Fork Springs. "Renew, or not renew, that is the question"

Trying to sort out front fork excessive travel on my 2000 ST1100 ABS/TCS/CBS. Stripped forks, and not sure if springs need replacing. Existing springs are progressive, and measure 482 mm give or take, and according to the 'haynes' book makes them ok. They look good, no cracks or signs of weakness. So my question is... is there another way of checking if springs need replacing.
There is alot mentioned about preload, but if I can get the forks to dip about 5" just by pushing down with front brake on, is preload going to do anything.? The metal spacer in R/H fork measures about 95 mm, and everything looks good having just flushed out all the muck and black oil. Anti dive all looks good.
I don't want to buy another set of springs if these ones are ok. Was planning on rebuilding forks and putting SAE 20 oil in. Any advice would be welcome

Thanks
Ian

I fitted the hyperpro springs from sportsbikeshop and I could feel the diference instantly,I think it has been the best upgrade I have made,I used motul 10wt fully synthetic fork oil.
My anti dive unit was probably ok too but I replaced the O rings and piston anyway.
there is far less dive in the forks now and the bike corners better.

ian tomo said:

I don't want to buy another set of springs if these ones are ok. Was planning on rebuilding forks and putting SAE 20 oil in. Any advice would be welcome

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20wt is too heavy. if you want to stiffen it up 15 wt is the highest you should consider, and 10/15 blend is also good. Many are happy with 10W. This is a personal preference thing that you'll have to sort out yourself.

you can also increase the preload spacers to firm up the ride as well. Whether this helps depends on your weight somewhat, if you're 250lb or better you may want to consider going to a stiffer spring.

dwalby said:

if you're 250lb or better you may want to consider going to a stiffer spring.

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Just because the springs measured the correct length does not mean they are the right spring rate for your weight. Go to any of the aftermarket spring makers and they offer several different spring rates based on your weight.

I upgraded over a year ago and am happy I did. My springs measured in spec also.

Kevin

Sonic springs and fresh fork oil made a noticeable improvement in my 1100.

The right way to find out is to measure the suspension sag with your normal riding weight on the bike then again with just the bike alone. The difference the rider and cargo make tells you if the spring rate is within a range that can be adjusted with preload. The springs aren't worn out if they measure to spec length but like Kevin said they may not be correct for your riding weight.

If you go to a spring seller of course they'll sell you new springs. That's why you check the sag first.

Fresh oil is cheap compared to new springs. Try the new oil first, then decide if you need new springs.

I've always found any Honda I rode to be under-sprung and I'm no heavy-weight. Checking sag as the first step makes sense but since you've already got the forks apart you could play with the spacers and oil a little. But you won't know what the sag is with the OEM spacers.

As stated, I'd first go with 10 or 15w fork oil.........AFTER those forks are completely dis-assembled and cleaned with CLEAN solvent and re-assembled. As nasty as the oil can get(sounds like it in this case), if not completely dis-assembled and cleaned, whatever you do as far as oil weights IS an exercise in futility.

Excessive fork travel is an indication that your springs are too weak for the load you are asking them to support; you can check this more precisely by measuring the "sag", as mentioned above. In short, if your springs' rate is too weak, it does not matter if the springs are "worn out" or not. Pre-load cannot cure an incorrect spring rate, nor can fork oil.

It sounds like you've already disassembled the forks, so you can no longer check sag, so you may as well consult with spring manufacturers and determine the correct rate for your bike and its expected cargo. (Or re-assemble everything just to measure the sag...) Based on your initial concern, it is likely that your sag measurements will show that the spring rate is too weak, so re-assembly just to confirm this would not seem like a good use of your time. That leaves choosing the right spring rate...

OEM springs are usually considered too weak for most western riders (and luggage), but some spring charts may be more suitable for sporting motorcycles than touring motorcycles, so you'll have to choose carefully.

Ciao,

Even if the stock springs are not sacked out, after market progressive ones will make a huge difference in the ride and in my opinion the upgrade should be done.
In a different thread,,, ask who felt it was a waste of money. I will wager few will feel like that.
FWIW,,, take your forks completely apart so you can do a complete job of cleaning, and inspection of the wear items.

Throw away those P.O.S progressively wound springs and get some straight weight springs matched to your weight and riding style. No need to use anything heavier than 10W with a good spring....

I see your in Europe. Hyper-Pro, Wilbers, etc, can help you select the proper springs, oil and oil level for YOU.....

Ian,
Some good information here from others but we are missing a lot of information for real advice.
The most important would be how do you ride the bike. Do you want to use the Sport side of the bike or the Touring side, or both?
How much do you weigh? Do you ride with two up or with extra gear?
Probably the most important is how much money do you want to throw at it.

My opinions are just that, my opinions. I mess around on bikes and have made changes to the forks on a few bikes mostly the ST 11 and 13's but have done a few Gold Wings as well. NOTE,,, this does not make me an authority but it gives me an OPINION.

