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erik
29th December 2004, 22:31
Ahh, work. . . Ohh look , home time!

Anyways Yams oft have soft forks. Haven't we had this discussion before? I’ve modified fork springs like this on everything from my MB50 to the KDX to the RF900. Just have to watch for coil bind (work out stroke & space between coils & make up a spacer to replace removed length. Nowadays I just cut the coils with a disc grinder & heat the top coil with a propane torch to flatten it.

Works on forks & shocks
click here for stiffer springs for like FREE (http://www.off-road.com/dirtbike/tech/2002spring/)

Quoting from jrandom's fzx thread (http://www.kiwibiker.co.nz/forums/showthread.php?t=7444)...

Yup, I think you've mentioned that before. I often have to hear stuff a couple of times for it to sink through my skull... :whistle:

I've just pulled the springs out of the forks and measured the fork travel, the spacer size, the spring size etc.

The springs seem to be roughly dual rate (the spacing of the coils increases slightly on the section with the wider gaps).

Does this mean that I really need to remove coils from both ends of the spring? Or should I just remove them from the wider-spaced end to increase the higher-end spring rate?

This is going to be interesting...

Posh Tourer :P
30th December 2004, 07:47
If you cut from the thin end, won't it just make them shorter with the same spring rate, = bottoming out earlier?

erik
30th December 2004, 08:18
If you cut from the thin end, won't it just make them shorter with the same spring rate, = bottoming out earlier?

which end is the thin end?

From http://www.partsmag.com/0409/Progressive-0409/Prog-Susp-0409.html


Dual-rate springs have a “step” in their compression. A 10-20 spring, for example, will require 10 pounds to compress it an inch until the light coils bind, and then 20 pounds per inch.

So I'm thinking it might be good to increase the rate for the light (close together) coils as well as the rate for the heavier (wider spaced) coils.
Although I guess if I'm mainly worried about bottoming out, I could just leave the light coils and cut the heavy ones.

Thinking more about this and how dual rate springs work makes progressive springs seem more desireable. But I think I'll give this a go first.

Motu
30th December 2004, 08:35
You want to stiffen up the soft part of your spring,so take it out of the close coils.

Springs follow sound scientific principals,but defy logic when you try to figure them out with only our little brains.Looking at my 2 shocks yesterday I was shocked to see the TT spring much shorter than the XT - shit,this is going to be too stiff I thought,but then counted the coils and found they were the same - the TT has closer pitch coils,this will be softer than the course pitch XT spring,they are probably close to the same rate,but won't know until I fit it.

Posh Tourer :P
30th December 2004, 09:15
Yeah gets me every time too.....

If you cut from the open coils, wont it give you less range of hard rate spring and therefore easier bottoming out?

FROSTY
30th December 2004, 10:30
Erik--before ya go cutting anything--try fitting slightly longer spacers on the springs and maybee a slightly heavier rate oil.

2_SL0
30th December 2004, 10:54
I put a heavier weight oil in the FZR 250 forks, it did the trick for me. But I didnt really push the bike very hard.

erik
30th December 2004, 13:23
As I understand it, the close together coils soften the springs by increasing the overall number of coils in the spring.
But because they are close together, they bind against eachother far before the rest of the spring does. When they bind, it essentially shortens the spring as only the wide-spaced coils are active. Because only the wide-spaced coils are active, the spring is stiffer (fewer coils = stiffer spring).

So by cutting the wide-spaced coils, I'd be stiffening up the springs when they're under heavy loading, which should help prevent the forks from bottoming out.

If I went overboard and cut too much off, I could end up with the forks bottoming out due to the springs binding, so I'll have to be careful of that.

I guess I should just try longer spacers first. Gotta find myself some 30-32mm dia. exhaust tube.
I've found a couple of articles about suspension tuning that have helped me understand a bit better and given me some ideas of things to measure and what to aim for with the setup:

http://www.strappe.com/suspension.html
http://www.mi-hsta.org/Articles/Suspension%20Setup.htm

I kinda have to wait till I've got the bike on the road again so that I can make modifications and then test them. I've already put some 15W oil in the forks and it doesn't seem to have helped, maybe I'll try thicker oil at a later stage, but I think the springs are really the main issue at the moment.

