adding stiffer RaceTech springs to the above be enough to noticeably fix the front end dive?

3) Is there a need for the expensive emulators that RaceTech sells? I want to avoid these if just the new oil or springs will be enough.

Thank you for looking.

FZRgarret

[taiden]

hey hey, im no FZR expert and you will definitely want to do your research... but....


for what it's worth I've noticed that on a lot of different bike forums people find that going a step heavier and adding just a liiiiittttle bit more fork oil than factory specs helps a lot with the dive.

If I understand the reasoning correctly adding more fork oil removes the amount of air in the fork... air compresses so less air = less easy compressing of the forks.


again this may not be a good idea on the FZRs but it might be worth some research

[FZRGarret]

Hey Taiden thanks for the response. I have read about adding more fork oil than the factory specs call for, I guess the only downside is that it can cause the oil seals to blow out. I understand its annoying when people post the same thread topics all the time because they are too lazy to do some research. I have searched and found multiple how to's on the subject but no one seems to clarify the results. Some people seem to think just changing the oil is enough while others say it won't make any difference. I just don't want to have to do the job twice.

[_Will_]

You're correct that too much oil causes fork seal leaks, less air = more pressure = leaky seals. I just switched to 20w from whatever was in there before and noticed an immediate difference. No more front end dancing over RR tracks, no more see saw action on speed bumps, etc. That's really the damping more than anything. There was a recent thread on suspension where two great suspension write ups were posted but I'm on my phone so you'll have to search.

[DonTZ125]

Oil level is a fine tuning aspect. Considering the FZR has no external adjusters, it is unfortunately the easiest adjustment to make! You are correct that too much oil will blow out your seals; that said, adding oil in 5mm increments, help with full-stroke bottoming. The oil level is measured from the top with the forks fully compressed & the springs out.

[_Will_]

viewtopic.php?f=8&t=6566

The thread

[sweekster]

1) Will replacing the oil seals on the fork and adding heavier fluid i.e. 15wt or 20wt oil alone make a noticeable difference in the front end diving?
FZRgarret

In an answer, yes. I ran 30w racing oil in my old bike (92 FZR600). Contrary to belief, that weight oil won't blow out the seals. It is, however, a lot stiffer. The reason I went with that weight was I didn't want any deflection or diving upon heavy braking. That, and I was being cheap trying to avoid buying new springs. The desired result was achieved in my case. I'm running 20w in my current bike (94 FZR1000). Couple that with a properly adjusted preload setting (my bike is adjustable) and the desired result has been achieved once again.

I would suggest trying heavier oil along with maybe a longer preload spacer BEFORE spending money on new springs. You may feel that's all you need for your riding style.

[yamaha_george]

OK,
let me step in at this point.
Adding more oil lessens the "air spring" above the oil, which if taken too far will blow the seals literally, you will know when you are getting close to blow point when the suspension is too harsh(as though it is almost solid.)

Changing the weight of oil say to 20wt from say 15wt will make the dive and dive recovery that much slower (not good on rippled surfaces.
Going from 15 to say ten will speed the damping to a point where the forks will "top out" the forks "clunk" as they open out to full height again.

Springs:-
Compound wound springs are a cheap fix as they are several rates of spring in one therefore they will do nothing very well and are a compromise.
Straight wound springs for your bikes weigh & you combined are better.
Race tech have a chart for find that prime rate for you.


I know you guys never want to spend money on the bike (preferring to spend it on booze & women) but the best ride is with emulators now the Race techs are expensive which is why I bought TSS PD valves from Australia yeh and even from there they were a lot cheaper!

The cheapest answer is to learn to do spring math. ***** If you know what your springs are rated at say 145 then you can get 180 springs from them by cutting the spring. BE AWARE cutting too much off can lead to spring binding ie the coils hit each other.

HOW to set up your forks :-

http://fzronline.com/wiki/doku.php?id=f ... ion_tuning By some old geezer and his mate

http://fzronline.com/wiki/doku.php?id=i ... _emulators

more details of fork work by the that old geezer


***** SPRING MATH explained by the world renown chassis & suspension guy, Tony Foale

There were several non-answers posted, trying to complicate this matter.  It
is very simple if we make a couple of reasonable assumptions.
If the spring is wound linear and if we disregard the effect of the end coil
flattening (only a small error is introduced with fork springs by
disregarding that, due to the large number of coils), then we can say that
the number of coils is proportion to the length of the spring. The spring
rate is inversely proportion to the number of coils and hence also to the
length.  Thus the spring rate of the 430mm spring reduced to 405mm is simply
430/405 = 1.06 in other words the rate will be increased by 6%.
You could also just count the before and after number of coils, but the
result will be much the same anyway.
KISS.

Regards

Tony Foale
info@tonyfoale.com
www.tonyfoale.com

[FZRGarret]

I don't think that $100 for springs is unreasonable if it will achieve the results I am looking for, I just don't want to get the bike all back together after just adding the heavier fork oil and find that the diving under breaking isn't resolved enough; my bike really dips low when I brake heavy.

Do I need to replace the two bearings in the forks that RaceTech sells when I do this job, or are the original bearings usually good enough to reuse?

Thanks everyone for all the responses.

FZRGarret

[yamaha_george]

; my bike really dips low when I brake heavy.

Do I need to replace the two bearings in the forks that RaceTech sells when I do this job, or are the original bearings usually good enough to reuse?

Thanks everyone for all the responses.

FZRGarret

FZRG,
when it dips like that do you hear a clunk? or seem to want to toss you over the bars ?
if so change springs according to the chart at Race tech website

As to "bearings AKA bushings " you will not know that till you have the forks in your hands and feel the play in the bushings.

[FZRGarret]

Hey Yamaha_George

Yes when I brake hard the bike feels like it wants to throw me off. I went ahead and ordered RaceTech springs, oil seals, dust seals and 15wt fork oil. I'll be sure to post my results when finished.

Thanks for the responses everyone.

fzrg

[ragedigital]

FWIW, I changed the stock fork springs to the recommended Race Tech springs and didn't feel that I got the desired effect I was looking for. I added a blend of 15 and 20 weight oil and it made an improvement.

[yamaha_george]

FWIW, I changed the stock fork springs to the recommended Race Tech springs and didn't feel that I got the desired effect I was looking for. I added a blend of 15 and 20 weight oil and it made an improvement.

D,
Odd because RT advice was not the same as my OZ suspension man at all, his worked ! The RT air gap was way different to my mans plus they recommended 10 wt he recommended 15wt