for wiki: rear vs front shock

[Phil B]

I'd like to update the wiki with good information on not only how/with what to ugprade front and rear shocks.. but
WHY and WHEN.

It currently has a nice writeup for the front springs:

Upgrading to stiffer springs provides several handling advantages:

    Better braking control, as the nose won't "dive" as much
    Better turning, since the bike will remain more level during braking before a turn

But nothing for when/why to upgrade rear.
Seems to me like mainly it's a question of when a rider weighs more than 180(?)lbs, or if you plan to do a lot of 2up riding?


I also would like to update http://wiki.gstwins.com/index.php?n=Upgrades.FrontSprings with someone's opinion of whether the "more expensive" springs are better.  It would also be nice to have informed opinions on progressive vs linear. Right now, it just explains the difference


I'm also wondering how I might be able to tell if my 2nd-hand bike already has upgraded front springs.

[jmelchio]

I upgraded both and I can give you my personal reasons but I'm not sure if they are universally valid.

For the front I didn't like the bike more or less from the day one. Too much diving when braking and sometimes bottoming out on our not so great local roads. I didn't really have any serious issues with the rear but I did notice it being very mushy when riding two-up.

So when it came time to replace the front I ended up getting a full set (front and back) from Hyperpro which are progressive springs which come with fork oil (15W). They are not the cheapest but I'm very happy with the results. The bike handles a lot better, breaking has improved a lot, I have a lot more confidence cornering and it feels a lot more settled when riding on the highway.
Two-up riding is like riding a different bike compared to the stock configuration. A truly amazing improvement.

Because I haven't tried it I can't compare with linear springs that are heavier than the stock ones nor have I tried riding a GS with a Katana shock or something like that. Judging by comments on the site I assume those setups work very well also.

Btw, I weigh ~185 lbs. fwiw.

[adidasguy]

Older stock springs: go over a bump into a driveway. If you hear a CLUNK then they're original. Also look for the dirt ring and see how far up it is.
Newer stock front: Similar, but not as bad. Also, that "CLONK" kinda feels like you bottomed out the wheel and the rim hit the pavement - but its the forks bottoming out.

Stiffer (like 0,85): Much better riding, no bottoming out going over a bump to a driveway (FYI: The entrance to my gym parking lot is where I noticed it most, also parking lot for my bank.)

Progressive: Soft for little mumps. Acts stiffer on bigger bumps (as the fork compresses) so you don't bottom out.

Have 0.85's on 2 bikes, progressives on the third. Overall, not a lot of difference but if I did lots of rough riding (like Seattle streets aren't bad enough: some potholes worse than a gravel road) I'd prefer progressive.

REAR: All stocks. Works just fine. Trey had a Kat shock when I got him. Too stiff. His butt was too high because of the longer length of the shock. Before changing rear, I'd first suggest adjusting it to be stiffer.

[Dr.McNinja]

Like Adidasguy said,

The stock springs are garbage. Front and back. Back is better if you never ride two up and adjust it to be stiff as possible. It's still budget garbage though.


Since the upgrade can be easily without removing the fork legs from the triple this will probably be my next upgrade over winter. Take your bike out to a parking lot, get it up to 45 mph, and then get on the front brake HARD. Your bike will dive so hard it almost chucks you over it. With progressives you'll dive a little and then the fork spring will stiffen up and keep you level. It makes the bike much more predictable (and safer) in turns and stops.

[burning1]

Hi Phil,

Thanks for updating the wiki. To answer your question, there are a few reasons someone might do the rear before the front, but the the main reason is pretty straightforward; cost and simplicity. A good R6 or Katana shock can be had for ~$60 on ebay. Installation is a matter of putting the bike on the center stand, removing a few bolts, and popping the new part in place.

Information dump below... I'd advise re-writing it for easier consumption.

Doing the springs (properly) is a little more complex. Since used spring upgrades aren't readily available on ebay, expect to spend ~$100 on a pair of new springs, and ~$20 on fork oil. Although the procedure can be done with readily available tools, some specialty tools can help or may even be required (impact gun.)

Ideally, both should be done at the same time, since each end balances against the other. With that said, IMO, the GS500 benefits from fork upgrades more than it benefits from a new shock.

I highly recommend Sonic Springs. They are less expensive than RaceTech, and the owner shows up on GSTwins from time to time to offer technical advise.  I've personally run Racetech springs - they are a high quality product.

.85 springs seem to be a very popular spring rate here on the GSTwins website, suitable for riders in the 160-180lb range. .90s for those heavier than 190. With that said, the best bet is to contact your suspension expert or spring manufacturer for a specific recommendation for your weight.