Feck this is fun though :)

FROSTY
30th December 2004, 13:47
Mate a lil secret re Yamaha suspension tuning--dont tell the other Kbers
Go out and get $4.00 worth of 20c pieces (may be 50c with your bike)
Glue 2 stacks of 5 coins together with a dab of superglue.
You can then simply unscrew ya fork cap -toss one stack of coins in each fork leg and presto fork springs are preloaded by aprox 12mm.
If it aint enough -sweet as -pull em out -glue another coin on the stack etc etc.
Saves shit loads of cutting and fucking around. Trust me It works-Ive done it.
Ohh and the bonus is if ya ever run outa gas and money --unscrew ya fork cap and ya got money for gas home. :killingme
same principle applies to thick penny washers btw but theyre usually harder to glue.

avgas
30th December 2004, 14:09
Mate a lil secret re Yamaha suspension tuning--dont tell the other Kbers
Go out and get $4.00 worth of 20c pieces (may be 50c with your bike)
Glue 2 stacks of 5 coins together with a dab of superglue.
You can then simply unscrew ya fork cap -toss one stack of coins in each fork leg and presto fork springs are preloaded by aprox 12mm.
If it aint enough -sweet as -pull em out -glue another coin on the stack etc etc.
Saves shit loads of cutting and fucking around. Trust me It works-Ive done it.
Ohh and the bonus is if ya ever run outa gas and money --unscrew ya fork cap and ya got money for gas home. :killingme
same principle applies to thick penny washers btw but theyre usually harder to glue.
Finally some good ol'e school logic, that my dad taught me.
This works a charm (ive done it on my other bikes). Good on ya frosty

Gixxer 4 ever
30th December 2004, 21:49
I put a heavier weight oil in the FZR 250 forks, it did the trick for me. But I didnt really push the bike very hard.
Yep this is good advice. You will get a good result from this and it can be set back should you not be happy. The thick oil will help no end. I would not cut when you can pack the top with coins ( or washers ) as Frosty said. This really is the solution.

F5 Dave
31st December 2004, 09:53
Eric, you are on the right track.

To the others with your thick oil & preload ideas; respectfully
–Wash your brains out with soap!

The thick oil will increase compression damping which will make the bike less prone to dive under braking, but this will also affect rebound damping. Worse these simple forks are orifice limited so High speed compression damping (like stutter bumps) will cause the forks to lock up.

More oil will decrease the air gap which will help slightly, but go too far (ie not very) & air space will run out & hydraulic/take the fork seals out.

Use springs as springs

Preload: If you look at a graph of a spring the line as it compresses say ‘x’ being kilos & ‘y’ being centimetres, then the steepness of the graph will be the spring rate. (ignore progressive or 2 rate springs for the moment). Adding preload will not alter this ‘curve’ (straight line) but simply increase it’s position up the ‘x’ axis (at the intersection 0 cm with some preload to start with).

In the big picture lots of preload & a soft spring tends to make the initial hits hard & the spring rate comparitively flat, so it would be harsh at the start & travel full stroke moderately easily.

Preload certainly makes it feel stiffer when you push on the forks, but should only be used to get the right amount of sag positioning the ride height correctly, not to compensate (poorly) for too soft of a spring.

Note: Too much preload will cause coil bind


Coil bind: Yes you must make an educated guess here. If you think it is going to get close you have to measure the spaces between the springs, add them up. Take away the amount the spring is compressed when you screw the cap down, then take away the full fork stroke & come up with some breathing space.

I’ve usually taken from the closely wound side as it means the wire is easier to bend flat again & usually the bike responds well to this as it will be riding higher on the spring & the total spring rate WILL be higher so prevent bottoming. I use thick wall PVC pipe (plumbing) which is hella strong in compression & has been used by zillions of racers as it is cheap & comes in convenient sizes.

scroter
31st December 2004, 14:44
Quoting from jrandom's fzx thread (http://www.kiwibiker.co.nz/forums/showthread.php?t=7444)...

Yup, I think you've mentioned that before. I often have to hear stuff a couple of times for it to sink through my skull... :whistle:

I've just pulled the springs out of the forks and measured the fork travel, the spacer size, the spring size etc.

The springs seem to be roughly dual rate (the spacing of the coils increases slightly on the section with the wider gaps).

