What a difference some front preload makes

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I'd give these a shot (although I think they're over-priced).

CBR900RR's from 92-99 also used a 45mm fork, so while I wouldn't guarantee a fit, I'd be surprised if the fork thread size and the damper rod thread size were different to the ST13. The missing damping adjusting screw shouldn't cause a leak as the ST13 damper rod is solid; one could add some thread tape if a better seal was needed.

http://www.ebay.com/itm/98-99-Honda-CBR-900-RR-Fork-Suspension-Cap-Cover-Upper-Lids-/162064509921?hash=item25bbcc2be1:g:e0YAAOSw3v5XIpBt&vxp=mtr
 

dduelin

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I have thought the same thing. CB1100 adjustable caps fit my NC700X. Surely let us know if these fit.
 
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OP
JimGregory
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Thanks but no.
That was not meant to be insulting. You had said you never checked your front end sag and basically I was recommending that you think about it. If you don't want to then simply don't. Although I bet you are.
 
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I'll never see those days again! I'll have a look at the RaceTech chart to see rates of where I want to be vs where I am. I should check sag.
155 can't remember when. :confused: I added RaceTech 1.0 as I did not like the dive under hard braking. SAG was not horrible at roughly 41 mm, but knew the target was about 35. A 15% reduction and spring increased by about 15%. Cut my spacer to match original spring and spacer length with the new RT spring and nailed the SAG at 35 first time. :D New Honda Std weight fork oil at 135 mm and I like my ride much more.
I recommend a spring to match your weight.
 
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Racetech has a replacement cap that adjusts the preload, compression and rebound. Down side is it part of a kit.
I noticed a couple of posts about adjusting the rear the rear spring. A couple of years ago, I was having to almost crank the adjuster all the way in. I saw a thread from IGOFAR on how the check and fill the fluid in the adjuster.
There was very little fluid. After the service I only used 30% of the adjustment.
I weigh 215 pounds. As soon I find some extra $$$$ I'm going to buy the right spring for my weight.
 
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Kevcules

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I've only had my 2008 St1300 for about a month now,but I'm concerned with the ride. It should be able to handle the bumps better that it's doing. I've lowered the spring preload on the rear a few turns already and now it will sag about an inch when I get on it. The damping is good too, it returns quickly.
The front has very little sag if any. I noticed today that it may drop 10mm. (I weigh 170 ) From what I'm reading , is it possible I've got aftermarket springs? The front feels very hard to compress when rocking back and forth with the brake on. If I decide to take things apart this winter, how can I determine if I have the OEM springs? Also, should I replace the seals if I have the fork all apart? Should I just try shortening the spacers and replacing the oil to get more sag?

thanks
 
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If you have it apart, you might as well have new seals and sliders on hand. Cheep insurance.
The spacing for factory springs change from one end to the other.
 

dduelin

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I've only had my 2008 St1300 for about a month now,but I'm concerned with the ride. It should be able to handle the bumps better that it's doing. I've lowered the spring preload on the rear a few turns already and now it will sag about an inch when I get on it. The damping is good too, it returns quickly.
The front has very little sag if any. I noticed today that it may drop 10mm. (I weigh 170 ) From what I'm reading , is it possible I've got aftermarket springs? The front feels very hard to compress when rocking back and forth with the brake on. If I decide to take things apart this winter, how can I determine if I have the OEM springs? Also, should I replace the seals if I have the fork all apart? Should I just try shortening the spacers and replacing the oil to get more sag?

thanks
You might want to accurately measure both types of sag so you know exactly what you are working with. The amount the bike sags under it's loaded weight including you tells a lot and the picture is complete when added to the amount it sags without you on it. The difference helps to tell if the spring rate is OK for a 170 pounder.

The stock springs are about 245 mm long (about 9.6"). Aftermarket springs will be a different length. That is the best way to tell. Springs are wound two ways. One has coils of equal spacing the length of the spring and the other has coils closer together on one end. Aftermarket springs are of both types - the stock ones are the latter, which are progressive.

Regarding replacing the seals - hard to tell. How many miles does the odometer show and was the fork oil ever changed? Changed regularly if high mileage? You won't be taking the forks apart very much to change the oil and check the springs.
 
