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Discussion Starter #1
I need to order my rear Hypercoil spring but there is no calculator on the website on which rate spring to use. I wanted to see if some of you who have done the rear spring upgrade mod could offer some advice.

I am 230 lbs with my gear on (some winter weight ;), should lose 10lbs when I start running again). The bike needs to function as a commuter(why I got it initially) but I really want to ride the twisties (both local and in the mountains). I don't have any plans for the track as of now, but I said that of cars once too. I've beefed up my car suspensions too, so I don't mind a stiffer ride, but it still needs to be able to handle real life roads(bumps, bridge joints, broken pavement) with out bouncing me off the seat(like my cars do ;D).

I'd appreciate any suggestions or your experiences.

Thanks :)
 

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You could go at least 450# rear and could even use a 500#, slightly stiffer. Then .90kg fronts and emulators. I'm running a 450# rear and .90 fronts at 200#. I could tolerate a little stiffer at the rear on the street and would prefer it for the track. I feel like I'm right in between and could go either way on the street. The front's fine at my weight.

If you were considering track riding too, definitely do the 500# rear and even consider .95 fronts. You're right in the middle with this.

At the rear, expect about a 1 1/16" sag differential (free to static) with a 450# and about 15/16" differential with a 500#. I don't think you'd want anything stiffer on the street. Reference my write-up if you don't know what that means.
 
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dad said:
I'm running a 450# rear and .90 fronts
Thats the same setup I use, I'm about 240lbs. But for the street I almost wish I had gone for a 400# rear spring. The 450# seems a little too stiff at times. You probably won't go wrong either way, just depends if you want really firm suspension or slightly less so.

Rich
 

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Discussion Starter #5
I probably wouldn't go to #500; 400 or 450 sound pretty good. The hard part is knowing how firm it is (dad, I know you are a racer so you are probably used to taking a pretty good shot). As I said in a car it's not such a big deal if you hit that unavoidable pothole and find your head ricocheting off the roof. You just throw in a Yeeee- haw and keep going ;). On a bike at my current skill level I'm afraid the same incident might lead to vehicular control issues that I'd rather avoid. On the other hand, I'm afraid a 400 is a little close to the stock(300#?) to go through the same work and get less improvement. Afterall just my weight alone sounds to be way past the stock design criteria.

I know it is still subjective, but if you hit a good pothole how hard a shot do you get? Is it painful? Any airtime off the seat? Just trying to get a better handle on you perspective.

I really appreciate the insight; without it I'd be shooting in the dark.

Thanks so much!
 

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I just checked all of my notes again. Forget the 500# especially with your expressed preference. You'll be fine with the 450#. You might still like the 400# but it's really on the verge of being too soft. The 450# is probably perfect for the street and still OK for the track, just over the edge of being too soft for the track. 500# would actually be on the edge of stiff for the street. The only thing that suggests a little stiff will be OK is that the shock is still soft.

As far as being too harsh and hopping around on the road, that's NOT an issue. That's the whole point of NOT going too stiff. I think if you do the springs as suggested, both ends, and the emulators, you'll find it actually rides BETTER than stock as well as feels better, much more confidence inspiring. The one item that may make it feel harsh on the street is NOT using emulators. And if you use 15W fork oil w/o emulators it may be real bad. The big bumps will be harsh but because of the forks' inability to react fast enough, not because of the springs.

The only other item that some get wrong and can cause the bike to skip around on the road is setting the sag too high, not enough. The suspension can't follow the road adequately because it tops out too easily when trying to extend. That can happen with any springs but can even be worse when the spring's too soft but wound up tight anyway, trying to get it in range when plainly it's just not enough spring.

It's not correct that a properly sprung bike will feel harsh or jittery. The only reason you set the track a little stiffer is the idea that bumps will be hit at 70 MPH average vs: 45 MPH for the street. A well set up bike actually rides pretty nice, track or street. Good luck.