Does this mean that I really need to remove coils from both ends of the spring? Or should I just remove them from the wider-spaced end to increase the higher-end spring rate?

This is going to be interesting...

i dont know about cutting them but if you do youll have to increase the size of the spacer to take up the space obviously. i wouldnt cut them at all. i dont know what kind of damping youve got on that. if its got high speed and low speed then dont change the oil weight. if its just damping then increase it to heavier weight. another thing you can do is add more fork oil, all it does is make the air pocket smaller making your shocks feel harder at the bottom of the stroke(just like a progressive rate spring, which is what your springs are). i dont know how much your willing to spend on it but new springs are usually under $300. losing the progressive rate springs for linear ones and adjusting your fork oil level would be a start.

scroter
31st December 2004, 14:46
Eric, you are on the right track.

To the others with your thick oil & preload ideas; respectfully
–Wash your brains out with soap!

The thick oil will increase compression damping which will make the bike less prone to dive under braking, but this will also affect rebound damping. Worse these simple forks are orifice limited so High speed compression damping (like stutter bumps) will cause the forks to lock up.

More oil will decrease the air gap which will help slightly, but go too far (ie not very) & air space will run out & hydraulic/take the fork seals out.

Use springs as springs

Preload: If you look at a graph of a spring the line as it compresses say ‘x’ being kilos & ‘y’ being centimetres, then the steepness of the graph will be the spring rate. (ignore progressive or 2 rate springs for the moment). Adding preload will not alter this ‘curve’ (straight line) but simply increase it’s position up the ‘x’ axis (at the intersection 0 cm with some preload to start with).

In the big picture lots of preload & a soft spring tends to make the initial hits hard & the spring rate comparitively flat, so it would be harsh at the start & travel full stroke moderately easily.

Preload certainly makes it feel stiffer when you push on the forks, but should only be used to get the right amount of sag positioning the ride height correctly, not to compensate (poorly) for too soft of a spring.

Note: Too much preload will cause coil bind


Coil bind: Yes you must make an educated guess here. If you think it is going to get close you have to measure the spaces between the springs, add them up. Take away the amount the spring is compressed when you screw the cap down, then take away the full fork stroke & come up with some breathing space.

I’ve usually taken from the closely wound side as it means the wire is easier to bend flat again & usually the bike responds well to this as it will be riding higher on the spring & the total spring rate WILL be higher so prevent bottoming. I use thick wall PVC pipe (plumbing) which is hella strong in compression & has been used by zillions of racers as it is cheap & comes in convenient sizes.

sorry i didnt read this before my comment. but i agree with it.

2_SL0
1st January 2005, 21:36
All Iwas wanting to achieve with mine was to lesson the dive factor when heavy breaking, the heavier oil did this perfectly without causing any side effects. Othere than that I would start looking at a set of aftermarket springs, and to top it off a set of Gold valves. But that would cost money.

Bonez
1st January 2005, 21:55
All Iwas wanting to achieve with mine was to lesson the dive factor when heavy breaking, the heavier oil did this perfectly without causing any side effects. Othere than that I would start looking at a set of aftermarket springs, and to top it off a set of Gold valves. But that would cost money.
Are they made from gold?

2_SL0
1st January 2005, 22:04
Race Tech's Gold Valve Kits.



http://www.racetech.com

:niceone:

DEATH_INC.
1st January 2005, 22:28
I've always cut 'em off the close coils,these are softer and we want to harden the spring,so removing a few of these will get it into the stiffer part sooner(they coil bind first).Plus you'll remove more coils(increase the rate more)for any given length you cut off.
There's a no of factors that determine spring rate;diameter of the coil,diameter of the wire,no of coils and coil pitch(to a lesser extent)and of course wire composition.We can't alter any of these except for the no of coils so this is why we cut 'em.

erik
1st January 2005, 23:08
hmmm.

I haven't done any cutting yet, and still aren't sure exactly what I'm going to do, but I'm getting there.
I've been trying to figure out the fork spring rates and having a bit of fun making contraptions to measure them.
First I tried just putting a steel tube in a block of wood to support it, then slipping the spring over it and putting weight plates on top of it and measuring the changes in length. But I couldn't compress the spring enough as I ran out of weights...

