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Alright, I have been needing to get this rolling since I finished up my DS7 at the end of last year and what I plan on doing is documenting what it takes to get my bike's suspension set up after a front end swap and mono shock conversion. I see a lot of these type of swaps where guys do a mono shock conversion but never explain the pains of actually getting the bike to suspend properly. Maybe it just never happens for some.
Now I don't have any road racing experience or setting up a road motorcycle but I did race motocross in the 90's and the early part of the 2000's. I do understand sag, high speed and low speed compression and rebound so I have a start.
Up until now I have ridden the bike as is. The list of suspension upgrades are:
2001 ZX600E forks. Preload adjustment along with Compression
2008 Ninja 250 Swingarm and linkage
2006 GSXR600 rear shock and stock spring(525ft/lbs). Preload, Hi and Lo speed compression and rebound. This what the hot upgrade for EX250's on the ninjette forum.
The geometry is the pretty close to stock minus the obvious addition of wheelbase length.
Right now the bike handles good in a straight line with no front end swapping. I've only gotten the bike up to about 85mph but it felt stable at that speed. In a long turn it kind of feels like it wallows about and never really settles in. It does feel flickable in tighter turns. Our roads here are pretty bad, well really bad in spots and going over road patches and potholes doesn't make me feel like I'm about to pogo right off the bike.
So far the settings are:
front:
sag: 30mm
rebound : 2 clicks out of 4 clicks total
rear
sag: 25mm
Hi speed compression : 1 turn out of 4 total
Lo speed compression : 1 turn out of 3.5 total
rebound : .5 out of 4 total
I have not measured oil height in the front end and I know that this is very important since this is the only way to adjust compression on these forks but I haven't figured out a way to do this easily by myself. On my dirt bikes it wasn't a big deal to drop the front end and then hold it back up to reinstall the fork caps but this machine is a lot heavier than an aluminum framed dirt bike. Ideas are welcomed. I'll try to find the geometry stuff for the front end or measure it all over again to post it up and do a bike weight comparison.
Without knowing what bike it is and the way you've set up the rear it's pretty hard to diagnose stuff over the net.
The good thing for you is your shocks / forks have very few adjustment settings so it won't be too much hassle to try them all and see which setting works the best (my old ZX9 had infinite pre-load, 12 compression and rebound settings on the front, then on the rear it had pre-load, 12 compression and re-bound settings....)
As far as changing you fork oil goes - they don't put drain screws on modern bike forks anymore which is a PITA. If you are working under a house or have a beam above you can use a ratchet strap to take the weight off the front and undo the caps. If you just want to reduce your static sag you can put a shim under the cap to stiffen the fork a bit.
As Hillsy mentioned it's quite difficult to diagnose with out a thorough understanding of your setup. I recommend you buy racetech's suspension bible and start a journal where you document every change and only do one change at a time. Personally I think suspension setup is one of the hardest and most important things to do on a bike. It took me 3 months to get my Aprilia dialed in and I still think there is room for improvement. Good luck.
Static sag is in the ballpark, but we have no idea about damping until you try some changes and document what happens. BTW was sag measured from fully extended to just the bike sitting there or with you on it?
A good place to start with both spring rates and damping is to get a helper to stand there and just stop the bike from falling over as you try a couple of things. Press down firmly at the rear of the tank. The bike should compress smoothly an at the same rate back and front and it should rise evenly at both ends.
Start with damping backed all the way off to test spring rates first. If one end goes crashing down or is as hard as rocks, you know the spring rates are off and that has to be fixed first. Hard or soft is a bit of a personal preference, but the ends should start off matched reasonably well.
With damping backed out, it may still be too "firm" at one end or both ends and one end of the bike may be sluggish to drop or to rise. Lighten up the damping if possible at that end. A good rule of thumb is that it should take one second to rise and a little less to drop. If it comes up or drops too slowly the damping is too stiff.
Once the bike is balanced ride it again and see how it rides. Add or delete damping a couple of clicks at a time and see how the bike reacts.
Flicking in easily is partly geometry and partly set up. The wallow may be frame flex or it could be spring/damping at the rear end. Are you 100% sure that it's the back end wallowing and not the front end moving causing the rest of the bike to follow?
After you get the basic set up close, the next thing to look at is under hard braking and hard acceleration does the front end or rear drop too much? Is there too much weight transfer? And on your less than smooth roads, comfort will be more important than geometry at race speeds. It's a series of compromises to find what works best for you.
What you will probably find is that the set up for smooth fast roads may be different to bumpy roads with waves in the surface where you might want softer damping and more travel.
Thanks for the replies guys. I don't want to come off the wrong way but in my first post I wasn't looking for a diagnoses. I just want to document the setup of a bike that has a Frankenstein type suspension setup. I don't think that I've ever read a "build" where someone did a front end swap or mono shock conversion and tried to document the setup. I really believe that most people that do those types of builds just ride it as is whether the suspension sucks or not. Hopefully I can capture some of the trials of doing a setup and making it work well.
Teazer, I really need to get out on the bike again and pay attention to what part of the long sweepers it wallows in and where is it coming from. From what I can recall it was near the apex of the turn but then again at that time I was just stoked to be riding the bike and not totally focused on how it was reacting. As far as the sag, I checked it like I did on my motocross bike with my wife as my helper. I measured from the axle to a fixed point near the rear seat area with the rear end FULLY extended and then sat on the bike with my feet up on the pegs and measured to that same point again. I always referred to that as race sag but it may be different in the road going world. For the front end, I used a cable tie around the fork tube and did the same process as the rear.
