Author Topic: Fork Springs, Anyone tried fixed rate springs?  (Read 4490 times)

Offline Piet

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Fork Springs, Anyone tried fixed rate springs?
« on: August 26, 2014, 05:53:29 PM »
Just wondering if anyone has tried fixed rate springs rather than progressive springs?
I have just ordered some Sonic Springs from the USA and will give them a try as soon as they arrive.  To my way of thinking the argument that fixed rates actually use the travel more effectively makes sense. 
Will keep all posted on progress but looking forward to feedback on the experience that others have gained.

« Last Edit: January 16, 2015, 06:49:09 PM by Piet »
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Offline HunterTodd

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #1 on: August 26, 2014, 06:13:31 PM »
A fork upgrade is on my agenda too so I will be interested in your experience.  In the meantime. The V4 badge on your picture I take it you got from Bikequip in the UK.  They are sold in sets but I only want one. You wouldn't have a spare which you would like to sell would you?
 

Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #2 on: August 26, 2014, 06:32:52 PM »
Yes thats the logo, but its just a copy and past off their web site.  I did not purchase the badge.  I like the badge but have not liked it enough to pay for it.
« Last Edit: September 29, 2014, 09:52:26 PM by Piet »
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Offline Brock

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #3 on: August 26, 2014, 06:58:52 PM »
I recently saw a program on springs, that explained how they work quite well eventhough it was aimed at off road racing.

Progressive springs are designed to operate over a range of resistance (for want of a better word)  for example 100 to 250 kilos where as fixed rate only works at a specified value i(e 150Kg) This means at 150 Kg, the spring would be fully compressed therefore no more travel. The progressive starts to compress a bit earlier, soaking up the small bumps, but leaves more travel for those pot holes. I think a progressive would be better for me, as I'm a tad heavy..

Have a search on google for more info.
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #4 on: August 26, 2014, 07:25:41 PM »
Hi Brock,  I too had read information applying the same logic as you share with us.  I really liked the explanation I got from Sonic's web site (might end up just being sales blurb, and I was sucked in) but to me it made a smidgen of sense so thats what makes me want to try it.   The info is taken from this web address,
http://www.sonicsprings.com/catalog/tech_articles.php?osCsid=cfb99b6db3bb8cbb9a65d172d9af0118

Straight-Rate Springs vs. Progressive Rate Springs
Over the last 20 years, one of the biggest changes in the aftermarket motorcycle suspension world has been the virtually complete switch from progressive rate springs to straight rate ones. I think itís safe to say that thereís not a single reputable suspension tuner who advocates progressive springs. The question is why? Whatís the problem with a progressive rate? Why are straight rate springs better?

One of the problems is that bikes, street bikes anyway, just donít have enough travel to take advantage of progressive rates. The soft initial portion gets blown right through, leaving a limited amount of travel for the stiffer portion to deal with. This results in less compliance, less traction and a harsher ride. Another issue is damping; Damping rates, particularly rebound damping, need to be matched to the spring rate. With a progressive (i.e. variable) rate, thatís impossible. Damping is always a compromise and a progressive rate just makes the balancing act that much more difficult. Adding to the problem is that modern forks actually have 2 spring mediums, the steel coil and the air trapped inside. The air is intrinsically a highly progressive spring. Adding a progressively wound steel spring to the mix is just making a bad situation worse.
« Last Edit: August 26, 2014, 07:45:32 PM by Piet »
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Offline alans1100

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #5 on: August 27, 2014, 12:56:22 AM »
I've replaced the rear shock with a Progressive (name of company) shock but when comparing the new with the old OEM I found that the new one had a straight rate spring and the OEM was a progressive.

A little hard to compare old and new since the old shock was well past its useful life but the new one feels a lot firmer than what the OEM felt like when I first got the bike. I have no issue with the front OEM set up other than the usual fork seal going every few years which is all ways the RH one.
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #6 on: August 29, 2014, 10:04:06 PM »
Interesting observations Alan.  I have also been looking at the rear shock options.  I read with interest Streak's decision to buy Ikon shocks and that he was very happy with them.  I priced them this week and now they sell for $660.00.  I tried dealers but they did not offer lower prices to me.  The dealer told me they were offered 15% discount on the list so could not provide me with any advantage.
The Ikon 3610 has a lot of coils in its progressive spring but many turns are very heavily compressed with little compression left.  The Progressive 465 you purchased is a fixed spring and would use the whole spring for its functioning.  I looks more logical to my way of thinking.  The P465 also uses a more hefty shaft and larger diameter tube.  I know that bigger is not necessarily better, but when I added pricing into the mix I have decided to try the P465.  I paid A$ 467.00 and that includes $60.00 of postage.
I ordered them from ebay and will await arrival from the USA. 
« Last Edit: August 29, 2014, 11:02:13 PM by Piet »
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Offline Streak