So then I thought maybe I'd use a 25litre water container and add more water to that for more weight, and just balance it on top of the weights already on the spring. I ended up borrowing my neighbours bathroom scales and balancing everything on top of them so that I didn't have to measure the water precisely.
But I still ran out of weight, even with the old car rim (9kg) the weight plates, and the 25litre container of water (and it was kinda unstable to boot...).

Possibly I was getting a bit carried away by this point, but I ended up making a contraption to measure the spring compression under different amounts of weight. I had to buy some cheap ($9.75) bathroom scales because I couldn't modify my neighbours ones ;) and I had to get a few other bits and pieces, but the end result works pretty well. It's basically bathroom scales with a couple of bits of wood on top and bottom to stiffen the case, and a threaded rod attached to the bottom case and passing through a hold in the top case. I had to make the dial smaller so that I could position the rod close to the centre of the scales. A couple of bits of pvc tubing and a few washers and a wingnut completed it. (see attachments)

Anyway, I've got a graph of the spring rates now (see the attached gif) and you can quite clearly see the two different rates and the point where the close coils bind and the rate changes.
Just for interests sake at this point I've marked the approximate positions of the total fork travel, the static sag (haven't measured the laden sag yet, will get around to it soon), and the preload.

My next step is to read more suspension setup articles... just as soon as I get a decent nights sleep :sleep:

Thanks everyone for your input so far, it's informative and helpful :niceone:

erik
3rd January 2005, 20:52
Ok, I've got a question:

Do bikes always bottom out the forks when doing stoppies?


The reason I ask is because I tried to calculate the max force the forks would experience, and the figure I ended up with would require a far higher spring rate than what I've seen advertised for other bikes (approx 1.75kg/mm as opposed to 1.05kg/mm highest I've seen advertised).

I guess I should forget about trying to calculate a spring rate to aim for and just try to increase it a bit from what it is.

Blakamin
3rd January 2005, 21:02
The reason I ask is because I tried to calculate the max force the forks would experience, and the figure I ended up with would require a far higher spring rate than what I've seen advertised for other bikes (approx 1.75kg/mm as opposed to 1.05kg/mm highest I've seen advertised).

:blink: did you say something??? calling JRANDOM!!!!!!

avgas
3rd January 2005, 21:41
Ok, I've got a question:
Do bikes always bottom out the forks when doing stoppies?
The reason I ask is because I tried to calculate the max force the forks would experience, and the figure I ended up with would require a far higher spring rate than what I've seen advertised for other bikes (approx 1.75kg/mm as opposed to 1.05kg/mm highest I've seen advertised).
I guess I should forget about trying to calculate a spring rate to aim for and just try to increase it a bit from what it is.
yes and no, it really depends on the springs and the rate of recoil they have left in them. As mentioned before,basic springs (not progressive) are an exponential based systems. So what actually happens is on the top of the curve u will end up with 3 or more times the initial weight/distance measurement. By preloading the spring however this does compress the "compression curve" and will give a little increase in height during overload (stoppie etc). But this height is just a buffer - so it still "bottoming out".
If you really want perfect forks though a fork kit can go right way.
I acutally run a lighter oil, as i find the forks have better response rate. And i dont end up bunny hopping anywhere anyway.
I have seen a few forks that didnt bottom out while doing stoppies, but they were heavy loaded for lard asses - and prob not that comfy to ride on.
At the end of the day - if u want to spend money on ya bike, those gold kit are really good.

F5 Dave
5th January 2005, 08:48
Whoa! I think you are a bit out in the calculations for what you require, did you assume TWO fork springs?

For example my 750 yam uses .8kg springs & that will be a sight heaviers than the 250. In that link about Racetech has a useful spring calculator, choose a bike the same weight as yours (no linkage on the front of course) & make sure the rider weight is in pounds. Choose Street & the recomendations they give are often on the heavy side I'm told.

