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Fork & Shock Improvements for Café Conversions (Read 2797 times)
Gary_in_NJ
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Fork & Shock Improvements for Café Conversions
01/19/15 at 09:42:38
 
The RYCA guys got a lot right with the design of the CS-1. From its mechanical simplicity and purity to its aggressive looks; the CS-1 is a perfect homage to the classic single cylinder café racers of the 50’s & 60’s. However, if there is one aspect of the transformation from LS650 to CS-1 that can be improved – it is the front & rear suspension. RYCA’s solution of reducing the fork stroke to lower the front by 50mm has two significant drawbacks; 1) fork travel is reduced to just 75mm and in order to keep the forks from easily bottoming, 2) the fork springs are highly preloaded leaving little in the way of suspension compliance. This approach detracts from an otherwise elegant design. I wanted to build a RYCA CS-1, but if I was going to commit the time and money to build a café racer I wanted to ensure that the front suspension was appropriate for a “sporting” street bike.

In making my CS-1 I have developed a solution for the forks that will:

1.      Retain the full 127mm of fork travel at the slider ( there is an additional 13mm at the top-out spring)
2.      Improve compression, damping and rebound to be similar to a cartridge type fork
3.      As a result of 1 & 2 above, significantly improve ride & handling
4.      Maintain the cool stance (50mm fork drop) of the CS-1 while improving the aesthetics

Here is a breakdown of my solution.

Retain the Full 127mm of Fork Travel
No doubt, one of the reasons the CS-1 looks so darn cool is because of the way Casey raised the rear of the bike via an 18” wheel and longer shocks and lowered the front end by reducing fork travel by 50mm and using an 18” front wheel. Not only does it look cool, but it effectively reduces the rake and trail allowing for quicker and lighter steering. While this approach works perfectly for form; the fork solution is not very functional. Reducing travel AND stiffing the forks via highly preloaded springs is the perfect recipe for an uncomfortable and non-compliant suspension. It’s like riding a jack-hammer. Besides, you never want to give up suspension travel.

Given the limitations of the LS650 fixed position upper triple clamp, RYCA didn’t have much choice but to shorten the stroke of the forks. But there is a very simple solution to replace the stock upper triple clamp so the forks can be adjusted (raised) to attain the proper stance. I purchased a LS650 lower triple clamp from eBay for $25 and converted it into an upper clamp. The entire process is simple and takes less than an hour. If you can modify the LS650 frame for the CS-1 conversion, you can modify the lower triple clamp into an upper triple clamp.

The lower triple clamp has the steering stem pressed into position. Using a cut-off wheel, band saw or saws-all simply cut the stem flush with the top of the clamp. From there you will need to drill-out the center hole from 0.8125” to 0.8750” (a Unibit in a drill press works great). You should also cut/grind off the steering stop blocks and polish/blend the surface.  In fact, cut the steering stops off first as it will give you a lot more room to maneuver around the steering stem when you cut it off. With this upper triple clamp in position, you can now slide the forks up in the triple clamps. You DON’T need to slide the forks up by 50mm, more on this later.

If you are using RYCA’s speedo & tachometer brackets you will need to fabricate a means to mount the brackets to the lower part of the new upper triple clamp. You can make use of the unused headlight mounts in the upper triple clamp and fabricate a simple adaptor plate. Alternatively you can use the RYCA brackets as a template and fabricate a custom instrument bracket out of 0.125” aluminum.

Just as I finished making my custom upper triple clamp RYCA introduced their own upper triple clamp that allows for adjustment of the forks as well; best of all – all of the work is done for you – at a cost of $250. It’s the old time-money trade. There is another difference that tilts towards using the modified triple clamp and that is the height/thickness of the T-Clamp at the pinch bolt. I will explain more on this later.

Improved Damping
I worked with Matt Wiley at Race Tech to develop a suspension solution for the LS650 forks. This solution will work for a café conversion and an unmodified LS650 (although the spring rates and valve setup will be different). Using a Race Tech Gold Valve Emulators (part number FEGV S3801) and linear-rate fork springs (part number FRSP S29380XX, XX is replaced by rate) you can significantly improve the damping (compression & rebound) of the conventional damping-rod forks used on the LS650. I’m not going to go into a lot of explanation on this as there is great documentation on the Race Tech website (racetech.com) as well as dozens of technical articles on the internet, but here is some info from Race Tech’s FAQ:

“Damping rods while inexpensive to manufacture have major limitations. To create compression damping, oil is shoved through a hole or holes. Shoving oil through holes creates very little resistance to flow at low vertical wheel velocities as when hitting a dip or gully or applying the front brakes. This allows the forks to shoot through the travel fairly easily, diving or bottoming in these situations. On the other hand when the wheel hits something square edge, especially at speed, it needs a lot of oil to pass through the damping holes very quickly. Unfortunately the nature of shoving oil through holes is that as the wheel velocity increases the damping force increases with the square of the velocity. In other words if you double the velocity you get four times the force. This means the hole basically "hydraulic locks" resulting in a harsh spike. Damping rods give the worst of both worlds; they are both too mushy and too harsh at the same time.

