New fork springs? But that costs money!

[fudge12]

Let me warn you now, there's going to be math.  tl/dr version: cutting the stock front springs makes them stiffer.

Ok, so I recently picked up my '87 FJ12.  It has good points, but it has bad points.  The front suspension was a definite bad point.  Way too softly sprung.  First response, as usual, is put a different spring.  However, says I, there may not be a need for that.  According to racetech, the stock spring is .65kg/mm, and I need a .942kg/mm spring.  I pulled the stock springs out, and they measured 19" free length, .185" wire diameter, 40 active coils.  This equates to .5kg/mm.  However the stock coil is split into two separate coil sets, 15 that are .125" spacing and 25 that are .325" spacing.  Further, there's about 2" of preload built into the fork caps.  So, here comes the math.  The close coils are the 'progressive' part of the spring.  as soon as the spring compresses more than about 2" they go coil to coil and are no longer a spring, they're a bumpy cylinder.  This is based on .125" space between coils times 15 coils equals 1.875" of compression in that part of the spring.  The looser coiled section, at .325" times 25 gives about 8.125" of compression before they're coil to coil.  This gives a total of 10" of compression available on the spring.  Minus 2" for the fork cap preload, the spring can still compress 8".  The fork travel is supposed to be 5.9", so we'll call it 6" for rounding.  Carrying on, we can now see that we can cut just a bit less than 2" of free space out of the spring and still not be lock to lock on the rest.  Going to some of the spring rate calculators online, I looked at the two sections of the spring separately and figured that if I cut my spring to 28 active coils, it should bring me right at .95kg/mm.  So, I grabbed the grinder, cut it down to 28 active coils, cutting off most of the progressive section, heated, bent and ground the top coil to match oem, and cut spacers from a pair of old fork spring spacers to bring the length back up to 19" overall.  Set the oil level to 6", put everything back together and did some tests.  With no additional preload, static sag is now .3", and race sag is 1.9".  That's as close to correct as you could hope for, based on race sag being 1/3 of available travel.  I took it out on the road and specifically hit some of the crappiest asphalt I could, when I came back I had used about 4" of my travel.  So from that standpoint it's a bit stiff.  From my MX days the thought was that you should bottom out once per lap since that meant you were using all of your travel.  So anyway, the ride is much better and much less wallowing.  The front is stiffer, but that's what I was going for.  I still have comfortably more free space in the spring than fork travel so I'm not worried about going coil to coil.  I do have to replace my fork seals soon, so when I do that I'll go ahead and take about .75" off the spacers I made to soften it up a little, since that seems to be about the travel available in the preload in the fork caps.  So, no money spent to get the right fork springs, just a bit of time and math.  Now I have to come up with something for the rear end.  Pics when I get them off my camera.

[fj1289]

I'd see if someone could send you some stock springs and try cutting again -- just a good bit longer.  Like I was taught when making a cut on the lathe - take off half of what you need to cut, doing so progressively until you "sneak up" on the size/clearance you need instead of cutting it all at once.  This would be a great budget "how-to".  I've read similar accounts of cutting the progressive brand springs to eliminate most of the close coils to yield a nearly straight rate spring of a suitable rate. 

[Pat Conlon]

The Race Tech spring rate calculator assumes you will be using the Race Tech cartridge emulators to control the heavier (straight rate) springs.

I would never consider using heavier .95kg/mm fork springs with my oem damper rod fork valving which was not designed for that heavy spring rate....

A Pogo stick comes to mind.

[fudge12]

FJ1289, I was taught the same thing but the problem comes in making new spacers every time you adjust the length of the spring.  I figured the math was solid enough to take a chance.  Worst case scenario, I needed to buy new springs and if these didn't work out I'd still have to buy new springs. Best case scenario is these work and I don't have to buy new springs.  So far they're working great.