If you do it and are ready to install, check me again for numbers to pre-load the shock to on the bench. Installed it will be perfect sag or AWFULLY close.
 

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Have you considered links for raising the rear, too? You might want to do that at the same time. Fog's or mine are furnished with a 1/16" kick at each end that moves the span of the link out 1/16" and clears the new fatter spring w/o using longer bolts. It'll steer lighter, buy a lot of corner clearance, and all for one price. :)

If you don't and are using the stock links you should consider a washer on each side to space them out about 1/16" to insure thay don't hit the new rear spring. Then, that requires either longer bolts or at least using loctite on the nuts at assembly. You'll lose the self locking feature on the factory nuts due to the washers.
 

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Here's a chart I worked up to be used as a guideline for rear shock street spring rates. It's a guideline only and applies to EX-500's only. Spring rate and the corresponding rider weight.


Spring Rate______Minimum_____Optimum_____Maximum

300#_____________115_________135_________150___

350#_____________135_________155_________175___

400#_____________160_________180_________200___

450#_____________180_________200_________220___

500#_____________200_________225_________250___

550#_____________220_________250_________275___
 
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dad said:
Just curious. What rear sag are you running, Rich?
Just checked, measures 1 3/8". I guess firm is subjective, its not bouncing me off the seat by any means. But it is firmer that anything else I've riden. Then again, my last bike was 25 years ago, a KH 500 triple, not exactly known for handling.....

Rich
 

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RichC10 said:
dad said:
Just curious. What rear sag are you running, Rich?
Just checked, measures 1 3/8". I guess firm is subjective, its not bouncing me off the seat by any means. But it is firmer that anything else I've riden. Then again, my last bike was 25 years ago, a KH 500 triple, not exactly known for handling.....

Rich
Then the free sag is about 3/16"?
 

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Discussion Starter #11
I decided to go with the 450lb spring; seemed to be best according to the chart. Thanks so much guys for all your input in helping me decide.

I'd love to get new dogbones and a spring cup, but with a growing family I really have to ration the money out. I've always fabricated my own parts for cars and I've got the materials here for free so I'm going to try to make my own (according to the examples you guys have both posted). I've got to save money toward a set of good radials(pilot powers most likely) because I'm still on the stock rubber (only 3000 miles and still plenty of tread but over 6 years old now :-\).

Thanks again! :)
 

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That sounds good. On assembly, pre-load the spring to 9/16" and install the shock. Carefully measured that should bring the free sag in at 1/8" to 3/16" and the static sag right around 1 3/16". You may need to tweek it but not much. Once you get your measurements, if you need to adjust, divide any desired change at the wheel by 2.85 for the change required at the shock.

Will you be doing anything with the front?

Good luck.
 

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Discussion Starter #13
Yes, definitely. I'm going to go the thrifty route again(for now) and cut the front springs and make some metal spacers. I've got the formula for calculating the spring rate and may do it twice to learn about the feel. I'll also be going to 10W synthetic fluid in the forks. I'm still debating as far as raising the front, because I won't need the clearance for cornering anytime soon. And then I'll be saving toward emulators. After the tires that's the next priority on the list.

Thanks :)

PS. Thanks for the spring preload measurements; that will save me a lot of time!
 

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2001ex500 said:
Yes, definitely. I'm going to go the thrifty route again(for now) and cut the front springs and make some metal spacers. I've got the formula for calculating the spring rate and may do it twice to learn about the feel. I'll also be going to 10W synthetic fluid in the forks. I'm still debating as far as raising the front, because I won't need the clearance for cornering anytime soon. And then I'll be saving toward emulators. After the tires that's the next priority on the list.