An Emulator is a valve that sits on top of the damping rod and is held in place with the main spring. To install them simply remove the damping rods and drill out the existing compression damping holes so they are so large they do not create any appreciable damping. Then during reassembly simply drop the Emulator on top of the damping rod. The Emulator creates the compression damping of a state-of-the-art cartridge fork. The ride is both firmer and plusher than the damping rod and is completely tuneable.”


I’ve used Gold Valve Emulators many times in the past (street and dirt bikes) and have always gotten outstanding results. Race Tech has supplemental tuning instructions for vintage racing bikes and these instructions apply to café conversions as well. The instructions call for drilling additional small holes in the base of the emulator valve to improve low-speed flow. By following these instructions you will have dual-rate valving that provides low speed compression damping and high speed compression damping via the Emulator.  My tuning details are at the end of this write-up.

When using the Gold Valve Emulator you’ll need to use Rach Tech’s linear-rate springs. Progressive-rate fork springs just don’t work in a fork that has proper compression valving. The problem with progressive-rate springs is they attempt to do what proper valving actually does. Progressive-rate springs can have unpredictable or undesirable performance characteristics; too soft in the initial stroke (most notable with brake dive) and too stiff in the later portion of the stroke (resulting in a harsh ride). Preloading doesn’t solve the problem, it just transfers the problem to a different portion of the stroke or eliminates that usable portion of the spring…at which point you might as well be using a linear-rate spring.  

Using springs that are properly selected for the application and the rider’s weight (I used 0.70kg for my 170# weight) will allow you to set the correct suspension sag for the bike. For a street bike you should aim for 25% to 30% of your suspension travel for total sag. Since we have the full 127mm of travel available to us, this equates to 32mm to 38mm of sag. Ideally you should aim for 35mm of total sag with the rider on the bike.

Remember I said that we don’t need to raise the forks in the triple clamp by 50mm? Here’s some guidance on how high to raise the forks and maintain the design stance of the RYCA conversion. The stock gap between the top of the fork slider and the bottom of the lower triple clamp is 187mm. If you were to add RYCA’s 50mm spacers (which we won’t be doing) that gap is reduced to 137mm. That’s our target gap/stance. RYCA’s fork solution has zero sag so that 137mm fully extended gap is present with or without a rider on the bike.

One of the advantages of using the modified lower/upper triple clamp is that sits 13mm higher than the stock t-clamp at the top of the fork tube location - the stock clamp is 23mm where the new clamp is 36mm at the pinch bolt. Further, the OE forks were recessed 6mm from the top of the OE triple clamp. By raising the forks to be flush with the top of the modified triple clamp we’ve already made up 19mm of the needed 50mm, resulting in a 168mm gap fully extended.

Of the 35mm of total sag we built into the suspension about 10-15mm of that will be present even without you on the bike (free sag), reducing the gap to 152mm-147mm. If you raise the forks (measured at the top of the tube, not the cap) by 16-21mm above the triple clamp you will have a gap in the desired range of 137mm allowing you to retain that proper RYCA stance. I say just set the fork tube raise at 25mm and be done with it.  

Important Set-Up Note: You can raise the forks as high as you want, but you should leave a minimum of 127mm (fully extended) between the top of the fork slider and the bottom of the lower T-Clamp. Otherwise your sliders may come in contact with the lower triple clamp during extreme braking. It’s up to you – you have about 10mm of available adjustability. The higher you raise the forks the faster the steering geometry. Since RYCA’s solution has zero sag, the rake is 29 degrees whether you’re off the bike or riding it. With 35mm of total rider sag deployed you will have about 28 degrees of rake when you are riding the bike. Using the available 10mm will get you in the range of 27 degrees of rake.

Users of RYCA’s Upper Triple Clamp: At 23mm RYCA’s new T-Clamp is the same height as the stock unit. If you use this upper T-Clamp the forks will sit at a range of 29-34mm above the triple clamp when adjusted for a 137mm gap. This could look a bit odd, especially at the higher value. If I were to use the RYCA upper triple clamp I might consider using a 10-15mm travel spacer between the damping rod and the top-out spring. In order to keep the suspension compliant I would compensate for the travel spacer by reducing the preload spacer. Just follow the set-up instructions below and it should all work out.