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #7 on: August 29, 2014, 10:23:33 PM »
I went with the ikon as I was looking at a rebuild of the original or going progressive, I did alot of 2up riding loaded with gear, I was torn until talking with saaz his thoughts where as below:

Original and progressive fully loaded 200kg working near 85-95%, ikon working at 60%, I went with ikon and it was superb.

interestingly pricing I bought the shock from toowoomba honda for $550 if I remember right.
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Offline alans1100

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #8 on: August 29, 2014, 11:46:48 PM »
Interesting observations Alan.


This is my Progressive install. The only change I've made since then was to adjust the dampening to position 2 (for two up) and 3 is ok when the trailer is loaded and riding two up. I wasn't sure if I adjusted the preload two or three turns after fitting but I aimed for a compromise between one and two people so far so good.

http://ozstoc.com/index.php?topic=4738.msg50795#msg50795

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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #9 on: August 31, 2014, 07:35:52 PM »
Streak,
In your comment about your Ikon shocks you mention some data supplied by Saaz,

"Original and progressive fully loaded 200kg working near 85-95%, ikon working at 60%,".

Forgive me but I am a bit thick and am not sure I understand what the percentages are actually referring to.
I asume that both Ikon & the P465 would be very similar in dimensions, in terms of overall length & travel otherwise it would be a very different dynamic.  The Ikon people told me the 3610 had 55mm of travel (or something close to that number).  I expect the P465 to be the same.  So can you help me to understand what it was that Saaz was higlighting?
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Offline Brock

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #10 on: August 31, 2014, 07:43:38 PM »
Saaz was saying, that the progressive was about 90% compressed in normal use, leaving only a little travel for bumps. The Icon wasnt being loaded as much, so had more travel left to soak up the rough stuff.
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #11 on: August 31, 2014, 07:57:17 PM »
Thanks Brock,
So with a load of 200 Kg, 90% of the P465 shocks 55mm of travel would equate to just 5.5mm left to soak up the rough stuff. ???

« Last Edit: October 01, 2014, 05:44:22 PM by Piet »
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #12 on: September 26, 2014, 12:49:03 AM »
Today I completed the install and setup of my P465 shock.  What I have learnt, (I know I might need to learn more and would welcome it) is that I think the shocks in the comparison were not setup correctly and certainly were not setup equally for an apples with apples comparison.

To explain,  I weigh 100 Kg, and when I sit on the bike I need the shock to sag a small percentage, leaving the majority of its travel to work with the varying road conditions.  To set it up I had to "preload" the spring by adjusting down or compressing the spring until I obtained the right ratio of sag vs total travel.  Lets imagine 20% sag and 80% travel.
Now add a pillion who weighs 100Kg.  If I change nothing, the extra 100Kg will cause much greater sag, perhaps 50% sag 50% travel for road conditions.  Thats not a good setup.  It would be much better to increase the preload, compress the spring further so that the full 200Kg causes the original 20% sag.  This still leaves the 80% travel for the road conditions. 

If this is true ... then what it means is ... to say a P465 with 200Kg load compresses to 90% of its travel means the unit had very little if any preload set.  Of course it sagged so much.  If the Ikon with the same load (200Kg) compressed to 60% of its allowed travel it started with a higher preload but still was not set up correctly.

I am absolutely confident I could install either the Ikon or P465 and set them up with a common load and get the sag exactly the same, exactly where it needed it to be.  I am not making any comments about the dampening or the quality of the unit in use and the end result on suspension and handling.  Sadly I don't have an Ikon shock to use, to swap out and then test.  I would love too but it is not going to happen. 
My observation tells me the numbers are either completely out of context and the understanding is wrong or if in the right context then we are simply nowhere near setup correctly.
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #13 on: September 26, 2014, 01:27:10 AM »
As mentioned above today saw me wrap up my winter maintenance and got everything back and installed ready for some good fun riding this summer.  Starting from front to back.

Installed Sonic fixed rate Springs in the forks with new oil seals and dust covers.  Used Castrol 10 wt oil because its actually lower in weight and probably closer to a true 7 weight.  I set the sag at 32mm in the front end with me on board at 100Kg

Flushed both clutch, front & rear brake lines and filled with new fluid.

