Setting Race Tech Fork Spring Static Sag

dhall854

Retired, ready to RIDE!
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756
billo - interesting video. Thanks for posting.
I've always wondered how an upside-down fork would work and feel on the ST1300. Your video shows the constant fore-aft flexing of the sliders that I see when glancing down sometimes on bumpy roads.
I've installed the Race Tech fully adjustable front suspension system and the Race Tech remote adjustable rear shock on my '08 and really like the way they work after getting them adjusted to my preferences.
Dale
 
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Idaho Falls, ID
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'08 ST1300ABS
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8741
My book shelf go-to reference is Trevett's Sportbike Suspension Tuning. The founder of Race Tech, Paul Thede, is used as a reference for this book's measurement methods. Many tuning guides refer to Thede.

I hope the PVC holds up...........its been in there 85,000 miles and PVC spacers are used by aftermarket spring suppliers and tuners. I see them them every 15 to 20,000 miles when I change the fork oil, they are plenty strong. Have you measured the load bearing capability of a 45 mm OD steel tube with .5 mm wall thickness?
I have Trivett's book too. All good references. The RaceTech spacers are 1.0 mm wall 6061-T6 aluminum tubing. You had mentioned using sink tailpiece tubing which is quite thin (maybe not much over 1.0 mm). I could see using maybe Sch.80 PVC pipe, which is probably about 3 mm thick (without looking it up).

I talked to both Brad and Terry earlier today. I also had them send me the installation guide for the kit which I will look at tonight. According to what they told me, with a spring selected by their "Spring Selector Tool" with accurate street clothes weight (they allow 15# for riding gear load), standard frame geometry, the preload adjusters set "full out", and factory oil level (130 mm below top of fork), their provided spacer should result in the averaged rider sag (down from rebound extension and up from compressive loading averaged) should put you in the 35 mm range. We did not discuss the anti-top-out spring effect, but it is pretty high rate on the ST I think, so the rider sag should not be greatly affected by not considering that change (it is discussed in the RT Bible how to account for it). They do provide several shims with the kit, and the adjusters give about 20 mm of additional preload adjustment as well.

I plan to do this as soon as I can scrape up the beans to do it (RaceTech does give a 20% discount to ST-O forum members). With the valve and cap hit, springs, fork oil, bushings and seals minus 20%, it's still going to be over $700.

I am hopeful for a really noticeable improvement...will let you know once I have first hand experience..

Ride safe,
 

dduelin

Tune my heart to sing Thy grace
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I have Trivett's book too. All good references. The RaceTech spacers are 1.0 mm wall 6061-T6 aluminum tubing. You had mentioned using sink tailpiece tubing which is quite thin (maybe not much over 1.0 mm). I could see using maybe Sch.80 PVC pipe, which is probably about 3 mm thick (without looking it up).

I talked to both Brad and Terry earlier today. I also had them send me the installation guide for the kit which I will look at tonight. According to what they told me, with a spring selected by their "Spring Selector Tool" with accurate street clothes weight (they allow 15# for riding gear load), standard frame geometry, the preload adjusters set "full out", and factory oil level (130 mm below top of fork), their provided spacer should result in the averaged rider sag (down from rebound extension and up from compressive loading averaged) should put you in the 35 mm range. We did not discuss the anti-top-out spring effect, but it is pretty high rate on the ST I think, so the rider sag should not be greatly affected by not considering that change (it is discussed in the RT Bible how to account for it). They do provide several shims with the kit, and the adjusters give about 20 mm of additional preload adjustment as well.

I plan to do this as soon as I can scrape up the beans to do it (RaceTech does give a 20% discount to ST-O forum members). With the valve and cap hit, springs, fork oil, bushings and seals minus 20%, it's still going to be over $700.

I am hopeful for a really noticeable improvement...will let you know once I have first hand experience..

