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.
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