Front Fork Springs?

[toothandnail]

I have a 99 321 and I am trying to figure out what to do about the front fork springs. I pulled them today to replace the seals. I had also noticed that they were sagging more than the recommend "race sag". I pulled the springs to shim them and noticed that they had already been shimmed about 3 inches by the previous owner. My question is should I make a larger shim or get replacement springs. I wouldn't mind to go ahead and replace them. Problem is I don't know where to get them. I have found replacement springs for the 06-08 pro with a 20% stiffer rating. Would these work or are the demensions different? Any help would be much appreciated. Thanks!

[jse]

I have a 99 321 and I am trying to figure out what to do about the front fork springs. I pulled them today to replace the seals. I had also noticed that they were sagging more than the recommend "race sag". I pulled the springs to shim them and noticed that they had already been shimmed about 3 inches by the previous owner. My question is should I make a larger shim or get replacement springs. I wouldn't mind to go ahead and replace them. Problem is I don't know where to get them. I have found replacement springs for the 06-08 pro with a 20% stiffer rating. Would these work or are the demensions different? Any help would be much appreciated. Thanks!

I doubt that the 06-08 springs will work as they are for the 40mm Marzocchi tubes and you have the 38mm GasGas tubes. The "shim" you refer to is the preload spacer and my guess is that it is the stock one. I'd try adding about 8-10mm to the length of the ones in the forks by making another one from schedule-40 (thick wall) pvc and I think it's the 1" size (take one of the old spacers with you to check the size at the hardware store).

If you are having bottoming out problems with the forks, try adding 30cc's of fork oil to each leg, which will reduce the air pocket at the top of the tube. The air gap, or pocket, affects the last third of fork travel and the compression of the air in that pocket acts like a secondary fork spring under full compression.

Last resort would be to replace the springs (your local GG dealer can get them for you), but my guess is that you can fix the problem for a lot less cost.

Jon

[toothandnail]

My main concern is having too long of a shim in there. The shim currently in there is 3 inches long (not the stock one) and is made of the pipe like your were talking about and I was just concerned of how long it can be before having to replace the springs. Anyone have prices on new springs or better springs? Thanks.

[grahamjayzee]

If you have a bit of patience, you can work out the maximum spacer size you can use.

The problem is when the spring becomes 'coilbound'; ie all the coils are all touching. You can work out the coilbound length but counting the 'gaps' between coils and measuring the wire thickness. Multiply one by the other and that is how long the spring will be fully compressed. You can then work out the space needed in your fork by taking out the spring and oil, inserting a rod and marking on it where the top of the fork leg is with the leg fully compressed.

If your fully compressed spring + any spacers is greater than this measurement, it will become coilbound before you use up the available fork travel. If this is the case, you need new springs. If you still have some space, like JSE suggests, make up another preload spacer.

Good luck

Graham

[jse]

If you have a bit of patience, you can work out the maximum spacer size you can use.

The problem is when the spring becomes 'coilbound'; ie all the coils are all touching. You can work out the coilbound length but counting the 'gaps' between coils and measuring the wire thickness. Multiply one by the other and that is how long the spring will be fully compressed. You can then work out the space needed in your fork by taking out the spring and oil, inserting a rod and marking on it where the top of the fork leg is with the leg fully compressed.

If your fully compressed spring + any spacers is greater than this measurement, it will become coilbound before you use up the available fork travel. If this is the case, you need new springs. If you still have some space, like JSE suggests, make up another preload spacer.

Good luck

Graham

That's a good idea. As long as you don't run into coil-bind territory, you are in good shape. Provided the rider weight is in the 11-13 stone range (I may be one of the few riders in the U.S. that has an idea of what a "stone" weighs ) you can probably work with increased preload spacers and oil level (the size of the air pocket at the top of the upper tube) to get you to where you need to be, heavier than that and it might be a good idea to start with new springs.

I didn't have an old 99' 321 spacer handy, but I had the old 96' JTR370 spacer I took out of my old bike (forks are similar internally) and it measured 2 3/8th inch (60.85mm), so that may give you an idea of what the stock spacer length may have been. So, time and cost (and interest) will dictate your decision. I'd follow Graham's advice if you want to work with the old springs and make a spacer to adjust, or you can just opt for a new set, but if your weight is greater than the load the forks are set for (or your riding style puts an extra load on the forks), you'll still probably have to make a new spacer.

I like the "process" of playing around with the components to see what I can make up that works better than the original design, others are more interested in the "goal" and just replace the parts and be done with it. So, your level of interest will also be a factor in new springs or not.

Jon

[grahamjayzee]

All correct Jon!

One thing though, preload and spring rate are 2 very different aspects to the way the suspension works. Preload affects the point at which the spring starts to compress (how much static weight it can support), rate affects how much it deflects trying to absorb a given amount of energy. If you are a heavier rider, the bike/ rider combination has more energy, so a hit of a certain size has to be absorbed by the spring, so rider weight makes a difference. However, on a trials bike we are after maximum traction, so supple suspension is what we are looking for. As such, unless you are a very heavy individual or have really hit the mince pies, preload to set a reasonable amount of static sag is probably the best way to go.

If you get on the bike and the forks bottom out, new springs are the way!

It can all get a bit confusing as all the aspects interact and you can (partially) cure any one aspect with any other. For example, soft springs will make the suspension more likely to bottoming out. Preload will not change that, but heavier spring rates or increased compression damping (or heavier fork oil) will. Heavier springs will mean less subtle action over small surface irregularities, more compression damping will make bouncing the bike hard work...

However, I think you are dead right Jon, toothandnail is best off having a fiddle. I think ensuring the springs haven't sagged past the point of no return first, and then trying some spacers is a very good starting point. If the front feels too soft, a little more oil to reduce the air gap. If the increased preload makes the rebound rather sharp, and extra click or 2 of rebound damping if you have this option, or up a grade of fork oil.

All good fun!

Graham

[toothandnail]

I weigh 170 lbs. If the stock spacer in your bike was 2 3/8" I am not as worried as I was. I will try and make a new spacer and if that doesn't work I will go ahead and get some new springs. Thanks.