Looking Cool
Here’s an opportunity to improve the aesthetics (form) and function of your CS-1. You can replace the stock LS650 38mm fork caps (you no longer need the flange on the OEM caps) with fixed or adjustable fork caps. Using adjustable fork caps will make the process of setting fork sag much easier and will give your forks a modern “race-bike” look. I found a few sources for 38mm adjustable fork caps on Amazon and eBay. I ordered a set for a Yamaha SRX400 from eBayer ericzzh715 for $35.99. A bonus advantage of replacement fork caps is that they will sit nearly flush with the top of the fork tube, versus the OEM caps that sit 7mm above the top of the fork tube. That’s an additional 7mm that the forks won’t protrude above the T-Clamp. Since you don’t have that unneeded flange on the cap you can remove a fork tube without disassembling the triple clamps and clip-ons.

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« Last Edit: 12/15/16 at 06:22:29 by Gary_in_NJ »  

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Gary_in_NJ
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Re: Fork Improvements for RYCA Café Conversions
Reply #1 - 01/19/15 at 09:43:13
 
Finally, to further improve handling I’m using the fork brace offered by RYCA to reduce fork flex. This too looks cool and, more importantly, reduces fork flex during cornering and braking. The brace makes the front end of the bike more predictable and reduces the potential of tire cupping and irregular wear.

My total investment for the above is about $500; $25 for the Triple Clamp, $36 for the Fork Caps, $110 for the Gold Valve Emulators, $125 for the springs and $190 for the fork brace (price the Race Tech components on Amazon to get the best prices). With all of the above changes you will have a bike that rides and handles as good as it looks – and a much better ownership experience. You’ll love riding your CS-1.

Modification & Tuning Details
•      Drill out existing damping rod compression holes to 1/4” and add additional holes for a total of 6. There should be a pair of holes opposite from one another (180 degree spacing) and a single hole opposite of another single hole (also 180 degree spacing) for a 2-1-2-1 pattern at 90 degree intervals. The single holes can be drilled out to 5/16”.
•      Drill out the dimples on the base (under the spring) of the GV Emulator so you have a total of 4 holes. This will improve the low-speed compression damping.
•      On the Emulator use the 40# (Blue) spring at an initial setting of 2.5 turns. Adjust as needed in 1/2 turn increments to obtain the desired compression damping. If you need to go below 2 turns, replace the blue spring with the 26# Silver Spring and start at 3.5 turns.
•      Use 15w fork oil at a height of 130mm (GV in, spring out, tube at bottom of stroke)
•      If using Adjustable Fork Caps, set all the way out (retracted). Cut preload spacers so the top of the stack is about 7mm below the top of the fully extended fork tube. This will provide a baseline preload of 15mm (the cap is 22mm fully retracted). Use this setting whether you are using a modified upper triple clamp or a RYCA upper triple clamp with a travel spacer.
•      Set the fork height at 16-21mm from the triple clamp to the top of the fork tube (or 137mm from bottom of lower T-Clamp to top of Slider). If using RYCA’s upper triple clamp a 137mm gap will result in a fork height of 29-34mm above the t-clamp – consider the use a travel spacer between the top-out spring and damping rod.
•      Target Sag; bike only 10-15mm; with rider 35mm
•      Rule of Thumb: The first 1/3 of fork travel is controlled by the spring and is used mostly for sag. The next 1/3 of travel is controlled mostly by the GV Emulator. The final 1/3 of travel is affected by oil height. If initial compression is too soft (fork travel is too fast), increase the spring tension (tighten) of the GV Emulator in 1/2-turn increments. Do the opposite if it’s too stiff or slow. If the final 1/3 of travel is too soft and bottoms, add oil in 10cc increments. Do the opposite if you can’t use 85-90% of all fork travel. If you need to slow rebound switch to a heavier weight oil (by the same manufacturer as there is no consistency between manufacturers). Do the opposite to quicken rebound.
•      If you cannot achieve the desired free sag setting (10-15mm) with the range available of the adjustable fork caps, it is an indication that the spring rate is incorrect. I know this seems counterintuitive, but if there is too much sag - the spring rate is too high; too little sag indicates that the spring rate is too light. A great resource for setting sag can be found at http://www.ntnoa.org/suspension_preload.htm

As you can see, you now have all of the same adjustments as modern cartridge forks (preload, high-speed compression damping, low-speed compression damping and rebound). Since you don’t have “clickers” you’ll have to somewhat disassemble the forks to make adjustments. Oil level changes are easiest; simply remove the fork cap (one at a time so the bike doesn’t squat down) and add/remove a measured amount of oil. To make changes to the Emulator, remove the cap, spacer, washers and slowly remove the spring with a turning motion so the oil says in the fork. You can then remove the Emulator with a magnetic parts chaser. For a whole-sale change in the fork oil you’ll need to remove the fork, disassemble, drain and reassemble using your original technique and procedures.