Thanks :)

PS. Thanks for the spring preload measurements; that will save me a lot of time!
I've not cut springs on this model so I don't have any specific recommendations that I know work but it IS a viable alternative. I'll give you some generic guidelines for this as considerations. While not all may apply in this instance they are good considerations to treat as generic knowledge for this type of work. Forgive me if they are things you already know but even if you don't need them, maybe they'll be helpful to a lurker following this. :)

I'm 90% sure those front springs are progressive wound. I don't remember for sure. If they are, which end you cut will make a big difference in the end result and over the range of travel. Make your cut at the soft end, the tighter spaced coils, to get the rate higher but also more linear. Put the cut end up against your spacer.

If they are progressive wound that end would normally be installed at the bottom. If so, flip the spring with the cut end up. Make sure the bearing area of the original top end is OK where it will settle well against the lower shoulder. It might be good to use the washer that's normally at the top against the spacer and move it to the bottom if you're not sure. If you do, you will need to find a washer to use at the cut end (top) so that the cut end will register well against the spacer. Never put the hard spring against a soft spacer, especially if you use PVC pipe to make the new spacer. Always use a washer between those faces.

If you have to flip the spring, take an extra minute to inspect the ground flat end for sharp burrs that may project out past the diameter of the spring. If they are there, they can gouge the inside of the tube and screw up the shock piston ring as it travels over that spot. If there are any such burrs are sharp edges they need to be ground back to assure they can't rub the inside of the tube. That end would normally have been installed at the top where it doesn't move and also where a score mark will not effect a sealing face. Therefore they are sometimes not dressed to make sure they can't rub. This may not be required as you may not have to flip them if they're not progressive and you didn't cut that end.

Even if they're NOT progressive, still check both ends before to cut because sometimes they'll wind that very last coil slightly smaller diameter to assure it clears, can't rub on the ground flat edge. If that's the case, smaller diameter at the last coil and NOT progressive wound, don't cut that end and none of this will matter. Good generic stuff to consider although it may not apply to these. Check it all to be sure, though.

You can rig up a bathroom scale to prove out your work, your new spring rates. Take the spring cap out but leave the spring in the tube to guide it. Get a broom stick or some equivelent tool to push the spring down with. This way you're getting direct spring readings without any error from fork stiction. Get someone to help stabilize the thing and to help with the readings, standing it up on the scale as you press down on the spring. Make sure to subtract the dead weight of the fork out of your readings.

The ratings can be taken in pounds of force per inch of compression. Pre-load about 1/2" to settle the spring and call that number zero. Then check over a couple of inches to prove the readings and your arithmetic. To do this, put a mark on your broom stick to align with the fork tube top at about 1/2" compressed, then make a couple of more marks at even inch increments. Compress the spring to each of those marks and get your readings.

The number .455 is used to convert kilograms pounds. If you know the kg, divide it by .455 to get lbs. If you know the pounds, multiply it by .455 to get the kg. Then to convert those numbers from kg per millimeter to pounds per inch, use 25.4 multiplier. Per millimeter times 25.4 will give give per inch. Per inch divided by 25.4 will give per millimeter.

Example: Convert standard .90kg per mm rating to lbs. per inch rating.
.9 /.455 = 1.978
1.978 x 25.4 = 50.24
So we would look for a 50# reading per inch compressed on our bathroom scale. 2" compressed would be 100# and so on. Convert your actual readings back to kg per mm to see how they fit the recommendation charts. I would think .90 is what you're after.


Then reconsider the fork oil level as that is your new progressivity adjustment. With these as soft as they are they run a relatively high fork oil level as stock. The stock is recommended at 4 5/8" but with the right spring that will be too progressive. The .90's that you should be striving for will only require about a 5 1/2" oil level and possibly as little as 5 7/8". 4 5/8" with the right spring will be too progressive and will show up as too much unused suspension travel on hard braking. BTW, that very high fork oil level is a patch to the very soft springs. Light springs for a light rider yet very progressive for bottoming with a heavier rider. A compromise that tries to address all situations but still a very big compromise.

