Shorten fork 1 inch

TerryS said:
You quoted the correct part of my post "to reduce the travel". That is what spacers or longer top-out springs will accomplish, where I would define travel as the full range of fork movement from topped out to fully compressed. The spacers also "shorten the fork" which is what the PO was seeking.

Reducing the preload on the main spring or changing the spring length will change the ride height. It depends what you want to achieve. Just putting softer or shorter springs will change the ride height but would not be my choice for control as there will be a point after an extension (e.g. riding across a dip) where the fork will be in free-fall with little or no spring to absorb chassis energy. Using a top-out spacer keeps the fork under control throughout the full range of movement, and allows the use of a correct spring rate to keep the static ride height at around 1/3-1/4 of the full travel.
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let's ignore the softer or shorter springs option for now, I was looking at this from the perspective of putting in a shorter preload spacer with the stock spring. That will lower the ride height, which was his goal. As long as the spacer provides some spring compression with no weight on the fork, if the fork needs to extend there is spring tension, so I'm not seeing the free-fall possibility you mention. Or is there a point where if you don't have enough spacer preload the extension force from the spring is just too weak to be practical, and that's why you want the longer top-out spring?
 
If I read correctly the OP had already lowered the bike by an inch and was looking for lots more. Normal preload for a straight-rate spring would be around 15mm, so to lower the fork by 3 times that would mean running a spacer 30mm shorter than the gap between the spring and the fork cap. If you have a preload spacer that puts no tension on the spring then unless the spring rate is significantly increased you would run the risk of excessive bottoming under load because the spring would be significantly less compressed than normal at the point the fork tube hits the bottoming stops. In my view you are better off keeping or slightly increasing the spring rate, and limiting the full extension of the fork with changes to the top-out limits. This keeps the fork sitting at the preferred sag range to deal with dips while keeping the wheel in contact with the road at all times.
 
TerryS said:
If I read correctly the OP had already lowered the bike by an inch and was looking for lots more. Normal preload for a straight-rate spring would be around 15mm, so to lower the fork by 3 times that would mean running a spacer 30mm shorter than the gap between the spring and the fork cap. If you have a preload spacer that puts no tension on the spring then unless the spring rate is significantly increased you would run the risk of excessive bottoming under load because the spring would be significantly less compressed than normal at the point the fork tube hits the bottoming stops. In my view you are better off keeping or slightly increasing the spring rate, and limiting the full extension of the fork with changes to the top-out limits. This keeps the fork sitting at the preferred sag range to deal with dips while keeping the wheel in contact with the road at all times.
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Yeah, what you say makes sense in that context, but I think you misread the original post. He has the stock forks raised 3/4" in the triple clamp, presumably with stock spacers since he didn't specify he had modified anything internal to the forks, yet. He was asking about options for 1" of additional lowering. So I'm thinking just shortening the stock spacer by 1" would get him the extra inch of lowering, but would still apply some preload to the stock spring, and should not cause the situation you describe. Mine hasn't been stock for 20 years so I forgot what the stock measurements were. I seem to recall it had more than an inch of preload, but can't say for sure.
 
Find a 17 front wheel I thing someone has done this before. That would keep your soft suspension and get quicker response.
 
jspringator said:
I spoke to the nice folks at Traxxion, and they could do the job for $500. I'm not sure what all that includes. The problem is that I would have to separate the forks from the bike and ship to them, or take the bike to Atlanta.


I have a pretty good independent mechanic locally who used to work for a dealer.
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Hey Jim. I'd be interested to hear what's included for $500. I just had them do my forks (you may have seen the thread). The rebuild is $200, springs and spacers are $120, a revalve (emulators etc.) are $150. I feel that's reasonable. If you're changing the whole geometry of the bike by lowering it, it would be advisable to have some professional help. If it's not done right, it could lead to some very serious consequences. Removing the forks is easy once you get the front wheel off. I'm sure your mechanic could help you with it if you're not comfortable doing it. Shipping for me from NC was $22 plus insurance.
 
RobbieAG said:
If you're changing the whole geometry of the bike by lowering it
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Lowering the bike evenly doesn't change the geometry. He lowered the rear which slows handling. In lowering the front (less than the rear was lowered) he's returned the geometry closer to factory. It looks like he wants to lower it a little more to even it out which should make the handling pretty much the same as stock except lowering the cg this —><— much and any changes in fork/road compliance.