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CS-1_Forks_001.jpg

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Re: Fork Improvements for RYCA Café Conversions
Reply #2 - 01/20/15 at 05:21:30
 
This is definitely a thorough and well planned change, and I agree that keeping the available fork travel is a big improvement over installing spacers that lower the front end....reduce travel......and make for an excessive amount of pre-load.

I might even be intrigued enough to try these emulators and springs in my bike soon.

And while the theory of all this seems sound - at this point this is untested, as it does not appear your bike has been ridden yet.

Looking forward to the completion of your bike...and a Build Thread in the Rubber Side Down section.
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Gary_in_NJ
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Re: Fork Improvements for RYCA Café Conversions
Reply #3 - 01/20/15 at 14:41:28
 
My bike is being assembled and I wont get a chance to dial in the suspension until the salt and sand are off the road. However, with that said I have a lot of experience with suspension set up and I'm certain that I'm quite close with my baseline. Matt and I discussed in detail the set up for the CS-1. The only real unknown is my baseline spring rate. I chose 0.70kg and 0.75kg was a possibility as well. My experience tells me to err on the lighter side for a street bike. If I need to go heavier, Race Tech will provide a swap out.

I have photos to post of the damping rod and emulator modifications. I'm on the road this week and won't have access to post them until the weekend. I'll also provide a measurement for the spacer. I was able to reuse the stock spacer and I think I cut it down by about 10mm.
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Re: Fork Improvements for RYCA Café Conversions
Reply #4 - 01/20/15 at 19:36:15
 
That was an excelent post Gary and I read it several times.  I bought a new S40 and have read many reports of people grinding footpegs and mufflers while cornering.  Not something I wanted to hear of course.

Raising the back seems simple enough by changing shocks but the front end seemed a bit problematic.  After reading your report I feel a bit better.  Thanks.
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Re: Fork Improvements for RYCA Café Conversions
Reply #5 - 01/23/15 at 08:21:31
 
The RYCA Cafe' (and most clones of their design)will have a similar weight without the rider - for me the big difference would be the extra couple of gallons that my fuel tank can hold.

What is the best way to determine what rate of springs to use in the forks?

Should I weigh the front of my bike with and without the rider?

Should I measure my current pre-load and sag with the stock springs?

Currently I do use a lot of my available travel....I have installed 0.5" spacers to lower the front end, and I have dropped the tubes in my forks about 1.5".
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Re: Fork Improvements for RYCA Café Conversions
Reply #6 - 01/23/15 at 09:28:10
 
RaceTech has a spring rate calculators on their webisite (Search on the Menu Bar then Spring Rate). The calculator for the LS-650 should not be used for café conversions as our bikes weigh about 60 pounds less and our weight distribution is vastly different front-to-rear. I used the calculator for a Yamaha SR500 as it approximates our bikes fairly closely and it’s also a bike that typically gets modified into a café racer. When using the calculator simply click the “Street” riding type and enter your weight. You can update the bike weight for your specific bike. This is “fairly accurate” and should get you in the ball park for spring weight. Always round up to the nearest suggested spring value. The next highest value can also be used due to our forward weight bias with a rider on board. For example; the calculator suggests a rate of 0.688kg for a 170 pound rider on a 310 pound bike riding on the street. That rate doesn’t exist, so I rounded up to 0.70kg. I could also use 0.75kg, but my experience tells me that I’ll be happier with the lighter spring – it’s slightly more plush – and I can achieve the correct free and total sag. If you are “Joe Street Racer” (no judging – I use to be him and enjoyed it) I’d suggest going for the heavier spring.

If you have two bathroom scales you can get the weight of your bike (full fuel) by placing a scale under each wheel. I’d be interested in knowing the weight distribution.

