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Old June 13th, 2015   #1
marv02
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Default Up Grading fork springs ST1300

I have a leaking fork seal I figure as long I going to take the forks apart I throw in a set of better fork springs.

We let gets this out way I am CHEAP LOL.

I looked at Sonic Springs I looked at Race Tech and Progressive springs they are with in $30.00 of each other.

I looked what else the Race Tech springs what other bike it will fit come to find out the Kawasaki ZX line uses the same springs in there forks same dimensions the Honda RC51 and couple other bikes use the same springs also.

Race tech calling out for 95KG spring and Sonic calling out for a 100KG springs.

Kawasaki ZX14 is a 100KG spring stock I picked up a used set off E bay for $39.00 free shipping.

So if you want to up grade you're fork springs and save a couple bucks here is a way to do so.

I am also going with 7wt fork oil I will adjust fork oil level as needed after I take it for a ride when all the parts come in.

I will start looking for another rear spring one of theses days also.


My ST is my summer commuter it is not a race bike and I don't want to dump $2000.00 in to the suspension it rode good with the stock springs for what I used it for but as long I going to change the seals out it a cheap upgrade this way and should get better feed back from the front end now.

And the MPG of the ST is much better than my 4X4 GMC Yukon XL.
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Last edited by marv02; June 14th, 2015 at 11:29 AM.
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Old June 14th, 2015   #2
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Default Re: Up Grading fork springs

Pans are great to work on the forks, I reckon I can get mine off in half an hour, even the handlebar reservoirs look after themselves.

Quote:
Originally Posted by marv02 View Post
I am also going with 7wt fork oil I will adjust fork oil level as needed after I take it for a ride when all the parts come in.
.
Why? do you find the front too harsh? also why adjust the level, I thought the level with the springs out was what they were designed to run at, I don't understand why you would want to do this.
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Old June 14th, 2015   #3
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Default Re: Up Grading fork springs

Quote:
Originally Posted by marv02 View Post
I picked up a used set off E bay for $39.00 free shipping.

.

Used springs, umm.
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Old June 14th, 2015   #4
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Default Re: Up Grading fork springs

Quote:
Originally Posted by SinNH View Post

Used springs, umm.
The absolute first thing I thought of.

Most street bikes today run progressively wound springs.
We have enough history with the ST's suspension to know progressively wound springs are not a good choice. We have very little fork/shock travel to start with and with progressively wound springs you simply give up too much travel on the soft end, setting proper sag is virtually impossible.

The 7wt fork oil I have no problem with.
The ST's front end is grossly under sprung and over-dampened, as is the rear.
Again the history from those that have played with spring weight and fork oil has shown 7wt to be the preferred fluid.

Short of a complete $2000 remodel of the forks, new Traxxion cartridges, straight wound springs in the proper weight for you and your riding requirements using 7wt fluid looks to be the acceptable solution. Fluid levels are no longer a great concern once the proper springs are installed. The spring makers recommended levels look to be quite accurate.
Oil level on the stock setup is used to soften the blow just before the fork bottoms by using the air "gap" as a air shock. Shorting up the "gap" with a higher oil level will almost insure seal troubles


Paul

Last edited by PaulRB; June 14th, 2015 at 06:36 AM.
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Old June 14th, 2015   #5
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Default Re: Up Grading fork springs

Agree with Paul, if you put stiffer springs up front you can drop the oil level. I think Honda sets the front springs too soft then tries to ward off bottoming by using excessive compression damping and a high fork oil level. The air space above the oil is actually another spring in your system, the smaller that space the faster it's rate rises on compression. The high level that Honda uses makes for an excessively progressing "spring" rate up front. If you are talking about an ST1300, I've found the Sonic 1.2 (120kg) springs, 5wt oil and Sonic's recommended oil level to proved a very plush and controlled ride. One note, I do have the Race Tech gold valves in my fork as well. As the front sag is better set now, that and the rear Race Tech rebuilt rear , together do a better job of keeping the hard bits of the tarmac in the canyons too.
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Old June 14th, 2015   #6
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Default Re: Up Grading fork springs

First my racing days are long gone Riding the stock bike is fine for going back and forth to work and back.

If I wanted to spend a blue fortune on the suspension I could but I don't want to.

As used springs Race Tech calling out for a 95KG spring the ZX is a 100KG spring even if the used spring has lost some if stiffness it should put more at 95KG.

Yes Sonic is calling out for 1.1 or 1.2 Spring and what I read there on the stiffer side that I don't want.

Fork oil level makes a difference the weight of fork oil also effect the suspension the forks work as in air gap there different tricks that can be done to fool the fork that the air camber size by ad on Sub Tanks Ect.

But it more or less my fun Commuter so it don't matter that much.

I been riding and race bikes most of my life and yes I know how to set up suspension system but this not a race bike it for cruising so why do I want to dump $2000.00+ worth of suspension work in to it might as well put a set of upside down forks on the bike to start triple trees.
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Old June 14th, 2015   #7
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Default Re: Up Grading fork springs

I was trying to give a cheaper option to other instead of spending $100.00+ for a set of springs and find out there don't like them then take them back out and have those $100.00 spring sitting in the back of there garage.

Or try to sell them to someone else.

Some of us do our own work that saves us all kinds of money other have it do this also saves them money.
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Work on my own bikes built many from the ground up many one off customs not one of my bike has ever stayed stock for very long.
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Old June 14th, 2015   #8
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Default Re: Up Grading fork springs

I've been riding over 150,000 miles on the stock springs in my 2005. I measure the springs every time I change the fork oil (between 15,000 and 20,000 miles) and the springs always measure within the Honda published spring length. In fact they are always the same length. Springs may get weak with mileage but not OEM ST1300 springs.

I can't speak for the KYB springs in a ZX-14 but I wouldn't expect much change in spring length. Most bikes don't accumulate much mileage.

At 56,000 miles I fettled my forks by adding 16mm of preload in order to set the rider sag correctly for my 150 lbs and changing to a mix of Honda Showa fork oil that is 6.7 weight. There was a period of trying different fork oil weight but this set up works great for me. Static sag indicates the spring rate is good for my weight and riding style. Suspension shops generally recommend straight rate springs for the ease of matching damping rates to spring rate but the first thing a reputable suspension shop should tell you (after they tell you to throw away your stock ones and buy the stuff they peddle) is that nothing is black and white and a range of suspension performance must meet different riders' preferences and style of riding. The ST1300 is a touring bike with a sporty edge. If adding preload and using a thinner fork fluid 100,000 miles ago didn't work for me I'd moved on to different springs and/or valving.
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Old June 21st, 2015   #9
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Default Re: Up Grading fork springs

Up Date I pulled the Forks apart And found the bushing good a worn out so I ordered a new set.

The bike has 62k on the clock.
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Work on my own bikes built many from the ground up many one off customs not one of my bike has ever stayed stock for very long.
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Old June 22nd, 2015   #10
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Default Re: Up Grading fork springs

A good reason to change fork oil now and again. 62,000 could show minimal wear. Mine were barely worn at 52,000. I changed them anyway as I had the parts on hand and the firms apart. That was 101,000 miles ago.
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