Bandit Alley
MODEL SPECIFIC => SUZUKI BANDIT 250 & 400 => Topic started by: chef on November 04, 2008, 10:05:33 PM
-
After rebuilding the beloved B4 almost i still have issues with the front suspension....fork seals have been replaced,correct fluid,levels etc....no leaks or pits but the front end just feels hard & soggy i guess the best way to describe it...feels like its just pressure from the oil,so i am thinking maybe install prog springs.
Any input on what the benefits are would be helpful as its quite an expense shipping any parts to Bali.
Cheers.Matt.
-
Try a lighter oil and slightly less. I went to 5 weight and .5 oz. less and it made a big difference.
-
Hard & soggy? Isn't that the opposite? Anyway, the progressive springs are there to find some mid-way in the damping of the fork, because there are no damping adjustments available. If you want traction under heavy load, (read fast cornering, hard braking, braking into turns) you would need a stiff setting or the fork would bottom out. But that would make the bike behave terrible in low speed hairpins. So a progressive spring gets stronger as the load increases. Maybe you are way under or above the average weight the bike was designed for, then you would need springs with a different spring rate than stock. The only thing that changes with the type of oil you use and the height of the air chamber is the damping characteristics of the fork, not the stiffness.
-
Hard & soggy? Isn't that the opposite?
Maybe too hard on compression and too slow on rebound? I can see slow rebound being described as "soggy".
-
Herr Tod I love that kind of talk. It's an area that I have just got into. I bought a 07 B12.5 and was completely upset with the harshness of the front end. Was thinking of a big buck fix when a friend suggested working with what I had. My scooter came with s008 fork oil and let me tell you that is some thick shit. Changed to Ams 5 weight and it was an improvement. Decreased the spring preload and found that to be the wrong direction. Have increased the spring preload (increased the air pocket) and found an improvement. That air thing is a factor that I never dreamed of.
-
great for old men on old bikes :stickpoke:
-
Usually my approach to forks is to overhaul them first. Mostly I stick to 10W oil and the stock air chamber. Then I turn the damping to fully closed, compression damping closed, rebound closed. I turn out the spring pre-loader. Now strongly press down on the fork, it will see-saw. Turn in the spring pre-load until it stops doing that, that is about the right setting. Usually I can leave the compression damping fully closed, maybe half a turn open otherwise the fork will be too soft and it will bottom out under heavy breaking. I set the rebound damping to a setting that makes the fork go from compressed back to it's origin in about one second.
Then I put a tie-wrap on one leg's inner tube and take it for a ride, doing everything I normally do and some things people would call 'stupid' like braking hard on a road that has many heavy bumps. After all that the tie-wrap should be *just* touching the bottom of the fork (in the case of an upside-down fork). So if you would ever go through a pothole while the bike happens to be on just the front wheel the fork won't bottom out (hopefully). I adjust the spring pre-load depending on where the tie-wrap is until I get it where I want it to be.
The compression fine tuning is a matter of taste. Kind of difficult to determine what to do with it in the beginning. To get a feeling for it I'd try the extremes of both the front and rear rebound and compression dampings. Just turn it all the way in, go out and ride, turn it all the way out, ride again, do it halfway, ride again and so on until it's clear which setting does what. Then adjust bit by bit and test ride on the same road under the same conditions, especially note the tire temerature.
And then some... suspension is a bit weird and can get you frustrated. It's always good to write down a basic setting that you know will work for you with your bike and your current tires. Otherwise you'll be chasing your tail.
Back to the springs, before I replaced the B4's fork for a GSXR one I replaced the stock springs with progressive springs. It made the fork much harder and the damping characteristics changed a lot. I did go from 10W oil to 5W though, so I can't really say what the springs would do on their own, if I had stuck with the 10W.
Doesn't have anything to do with old men in my opinion, it's just one of the few things one can do to set up a fork that doesn't have damping adjustmens on the outside.
-
You haven't seen rough roads. New Mexico's idea of a road crew is 2 wetbacks and 1 shovel. They knock down the sagebrush and throw oil at it. Hard to tune for. Beautiful country though.
-
I really did not like the progressive springs I had in the bike. Ride either wallowed or was too stiff, really not progressive at all. There was also no way that going to a lighter weight oil was going to help things as the rebound was already too fast with 10wt oil not to mention under braking the front end would nose dive completely through the travel.
Of course this depends on how much you weigh or what you're looking for as far as ride quality is concerned but being on the more aggressive end of the spectrum, besides a USD upgrade straigh-trate springs for your weight, an oil change and emulators are the best way to go.
It's a damper rod fork, the lowest common denominator suspension. They're aweful stock but can be made much more bearable with some well thought out parts.
-
I really did not like the progressive springs I had in the bike. Ride either wallowed or was too stiff, really not progressive at all. There was also no way that going to a lighter weight oil was going to help things as the rebound was already too fast with 10wt oil not to mention under braking the front end would nose dive completely through the travel.