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Agree with first measuring the sag accurately. Most aftermarket springs are installed with approx. 15mm of preload, and (again depending on your true sag numbers) I would not reduce that very much. It is better to have the right spring rate for your weight. Aftermarket springs may have the spring rate etched into one of the coils and that might help you identify them.
 

CYYJ

Michael
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35-38 mm of rider sag is a sweet spot reported by other ST riders. Mine was 47 mm at first check and set to 36 mm with 16 mm of preload over stock.
Hello David:

I need some guidance from you about this whole "sag" issue. After completely overhauling my front fork system (ST1300 Front Fork Overhaul), I have 44 mm of sag in the front. I weigh a little more than you (180 lbs fully dressed for riding), and I typically carry about 30 pounds of cargo in the saddlebags.

You stated that you reduced your sag by 11 mm by adding 16 mm of "spacer tube" (spring collar, to use the Honda nomenclature) length. From reading other posts you have made on the subject, I understand that you replaced the existing 200 mm long spring collar with a 216 mm long spring collar.

I would be quite happy with an identical 11 mm reduction in sag - that would take the sag down to 33 mm, which I think is probably "OK". In a perfect world, I would target the same 36 mm sag that you achieved, simply because you have reported that you are happy with this amount of sag, but I don't want to start juggling numbers around (different payload weight, different new spring collar length, etc.) and wind up with an unsatisfactory result.

Having said all that: Do you think that if I replaced the stock 200 mm spring collar with a 216 mm spring collar, just like you did, that would result in my sag decreasing from 44 mm to 33 mm?

Bonus question: If I want to achieve a sag of 36 mm (same as you), what length do you suggest I use when fabricating the new spring collar?

Michael
 

Whooshka

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OK so can somebody please fill me in... but changing out the fork caps without the internal pieces won't do anything. Or am I missing something here?
 

dduelin

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Hello David:

I need some guidance from you about this whole "sag" issue. After completely overhauling my front fork system (ST1300 Front Fork Overhaul), I have 44 mm of sag in the front. I weigh a little more than you (180 lbs fully dressed for riding), and I typically carry about 30 pounds of cargo in the saddlebags.

You stated that you reduced your sag by 11 mm by adding 16 mm of "spacer tube" (spring collar, to use the Honda nomenclature) length. From reading other posts you have made on the subject, I understand that you replaced the existing 200 mm long spring collar with a 216 mm long spring collar.

I would be quite happy with an identical 11 mm reduction in sag - that would take the sag down to 33 mm, which I think is probably "OK". In a perfect world, I would target the same 36 mm sag that you achieved, simply because you have reported that you are happy with this amount of sag, but I don't want to start juggling numbers around (different payload weight, different new spring collar length, etc.) and wind up with an unsatisfactory result.

Having said all that: Do you think that if I replaced the stock 200 mm spring collar with a 216 mm spring collar, just like you did, that would result in my sag decreasing from 44 mm to 33 mm?

Bonus question: If I want to achieve a sag of 36 mm (same as you), what length do you suggest I use when fabricating the new spring collar?

Michael
Michael,

As you know, the OEM springs are progressive. With a riding weight approximately 35 lbs more than me the springs are further up the Y axis and require more force to compress a given amount so I believe 216 mm spacers wouldn’t provide the same 11 mm. How much sag reduction 16 additional mm of preload would give your weight I don’t know.

I’m at the riding weight edge of being able to retain the stock springs. I’d use Race Tech’s spring calculator found on their website to estimate the spring rate suggested for 180 plus 30 cargo. If you just want to experiment with the stock ones I think I’d try 220 mm spacers and see what you get with that.

Remember in the discussion about fork rebuilding tips the suggestion to turn the tube to the fork cap when engaging the threads because 20 extra mm of preload will have to be overcome. You could also gin up a jig or fork compressor or get a friend to help.
 
