2nd Gen Jekyll - Propper Rear Suspension Setup
Cannondale did not give us a proper sag meter (yet) and we all know the best way to set suspension is based on actual sag. So I decided to build a low tech sag meter that should work for every 2nd Gen Jekyll, and cost us NOTHING to make. I made a similar one for my Scott Genius with its pull shock, and it worked wonderfully. I will explain my logic here and if anyone has any suggestions PLEASE let me know.
My process was;
- Determine the stroke length of the shock
- Determine the proper center-to-center length of the shock at the proper 33-40% sag
- Bend a coat hanger (or spoke, etc) into a square-u shape that matches the center-to-center length of the shock mounting bolts when the shock is at proper sag
Why 33-40% sag? That is what Fox recommends for the DYAD RT2 Shock in their OE DYAD RT2 setup Guide. They say "To attain the best possible performance from your Dyad RT2 shock, it is necessary to first set sag. The recommended sag range is 33%-40% of total travel. The Dyad RT2 Travel Adjust feature enables you to set sag deeper than any other FOX air shock, without sacrificing the pedaling platform necessary for best climbing efficiency." I also read elsewhere that when you put the bike in elevate mode the shock reduces sag to 22%. Having ridden the Jekyll and the Genius I would assume that this is from the 40% sag, as the rear becomes substantially stiff in elevate mode.
I measured my unweighted shock length (shock fully closed) at 6.125, center-to-center at the mounting bolts. I removed all the air from the shock, had someone lean on it to fully compress it, and measured the fully compressed suspension (shock fully extended) shaft length with micrometers at 47mm of stroke. This means 40% sag would yield 18.8mm of stroke and 6.865 inches (174.375mm) of shock length at the bolts. 33% sag would yield 6.735 inches (171.075mm) of shock length.
What is next, bend a piece of wire (I used a wire coat hanger) into a square U shape with each end as far apart as the shock bolts should be at proper sag you desire. As noted below I am making one for 33% and one for 40% sag.
How do you measure sag? On the Genius I could do it while siting on the bike with my device without anyone to assist me. I am trying it tomorrow on the Jekyll so I am not sure if I will need 2 people with this bike. Anyway, you sit on the bike in flow mode after setting the air pressures noted for your weight on the frame sticker. Then see if your "Sag-O-Meter" matches up with the bolts. If the bolts are shorter then the "Sag-O-Meter" remove some air pressure, if the bolts are longer than the "Sag-O-Meter then add air pressure. Then sit on the bike and check again.
Some things to remember. First the air pressures in both chambers must be adjusted each time. There is a specific ratio of positive chamber pressure to negative chamber pressure to make any shock work right. You must maintain this ratio as you adjust to the right sag. You could calculate this ratio based on the sticker, but my advise is stick with the numbers on the sticker. If you are too stiff in the rear step down one level on the sticker, and so one. Second thing to remember is if your fork is at 15% sag when you set the rear to 40%, and then you set the fork to 30% sag you need to adjust the rear shock sag. This is because as the front sag is increased weight transfers from the rear to the front and will change the rear shocks sag. I know this from my motorcycle days and know that it will change the balance front/rear of the suspension in a poor way.
My advice, once you figure out what air pressures you need front and rear, WRITE THEM ON THE BIKE! I plan to put a dot with a Sharpy on the frame sticker and make a PTouch sticker for the ft forks pressure. This way I can easily know what pressure I need when I get to ta trail head without going through the process above EVERY time.
It is late here so I will try this tomorrow, take pictures and see how the ride goes. I plan on running my rear at 40% (174mm)(push end of the scale) and my fork similarly plush at 38mm of sag as recommended here on Fox's page for the OEM 130mm-150mm Talas 32 1.5" steer tube fork manual. My theory is that the bike is an All Mountain bike, so I want it plush. If it is too plush at a given moment I can always push the button and stiffen the rear up for climbing (beauty of a Jekyll). Also note that adjusting the Talas from 150-130mm does stiffen the forks air spring similar to how the rear shocks sag changes from Flow to Elevate Mode. I will also make a second sag meter set at the minimum sag setting of 33% (171mm), set the fork up at the min setting of 15% for an XC setup. Then I will note the XC and AM pressures on the bike on stickers as noted above. This will let me, at a glance, choose either an XC or AM setup quickly at the trail head.