Remember, lower level is more air, therefore less air spring, therefore less progressive. I'd start low, maybe around 5 7/8". Wrap a wire tie on one of the fork legs to use as a travel indicator. Check it after some hard braking and after your first few rides. If you've never bottomed, done some real hard braking and/or hit some pretty good bumps, yet still have about 1/2" of travel left, that's probably pretty good. If you've bottomed, add oil, maybe 1/4" at a time until it leaves you at least 1/2" reserve travel. And if you've not used full travel (less 1/2" to 3/4" for reserve) consider removing 1/4" at a time until you have the right full travel range. Monitor it over time to be sure it's good.

Another trick to make it easy to read the fork bottoming travel once it's together, is to trace a line with a Sharpie permanent marker at the fully compressed position while the springs are out and you can fully collapse the front easily. Clean the tube with something like carb cleaner where you'll be tracing it so the mark won't wipe right off, collapse the front, and then trace around the tube at the fork seal. Do both legs. Then, leave a wire tie around the leg while riding. It will get pushed up to the max travel position while riding and with the traced bottom mark, you'll be able to tell at a glance how close you've come to bottoming. Makes life easy.

To cut your front spacers, if you get in the range of .90 springs, your pre-load on the front springs will be in the range of 3/4" to 7/8". Drop the spring in, extend the tube and measure from the top of the tube down to the top of the spring. You can figure out the measurement by measuring the top plug/cap height, snap ring groove location down in the tube, and figure out what spacer length you will need to pre-load at about 7/8". Expect that dimension to be about 1/4" less than the very top of the tube, again, tube fully extended, not compressed as you would do for the fork oil level.

BTW, it's better to work out your spring spacer before to put in the fork oil so that you're not dealing with the oil dripping all over as you put the parts and tools in and out of the tubes. Put the oil in last. Make sure the front static sag is at least 1 3/16", not more than 1 3/8". You can even fully assemble the front end to the bike and get your sag readings without the fork oil in. That way, if you need to trim the spacer, you can remove it without dealing with the mess of the oil. Just don't test ride without fork oil. :eek:

Refer to that suspension guideline post I made if any of this isn't perfectly clear. What's neat is here's a real world exercise using that information. If you take the time to understand those posts and then complete this job, you'll have a real good grasp of the principles and they don't change one bike to another.

Good luck.
 

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Holey moley. :eek:
 

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Discussion Starter #16
That which I know is still good to hear again(not that I knew all of that either). And the step by step is very helpful. If the springs are progressive then really you do need to go to a empirical method of determining the rate, such as the scale. I was thinking they would be linear, in which case you can calculate and measure your cut pretty accurately. Seems like Kawi has used the less expensive and more basic technologies in the suspension before so I expected linear springs. It's all good.

One thing I'll throw out there for everyone about cut springs I've picked up, is it is NOT reccommended that you try to heat up and bend the cut end flat like would be found on a normal spring. I've seen that come up in other posts. From a metallurgical standpoint, it is too easy to cause the spring steel to become brittle when you heat it that hot(and don't quench it at specific temperatures, etc), and the brittle end will fail at the worst possible moment (when you've done something to put a great stress on it). There are several good heat treating sites you can google about this kind of thing.

Thanks dad, for freely sharing your knowledge again! :)
 

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Discussion Starter #17
I do have a question about the fabrication of the rear cup that maybe one of you can answer. From Rich's post about the DIY spring cup, I make the two new spring seats first, that part is pretty clear. Then I cut a spacer (out of plumbing pipe or even EMT electrical conduit has a fairly substantial wall) for the bottom of the spring assembly because the hypercoil spring is shorter than the stock spring. The height of that spacer is determined by what? Is the spacer measured so that the free length of your new Hypercoil assembly will match the free length (unsprung) of the stock spring?

Thanks :)
 
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2001ex500 said:
The height of that spacer is determined by what? Is the spacer measured so that the free length of your new Hypercoil assembly will match the free length (unsprung) of the stock spring?

Thanks :)
You got it, it needs to be close to the same length.
 

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I can make those spring cups for you.

FOG
 
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