You should be using “a lot” of your available fork travel – about 90% under severe braking. If you are using a lot during normal riding it’s an indication that the oil level is too low or the spring rate is too light. A good way to determine fork travel usage is to put a zip tie on your forks. It shouldn’t be so tight that it’s hard to move, nor too loose that it won’t hold its position. Go out for a “normal” ride and see where the spacer is sitting. If you have 4-1/2 inches of travel (5 inches less your ½ inch travel spacer), I’d expect to see the zip-tie around 2-1/4 to 2-1/2 inches from the wiper. More usage would indicate a spring rate that is too light. Then go out again but this time include a few “emergency stops”. In this case the zip-tie should be around 4 inches. If it’s more you need to add fork oil.

All of this is assuming that your free sag and total sag are correct. If these don’t meet the guidelines above (10-15mm free and 35mm total) then these calculations won’t tell you very much. Since you have raised the tubes in the clamps by 1-1/2 inch, I’m assuming that you don’t have much sag in the system.  Also, the stock springs are progressive so they are both too light and too heavy. The only use I had for the OEM springs was to determine the correct length spring.

Race Tech loves working with racers and tinkerers and will work with you to get your suspension correct. If you order an Emulator and Springs and can’t get the sag correct, they will use your measurements to determine the correct spring rate and swap-out the incorrect springs for the correct ones.
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Re: Fork Improvements for RYCA Café Conversions
Reply #7 - 01/23/15 at 10:31:51
 
Thanks - I will weigh my bike and let you know.

Instead of having 2 scales - you can get by with a single scale as long as you have a block the same height of the scale under the other wheel to keep the bike level.  It is really handy for me that our home scale is the same height as a 2x4 laid on it' side.  (I have to be sure to get the tire tracks off the scale when I return it to the bathroom....so my wife doesn't know what I was doing).

And for that 7mm gap at the top of the fork tubes where the cap doesn't cover - I found an O-ring that fit in that groove perfectly and it looks like it belongs there.
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Gary_in_NJ
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Re: Fork Improvements for RYCA Café Conversions
Reply #8 - 01/23/15 at 10:42:27
 
Yes, one scale with a wood block will work just fine.

There is an o-ring that is attached to the fork cap. That should be inside the groove that sits just above the threads on the cap. It should look like this:
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Re: Fork Improvements for RYCA Café Conversions
Reply #9 - 01/24/15 at 14:21:59
 
Here is a better photo of the difference in the caps. BTW, the flange on the OE is not 7mm, it's 12mm.

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Re: Fork Improvements for RYCA Café Conversions
Reply #10 - 01/24/15 at 14:32:18
 
Here are some photos of the fork modification and assembly. The first set of photos show the modifications to the base of the Gold Valve Emulator. This photo shows the spring base in place in the Emulator valve. You can see there are two holes and two dimples. Next to the Emulator is a base plate where the dimples have been drilled out to 7/64".


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Re: Fork Improvements for RYCA Café Conversions
Reply #11 - 01/24/15 at 14:33:57
 
This is an action shot of me drilling the dimples out. Make small cuts so it doesn't spin out of your fingers. Use cutting fluid. I use BoeLube paste as it makes drill bits cut like a hot knife through butter.
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« Last Edit: 01/24/15 at 17:13:51 by Gary in NJ »  

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Re: Fork Improvements for RYCA Café Conversions
Reply #12 - 01/24/15 at 14:34:41
 
BoeLube, invented by Boeing. Best lube available.
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Re: Fork Improvements for RYCA Café Conversions
Reply #13 - 01/24/15 at 14:36:22
 
When you reassemble the Emulator, replace the yellow spring with the blue spring. If testing shows that the silver spring works best, I'll update the instructions. When you reinstall the spring you'll be setting your initial valve tension. Hand tighten the post into the valve base so the spring doesn't move on the post. Add the nut at the bottom so it just contacts the valve, then make your initial setting by rotating the hex fitting on the post by 2-1/2 turns (or hold the post and tighten the nut by 2-1/2 turns).
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Re: Fork Improvements for RYCA Café Conversions
Reply #14 - 01/24/15 at 14:42:12
 
Here is a 0.70kg fork spring shown next to the OE progressive rate spring. The OE springs are 405mm long and the RT springs are 375mm. This difference is accounted for with the height of the Emulator valve (16mm), the longer depth of the fork cap (12-25mm) and the spacers. Also, the OE springs are 31.8mm in diameter and the RT springs are 29mm in diameter. Race Tech has springs that are 31.8mm wide, but the rates are too high for my weight. If you weigh over 210 pounds, consider FRSP S3234 springs. They are 32.7mm in diameter and start at a rate of 0.80kg. They are 340mm long, which means they are lighter. If these came in 0.70 or 0.75kg, I would have gone with that part number.
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« Last Edit: 01/24/15 at 17:30:29 by Gary in NJ »  

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