Last edited by Duc Hunter; 03-12-2011 at 06:58 PM.
I just followed my process above to set my sag. My bike has 50 miles on it and my weight as I sat on the bike to set the sag was 216lbs (meaning in cloths etc). It turn out that the 375/318 rear shock setting is perfectly at the 40% sag, and 90psi in the fork is as well. What is interesting is that shock setting is for a 200-209lb rider, and the fork setting is for a 185-200lb rider. This means I am one step down on each for the AM sag.
Keep in mind I am using the Scott high pressure pump from my Genius. I like it because once you pump to the desired pressure it has away to close off the hose before removing the pump from the shock.fork. This means it looses less than 1 psi when you remove the pump. Many pumps loose over 5psi just removing the hose, as the valve on the shock does not close instantly as you unscrew the pump.
I also realized if you have 2 people and micrometers it will be easier to just sit on your bike, and have your friend measure the sag on the shock with micrometers (how extended it is at the shaft, micrometers fit right in there)(18.8mm for AM and 15.5mm sag for XC).
Good to know. Cheers
Cannondale: Team Scalpel, Flash Ultimate, Hooligan 9
Lynskey Pro26 with custom Lefty head tube
Santa Cruz Nomad carbon
So it looks like I get just at 19mm of sag in the rear shock (40% sag) with 376psi/318psi in the rear shock. For the fork I need 90PSI for 37mm of sag, very close to the All Mountain 38mm.
At 210lbs without clothing it looks like I need to be one step down on the shock based on the sticker for the rear shock. 376psi would be the proper pressure if I was 200-209 ready to ride, but being dressed with a camel back on etc should add weight to me, which should move my air pressure needs up to 395psi. But that air pressure gives me a more XC sag of 15mm. I did note that when I stepped down the shock to the 358psi setting I had 23mm of sag, far too much according to Fox's recommended range of 33-40% sag.
For the fork, the 90PSI is for riders of 185-200lbs according to Fox. Similar to above, I should need to be 100psi because I fall in the 200-215lb range without cloths. Ready to ride I should need 110 because my weight would fall in the 215-230lbs range (half full CamelBak etc). But at 110 I get WAY too little sag. 100psi gives me just about perfect XC sag.
All this sag crap is great but how does the bike "feel" at 90 front/376 rear? The front feels slightly more plush than the rear. Now I have been running 25psi in the front tire and 30psi in the rear, but they both have about the same amount of "bag" so that should not be it. Still in Flow the front feels slightly more plush than the rear on the little stuff. On big hits they are pretty even. In Elevate mode/120mm on the fork there is no way around it, the rear is stiffer than the front. It is noticeable, but not bad. Especially since the bike climbs really well in Flow, so Elevate is only used on short steep climbs or long smooth ones where it wont matter.
What have I learned, bottom line? For the shock set that air pressure based on the sticker, but use your body weight without clothing for a plush setting (AM), and go up one level from that for a firmer (XC) mode. That should get your sag correct if your results are like mine. For the fork I would run 1 step below what the Fox site says for your body weight for an plush setting, and run at your body weight for a firmer setting (again your without clothing body weight). If you feel, based on this, that the fork is more plush than the shock, just bump it up one level, again all based on Fox's recommendations on their site I noted above.
I would love to hear what others think? We lucky few.
"My advice, once you figure out what air pressures you need front and rear, WRITE THEM ON THE BIKE!"
My advice is to WRITE THEM ON THE PUMP! or better yet use a label maker and stick them on the pump (or the bike if you have to) any one taking a sharpie to my bike is a dead man walking.
Anyone ELSE taking a Sharpie to my bike will quickly become "Pink Mist" as well. I believe I also suggested in my first post to use a PTouch as well, if you want a sticker. For those that don't know, a PTouch is a label maker. Writing i ton the pump is problematic for me because I have gone on trips and forgotten my pump, they can get lost etc.
Originally Posted by sp3000
Dyad Rt2 set up?
I came across this post regarding the Fox DYAD RT2 settings. I found it pretty helpful so thanks for that...
at 150-155lbs rider weight.
- I pumped my positive air up to 250lbs
- Negative air up to 200lbs
- 12 clicks out for flow mode rebound
- 10 clicks out for short travel rebound
What do YOU suggest?
-Thanks for your time,
Last edited by s570e; 06-11-2013 at 07:55 AM.