I need to stiffen the stock front suspension on the cheap, and I know thicker oil and more will help. Spec is 110mm from the top and 15W oil, but it doesn't list max height. Any advice here?
I weigh 170lbs with gear and ride this fast, hard, and often low...with knee down sometimes.
In my opinion I wouldn't try to mess with the suspension "on the cheap." If doing so was effective nobody would spend money on correct spring rates, preload settings, or valve emulators. The perception of stiffness will not necessarily make your bike easier to handle when it matters most. Would you try to modify brakes or tires on the cheap?
Additionally, if my understanding of our forks is correct, increasing the fork oil hight will only stiffen the perceived spring rate at the very end of fork travel. I trust that the Suzuki engineers designed for a specific air gap and I would feel uncomfortable messing with that aspect of the engineering without knowing how it effects the whole system. You may be asking to blow fork seals or shorten the suspension travel. I have never seen anybody suggest changing the compressed oil height.
When you're choosing a fork oil weight remember that you are not only changing the compression dampening but also the rebound dampening. Too slow rebound dampening can get you into trouble if you are riding hard and fast as each bump effectively eats into your available suspension travel. I would not use anything thicker than 15W without careful testing.
What exactly about the forks are you trying to fix? Have you already properly set the pre-load on the front and rear? Remember that break-dive and bottoming out of the fork are not necessarily indicators that your forks are not stiff enough. Break-dive is a necessary condition of having telescopic forks and even more so given the rudimentary design of the GS 500 forks. Trying to redesign the forks to fix brake-dive may make around-town riding more enjoyable, like its "on rails," but it will only cause problems when you're really pushing your forks hard. You also don't want to over correct for bottoming out of the forks. Occasional bottoming out of the forks just means you are effectively using the entire range of travel of the forks. That's a good thing. If it's happening more than once or twice per ride, when you are pushing the bike hard, then you do need to think about stiffer fork springs (but first check to make sure you have the correct pre-load sag).
When I was new to riding and pretty much everything motorcycle related, I thought that all I had to do was switch to 20w oil in the forks and have new seals put in. At the time, I was right around 125lbs (not adding in gear) ... but I still didn't like how the front end felt the more comfortable I got riding... especially once I started taking passengers from time to time.
I know that probably won't help in this case but I figured I'd post about what happened to me.
Currently I weigh 147 (again, not adding in gear) and after using the sonic springs rate calculator and talking with Rich Desmond, I'll be rebuilding my forks with the proper springs for my weight and riding style and 10w oil. I was surprised when he said to stick with the 10 but... as we all know, he knows what he's talkin' about! And this time I wanted to do it right.
I'm interested in this thread to learn more about the forks on our bikes, suspension etc. I have to get ready for work now but I wanna re-read your information Bluesmudge and process it in my head :cheers:
Thanks for explaining. Where are directions for setting preload and such? It's not in the SM. Im confused as to why I should have to adjust it though. Backrgound: although a bit soft, it was good enough when I got the bike 3 years ago. It became more and more soft last year. So, I replaced the 10 year old factory-installed oil in there and checked the seals, seals are good. The only thing Ive done is change the oil, and I installed everything just the way it was originally. When I tested it yesterday, it still felt too soft, dipping to easily. It does not, and never has, bottomed out though. The tank is off, could this make a difference? 5 gallons of fuel with tank weighs about 50 lbs. Would it feel stiffer if I threw all that back on and tested?
EDIT: I think I know what I did wrong: the bike is drained and stripped. The tank it removed, and so is the muffler, and fairings, and oil, and fuel, and I gained 5 lb over the winter. Add it all up and its about 120lb lighter than when I rode it last. So, this is humbling, sorry to waste your time!
First: the bike does need stiffer springs for most people of average weight ( Aussies and US).
Second. If you raise the spring rate you MUST increase the rebound AND compression damping to match. Changing oil will change the damping rate of both by the same percentage ( not the same amount in actual force).
The cheapest way to stiffen the springs is to shorten them . The amount you shorten them is a simple function, until you exceed the interspring distance ( plus overload factor) . New rate = old rate X the original number of coils / new number of coils. eg cut it in half and it doubles in rate. There is NOT SUCH THING as a progressive coil spring, unless the spring is coil binding as it goes through it's travel ( something that sould NEVER happen).