Of course this depends on how much you weigh or what you're looking for as far as ride quality is concerned but being on the more aggressive end of the spectrum, besides a USD upgrade straigh-trate springs for your weight, an oil change and emulators are the best way to go.
It's a damper rod fork, the lowest common denominator suspension. They're aweful stock but can be made much more bearable with some well thought out parts.
I'm GSXR400 Racer and I approve this message...hehe
-
Thanks for all the input guys and will be sure to try some of those suggestions after i really sort out the back end & see what effect that has on the front.
Got a used Fox shock & the guys at Fox racing have been very helpful in identifying the model & sending me a complete detailed installation & set up guide,the ride height seems higher but it just doesnt feel like it has much rebound so am hoping the spring isnt shot.
We have tested it several times & found no leaks but after bouncing the bike a few times there isnt any pressure in the unit.
Its at the shop now being refilled with nitrogen & will see what happens after that.
Am looking forward to a semi comfortable ride after getting these issues fixed.
Oh yea...my weight is about 70 kg.
-
The stock springs are dual rate, at least in my '93 b4. The initial rate is 0.63kg/mm until they get compressed about 103mm then it changes to approximately 0.94kg/mm.
Here's the spreadsheet with measurements I took and a couple of graphs, and also a dwg with the bandit springs and some other bike's springs:
http://cid-b37a983fa606d24a.skydrive.live.com/self.aspx/Stuff/bandit%20fork%20springs.xls
http://cid-b37a983fa606d24a.skydrive.live.com/self.aspx/Stuff/bandit%20spring-rate%20graph.dwg
I love this stuff, I guess I miss being at uni and doing labs where we got to make graphs and measure things etc.
Anyway, progressive springs are similar to dual rate, except that instead of a kink the rate progressively increases in a curve.
As I understand it, a low rate means the forks compress further given the same bump, but also that they'll extend further when accelerating because the force in the spring doesn't decrease as quickly as a higher rate spring. So softer springs means the forks will dive more under brakes and also extend more on acceleration. Also with a soft spring, to get the correct amount of sag will require a larger amount of preload, which means the force in the springs when the suspension is fully extended is fairly high, so when you're accelerating hard and the weight is transferred to the back wheel, the front wheel will be more likely to skip on bumps because of higher preload/spring force.
So to me, I can't see the advantages of a progressive or dual rate spring. IIRC, I've read comments from the local Ohlin's guy and maybe also Paule Thede (RaceTech) that recommended against progressive springs.
-
I guess it's just individual preference, I love progressives. I had my B4 for about 2500 miles when I crashed. The bike was fortunately repairable and I had progressives put in. When I got the bike back it was transformed by those springs. The whole machine felt so much more responsive. I never looked back. Next bike I get will probably get progressives dropped in immediately.
-
do your self a favor an get straight wound for your weight and racetech or whatever valve kit you can and be even more amazed at how something that is set up for you really feels
-
....and I approve this message....
I can definatly wait another 4 yrs to here that again. :grin:
do your self a favor an get straight wound for your weight and racetech or whatever valve kit you can and be even more amazed at how something that is set up for you really feels
Amen Brother! :clap:
-
>>do your self a favor an get straight wound for your weight and racetech or whatever valve kit you can and be even more amazed at how something that is set up for you really feels<<
I wouldn't argue that a custom setup will yield better results, but it's a no-brainer to throw progressives in a fork and instantly improve a bike's handling. I wouldn't know what the springs and valve setup you mentioned would cost, but the progressive set me back $70, which I thought was a decent price for a significant improvement.
-
$90 for straight wound with weight of your choice... 100-130 lbs. about .75-.80 140-180 lbs about .80-.90, 190+ .90-1.0 springs dont hold me to this but it will get you in the right direction. I run .85's traxxion dynamics springs and valving in my weapon.
-
with staright wound you have consistant feedback well worth the $20 bones more. :beers: :motorsmile:
-
the valving is a extra added bonus latter down the road for like $110 i think...
-
You know, I'll keep the concept in mind, but I'm looking down the road at maybe an SV650, and it would probably be better to invest in that bike's front (and rear) end and leave the B4 as is. I can live with the B4 with the progressives.
While I really don't know a lot about rigging up a bike, I'm beginning to realize that my riding skills can use a more responsive machine. I need to get some track time in as well, I've considered tripping down to Road Atlanta and taking the Swantz course.
On the street, however, I'd like to have something that will be a bit more responsive yet still be good for distance. I think a well set up '650 will do that for me at this time.
-
The SV has the same crap-tacular front end as the B4, right down to the brake mounts on the forks (albiet with one extra). The rear shock is also in the same league and if you spend any time in their forums as well, you'll see that it's another weak point.
You should make sure to budget for suspension accordingly if going down that road. I know Traxxion Dynamics has a drop-in kit with premodified rods for the emulators for the SV and guys commonly adapt Kawi and GSXR rear shocks.
If anything, the B4 and SV are country cousins suspension-wise. Performance-wise, I'd ask Eric since he's been to the track with both and he can give you a bit more insight. I just wished that the little bike had the same aftermarket that the SV does.