When replacing springs, it's a good idea to replace the fork oil as well. 15 weight is a good starting point if you're using the stock damping rods. Although 20 weight is usable, I'd recommend starting with 15 weight and only going to 20 weight fork oil if you decide 15 isn't thick enough.

Keep in mind that heavy oil will tend to be thick when you first start your ride. Take it easy the first few miles so that your suspension can warm up. I've saved a lot of slides caused by pushing the pace on a cold suspension.

I strongly advise against installing progressive springs on the GS, or any bike for that matter. Progressive springs make it nearly impossible to set sag correctly, and will tend to make the upper part of travel too soft, and the bottom too stiff. If you want more bottoming resistance, it's better to use the correct straight rate spring, and raise the oil level. The oil level controls the progressive pneumatic spring created by trapping a sealed volume of air in your fork. Keep in mind that oil level truly is progressive in it's damping characteristics; progressive springs are usually just dual rate.

Fork oil level is extremely important for getting the correct damping characteristics out of your forks. Oil level is measured by removing the springs and spacers, then compressing the forks as far as they will go. Measure from the top of the chrome tube to the oil. As you add oil, the distance will go down. Lower numbers means more oil. More oil means more bottoming resistance, but too much will cause the forks to hydro-lock, which will make them bottom out early and will blow out your fork seals.

A medical syringe and length of tubing is very helpful for adding oil. A fork oil level tool is just that, with a ruler built into the syringe; by adjusting the stop on the ruler, it's trivially easy to set the tool, overfill slightly, and suck out any excess oil. The tool might be worthwhile if you plan to maintain your suspension - you really should replace the fork oil once a year.

Stock oil level with stock springs is 99mm, and it should be safe to go as high as 90mm. With aftermarket springs, 120mm is a good starting point. The absolute highest level you should run the oil is 100mm, though with especially stiff springs, 110 is probably safer. If you are using the correct spring rate to begin with, it should *not* be necessary to raise the oil level that high.

Cartridge emulators, such the RaceTech emulators and Ricor Intiminators are a very worthwhile purchase for the GS500. While spring upgrades and fork oil can help with the squishyness of the GS500 suspension, they can't fix the fundamental flaw of the ported piston design: too soft against braking forces, too firm against bumps. Emulators will fix that problem.

Installation of emulators is pretty straight-forward... Emulators require machining out the compression ports on the piston, Intiminators are drop in. Hardest part of installing emulators is removal of the piston (required anyway if you want to replace the fork seals;) and the required machine work will take 5 minutes at a local shop, or a drill press. Hand drill will not work here; I've tried. It ended in tears.

Intiminators aren't supposed to require any machine work... But I can't recommend them as I've never tried them.

Regular maintenance: You should change the fork oil once per year, regardless of what internals you have on a bike. Fork oil thins out, and fills with metal shavings from the springs and tubes with use. The shavings will make it even thicker when cold, and the degradation of the oil will make it thin even worse when hot.

Anyone who's seen my race photos can attest that it's possible to drag elbow on a GS500 with nothing more than a fork brace, the internal work mentioned above, a shock, and some good tires.

Rear shocks that are known to work:

As far as I know, any Katana 600 and 750 shock will work, however both shocks were re-designed in 1998, so I'd generally recommend looking for the newest post 98 part you can find. Spring rate on both shocks is similar, around 1.2kg/mm. The Katana 600 shock is slimmer, and said to be a straight bolt on fit for pretty much any bike. The Katana 750 shock is a little fatter - I've heard reports of it being a bolt on upgrade, but personally had to grind the coil to get it installed.

The 1998+ Katana 750 shock is the best of the Katana shocks. It features compression, rebound, and preload adjustments, and uses a charged nitrogen design, with an external reservoir. The shock is rebuild-able, and a suspension expert could probably replace the remote reservoir with an after-market unit for improved performance if desired. When installing, be careful to secure the remote reservoir to the GS500 frame. On my race bike, it was possible to tuck the reservoir under the seat, next to the airbox. The performance benefits of the 750 shock should be weighed against the installation hassle before deciding which part to buy.

With both Katana shocks, the stock GS500 bolts, spacers, etc should be used - the only part that needs to be replaced is the shock it's self.

Katana shocks are extremely stiff, both in terms of spring rate and damping characteristics. Before installation, back out preload most of the way; I only had a few threads of rebound showing.... But be aware; on the bike, it's much easier to remove preload than add it. Rebound likewise should probably be towards the lower settings.