On that site I gave with the spring article there is another on measuring springs using a lever & tape measure + scales, though I am impressed with your elaborate spring holders. Personally I'd just make them a bit heavier & try it.

scroter
5th January 2005, 11:44
i wouldnt bother trying to calculate your current springs weight its progressive therefore different weight at one end than the other. cutting is extreme, if you do, dont forget to flatten the end youve cut. i still would reccomend linear rate springs as the air pocket left above the fork oil is like a progressive spring anyway, eg. add more fork oil will help with bottoming out without increasing the stiffness of the initial stroke. ie you should only notice it when hard on the brakes try it it works.

my suggestion contact someone in the know like ohlins or ray clee(whitepower) or suspension tech, they should be able to tell you the correct weight springs for your weight and the correct fork oil level to stop bottoming out. in my experience robert taylor(ohlins nz) usually advises rather stiffly sprung setups but then he will usually let you send springs back for either softer or harder springs if they dont suit.

erik
5th January 2005, 21:24
I'm pretty sure I got the calculations right, but I guess that the damping plays a large role in preventing the suspension from bottoming out. But since I don't know how to take that into account, I can't really go any further with calculations.

I think it is probably just time for me to adjust things and test it. I reckon I'll try increasing the preload just by itself at first. I read that preload should generally be set so that the laden sag is about 30 to 33% of the full suspension travel for streetbikes (http://www.strappe.com/suspension.html), and as it is my zeal is at almost 45%. After that I'll have a go at cutting the springs... :devil2: ;)

erik
15th January 2005, 12:05
Well, I cut the springs with an angle grinder last sunday. That was before I learned it was illegal to heat motorvehicle suspension springs...
Maybe I wouldn't have done it if I'd known before, not sure... :whistle:
So caz it's not entirely legal, I won't mention who it was that helped me bend the coils flat. But thanks for your help :niceone:

Before putting them back in the bike, I tried measuring their rate to see how they compared to the expected new rate and found they almost perfectly matched the predicted rate :) (see attached pic)
But, after compressing the spring, the last coil that had been bent flat stayed bent in the compressed position! :(
I guess I should've expected that since by heating the coil, the steel lost it's temper. :angry2: ;)
Now I'm worried that because the end isn't flat, it'll make the springs rub excessively on the insides of the fork tube. It wouldn't have been so much of a problem if I had cut and heated the top end, since it doesn't move in the tube, but because I did the bottom end, it's sliding up and down against the tube the whole time, so it'll probably cause significant wear and maybe excess friction in the forks.
I'm guessing it wouldn't be too good to turn the springs upside down either, as that would put the close-wound coils in the moving end and since they bind against eachother, and there are a whole lot more coils, it would probably rub against the insides of the forks quite a lot too.
That said, I'm pretty sure it wouldn't have helped much by cutting the top, close-spaced, coils because that would have only increased the soft rate of the spring before the coils bound.

So this morning I went looking for springs at a couple of bike wreckers on Barry's Pt road. Action bike wreckers had a whole heap of springs and let me look through them, and I found a spring that looked like it would be perfect for the job, but couldn't find it's partner! :(
Atomic bike wreckers said they only had complete forks, not springs by themselves.

I've heard of a place that can re-temper springs, so I'll try phoning them on monday (they seem to be shut now) to see if it's possible and how much it costs so that I can compare it to the price of new aftermarket springs.
I've heard it's about $120 for a set of car springs, if it's significantly cheaper for the fork springs, I'll give it a go, otherwise I think aftermarket springs will be the best option.

It's quite disappointing since I have really enjoyed measuring the spring rate and stuff. :disapint:
Oh well... at least I'm learning stuff and having fun. :)

erik
15th January 2005, 14:52
Or I could just be thinking and worrying too much. A mate said he reckons he'd just put them in and try it.

hmm...

Mr Skid
15th January 2005, 15:31
Or I could just be thinking and worrying too much. A mate said he reckons he'd just put them in and try it.

hmm...
Yeah! Go for it! What's the worst that could possibly happen?? :shifty:

DEATH_INC.
16th January 2005, 08:34
Sounds like you over-heated the coil(should only be heated to 'cherry'red and gently bent).I would've cut the close end,but you've done it now.
You could either hit the spring with a grinder and remove anything that sticks out from the od of the spring,or just put it in upside down,it won't hurt anything.
Give 'em a go,you need to see out your experiment to learn what you've done so it'll be better next time.Don't forget to replace what you've cut off with a spacer too,and I always add a splash more oil too( a capful or so).
If you're talking about Snells or Archers for re-tempering,don't waste your time....

erik
16th January 2005, 08:46
Sounds like you over-heated the coil(should only be heated to 'cherry'red and gently bent).I would've cut the close end,but you've done it now.
You could either hit the spring with a grinder and remove anything that sticks out from the od of the spring,or just put it in upside down,it won't hurt anything.
Give 'em a go,you need to see out your experiment to learn what you've done so it'll be better next time.Don't forget to replace what you've cut off with a spacer too,and I always add a splash more oil too( a capful or so).
If you're talking about Snells or Archers for re-tempering,don't waste your time....

