Front springs for my 2009 GS

[W201028]

Hi guys. Ive been looking around the boards, and although theres lots of people who have progressive or harder straight rate springs listed on their 04>, I cant find any sites that list springs for the 04-09 GS500F.

Ive read that not alot has changed minus carbs and exhaust ports, but I dont wanna blow 80-100 bucks to find out the springs I ordered for a 96 dont fit my 09. BTW Im a heavy rider, and im looking for .95 or more straight rate, or equivilent progressives. Also, can anyone tell me how much fork oil to use in mililiters? Im not big on the coathanger in the tube routine. Thanks guys.

[adidasguy]

http://www.sonicsprings.com/catalog/index.php?cPath=31_65&osCsid=88d78ee36246db22f08d880c6bc0feeb

The fork springs are the same for all GS-500's

To select the right springs:
http://www.sonicsprings.com/catalog/calculate_spring_rate.php?osCsid=88d78ee36246db22f08d880c6bc0feeb

[burning1]

Pouring a measured amount of oil in the fork tube is an extremely inaccurate way of setting the oil level, and oil level is critical for achieving the correct behaviour from the suspension. Measuring the oil from the top of the tube with the springs/spacers out and forks fully compressed is the correct way of setting the oil level. It doesn't matter whether you use a coat hanger or a fork oil level tool, so long as you get this measurement correct. 120mm is a good starting place for the GS500. Higher than 100mm risks hydraulic lock with after-market springs.

AFAIK, for the purposes of replacing the springs, all gs500 forks are the same, 89 to current.

[stafebak]

Pouring a measured amount of oil in the fork tube is an extremely inaccurate way of setting the oil level, and oil level is critical for achieving the correct behaviour from the suspension. Measuring the oil from the top of the tube with the springs/spacers out and forks fully compressed is the correct way of setting the oil level. It doesn't matter whether you use a coat hanger or a fork oil level tool, so long as you get this measurement correct. 120mm is a good starting place for the GS500. Higher than 100mm risks hydraulic lock with after-market springs.

AFAIK, for the purposes of replacing the springs, all gs500 forks are the same, 89 to current.

So, to clarify, as I did this wrong so I want to go check up on it now. I would dip a hangar down in there until it hits the dampener rod, and measure from that point? Just want to make sure I do it right.

[W201028]

Thanks for the tips. I wanted to be sure all the forks are the same before whipping out the credit card.

Ive always measured my dirtbike oil by ml, but I dont do too many things right with that bike. If its better to measure with a tool Ill do that when I replace the springs.

[burning1]

Here's the short version of how to set your fork oil level...

1. Fully drain your forks. They don't have to be bone dry, but you want the old crap out of there.
2. If you haven't already, remove the springs and pre-load spacers.
3. Pour about 350ml of oil in the fork leg.
4. Fully compress the fork leg.
5. Measure the distance from the *top* of the chrome tube to the top of the oil. For street use with sonic springs, I'd suggest you start with 120mm. Raising the oil level to 110mm will make the forks firmer, and add some bottoming resistance. But start at 120mm. (For the stock forks, this value is 99mm, and can be raised to 90mm.)
6. Repeat on the other side.

The professional tool for this job is a fork oil level too, that costs ~$30. But if you're feeling cheap, you can use a ruler to measure and a syringe with a length of tubing to add or remove fluid.

Getting the fork oil level right is extremely important. The volume of air in the fork acts like a spring, and small differences in the oil level can make a big difference in the fork behavior at the bottom of travel. Also, the right and left forks have different volumes, so going by a measured amount will probably leave the two legs with uneven levels, which is very dangerous.

[stafebak]

Perfect, thank you!

Here's the short version of how to set your fork oil level...

1. Fully drain your forks. They don't have to be bone dry, but you want the old crap out of there.
2. If you haven't already, remove the springs and pre-load spacers.
3. Pour about 350ml of oil in the fork leg.
4. Fully compress the fork leg.
5. Measure the distance from the *top* of the chrome tube to the top of the oil. For street use with sonic springs, I'd suggest you start with 120mm. Raising the oil level to 110mm will make the forks firmer, and add some bottoming resistance. But start at 120mm. (For the stock forks, this value is 99mm, and can be raised to 90mm.)
6. Repeat on the other side.

The professional tool for this job is a fork oil level too, that costs ~$30. But if you're feeling cheap, you can use a ruler to measure and a syringe with a length of tubing to add or remove fluid.

Getting the fork oil level right is extremely important. The volume of air in the fork acts like a spring, and small differences in the oil level can make a big difference in the fork behavior at the bottom of travel. Also, the right and left forks have different volumes, so going by a measured amount will probably leave the two legs with uneven levels, which is very dangerous.

[W201028]

I got my sonics yesterday and put them in. For my weight (240), the stock weight of the GS and a tank bag, they recommended .95kilos, but I bought 1Kilos since I ride a passenger alot.

They came with washers (i reused the stock ones, the washers they came with were smaller than the tubes), spacer material which I cut to make 1/2 preload, and I used 20w fork oil set to 115mm down. I also lowered my forks into the triples about 1/2 inch to fit my clubman bars better (they were hitting the caps before, screwing up the mount angle so that my bars were angling down uncomfortably).

Over all, my GS feels like a different machine. Over bumbs, potholes, bridges, these springs soak up everything, and the 20w seems to stop the pogo effect completely. I ride over a curb everyday from my driveway, and the stockers always bottomed out bad. The sonics do not, even over speedbumbs at moderate speed.