Flushed the cooling system, went with Evans waterless coolant.  Cleaned the overflow bottle out completely.  Found I needed to replace the hose clamp on the overflow line where it connects to the bottle because it did not seal properly when the clean bottle was reinstalled.  Glad I spotted that.

The engine oil & filter are not yet due for a change but run K&N filter and PM Lubricants 10W40.
The air cleaner was very clean and well oiled.  Genuine filter.
Standard plugs were all good.

Replaced the battery - necessity.  Went for the glass mat construction.

Removed the drive unit, cleaned it thoroughly, removed the rusty dry looking crud that had built up.  On removal of the drive unit found a lot of water in the drive tube so reinstalled with some Permatex non hardening sealant to stop water getting in again.  Replaced the 3 "O" rings in the drive unit and hit it with Moly 60.  New PM lubricants diff oil in the drive unit.

Fitted a rubber swing arm protector from Bike Quip in the UK, just to keep as much dirt away from the swing arm area and from getting sand and mud in under and between the fuel tank and the rubber that lives below the tank.

Installed a Progressive 465 rear shock and set the sag at 34mm measured at near axel centreline.  This too was just one-up at 100Kgs.

Returned all plastic, polished it up.  Can't wait to go for a ride and play with the dampening and check out the updated suspension.

The final item that is on order but has not arrived is the Saddleman Stealth seat.  I read Allan's report on his choice so decided it was for me especially after my Melbourne -Brisbane return trip in a week.  That was really uncomfortable and it took over a week to get my rear end feeling anything like normal.

« Last Edit: January 30, 2015, 07:37:12 AM by Piet »
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Offline Shiney

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #14 on: September 26, 2014, 04:58:53 AM »
Awesome work Piet :hatwave
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Offline Abe

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #15 on: September 26, 2014, 06:31:05 AM »
Great work there Piet, she'll be right for a long time now.  :clap


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Offline Greencan

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #16 on: September 27, 2014, 07:32:33 PM »
Quote
I set the sag at 32mm in the front end with me on board at 100Kg

How? :think1

 

Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #17 on: September 28, 2014, 01:56:18 PM »
To be honest perhaps more chance than skill.
Its a real pain to change it because it means disassembling and adjusting the spacer length, to change the spring preload.  So the desire to get it right the first time was very strong.  And once its assembled, checked, and you find its not quite what you desired, the thought of pulling it apart to change the spacer length is a pain in the proverbial.  Honestly, if in my case it did not come close to where I wanted it, I am not sure I would have turned around and made adjustments any time soon.

If one had progressive springs, then I think it would be next to impossible to calculate, because of the varying rate of compression.  (please checkout Greencan's method below this post, as thats a very clever way to do so)  In the case of fixed rate springs its a lot easier.  In my case the Sonic Springs are rated at 1.2 Kg per mm to compress.  Having two forks then 2.4 Kg per mm of compression of the front end.

The info I had read on Sonic Springs sort of indicated that perhaps starting with 19mm spring preload or 19mm of compression would provide a safe and good starting point for adjustment.

I tried to do up an excel spreadsheet that would allow me to look at varying loads and see what would sort of sag would occur.  The thing that stumped me most was I had no idea what the weight sharing was between front and back wheels.  The spreadsheet was based on 50/50 front and back but I am certain that this number is wrong.  (you will see why I say this later)
The way I worked it out was,
Take total bike weight, add rider and luggage weight for the average riding condition.  (I used 394KG) The assumption was half of the total weight was now on the front wheel.  (197Kg) That means I would have 98.5 Kg on each fork spring. Hold that number for future reference.

I then calculated that if I wanted 32mm of Sag then then I would have to preload the spring leaving just 38.4 Kg as sag.  Why 38.4?  Because 32mm sag, times 1.2Kg/mm equels 38.4Kg.
Its at this point I used the 98.5Kg of fork weight and subtracted the 38.4 Kg of sag to tell me how much to compress the spring.  60.1Kg or 50.1mm (60.1Kg divided by the 1.2Kg/mm = 50.1mm of compression)

50.1mm is a long way from the 19mm starting point others had mentioned.  I tried a spacer to obtain 50.1mm of compression but it was too tough to install and I knew something was wrong on both counts.  My 50/50 basis must be way off the mark.

This is where a bit of luck came into play.  I was guessing that 19mm was to soft and I would have to much sag.  50mm was going to be to hard with to little sag.  What could I start with and allow me to cut it down if needed?  I made a guess and compromised at 25mm, because I knew I could compress this and install, especially on the RH fork cartridge which is harder to work with than the LH fork.