Here we go. The biggest bang for the buck $$ would be straight rate springs for your weight and the way you ride. I'm not a big fan of progressive wound springs like the ones Honda installs in the bike. They have their reasons for doing this and many of the riders like them just the way they are. I did until I made some changes. Your springs are probably fine, as in spec.
If you were to go to racetech.com and use their spring rate calculator, more than likely you would come up with a spring rate at about 1.0 kg/mm or stiffer, compared to the .610 kg/mm (stock).
Oil wt. is not a good way to resolve your problem of holding the bike up and to my way of thinking it could cause some other problems, if you are a bit more aggressive of a rider. Oil weight not only affects the damping but also the rebound so it is a fine balance of doing both. Heavier weight oil might slow down the dive a bit (the spring should be doing that) but it also slows down the forks ability to rebound.
You also have the oil level which will factor into how the forks work.
Because you have one damping rod fork and one cartridge fork you can make some good improvements by going to a aftermarket vendor like ractech and get their recommendations for valving kit options. That is going to start to cost some money especially if you send them off to be rebuilt.
Bottom line would be (for me) spend about $125 - 150.00 for springs and set the bike up with the proper sag for your weight, or reassemble the forks with fresh oil and enjoy the ride until you want to throw some money at it

Bigmak96 said:

In a different thread,,, ask who felt it was a waste of money.

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Well, considering the proud costs of proper suspension upgrades (or any farkel for this matter), you'd rarely find one admitting...

Fact is: a firmer suspension means loss of comfort... just compare a town-car with a roadster...
I do run Wilbers and Hyperpro, their great improvement for harsh, sudden braking manoeuvres, evasive swerving, pushing the envelope in fast turns, increasing your payload, precise steering, cornering, etc...

But they show no mercy on rough, bumpy tarmac, like the frost beaten patchwork on alpine roads... where the OEM suspension just levitates, the sporty after-market suspension will knock through, with no mercy... this can/will cause rapid fatigue, sore wrists and more (like vibrating bolts and accessory brackets off)...
Took me quite a while to find my personal compromise on settings and fork oil (7W)...

My '94 ST still has OEM suspension... yep, compared with the fun/sporty '00 it rides like a sofa, but a really comfy one...
And both has its benefits...

IMO
more oil and spacers = pre load
heavier oil = rebound

Wow, Thanks guys, loads of good stuff to get my head around. I did the all the sag calculations a while back, front was about 35mm ish. Back after playing with preload adjustment was about the same or a tad less. I did a rebuild months ago but never flushed properly, this time took John 'O's advice and flush/ dump x3 with ATF fluid. Already I have noticed the anti dive works better. I have put everything back together again and will give it a whirl and see. I may just ask Santa for some springs.

Thanks again all.

Best thing I ever did was put the right springs in the forks......huge difference............ride well, ride safe............ff

I don't know if your springs are the stock items, but the RaceTech spring calculator says the stock springs are perfect for a rider weighing ZERO pounds !! Way too soft as most say.

And BTW, RaceTech doesn't recommend progressive springs - because they are too difficult to set-up properly since the preload will also effect the spring rate.

I replaced my stock springs with a set of RaceTech 0.95 KG/mm springs - the rate the RaceTech spring rate calculator recommended.

As far as the preload is concerned, RaceTech recommends that the preload is correct if the forks are compressed 1/3 of the total travel when the bike is off the stand and the rider is on the bike. The total travel for the ST1100 is 150mm , so with the correct preload ( determined by the spacer length ) there should be ( of course) 50 mm of compression.

I also installed the RaceTech Gold Valve & Emulator kit and also installed a fork brace. The ride is now "plush, but firm" as RaceTech likes to say.

ian tomo said:

Wow, Thanks guys, loads of good stuff to get my head around. I did the all the sag calculations a while back, front was about 35mm ish. Back after playing with preload adjustment was about the same or a tad less. I did a rebuild months ago but never flushed properly, this time took John 'O's advice and flush/ dump x3 with ATF fluid. Already I have noticed the anti dive works better. I have put everything back together again and will give it a whirl and see. I may just ask Santa for some springs.

Thanks again all.

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Sag as measured with rider and cargo is one of two numbers that indicate if the spring rate is "in the range" for your laden riding weight. The second number is sag without rider and normal cargo like a tank bag, tools, etc., just the weight of the bike itself on its wheels.

The first sag figure is with preload set to whatever is necessary to get sag in the area of 1/3 of available travel. If sag without weight of rider and cargo is just a little less than laden sag that indicates minimal preload and the spring rate is too stiff. OTOH if unladen sag is a lot less, say close to topping out then the spring rate is too soft and a lot of preload was required to compensate for rider and cargo.

Others may disagree but I think it's important to go through these minimal measurements before altering suspensions if only to rule out other problems like excess friction from bent or worn parts plus you are more knowledgable about the changes you'll want to make. One of the popular spring sellers has a calculator that recommends the same 1.2 spring for all riders over 115 lbs (ST1300) when the stock rate is .86 and another spring seller recommends yet another spring rate.

I upgraded to the Sonic Straight Wound springs and 15 wt oil and it is awesome!!! Best thing I have done to both of my st11's