Assuming no bits bind I don't know what bad things happen when lowering the rear other than slower handling and less ground clearance. If I recall correctly he said nothing drags.

Lowering the front of the bike more that the rear would give me pause mainly because I don't know what I'm doing. This would make the bike handle quicker and twitchy to some riders. I've always thought this lessened higher-speed stability.

I also assume for $500 part of that is Traxxion cutting the fork tubes and threading them for the caps along with whatever voodoo that they do... It would be interesting to know exactly what $500 gets him.
 
Robbie, I'd like to get some aftermarket straight springs, cut a spacer in each fork 1 inch, refill with standard fork oil and call it a day. I have to go a little stiffer because I'm shortening everything up. Any aftermarket spring will be stiffer than stock.

Is there an inch to be cut out of the spacer's you've seen on yours?

Gui is right. I'm just trying to get it closer to stock geometry. I'll still be a little tall in the front, but i'd rather err in that direction.
 
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ST Gui said:
Lowering the front of the bike more that the rear would give me pause mainly because I don't know what I'm doing. This would make the bike handle quicker and twitchy to some riders. I've always thought this lessened higher-speed stability.
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back in the mid-80s I messed around with a KZ1000 I owned at the time, brought some tools along on a long weekend trip and experimented with dropping the forks various amounts in the triple clamp to see what effect it would have on the handling. I seem to remember being around San Simeon on the coast highway and dropping the tubes about 3-4" just to see what would happen. I didn't leave it like that for long (didn't want to bash the fender into the lower triple clamp), and I don't remember it having any real negative effect on the stability, but I didn't take it up to triple-digits either. I'm guessing the sportbikes I owned later came with steeper fork rake from the factory than what I had created by dropping the tubes that far, and they were all very stable at high speed. My guess is if you start with a 700lb bike, with a long wheelbase and rake angle of the ST, you're not going to make it twitchy no matter what you do.
 
jspringator said:
Robbie, I'd like to get some aftermarket straight springs, cut a spacer in each fork 1 inch, refill with standard fork oil and call it a day.
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That was pretty much my intention (except cutting the spacer) until I ran into trouble disabling the anti-dive. Once I decided to send the forks in, it made sense to have them rebuilt because the bike has 57k miles on it and had original seals and bushings. They would probably need to be done before long anyway. Once I was there, it was only another $150 to have them revalved, so that's what I did.
 
I could get Sonic middle of the road firmness springs, and not disable the and dive, not revalve, put standard 7.5 weight oil back in, and cut the spacers 1 inch. I don't think sonic requires the anti dive be disabled. In the schematic I clearly see spacer I could cut on one side, but the other is more difficult to see. Would I be able to cut/remove an inch of spacers on both sides based on your experience? I would go on and get the seals and bushings replaced while I was in there.
 
jspringator said:
I could get Sonic middle of the road firmness springs, and not disable the and dive, not revalve, put standard 7.5 weight oil back in, and cut the spacers 1 inch.

In the schematic I clearly see spacer I could cut on one side, but the other is more difficult to see. Would I be able to cut/remove an inch of spacers on both sides based on your experience?
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The first thing to consider is aftermarket springs aren't necessarily the same overall length as the stock ones, so they often require different spacers anyway. You need to take that into consideration before getting started if you change springs, you'll need to recompute the sag numbers with the new spring rate and spacer combination. And, for comparison you'll need to know the stock sag values. If you keep the stock springs and just go with 1" shorter spacers there's nothing to compute. I think that would be possible given the stock spacer lengths, but I can't say for sure.

Regarding the spacers, on non-ABS bikes the left fork has the longer spacer that's clearly visible on your fiche reference, on ABS bikes that's the right fork. The other fork with the cartridge damper also has a spacer (at least the non-ABS version does) but its much shorter than the other one. It been 20 years since I changed mine, but I'm gonna guess the long spacer is maybe 5" and the shorter one is maybe 2". Keep in mind that because the forks are bolted together in the triple clamps they work as a pair, so you don't necessarily have to change both sides exactly the same way, its the combined difference that matters. I say that because the cartridge damper fork spacer is more trouble to change than the spacer on the non-cartridge side.

