Jump to content

Sag Mystery


Recommended Posts

Need help. Unable to set sag on RRs. We have a 900 and a 954RR. When we try to set the sag, the numbers never come out correctly. Over the last couple weeks, I?ve been trying to figure out this problem; I?ve tried online references, contacted dealers and consulted a couple track guys. Nobody has an answer.

 

I?ve only been messing with suspension for a couple years so I?m kinda green, but this shouldn?t be this hard. I got four bikes together to set sag: my gixxer, an R6 and the two RRs mentioned earlier ? all stock. The numbers came out perfectly on my bike and the Yamaha. Going by the numbers (for calculating sag) on the two Hondas, I ended up with maximum preload on front and minimum preload on rear and the numbers were still off. I found it strange that both Hondas reacted the same way. For now, suspension settings are back to stock. Anyone have any ideas?

 

A little background: 1998 900RR and 2003 954RR. Both bikes are stock and in very good condition with stock suspension. Geometry is good for both bikes. Stiction is good for both bikes. Factory suspension settings for a 180lb rider feel way off. Baselines that I?ve acquired from other riders give funky sag numbers. I just don?t get it. I?m relatively certain that I?m using proper procedure for setting sag: backing off damping, taking and calculating the numbers. I did after all, have no problems with the numbers on the non-Honda bikes. Additionally, had the numbers been wrong for only one bike, I?d suspect there were something weird with the bike. This issue although occurs on both bikes and in the exact same way. Any feedback would be greatly appreciated.

 

Thanks,

 

Sean

Link to comment
Share on other sites

Sean,

 

Which method are you using to set the sag? There are several variants going around (Static, 1G, with rider and without) also various measuring methods, and tales what the upper and lower tolerances should be (road or race).

 

The one I use is Static (with rider), where you measue the suspension fully extended (M1) then with rider in place, compress and let it rise by itself (M2), then rise and let it drop (M3). So add M2 and M3 and then divide by 2 (gives you the median) and then subtract that from M1. SAG = M1 - ((M2 + M3) / 2). I've found this method works well, particularly on the front.

 

If it was possible to not have any stiction or drag, M2 and M3 would be the same, but you'll find about 20mm difference at the front and about 5mm difference at the rear.

 

I originally found this method on the net using Google.

 

Cheers

Paul

Link to comment
Share on other sites

Or you could look at the thread before this one. I've written up how to set static sag with a rider - which I think is the best way because the bike has to deal with the bike and the rider in any event - the bike doesn't go 'round on it's own!

 

Figures I use are 30mm, front and rear. If that figure goes down to say, 20mm, then the suspension will feel 'harder' because there is less distance for the suspension to travel. If the figure goes up to say 40mm, then the suspension will feel 'softer' because there is a greater distance to travel.

 

Reading your post and maybe reading something into it, the damping and rebound settings come after the sag settings. And, they won't effect the sag settings - that is purely preload. Compression and rebound effect the rate of movement, not the amount. Wind them out one way and the bike will go boing, boing, boing! Set them too far the other way and it goes ooh, ooh, ooh!

 

It's all about balance.

 

Ft

Link to comment
Share on other sites

Thanks for the quick responses. Answering all questions: I use the static method for setting sag. My target sag measurement was 30mm. I thought the damping and rebound wouldn?t effect sag settings, but I backed them off anyway on the Hondas to eliminate it as a possible cause to the problem. Shooting for 30mm on all bikes, I was able to set sag on the Suzuki and Yamaha with no problems.

The anomaly in my situation is the two Honda bikes. On both bikes, I ended up with over 45mm of sag on the front ends? which would indicate the need to increase the preload to reach my target sag of 30mm. I increased the preload as far as it could go and ended up with 40mm. Since I couldn?t increase the preload any further, 40mm of sag was as good as I could get. I ran into a similar problem on the rear of both Hondas. Rear sag numbers were in the 15mm range indicating a need to decrease preload. After decreasing rear preload all the way, I ended up with about 20mm of sag. I could never attain 30mm of sag for front or rear on either Honda. It?s as if the range of the preload adjustments were outside the capability of what I needed to reach my target 30mm sag. As I mentioned, both Hondas displayed the exact same anomaly: too soft in front with no more room to tighten and too stiff in back with no room to loosen.

I?m certain that the measurements I?m taking are correct and the calculations I?m using are accurate. Thanks again for any possible feedback.

 

Sean

Link to comment
Share on other sites

how much oil or rather what is your oil level in the front forks on the honda's?

 

how much do you weigh and what is the rating of the springs?

 

the folks that taught me about suspension believe that the ideal spring rate requires NO PRELOAD to acheive the desired sag. (for starters). but i'm nobody and there are plenty of "guru's" in the suspension biz.

Link to comment
Share on other sites

air is compressible. oil isn't. (relatively speaking for our intent and purposes) just a thought. good luck.

Link to comment
Share on other sites

  • 4 months later...

I have an '02 F4i and have been having a bit of trouble myself. Well not reaIly trouble but, maybe a bit of confussion. After all I am a novice. My forks were shot. I work for a bike salvage so I got a set of springs out of a bent pair of forks that looked like F4i's and were marked '00 (or maybe it was '99 can't remember now) F4i but, they are 13 inches long whereas the '02 springs are 11 inches. They were the same diameter though the actual spring material seemed a miniscule amount thinner on the 13's I cut the spacers down by the difference and used 5 weight type B oil to the stock level. They feel great to me. Better than the worn out ones but, like I said I really wouldn't know. This is the only bike I've ridden and am at a loss for comparisons. The preload is set at 3 rings showing and comp is at 1 turn from full hard and rebound is 3/4 from full hard. I went from a 20,000 mile stock shock to a 5000 mile stock shock. The old shock was at 6 on the pre, 3/4 out on comp anad 1/2 out on the rebound. The new (to me) shock is at 3 on the pre., 1 out on the comp and 3/4 rebound. I'm having a bit of trouble with the balance front to rear. I guess I'm jus tlooking for some affirmation from some of you who know better. Does any of this sound right? I mean it feels okay to me , but just okay.

Link to comment
Share on other sites

When we set up the school bikes (or our personal bikes), we measure the static sag as the first step. This has been pretty well covered in the magazines, I'm sure you can get lots of data on this, but short version is:

 

You need to measure the bike with no weight on the front. Usually you can balance on the side stand and measure the exposed fork tube. Then, with the rider in place, feet on pegs, measure the sag--normal range is 25-35 mm. (obviously, this takes at least 3 people--when the rider is on the bike, someone needs to hold it, someone to measure too).

 

Then the same for the rear. Pick a point above the axel to measure, and measure straight up from that to a fixed point--even put a piece of tape on the cowling if you need to.

 

Like I said, this is a very short version, but there is lots of data on this, and we even have a little video we made and sell at the school for guys that want to see it done by Keith.

 

Start with the sag!

 

Best,

C

Link to comment
Share on other sites

sean, you have a spring rate issue...too soft up front, too stiff out back.

a make-shift spacer can be installed in the forks but, there's a possiblity of coil bind at full compression. that can reduce the effective suspension travel and/or damage internal components when it bottoms out. changing the springs, front and rear, is the correct solution.

 

a general rule for dynamic sag(rider on bike) is 1/3 of suspension travel and static sag(bike only) is 5-10mm out back, double that up front.

 

you were correct in turning the dampeners all the way out when checking for sag. it eliminates guess work when accounting for stiction.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...