Ride safe,
The stock spacers is what I referenced - they are not .5 mm but are just .7 mm wall thickness. Whatever is used for spacers the close fit within the ID of the fork tube helps keep the spacers in column. +/- 38 mm or 1.5" fits very closely and the stock spacers are this OD and nestle inside the hollow of the fork caps. Thin wall PVC seems impossibly light but in use it works just fine - but you have to use what makes you comfortable. I'm light - about 152 to 155 lbs in street clothing and the RT spring calculator keeps me in the the range of the OEM spring rate. Using spacers 16 mm longer than stock brought rider sag to my target of 36 mm. The first step I took was to get the sag right and I never felt the need to progress beyond using a somewhat lighter blend of Showa fork oil. This stage made a great improvement for me. No doubt the full Race Tech setup is very good, even better, but what I got to met my needs and has meet my needs all these miles. BTW, the factory oil level is 62 mm.
 

T_C

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We did not discuss the anti-top-out spring effect, but it is pretty high rate on the ST I think, so the rider sag should not be greatly affected by not considering that change (it is discussed in the RT Bible how to account for it).
No need to discuss what is not there. ST's (1300s at least) only have the air spring at the top of the fork and the main spring inside the tube thingy.
 
OP
OP
Reginald

Reginald

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8898
I would suggest you look at chemical compatibility of PVC with oil - could be an issue. Also, the extra thin-wall sink tailpiece tubing might not be the best bet. What yield strength did you use for the PVC tube in the buckling formula? Different PVC formulations have different mechanical properties.

Me personally - I'm not relying on plumbing plastic (never meant to be pressurized or load bearing) for a MC load-bearing suspension part. If that piece collapses on hard braking or a big bump/pothole, the front end will collapse, and that is NEVER a good thing. My free opinion, FWIW.
At WeSTOC XIX, I had a good conversation with Mat Wiley who is a Race Tech Rep and write the Tech articles for Rider magazine. He said that PVC is fine and Race Tech uses it in in some packages. He tested my bike and said the front preload was set well within the range for my weight.

I used the following in my formula for the PVC yield strength.
E = 400000 lbs / in^2 (Young's modulus of Elasticity: PVC Tensile Modulus of Elasticity, psi @ 73?F is 400,000 to 420,000 depending on manufacturer)

If you prefer steel go with it. But according with the buckling formula given it's not as strong resisting compression. The best material for compression is concrete but I would not recommend that. ;)
 
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I just didn't feel comfortable with the PVC spacer, so I went a different route. My older brother was a shrimper and had a length on 1 1/2 OD stainless pipe. I read and studied Reginald's write up on his spacer and washer process and how he had to take the forks off three times. I made some adjustments (estimated) for my weight and riding style. I used a 1KG Race Tech spring, 10 wt Bel Ray fork oil(62mm), and I took his final measurements and cut my spacer to match his. Deburring and rounding off all cuts made with a metal chop saw. BINGO! I put it all together and had 34MM of sag. 1st try. I took a little test ride before today's rain hit and all I can say is OOOOHHH YEEEEESSS!!!! I started with 56mm of sag with the stock set up. I thought Big Red 2 handled pretty well before, but this mod makes the stock set up feel...sloppy, for lack of a better description. Straight line riding was way more stable, no problem holding my line in curves, and just better over bumps. One tight curve that I usually dive into carrying about 40 mph, was easy at 45+. The labor part was a regular Mean 13 adventure. After the spring swap, I installed the right fork, and saw the dust deflector sitting next to my tools. DOH! Took it back off and proceeded to do the same thing on the left fork. Double DOH! I put thread lock on all the bolts during install. During the install of the MCL fork brace, I realized the I missed one bolt with the thread lock, so I pulled it back out. Naturally I dropped it and it went behind the brake lines and tubes on the right side. (Bolts go in but they don't come out) Had to pull the fork brace and all the lines on the right fork leg to retrieve the bolt. I almost pulled the tail light off because I figured I'd end up there anyways the way it was going. After all that, It was still worth every second and every penny spent on this mod. I'll be in North Carolina mountains in about 3 weeks, and I am so looking forward to this ride. Very grateful to have a forum like this to glean wisdom from. Without reading all the posts and studying, this could have been a lot less fun.
:tb1:
 
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Glad I ran across this thread and the buckling equation, which shows a typical 1" PVC spacer used on the ST1100 has a buckling force in the range of 60,000-80,000 lbs for the typical lengths used. Which confirms what's been said here many times, there's no reason to fear PVC pipe as a spacer material.
 
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