Anyone know how to stiffen the front on a CBR 1000 F -92 in a simple and cheap way? Can distances above the springs be used to increase preaload and is use of a heavier oil worth trying? The fork has been renovated with new seals.

 

Doing pre-load doesn't stiffen the springs. All it does is set the sag.

Using heavier for oil will only ajust the re-bound and you really need to do it to match the spring rate. Using too much re-bound with a standard spring will f*ck up the handling. Ajusting the fork oil level will stiffen the compression slighty, but idealy you want your fork oil level to be the same as your fork travel.

To get the best out of the forks just save ya $$$ and get some new stiff linear rate springs. Remember the springs in your bike are 16 years old and have been compressed millions of times. You guys in the US pay bugga all for springs so here is what you should do .

1. Buy stiffer springs to suit your weight.

2. Flush forks, replace bushes, seals and replace with heavier synthetic fork oil.

3. Re-valve with Racetech Valves or similar.

If you can afford it you will save a lot of $$$ by getting it all done at once. But no matter what I would definately get the springs done 1st.

Cheers
Big Rob

 

Thank's Trips, I agree completly.
/ Mike

 

I will relay what I've done to mine and it's an improvement and acceptable while not optimum. I should also mention that I prefer a suspension that's on the softer side of what's commonly acceptable at the track and especially prefer it as my bike is ridden much more on the street than track. These are fun but aren't the best choice for a track bike. That's part of the reason I stayed with easy tuning items rather than expensive components. It'll never be a 400 pound track tool and I'm not going to try to make it that. Plus, they're not so bad in front/rear match just as they come. I set out to do this using the standard practice and very generic approach to sportbike suspension set-up. If you look at this you'll find that these methods and measurements aren't brand specific but pretty typical because the goals and parameters are pretty typical. Also, I weigh 200#.

Mine is a '90 but I believe they are the same through '92. They are cartridge forks, '90 being the first year for that. Also, the standard bounce test, standing aside the bike and compressing and releasing with the downward force exerted at the back of the tank and the peg, the compression and rebound are very similar front to rear which is a goal of any re-spring and valving. Both end compress together, both ends return together. Too much rear rebound can be adjusted in but can also be dialed back out. A match in this fashion is probably more important than an optimum at one end while the other end isn't close.

Front end. You can measure the static sag (bike with rider) and compare it to the free sag (bike w/o rider). A differential of about 5/8" will indicate a spring that's about right in its sizing/rate. That's the range, maybe 11/16", that mine measured.

This can be done with a wire tire around one of the fork legs. It's easy to top the suspension out on the sidestand, pushing towards the stand to take these measurements. If you're in that 5/8" differential range then the spring's pretty close and may be able to be left alone. Much over 3/4" and you'll probably want to change it out. Reviewing the recommended springs using a chart from a supplier like Traxxion Dynamics suggests a spring that's actually stiffer than they make but the stiffest would be OK (a 1.0). They aren't typically working with 600# sportbikes. I left my stock ones in but wouldn't be against a 1.0 trial.

If the spring is OK and determined that you'll leave it in, now consider the static sag number. This is where mine was pretty far off. It should be in the 1 3/8" range, as little as 1 1/4". Mine measured 2 1/8" stock. This can only be corrected by taking it apart and replacing the spacer with a longer one. The additional spacer length will be about the same amount that you're trying to lift the front by. There is a slight lightening of the front so a slightly greater change is possible but will only tend to be a rounding error, not anything grossly different from the objective. In my case, I added 5/8" to the stock spacer length and wound up at 1 1/2", exactly what you would expect. I did that because I was experimenting at the time and was hesitant to change any more. The results are OK as is and were left there but I also wouldn't hesitate to go up the extra 1/8" now that I've ridden it. That would also fall right into the generic suspension set-up guidelines for sportbikes in general.

Another reason I left it a tad low was the fact that I was raising it substantially, and more in the front than the rear. That combination tends to steer heavier, was already a little heavier from running the 180 rear tire, and I was concerned it may get objectionably heavy steering. That proved to not be a problem but it IS heavier, most attributable to the wider rear tire that I use than the slightly raised front. For the street, put a 170 on and it's TOTALLY fine. A 180 will require a small amount of body movement side to side well before you would expect to need it. I

 

Thank's a lot dad for taking the time to share your knowledge ! I'll goe thrue all the steps you have adviced and am convinced that they will help to improve the handling. I can also see some general and sound advices in your reply that I didn't knew about before.

Right now I have no idea how the bike is handling, I bought it a few weeks ago and it is still winter here in Sweden. Another few weeks and the temperature will go up and nothing can keep me from the road.

So far the bike looks fine, no cam chain rattle cold or warm and no destroyded threads found etc. Intake valves were tight but not open and easy to set to spec. I have put new Michelin Power F/R which I hope will keep me off ground visits, they work very well on my GSX R1000. Have just started to remount all plastics. The top fairing was replaced since the one on the bike was heavily cracked and miserably repaired by cowboy builders. I was lucky to find an old but totally fault free fairing here in Sweden which has been nicely repainted at a shop.

 

You might want to leave it alone until you get a chance to ride it a little. Give you a chance to have first hand experience with what each way feels like. It's easy to switch back or alter if you're not satisfied. Those changes are easy to take on as a week-end project or when a few rainy days will hinder your riding time.