So I cut the spacers giving each fork spring 25mm of compression.  I fully expected I would have to later disassemble to fine tune the length of the spacers to obtain the 32mm sag I deemed as being optimal. 

Honestly I was blown away that the 25mm spring preload I used gave me exactly the 32mm I wanted.  Miles away from the 50.1mm I had calculated.  I concluded that my guess of the 50/50 front and back wheel load sharing is what really throws my calculations out the window, either that or I am completely an idiot and have absolutely no idea at all about whats going on, and just fluked it, in more ways than one.

Trying to answer your question made me go back to my spreadsheet and re-gig it trying to find out at what load between front and back would match the results I experienced.  I am guessing that 65% of the weight at rest (incl rider) is on the rear wheel and conversely 35% is on the front wheel.
I am sort of hoping someone might be able to confirm this if they have access to two independent scales one for each wheel.  It might prove that all of the above is just gibberish.
I hope this makes a small amount of sense and answers it for you.  Happy to answer any other questions.
« Last Edit: September 29, 2014, 10:07:50 AM by Piet »
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Offline Brock

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #18 on: September 28, 2014, 03:32:51 PM »
I'm not sure Im reading this right, but to me that seems to indicate 34mm of spacer to preload the springs about 50 Kg. If I read that right, then its not sag, as that would be how much the front dropped on mounting the bike.
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Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #19 on: September 28, 2014, 03:54:04 PM »
I cant comment on this Brock because I am not measuring the spacer but the compression of the spring.  What I can say is that the amount of spring compression is preload and NOT sag.   
Do the coments below help?

The spacer is what compresses the spring.  The dimension of the spacer is different in each fork leg, because the construction of the two forks is completely different.  So I was trying to convey the way I calculated it, without stating the actual length of any spacer because they are both different.  What is the same for both though, is how much each spacer compresses the spring.  Thats the preload.  Whatever weight is applied to the front wheel is shared by both fork springs and the preload must soak up most of that weight EXCEPT the amount that its sags.  So 32mm of sag @ 1.2Kg per mm is equivelent to 38.4 Kg.  The calculated weight difference (between single fork weight less the sag weight) can be converted to mm by using the 1.2Kg per mm constant.  Thats what the dimension of spring compression or preload has to be.

Where I suspect alot of confussion will come in is the difference between actual mm of spring compression and the length of the spacer required to compress the spring.  One is measuring the spring, the other is measuring the spacer.  It sounds obvious but it can be very very confusing.
« Last Edit: September 28, 2014, 04:46:52 PM by Piet »
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Offline Greencan

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #20 on: September 28, 2014, 05:29:26 PM »
Piet et al...afternoon.

OK, now having seen a pic of your replacement springs sheds more light on your method(s).

What I did (to set up un laiden sag), was to turn up a several spacers from a single piece of aluminium from 2mm up to 10mm, plus use a couple of 1.5mm steel spacers I'd been given from a Mate.

As my bikes are both the last model ABS/TSC/CBS varients AND I was using the original OEM springs, it was a relatively easy (2 minute task), to remove the RIGHT side stanchion cap and add or subtract spacer(s), as deemed necessary; until I got a combination of desired sag and ride comfort (using a 7wt oil in both forks).

Once I was happy with the above, I then added the total added spacers (this case was 8.mm), I removed 4mm from the RIGHT stanchion (to minimise the possibility of it becoming coil bound), and popped them in the LEFT stanchion, which is a little more time consuming.

But, your right, its a bit hit n miss.

Cheers, the can :-)
 

Offline Piet

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Re: Fork Springs, Anyone tried fixed rate springs?
« Reply #21 on: September 29, 2014, 09:58:16 AM »
Hi Greencan,

Thanks for your experiance.  That was very clever using just the one fork tube to do your adjustment, getting it just right.  Then taking the result, halving it and putting half in each fork leg. Very cool.  That would work perfectly with fixed rate springs.  I would hope it works perfectly with progressive springs too.  I expect it would be very close with small spacer dimensions as yours were.  I would be interested to see if it would hold true if the fork/spring design required longer spacers.  I then would imagine the progressive nature of the springs would affect the results a little.

Just a quick question, why work with unladen weight?  In doing so did you opt for a lower sag number, knowing that when you jumped on it would increase the sag.  If so that again makes it easier to work on.  The only question I would have then is how did you determine the lower sag number for unladen?  Did you measure the difference between laden & unladen right at the beginning of your work on the spacers?

« Last Edit: September 29, 2014, 10:19:03 AM by Piet »
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