Thanks for that, I'll try putting them in upside down.
Re: the heating, yep, I think we heated it above cherry red. I'll be more careful next time.

I was talking about Snells, a friend that's into cars told me maybe they could help. How come it's a waste of time?

erik
16th January 2005, 11:48
Ok, spacers made, springs installed, bike testridden. :ride:

It's definately firmer than before. I think I like it. But I think it's going to take a while to get used to it. I haven't only changed the springs, the tyres are also different (new, still just scrubbing them in), and because I've set the preload to 30% where before it was at 45% the front is 16mm higher, which I think was fairly noticeable, it seemed higher, but also I think it didn't seem as twitchy as it did when I first tried it with the new tyres and the old front suspension. Maybe I'll drop the trippleclamps down the forks a bit to liven it up, I'll wait and see.

I guess I'll just use the springs as they are and maybe open it up in a few weeks to make sure nothing nasty is happening in there.

Woo! :)

Milky
16th January 2005, 13:56
surely you could temper the springs slightly yourself... Not having done it before or being experienced in this sort of thing, I am not sure of the best way to go about it, but surely it is possible. :spudwhat:

FROSTY
16th January 2005, 14:51
Eric, you are on the right track.

To the others with your thick oil & preload ideas; respectfully
–Wash your brains out with soap!

.
You and I will have to agree to disagree here dude.
My advise is from real world experience specificly dealing with Yamaha mid 80's front suspension. In other words I've done it I know it works. :devil2:
Also keep in mind when offering advise (I mean this genericly not specificly) that the person you are dealing with is of questionable mechanical ability.
I don't doubt that an experienced person couldn't acheive the result you suggested.
But the result was as I suspected it would be

erik
16th January 2005, 16:32
Milky, I was thinking about it, but I think unless I quenched and tempered the whole spring, I think I'd end up with a soft bit between the old tempered bit and the new tempered bit.

Frosty, in the end it's my decision whose advice I follow. I made a small mistake because of my inexperience, next time I'll know not to overheat the springs.
I suspect that if I had simply increased the spacers so that the sag was at 30% and left the spring rates alone, it still would have been too soft.

F5 Dave
17th January 2005, 12:18
. ..
My advise is from real world experience specificly dealing with Yamaha mid 80's front suspension. . .

Gee me too, but not limited to.

PS: I should Advise you the word you were looking for is 'Advice'.



. ..
Also keep in mind when offering advise (I mean this genericly not specificly) that the person you are dealing with is of questionable mechanical ability.
I don't doubt that an experienced person couldn't acheive the result you suggested.
But the result was as I suspected it would be

And how does one gain mechanical experience?

Yup you have to roll your sleeves up & jump in. Bit of reading & advice is always nice.

Sometimes the best experience comes from the mistakes, but it was hardly an ‘I told you so’ moment.

Erik I'm glad you at least had some reasonable results. Think that article mentioned just heating it up enough so it would move with pliers.

So basically you have an end that is not flat? Hmm, I wonder if the preload spacer could be matched & just run the spring upside-down. It may tend to still slide sideways a bit but at the top of the fork I don’t think you would notice.

FROSTY
17th January 2005, 13:54
Milky, I was thinking about it, but I think unless I quenched and tempered the whole spring, I think I'd end up with a soft bit between the old tempered bit and the new tempered bit.

Frosty, in the end it's my decision whose advice I follow. I made a small mistake because of my inexperience, next time I'll know not to overheat the springs.
I suspect that if I had simply increased the spacers so that the sag was at 30% and left the spring rates alone, it still would have been too soft.
Not having a go at you eric. :wavey:
My methodology (sp) has always been to take the simplest solution first then ramp up to the next level if it doesn't work.