The other option is the 2006-2009 Yamaha R6 shock. The R6 shock is also a bolt on upgrade for the GS, however it uses a slightly different spacer and bolt than the stock GS500 part; if you're going to buy one on ebay, try to find one with the rocker arm and linkage. Failing that, the following part numbers can be ordered online, or from your local Yamaha dealer; expect to pay ~$20 total for them.

90109-12011-00 - Bolt
95617-12100-00 - Nut, U
90387-127W0-00 - Collar
92907-12600-00 - Washer

See them here, in the 06 R6 parts Fiche.

The R6 shock was redesigned for the 08 model year. Functionally they seem the same; the newer shock has a redesigned piggyback reservoir that's slightly smaller than the earlier version. Might be worth getting, since the older shock presses against the airbox slightly. But, with that said, older shock is what I had on my race-bike, and it worked flawlessly.

As mentioned above, the R6 shock is the perfect upgrade for most riders. It features preload, rebound, high speed compression, and low speed compression. It's rebuildable, well known, and can easily be modified or upgraded. Spring rate is about spot on for most average riders.

BTW: Most aftermarket R6 replacement shocks should also fit the GS. Use sanity though, when buying here. $600 shock is probably not a sound investment on our bikes.

How to choose between the shocks...

If you weigh much more than 200lbs, you'll benefit more from the spring rate of the Katana shock than you will the damping features of the R6 shock. If you're in the 150-200lbs range, the R6 shock is probably perfect for you.

There are a few other shocks known to fit; some early model GSX-R shocks will work. Late model shocks are too long. The RGV250 shock is known to work, but it has a soft spring and will raise the rear end of the GS up a little bit. Might be worth it for an extremely light rider, perhaps combined with lowering links. Be aware that this approach will somewhat throw off the progression curve of the GS500 linkage. I do not have personal experience with these shocks and cannot advise.

[Phil B]

... Take your bike out to a parking lot, get it up to 45 mph, and then get on the front brake HARD. Your bike will dive so hard it almost chucks you over it. With progressives you'll dive a little and then the fork spring will stiffen up and keep you level. It makes the bike much more predictable (and safer) in turns and stops.

Are you saying that you think stiffer, but still linear, springs, are basically the same?
Possibly until (X) amount of stiffness?  wonder how much (X) is, for an average (170 lbs) rider?

The racetech place had an estimator, which said I should probably be using .85 rated front springs.  Know how linear ones of those would do?

Whoops, burning1 update:  Why fork more than springs? Sounds like no amount of "fork upgrade" could fix the issue with softness  of springs?!?
oh wait.   http://wiki.gstwins.com/index.php?n=Upgrades.FrontForks explains that.
its basically replacing the ENTIRE FRONT OF THE BIKE. including springs as well.. gadZOOKS. $$$$
(which for me would include install $$$$)
yeah, think I'll stick with spring replace


PS: anything that involves "machining out" *anything*, does not count as "simple", in most people's books

But thanks for the great amount of extra info.

and I'm still wondering what "emulators" actually emulate. Sounds intriging, but something I do not understand

[Dr.McNinja]

... Take your bike out to a parking lot, get it up to 45 mph, and then get on the front brake HARD. Your bike will dive so hard it almost chucks you over it. With progressives you'll dive a little and then the fork spring will stiffen up and keep you level. It makes the bike much more predictable (and safer) in turns and stops.

Are you saying that you think stiffer, but still linear, springs, are basically the same?
Possibly until (X) amount of stiffness?  wonder how much (X) is, for an average (170 lbs) rider?

The racetech place had an estimator, which said I should probably be using .85 rated front springs.  Know how linear ones of those would do?

Whoops, burning1 update:  Why fork more than springs? Sounds like no amount of "fork upgrade" could fix the issue with softness  of springs?!?

PS: anything that involves "machining out" *anything*, does not count as "simple", in most people's books

But thanks for the great amount of extra info.

and I'm still wondering what "emulators" actually emulate. Sounds intriging, but something I do not understand

They emulate a cartridge fork. It's hard to explain how they work in a simple manner. A quick google will help you though.

[burning1]

Whoops, burning1 update:  Why fork more than springs? Sounds like no amount of "fork upgrade" could fix the issue with softness  of springs?!?

PS: anything that involves "machining out" *anything*, does not count as "simple", in most people's books

But thanks for the great amount of extra info.

and I'm still wondering what "emulators" actually emulate. Sounds intriging, but something I do not understand

Emulators emulate cartridge forks. The idea is simple: when the forks hit a big bump, they need to respond very quickly with a lot of travel.