Pat, I've never seen anything on their website that states their spring rate is based on using their damping, do you have a link?  And as for the pogo stick action of using a stronger spring with the stock damping, that's a common misconception that I didn't experience that in my test ride.  The purpose of the spring is to hold the bike up, ideally at a particular point in it's suspension travel.  That's it.  The damping acts only to control the unsprung weight, i.e. the front wheel and fork lowers.  Neither of those things changed.  It will rebound slightly faster due to the stronger spring, but in reality the difference is negligible.  The uncut spring sagged 3" with me on it, at full preload on the forks, which by necessity put it at 218lbs of preload (.65kg/mm=36.39 inch/lb rate, 1" of preload from adjusters, 2" of preload from fork caps, 3" of sag.  That puts a bump of 2" into the 291lb range.  My cut springs with a higher rate settle less than 2" with my weight, so it's math works out to 53.19lb/in, 2" of preload from the fork caps and 2" of sag puts me at 212lbs, pretty close to the 218 of the uncut.  Which makes sense, because the spring is still holding up the weight of the bike and me, and neither of those changed.  Now adding the next two inches of bump as above puts me at 319.14lbs.  The stock damping will not in fact be overwhelmed by the additional 30lbs of spring force.  It's less than a 10% difference.  10% difference is well within the range of adjustment that could be adjusted with different oil weight; going from the stock 10w to 12.5w would more than cover that range.

Also, for the ~200lbs of preload; the bike is 586lbs wet, with a somewhat forward bias.  I'm a svelte 200lbs, also with a somewhat forward weight bias.  Which means, roughly, that the front suspension has to hold a little more than half of my weight and half the bike's weight. 786/2=393lbs, divided by two fork springs means each spring has to hold a bit over 196lbs at rest.  They carry this weight regardless of spring rate.

[fudge12]

Pic of cut with spacer next to uncut

[FJ1100mjk]

Pat, I've never seen anything on their website that states their spring rate is based on using their damping, do you have a link?  And as for the pogo stick action of using a stronger spring with the stock damping, that's a common misconception.

Also, for the ~200lbs of preload; the bike is 586lbs wet, with a somewhat forward bias.  I'm a svelte 200lbs.

Using both Race Tech's and Sonic Spring's online spring rate calculators, yields similar numbers.

1.0 kg/mm from Sonic's calculator. (215 lb. rider weight including riding gear, no tank bag, 586 lb. wet bike weight, normal street riding on sport tour bike.)

0.95 kg/mm from Race Tech's calculator. (200 lb. rider weight w\o gear).

http://sonicsprings.com/catalog/calculate_spring_rate.php#calculate

http://racetech.com/ProductSearch/2/Yamaha/FJ1100/1984-85

**** Unless it's buried somewhere, or I missed it, I saw no mention of Race Tech's spring rates being tailored to their fork valves.

[Pat Conlon]

Ok, let us know what you discover.

I've had my FJ for a few years and I can say that I've never considered this mod, although other FJ owners have, back in the mid '80's.
I recall the general consensus was that the oem damper rod forks had severe rebound issues with heavy straight rate springs.
To get a perspective on what can be accomplished, I hope you get a chance to ride a FJ with cartridge emulators and/or IAT valves.

One last point regarding your math: Your 30 year old fork springs are not .65kg/mm.
Perhaps they were in 1987, but not today.
The spring steel Japan used in the '80's/90's was never known to be the most durable.

Still, I am interested in your results and impressions

[fudge12]

Don't get me wrong, I'm not saying that this is as good a solution as cartridge forks or cartridge emulators.  There is an inherent limitation with damper rod forks.  I simply offered this as a cheap alternative for people who would otherwise be spending $130 for a set of springs.  $215 for a set of cartridge emulators from Randy is a lot more palatable than $345 for both that and the spring.  I might could swing one or the other, but not both.  Now I don't have to.  Given the blue book value of my bike at around $1800, spending 20% of the bike's value doesn't make sense to me.  Getting a significant suspension improvement for free, that makes sense.  Now, if someone was willing to donate a set to me......

[Pat Conlon]

Good deal fudge, I'm glad you are happy with your mod

I shudder to think of how much I have spent on my '84.... I really don't want to know.

I can say without a doubt, that she is a much better motorcycle now, than the day I brought her home.
She is (much) faster, corners harder, handles better, stops quicker, more beautiful, and more comfortable...
....in all, she is a better motorcycle than I am a rider, and I'm ok with that.

As they say: It's all about progress, not perfection.

[ribbert]

.....spending 20% of the bike's value doesn't make sense to me.
 

I've spent 200% of the bikes value improving it and it makes sense to me every time I ride it.
If it was a straight out commercial investment you would be correct. However, I view it as an investment in riding (and I've invested plenty!), not over capitalising the bike.