Cornering feels much more predictable, and although I havnt ridden too hard yet, it does seem to turn in a bit slower, probably due to the front end raise, not the springs. At high speed on the highway though, it is rock solid, none of the shuddering I had previously felt in the 100 and up range. Also, brake dive has gone out the window. When tucked and braking, instead of falling forward over the tank, the front end feels so solid I think I could stoppie it with ease (not gonna try it myself, yet...).

I am really happy with these springs, and in the coming days I plan to get real low with them and put them to the paces. Thanks for the help guys, I'd be lost without this forum.

[burning1]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=280368971226

If you raise the rear end up a little, you gain some cornering clearance, and it can help return the front end geometry back to where it was before you lowered the forks in the triple clamp. If you take on this mod, check that you have sufficient clearance past your shock spring coils to raise the swingarm, and be aware that it will result in slightly more rear end jacking under acceleration. Obviously, it will make it even more difficult for short riders to flat-foot the GS as well.

[W201028]

Burning1: Its funny you say that, because I have been thinking about the SV650 shock swap for some time now. I hear thats about 3/4-1" raise in the rear. Would that really offset the front raise, or just raise the cg of the whole machine? I dont know much about suspension geometry, but in my mind, the closer the bars are to the front axle, the quicker the bike turns. Are you saying that raising the rear is the same as lowering the front, regardless of cg? Ive heard the term stinkbug before regarding some honda, and I dont want to end up falling over the tank.

[burning1]

There's no free lunch with geometry changes; pretty much everything you do has costs and benefits. The main impact of changing the steering geometry is how it affects your rake and trail numbers, not by it's impact on the CoG. E.g. raising the forks by 10mm will have an immediately obvious impact on steering behavior, but it only lowers the CoG by 5mm or so (remember, the CoG sits about halfway between the front and rear wheels on most bikes.) Raising the CoG back up by 5mm, by throwing a few heavy items in tank/tail bags won't have nearly as much an impact.

When you lower the forks in the triple clamp, the front end of the bike noses up slightly. Nosing up the bike shifts a little weight off the front tire, and increases the rake angle of the forks slightly. Increasing the rank angle of the forks increases the distance between the center-line of the steering stem and the contact patch of the tire (trail.) This increase in trail is what causes the bike to feel more stable, and turn slower.

If you compare the GS500 side by side with a modern sport bike, you'll notice that the angle of the forks is much steeper on the sport bike. This is part of what gives a sport bike it's incredible handling. The downside is instability. You'll also notice that almost every sport bike on the market comes from the factory with a steering damper, to try to control some of the unstable states of such aggressive geometry. It used to be a common mod on sport bikes to raise the rear end slightly to improve handling, but modern sport bikes are so aggressive that this is no longer a safe bet. In fact, some riders are now installing after market fork caps that are taller, permitting them to lower the forks in the triple clamp (raising the front end up.)

There are a lot of ways to raise the rear wheel. All of them have benefits and drawbacks.

1. Lengthen the shock.

In small amounts, this can work out just fine. A lot of the aftermarket shocks are adjustable for length, permitting quick changes to rear ride height. On some bikes, this can be accomplished by putting washers between the upper mount of the shock and the frame of the bike (doesn't work on our GS, obviously.)

In large amounts, this has major drawbacks. The largest drawback is that our suspensions are designed to be progressive. The is achieved by way of a linkage - on the GS, a lower link that sits between the frame, the shock, and a pair of dog-bone links which connect to the swingarm. At rest this linkage is usually fairly flat, and moves upwards as it compresses. Installing a fairly long shock will tend to cause this linkage to tilt downward at rest, creating a very wonky damping curve. I haven't explored this affect enough to be able to say how bad it is (or know if it might have any beneficial effects.)

Lengthening the shock has all the drawbacks of installing longer dogbones.

2. Install longer dog-bones.

This option has the same basic impact as installing a longer shock, except that the progression curve of the linkage is maintained. A longer linkage will increase the angle of the swing-arm, which will tend to shorten the wheelbase (slightly,) and will tend to increase the anti-squat affect on the rear wheel  (unlike a car, motorcycles tend to rise up at the back under acceleration.)

Raising the rear end this way will tend to shorten the wheelbase of the bike ever so slightly, and, like installing a longer shock, will raise the CoG, and provide more cornering clearance at the pegs and exhaust. It will also somewhat reduce clearance around the rear spring, which can be an issue for those with larger coils (e.g. Kat 750 shocks.)

3. Install a longer swingarm.

Not practical for most of us, but this option will tend to raise the rear end up somewhat. It also increases the leverage against the shock spring, somewhat reducing the effective spring rate of the rear shock. This approach can have a slight impact on anti-squat, but not as much as changing the swingarm angle.

4. Lengthen the wheelbase of the bike by installing a longer chain and adjusting the chain tensioners backwards.

On some bikes (including the GS,) this has the same affect as lengthening the swing-arm. Impact probably isn't significant enough to be worth the cost though, and it means that you may run out of adjustment range as the chain stretches.

Of course, there are many many other wild ways to mess with the frame geometry, including changing the swingarm pivot point, blah blah blah blah. As you can tell, my favorite approach is just to lift the rear end up a little using a pair of shortened dog-bones.