With a conventional fork, the speed at which the suspension travels is controlled by forcing oil through a hole. As we learned in fluid dynamics, resistance goes up with the square of velocity. Lots of velocity, lots of resistance. Little velocity, little resistance. The problem is that ideally, you don't want much resistance against high velocity movements, such as hitting a bump, but lots of resistance against low velocity movement, such as braking. That's the opposite of what we get with such a design. Because of these conflicting goals, conventional forks such as those on the GS require a trade-off port size, that's not ideal for bumps or braking.

Emulators add a spring loaded valve to the forks. The valve opens up when you hit a big bump, allowing lots of travel. Because the valve is there, the low speed ports can be very small, making the suspension much stiffer under braking. The cartridges can be tuned, by drilling more low speed ports, changing the spring, or adding some preload to the spring. They can even be modified (by Dave Moss of Catalyst Reactions) to have a small shim stack for low speed damping, as well.

Emulators aren't as good as full on cartridges, but are an easy install for the GS.

Emulators + Springs + a fork brace + shock will make the GS perform about as well as a modern $12000 sport bike for most riders.

Biggest problem with emulators vs. cartridges is that emulators only control compression; rebound on the GS will be a little stiff till the oil heats up.

By machining, I mean making a few holes larger using a drill press. IMO, the machine work was easier than disassembling the forks. BTW, the manual for the emulator recommends drilling a couple additional compression holes in the fork leg, but doing so is not required. You just have to enlarge the stock compression holes wide enough so that their combined diameter matches the internal diameter of the damping piston.

I recommend a complete front end swap for racers who are permitted to do so by their race organization rules. Cost is a little more than for the emulators, springs, and brace, but the performance is worth it. I do not recommend a complete front end swap for street riders. Trying to replace the handlebars, headlight & mount, instrument cluster mount, etc. is a huge, expensive pain in the butt, and the performance benefit is not justified.

Emulators cost $120-%150. Springs cost $100. I bought a brace from the Buddha for $40 or so. Shock is $60. Combine with a 110/70/17 race tire and a BT003RS 140/70/17 rear, and this is the result.

[burning1]

Keep the questions coming.

[Phil B]

and I'm still wondering what "emulators" actually emulate. Sounds intriging, but something I do not understand

They emulate a cartridge fork. It's hard to explain how they work in a simple manner. A quick google will help you though.

Gah...
Well, what I think you mean to say is, installing "emulators" in an old style (ie: gs500f) fork, makes the entire fork act like a newer style "cartridge fork". Which gives you the ability to have an adjustable "damping curve", rather than just "linear", or fixed-curve "progressive" springs.



incidentally, first google hit for cartridge fork is these good folks again:

http://www.racetech.com/articles/CartridgeForks.htm

erm.. soo.. does it make sense to get "Emulators", *instead* of new springs?
Why or why not?

[burning1]

Springs and emulators solve different problems. Springs control how far the suspension travels over a bump; emulators control how fast the suspension travels. The interaction is complex... I'll do another quick post on it below.

If you have to decide between the two, I'd recommend getting springs. Springs solve the major problems of the GS being too soft, blowing through all of it's suspension travel, bottoming out, and wallowing.

Emulators make the GS smoother over bumps, and more stable on the brakes. They can solve the problem of the bike skipping sideways over bumps while cornering aggressively.

Most riders don't buy emulators, since they are harder to understand, more expensive, more difficult to install, and because the springs alone solve most of the most obvious problems with the GS.

I would not recommend buying emulators without doing the springs as well.

[Phil B]

Hrmm...

I think my recent "off", may have been caused by a harsh rebound problem. Which emulators do not help with, and stiffer springs, may actually make *worse* ?

(sequence of events:
  HARDBRAKE, off-brake, start-lean-for-turn, hello-asphault )

[burning1]

Fresh oil would be the most obvious fix to your problem; as oil wears out, it gets thinner, thus less compression AND rebound damping.

Emulators do help with rebound, just not directly. Because they permit you to soften up compression damping, you can tune them to run thicker oil, which will help with rebound as well. EDIT: It's possible to do the same thing without emulators; drill out the compression port a little, run thicker oil. I would NOT recommend this approach, since I haven't done it, and couldn't advise as to how it would affect the overall compression/rebound balance. Hasty suspension adjustments are more likely to mess up the bike than anything else.

From what you described, it's hard to tell what the actual cause of your crash was. There's a lot of things I would look at before trying to determine fault.

[Phil B]

Fresh oil would be the most obvious fix to your problem; as oil wears out, it gets thinner, thus less compression AND rebound damping.

AHA....
well ,since my bike is 6 years old, methinks I need to replace the fork oil.
(although it's still looow mileage)
and while I'm doing THAT, may as well replace the springs while I'm at it :-/