Keep in mind though its not the fact that you have 5" to start with, so taking an inch off is possible. Its how much the spacer compresses the spring in the fork tube with no weight on the front end. If that is more than one inch, then shortening it by one inch will still compress the spring somewhat with no weight on the fork, which is what you want. On the cartridge damper side that spacer is captive between the spring and a nut at the end of the cartridge rod, same story there. When the cartridge rod is fully extended upward you need enough spacer length to compress the spring slightly with no weight on it.
 
As I try to think this through, if I have the springs lowered 1 inch, wouldn't it be impossible to also push the fork tubes up in the triple trees 3/4 inch because the top of the fender would hit the bottom of the triple tree?

What am I missing?
 
jspringator said:
As I try to think this through, if I have the springs lowered 1 inch, wouldn't it be impossible to also push the fork tubes up in the triple trees 3/4 inch because the top of the fender would hit the bottom of the triple tree?

What am I missing?
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yes, TerryS already mentioned that a week ago, and you quoted it.

For what you're trying to do there's a balance between ride height and moving part clearance. If you lower it too much, you could bash the fender on the triple tree during hard fork compression. Or, you could increase the spring rate to help prevent that from happening, but its still possible that an even harder hit on the forks could still make contact, and you'll have a stiffer ride quality all the time. That's why we cautioned against doing anything permanent to the forks, if you don't like it you're stuck with it after paying for it, and then need to find another set of forks if you want to go back.

The other option of cutting the spacer by 1-3/4" and putting the tubes in their normal position in the tree would give you the same ride height, but reduce your available fork travel by an additional 3/4" (compared to the option of lowering the tubes in the clamps). I think the forks would bottom out without hitting the fender on the tree, so you remove that hazard. But if you can't cut 1-3/4" of spacer off and still compress the spring with no load, then you run into the issues TerryS mentioned earlier about having the fork tube extending with no spring force.
 
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I didn't understand he was talking about the combination.

If I lower the forks internally by 1 inch by removing or shortening a spacer, can I still raise the forks in the TT, and if I can, by how much?
 
jspringator said:
If I lower the forks internally by 1 inch by removing or shortening a spacer, can I still raise the forks in the TT, and if I can, by how much?
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hard to say for sure, you'd need to measure it. One way would be to remove the fork cap and compress the fork with no spring, and see how far it can travel upwards. That may be a little pessimistic though, it may be that the spring coil binds before the slider actually bottoms out, and limits upward movement (I suspect that's not the case, but thought I'd mention it anyway as a possibility). To measure that you'd need something capable of compressing the fork fully with the spring installed, which is not very practical, so the first measurement is probably the only one you're going to be able to perform. The next question is even though the fork tube can theoretically travel that far, will you ever encounter that much force while riding. Its a crapshoot, and depends on how concerned you are if the fender hits the triple clamp occasionally.

What I'd do in your situation (assuming you absolutely need that additional 1") is shorten the spacer, drop the tubes 3/4" in the clamps, and put a zip tie on the upper fork tube to monitor fork compression on a short test ride. Then based on how much compression margin is left after that test ride I'd plan my next move from there. If you don't feel comfortable with the margin you see, put them back to level with the clamps and stop, you're still 1/4" lower than when you just dropped the tubes in the clamps, and it won't hit the fender with them level with the clamps. I've never tried lowering any bike, so I have little advice to give other than that.
 
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I found a shop in Louisville that specializes in suspension mods. I talked to him today for 10 minutes, and he knew what he was talking about. He is going to have to disassemble and cut the damping rod. I'm taking it to him Friday or Saturday.
 
Well, it's done. He didn't have to cut the springs. He removed a spacer from one side, and on the other had to disassemble the damper rod to remove a spacer and put it back together. He kept talking about being a 1/2 inch off and having to remove another spacer, but I didn't really know what he was talking about. He wants to start it out with the forks pushed up 1/2 an inch in the triple trees to see how it does. He was afraid the side stand would be too long, but I've already shortened it 1 1/4 inches. It should be fine.

I've got a spare centerstand. Is there anyway to shorten it?

He doesn't want me to pick it up until the ice melts from his parking lot. I can't wait to see how it does.
 
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