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As you know, the OEM springs are progressive. With a riding weight approximately 35 lbs more than me the springs are further up the Y axis and require more force to compress a given amount so I believe 216 mm spacers wouldn’t provide the same 11 mm. How much sag reduction 16 additional mm of preload would give your weight I don’t know.
It doesn't matter if the springs are progressive or not, as long as the weight applied is enough to overcome the preload force, the ride height will change by the length of the preload spacer. The spring compresses based on the weight its supporting, which is going to be different for every rider, but that's not important. For any rider, if the current ride height is X, then adding Y to the spacer will make the ride height X+Y. Since the rider weight (plus the bike weight on the front wheel) is constant, the spring will compress by the same amount regardless of spacer length, because its based on that weight, nothing else. What the spacer changes is how much of that compression distance is provided by the fork tube compressing under the weight of the bike/rider and how much distance is supplied by the spacer.

Because of fork stiction, calculating required spacer length is a bit of an inexact science that takes some trial-and-error, but you should be able to get it reasonably close by adding the amount of desired ride height change to the length of both of the existing spacers.
 
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MajorTom

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OK so can somebody please fill me in... but changing out the fork caps without the internal pieces won't do anything. Or am I missing something here?
Maybe. :) Sorry, but as you didn't quote anything I don't know which post you're referring to. Not being snarky, just trying to help. :)
 

dduelin

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It doesn't matter if the springs are progressive or not, as long as the weight applied is enough to overcome the preload force, the ride height will change by the length of the preload spacer. The spring compresses based on the weight its supporting, which is going to be different for every rider, but that's not important. For any rider, if the current ride height is X, then adding Y to the spacer will make the ride height X+Y. Since the rider weight (plus the bike weight on the front wheel) is constant, the spring will compress by the same amount regardless of spacer length, because its based on that weight, nothing else. What the spacer changes is how much of that compression distance is provided by the fork tube compressing under the weight of the bike/rider and how much distance is supplied by the spacer.

Because of fork stiction, calculating required spacer length is a bit of an inexact science that takes some trial-and-error, but you should be able to get it reasonably close by adding the amount of desired ride height change to the length of both of the existing spacers.
I think if the spring is free standing what you say is true about progressive vs straight rate but set up in a fork the spring is preloaded even with forks fully extended. When we add preload from a spacer and place the weight of the bike on it's wheels the spring is partially coilbound at the tightly wound tapered softer end and cannot extend to it's relaxed length. A progressive spring in the ST1300 fork is partially coilbound at rider sag and is somewhere on the Y axis where the plotted rate is still rising in a curve and increasing compression force does not result in a linear rise in ride height. When the entire amount of progressively wound spring is coilbound the rate becomes linear but not at the lower end of the graph or suspension travel where we set sag.

I've shown this too be true with three bikes that have progressive springs. It's another reason suspension tuners prefer to use linear or straight rate springs. No matter where the spring is during full travel of the fork it exerts the same resistance to compression and makes compression damping and rebound damping more precise. A progressive spring takes less force to compress at the bottom end of travel and damping becomes a compromise at either end of travel.
 
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I think if the spring is free standing what you say is true about progressive vs straight rate but set up in a fork the spring is preloaded even with forks fully extended. When we add preload from a spacer and place the weight of the bike on it's wheels the spring is partially coilbound at the tightly wound tapered softer end and cannot extend to it's relaxed length. A progressive spring in the ST1300 fork is partially coilbound at rider sag and is somewhere on the Y axis where the plotted rate is still rising in a curve and increasing compression force does not result in a linear rise in ride height. When the entire amount of progressively wound spring is coilbound the rate becomes linear but not at the lower end of the graph or suspension travel where we set sag.
It doesn't matter if the spring rate is linear or not, coilbound or not, putting a preload spacer into the chamber does one thing and one thing only. It changes the amount of travel the front wheel (axle) applies to the forks before the spring pressure reaches equilibrium based on the weight applied to the front wheel. It doesn't even matter if you have two different straight weight springs in each fork, or a straight rate in one and a progressive in the other. The spring compression distance will always be the same for a given weight applied to the front wheel, the spacer simply determines how much fork travel is used before equilibrium is reached. The spacer doesn't change the spring rate at all, that's baked into the coils, and the spring rate doesn't change based on where in the fork tube its being compressed. For a progressive spring the rate does change based on compression distance, but again, that distance is constant regardless of what length spacer is installed. The distance is the sum of the spacer + fork tube travel.

I can demonstrate this with some diagrams if you want further proof.
 
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