If you cut the spring you MUST rebed the end. Easy to do with a MAP torch IF you have practice. And regrind the cut end flat and right angles to the spring length.
This is what I had to do when after ordering the correct rate spring for the GS, the supplier sent a stock rate, which was way too soft ( I use GVE's as well so I can tune the damping correctly) and I couldn't be bothered sending them back.
I have been using this method since the 1970's when getting replacement springs in desired rate was simply impossible. NEVER had a problem using this method.
You MUST add the space distances ( ie the actual distances BETWEEN the coil metal, not centre to centre) and ensure that after the spring is the new length , that there is more than the distance travelled by the forks, plus a decent safety margin. The safety margin is dependant on the quality of the steel, but for the iffy fork spring Suzuki uses, I would not allow less than 20% of distance of travel ( so for 130mm travel you need spaces adding to at least 156mm).
You will then have to make a longer spring spacer to compensate . Plastic downpipe ( rigid) , steel or Aluminium TUBE is best, but not too thick walled, as you will remove too much of the available airspace used as the oil travels up the tube during the compression stroke.
As pointed out if you overdo trying to get a higher oil height compression ratio, you WILL blow your seals. As also pointed out it, really only has an effect from when the leg has gone through at least half of it's stroke to the max compression. It also introduces a rising rate to the travel which can make getting the damping matched difficult. Used a lot on race tracks when your bike doesn't have necessary adjustment and you need a quick fix to remove some dive under brakes but has associated drawbacks.
You biggest problem will now be matching the damping to the new rate. You can use higher viscosity fork oil, but you will have to experiment. For the street it is usually possible to get a workable solution, but as pointed out the compression AND rebound damping will change together.
You can get intermediate viscosities IF you use the same brand and type of fork oil and mix in desired proportions But it will not work if you mix different brands and different types ( mineral, synth etc). Fork oil viscosity is notoriously variable and the viscosity on the container only bears a passing resemblence to other such labeled products. Do not use ATF of other non shock oils because they all use a different standard to define viscosity.
Increasing the weight will make it feel softer until it gets near bottoming.
Changing oil can make it feel softer if you reduce the compression damping ( eg by lower viscosity), though not noticeably at "sitting on the bike" suspension speeds.
I still believe VERY strongly that if your are going to spend ANy money on your bike the order is
1: tyres. The most important thing on a bike to keep you alive
2. Suspension and Brakes PROPERLY setup and matched to rider and use. If you can't do it your self find a quality suspension place and get it done AND get them to explain what they have done. Of all motorcycle related specialities it is my experience that suspension places are on average the most professional and care about their work. They are usually very dedicated to their area.
If you do it yourself , LEARN as much as you can FIRST and get help where you can. Before you touch the suspension other than setting up with what you have. Youtube is your freind. Watch as many suspension setup videos as you can stand. Most are very good and explain the relatively simple process of basic setup. That will also help you identify fi you need more modification.
The Suzi brakes are basically pretty OK for it's function and quality pads are really the only thing they NEED ( reinforced lines are nice but not imperitive).
3. Anything else.
Note this list is for the bike. NO scrimping on helmet, boots ( YES BOOTS! not shoes) and protective properly fitting apparel is of any benefit whatsoever.
I am always impressed by the quality of the comments on this forum.
Darkstar, it sounds like your forks are fine since they never bottom out. You should just get used to the brake-dive as it can't be fixed on the GS500 stock forks without messing up your high speed compression dampening.
Go ahead and find a good YouTube video or article that covers the basics of setting preload. Preload adjusts the static sag of the bike and rider. Basically making sure that you are starting at the correct range of the shock/forks travel. If you significantly alter the sprung weight of the bike you have to readjust the preload. For street riding it is usually okay to set it for your average weight (i.e. if sometimes you ride alone and sometimes you ride with a passenger+ camping gear, maybe set it with you and a passenger on the bike).
+1 for youtube vids on suspension and good tires, that's for sure!