Noel

[andyoutandabout]

I too have often sort the cheaper option, fully aware of the total monetary value of the Fj. However, since the actual value of an Fj in real world terms far exceeds this amount, then blowing a wad of cash on the important things can be readily justified. Every now and again items that fall into the paying less could cost you dear category, make themselves painfully visible. An example being chains and the mess a broken one can cause as witnessed at this years West Coast Rally. Then there's the way less visible spending areas like fork internals. OK, so modding the springs is unlikely to causes catastrophic failure, but every time you ride it, your going to appreciate a good front end. Believe me I umed and arhhed and counted my pennies when Randy popped in the valve stacks and new springs, but the difference just weaving round the car lot was worth it. Every mile since, and that's now in the tens of thousands, has chanted, "Andy, you made a good decision".

[Bill_Rockoff]

spending 20% of the bike's value doesn't make sense to me

You sort of have a point, in that an awesome rear shock and new fork springs / valving are going to be $1,500 whether it's for a used $15,000 K1600GT or a used $1,500 FJ. If you just bought a K1600GT, you could probably find "new shock and fork springs" money vacuuming out the sofa, whereas upgrading the suspension on your new-to-you FJ will cost you "an entire other running FJ."

Then again, the $15,000 BMW already has a pretty good suspension, and it will get only marginally better with a top-shelf shock. By contrast, your FJ was built while Japan Inc. was busy discovering "horsepower" and hadn't quite gotten around to "handling" yet, so the spring rates and damping were lacking even when the bike was new, and it's a long way from new. Better spring rates and damping is "a whole new world" on the FJ.

My bike is in cosmetically rough shape (it has been on the ground a couple times) and it burns a quart of oil in a single tank of fuel if the engine is working hard. And after 113,000 miles, you can actually work this engine hard without going terribly fast.  As it sits, it is probably worth somewhere between $1,000 and $1,500. (Today is a high-value day because the tires and brake pads are new and the tank is full.)  For the last 40,000 miles, I have been riding it with about $400 worth of Race Tech fork valves and fork springs in front and $900 worth of Penske shock in the back. So, I spent about 100% of the bike's value on a good shock, good fork valving, and the correct springs for my weight. This is some of the best money I have ever spent. With radial tires (and a 17"x5" YZF600R rear wheel) and with new front brake pads in the FZ1 calipers, it will stop and turn like a modern bike - a well-sorted modern bike - and everyone who has ridden both likes it better than the Ducati 998 I bought last year. Every time I ride my crappy-looking bike with its amazing handling and magic-carpet rough-road performance, I congratulate myself on money well-spent.

I'm in favor of making your own thing if it's just as good as a store-bought thing, or of substituting a different better thing. (My wheel bearings didn't come from the Yamaha store, they came from the SKF store, and I was happy to do without the Yamaha part number for a 60% savings.) But I don't see any benefit in short-changing myself on replacement parts just because we all found a good deal on the buy-in. My $1,500 FJ is getting the good chain and sprockets every 20,000 miles instead of the cheap ones because it works better. I've tried it the $100 way, and it sucks every time. I'll do it the $200 way and it'll be right the entire 20,000 mile life of the chain and sprockets.

My sister's house in the NY suburb where we grew up cost about five times what I paid for the last house I bought in Ass Crack, Georgia.  I slept like a champ last time I visited her, because the bed and linens in the guest room were really nice. It would be a false economy to outfit my bedroom at home with a $30 set of scratchy-ass polyester linens stretched over a no-name crap mattress, just because duplicating the nice stuff in her house would cost a whole per cent what my entire house cost while the cheap stuff keeps the cost proportional.

[giantkiller]

It's funny I paid $600 for my 86 with 10,000 miles on it. I have put about $7,000 into it.
Including the 1350 motor 163hp/114 to. It's about 55lbs lighter than stock. And it makes me smile every time I ride it. It's my work of art. And worth every penny. But I also have a lot of fun doing it the hands on way. 2008 gsxr1000 front end. And Honda rear shock. Keep us posted and keep having fun.

[Pat Conlon]

When you park your bike, and when you walk away, do you find yourself turning around to look at her?

You do?

Yep, the FJ fire is still burning.

[aviationfred]

What Bill and Dan both said is awesome......


Fred

P.S.     by the way Pat...... Yes I do.