Like I said before I hope that we can get people to realize that suspension setup is crucial and worth the time especially when you start mix and matching parts from different bikes. You can't just throw a next gen set of forks on any old bike and expect it to work wonders on a 42 year old machine that it wasn't intended to be on. dang, did I just dis myself? Haha
I weighed my bike yesterday using the front wheel/rear wheel method and it came in at 329 with about 3.5 gallons of fuel and oil in the oil tank. From what I gather a stock DS7 is 321.9 dry so I saved some on weight with the upgrades. The EX250 where the linkage and swing arm came from weighs in at 330 dry so it's a tad bit heavier than my bike. The bigger problem lies in that the GSXR(rear) shock is sprung for a 354lb dry bike. Currently the preload has been backed off a good bit in order to achieve the current amount of sag so it's pretty close to the extent of adjustments as far as increasing sag. The spring on the GSXR shock is 525lbs. I am going to buy a lighter spring from Racetech based off of their recommendations.
I took it out for a ride yesterday and did notice that the front end felt high on the exit of the longer turns. It took slow tight turns okay but it did not inspire me to push hard through them. I'll back off of the rebound a click to slow that down up front and see what it does from there. The rest will have to wait until I get a new rear spring sorted out.
So if you can establish what spring rate you need, you can actually calculate within some margin of error the correct amount of dampening force. You will of course need to know your wheel rate and bike and rider weight. Then your unsprung weight, which is generally calculate on a trailing arm as all the mass past (away from the pivot) the 50% (length) mark on the swingarm. To calculate dampening you then use the natural frequency of an un-dampened spring, between the two masses. Using this frequency you can get fairly close on the force you need your damper to produce. Of course, the damper will need to hit a dyno to verify and adjust that amount of force. You will need to be a little math savvy, but it will save you ages in experimentation. Look up spring mass theory to find the calculations.
I will say this, the rate at which you move the damper piston in relation to the wheel (motion ratio) is extremely critical. Dampers generate different forces based on piston speed, so you are likely best off trying to get that damper piston to move at the same speeds as the GSXR did. Then going down in spring rate should you need to would mean that you might only be slightly over dampened. This perhaps is a less technical method of establishing good dampening, but it should be almost as effective, and certainly a lot less math intensive.
Sav0r I did have the rates for the rear end written down I just have to either find it or re-do it. Sounds like re-valving the rear shock may not be out of the question! Ohand Kelley, I'm trying to keep her from becoming a chopper. Lol
If you can find those stock rates and then measure your current you might get away with eyeballing a change. If someone has the shim stracker software you might even be able to calculate a reasonable change with it.
I haven't tweaked a whole lot in the last few days but I have been doing a bit of research. I re-set the rear sag according to the method that is posted up on the racetech site which takes the suspension stiction(don't know if that's spelled correctly) into account. I got the rear in line with the preload set pretty far out again but I couldn't dial in the front. I have the preload adjusters backed all of the way out and it still is just shy of the correct ride sag. To be honest I should have done more research into the spring rates when I was on a buying spree and trying to gather up the components to put this together. I have to admit that I made this harder than it probably needs to be.
I went ahead and bought a stock EX250 shock for the rear end since the damping should work with the linkage rate on the rear end. The GSXR shock would have to be re-valved and probably need to be lengthened to work 100% properly with the EX250 rear end. That's not out of the question but I have a couple of other priorities that I need to spend money on right now so it will have to wait and the baby ninja shock will do for now.
The front end should be a little more affordable but I'll need to find the correct springs and buy emulators to help dial in the compression. When I used a couple of spring calculators online they gave me the OEM spring rates that are in the forks now. With not being aboe to set the preload out front I would think that the stock springs are too heavy. One bad thing about buying used Ebay forks is that you don't know if they have been modified at any point. I'll have to dig around more to verify the correct springs because I'm sure that the formulas that are used in most online spring calculators are pretty generic.
Thanks for the heads up. I did notice in some of the pics of the kit they had a length of pipe included. In my moto days we would use pvc pipe to adjust preload. Is it the same on the street? Meaning like would pvc work with these heavier bikes?
Thanks for the heads up. I did notice in some of the pics of the kit they had a length of pipe included. In my moto days we would use pvc pipe to adjust preload. Is it the same on the street? Meaning like would pvc work with these heavier bikes?
Yes,I gotten spring kits that use PVC for street bikes from the aftermarket manufacturer,I've also used black pipe and washers to fine-tune..;I much prefer spring preload over air pressure in the forks,less stiction.
PVC is the preferred option. How much pre-load is there on your fork springs? If they are heavily pre-loaded, it may not be possible to get the correct sag. You may be able to slide the forks through the triples to get more suitable geometry. We used to set up our old TZ's with minimal sag - say 25mm because the damping was so poor that they dropped too much under heavy braking and I prefer the bike not to see saw. i.e. some weight transfer and suspension movement is good, but too much is too much. On the street you will probably want softer settings to absorb some road irregularities.
With what you have now, what happens when you do the tank test?
I probably could have asked that more clearly. With preload all wound out, how much are the springs compressed - it at all? ie how much would the top cap be sitting high if it was just sitting on top of the springs and not screwed in. Pull one top cap off and see. If it sits say 25mm above the fork, then perhaps minimum pre-load is still too much.
If there is little or no need to push down hard to get the cap back on, it's the spring rate that's too high.
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