I've also found some good information in the emails that motorcycle parts sites send me (like their newsletters and whatnot). BikeBandit has a section of How-To's with helpful vids as well!
+1 on what gregjet said. You can stiffen the springs for free by cutting them. I cut about 25% off of mine and doing so you wind up with about a 30% increase in stiffness, which I did to match the spring rate increase of my kat600 rear shock. I added extra spacer made from PVC pipe, I detailed all of this somewhere on this forum, you can search and find it. Now, the thing is, the PVC takes up more volume than the spring that you cut out, so therefore there is less available space for fork oil. So the fork oil height vs. air compression etc. is a bit of trial and error and good luck. I also detailed how I wound up. I used 20wt fork oil. I am very pleased with the performance.
I want to also head off some common misinterpretations. First of all, unless (and until) the suspension is "topped out", that is fully extended, preload is mostly used to set ride height. It does not affect stiffness AT ALL. The reason you add preload when you add weight is because by adding weight you increase sag, or in other words you move the static position of the suspension (ride height) lower in the travel. You add "preload" to raise the ride height back to where it belongs. The springs do not become stiffer by doing so. They will actually FEEL softer because there is more weight on them, and therefore they tend to deflect more due to increased weight. But they are not stiffer or softer. They are exactly the same.
The only way you would actually make it meaningfully "stiffer" with preload is to preload it so much that the suspension is topped out when the bike is sitting still with rider weight on it. This is a horrible idea and probably impossible.
If you have a USA bike then there's no preload adjustment for the front. The way you increase preload is with a longer or additional spacer. BTW you then have to compress the spring (more) to install the cap. This can be less than easy... This is why I say it's probably impossible to create too much preload in a non-adjustable GS500 fork, since nobody is strong enough to compress the spring enough to install the cap with that much preload.
BTW with my 30% stiffer springs the front end definitely feels firm on the road. It does NOT soak up bumps in a plush manner like before and it never bottoms out even with my 220lb weight on it.
There's something about weight and damping and spring rate that you have to take into account when choosing fork oil. Heavier oil will slow the suspension response, it won't make it stiffer. It'll just mean it resists fast movement, like small bumps. The goal of damping is to prevent oscillation, but also there's a balance between compression damping (bump compliance) vs. rebound damping. The thing is, though, the stiffer the spring, the higher the resonant frequency so it doesn't actually require thicker oil to dampen it. But the heavier the rider (and bike) the lower the resonant frequency, which does require thicker oil. So the point is, a lighter weight bike and rider is probably overdamped and heavier rider is underdamped.
Increasing the fork oil viscosity will have a noticeable effect on small bump response, and also a negative effect on traction and grip over small bumps. You can probably tolerate this on a race track which is far slicker than the road. Ditto that stiffer springs.
Quote from: Bluesmudge on March 08, 2018, 02:47:42 PM
I am always impressed by the quality of the comments on this forum.....find a good YouTube video or article that covers the basics of setting preload."
Me too man, and thanks guys. I'll checkout the videos.
Quote from: Bluesmudge on March 08, 2018, 02:47:42 PM
Go ahead and find a good YouTube video or article that covers the basics of setting preload.
After some research, I found unlike earlier models and UK, that late US models like mine don't have front damper adjusters. Apparently, the only way to alter preload with stock springs is to add/reduce length of the metal spacer. Longer spacer (insert cut PVC works) = more preload, shorter spacer (cut metal spacer down) is less preload.
Nice post mr72
Preload is a patch not a fix. To get proper function you need the right spring rate and damping.
Too much preload AND too little are both problematic.
First too little. Too little will make the from wallow .
WITH THE RIGHT SPRING RATE the proper preload will set the forks into to travel enough to allow the suspension to smoothly resist the damping and friction hytseresis, or move smoothly away from the rest position.
Too much will give what I call the "preload blues". Too soft spring for the bike +rider will require too much preload. The forks will resist until they overcome the preload force ( all good ) then , because the rate is too soft . blow through the rest of the travel too quickly.
Makes the bike squirrely and can chuck you in the wrong circumstances. They also will return to set position way too quickly causing head wobble ( overcome to some extent by the top out spring)