DEATH_INC.
18th January 2005, 19:47
I was talking about Snells, a friend that's into cars told me maybe they could help. How come it's a waste of time?
Because they don't know the alloys and original temper of the springs,they just guess.A large percentage of their compressed and re-tempered car springs sag after a while.....
Glad it worked out ok :niceone:

Warr
20th January 2005, 13:22
I see this thread is about done, but with so much expertise being shown thought I could tap into the same ... etc etc.

My '84 XJ900, Most riding is 2 up. Just had new fork seals fitted and with no air it hits hard when trying to get over anysort of bump. So top the air up and loosing oil out r/h leg. Reduce air to 10 psi (I think). Now oil under control but still inclined to bottom out. Especially when negotiating driveways at slow speed.

From reading all the above I like Frosty's $4.00 worth of 20c the most just top give it a bit more height. Or is a heavier grade of oil going to be a better solution.?

F5 Dave
20th January 2005, 14:39
Did you click the link in the quote of the first thread?

Air pressure just tends to make the forks bouncy (air isn’t a linear spring so will overwhelm damping if relied upon too much) + far more likely to blow seals.

Heavier oil & excessive preload will mask the symptoms but not effect a cure & have side effects like harsh on small bumps stuttering likely.

But go on, knock yourself out, fire in a weeks wages of 20c pieces & diff oil.


[edit]
Sorry I’m having a cynical afternoon.

DEATH_INC.
20th January 2005, 17:09
'preload' can be more accurately reffered to as ride height,this is all you're changing with it.
Remember,the spring holds the bike up,the oil(damping)controls how fast the suspension moves....

erik
20th January 2005, 17:19
I see this thread is about done, but with so much expertise being shown thought I could tap into the same ... etc etc.

My '84 XJ900, Most riding is 2 up. Just had new fork seals fitted and with no air it hits hard when trying to get over anysort of bump. So top the air up and loosing oil out r/h leg. Reduce air to 10 psi (I think). Now oil under control but still inclined to bottom out. Especially when negotiating driveways at slow speed.

From reading all the above I like Frosty's $4.00 worth of 20c the most just top give it a bit more height. Or is a heavier grade of oil going to be a better solution.?

From what I've read, the laden sag should be about 30 to 35% for street riding (http://www.strappe.com/suspension.html). As I understand it, if you have less sag, the front wheel won't follow depressions in the road as well (if I'm wrong here, or there is more to it, please comment).

You could try setting the laden sag to the correct amount using either the coins or some pvc tubing spacers, and if it still bottoms out or feels too soft, then you'll know you need to increase the spring rate with new springs or by other methods...

That's my 5c worth :)

Kickaha
20th January 2005, 18:11
'preload' can be more accurately reffered to as ride height,this is all you're changing with it.
Remember,the spring holds the bike up,the oil(damping)controls how fast the suspension moves....


I am sure someone will correct me if I'm wrong but I think they are slightly different otherwise why would you bother having seperate spring preload and ride height adjustment on some rear shocks

FROSTY
20th January 2005, 22:34
I see this thread is about done, but with so much expertise being shown thought I could tap into the same ... etc etc.

My '84 XJ900, Most riding is 2 up. Just had new fork seals fitted and with no air it hits hard when trying to get over anysort of bump. So top the air up and loosing oil out r/h leg. Reduce air to 10 psi (I think). Now oil under control but still inclined to bottom out. Especially when negotiating driveways at slow speed.

From reading all the above I like Frosty's $4.00 worth of 20c the most just top give it a bit more height. Or is a heavier grade of oil going to be a better solution.?
Specific advise regarding your bike.
If you can afford to I would pay the $120 ish dollars for a set of progressive springs.You wont believe the difference they will make.
I would dump the fork oil and replace it with 15 weight oil (50/50 10 and 20 weight). I would use 5-10ml extra oil in each fork leg.
Don't use any air at all
To get it just right you will need to experiment a bit on this basic formula but it will give ya a good benchmark to start wit.
Once ya have it real close use up to 10psi to do the really fine tuning.

ajturbo
20th January 2005, 22:52
i put in aluminium (sp?) spacers in mine.. (87 model) they were solid and aprox 40-50mm ( cannot remember the excate lenth) added the 15 w oil! also

this was done when brand new!!!! (after first service)


andy