When Ibis Mojo HD was released 3 years ago, there was no coil shock option available, as Ibis stated it was designed completely around an air shock. Shortly after, information about it's coil compatibility started coming and many suspension tuners praised its suspension design qualities making it perfect candidate for a coil. Ibis reacted and added Fox RC4 as a shock option because of it's adjustable progressiveness. So, how to describe Ibis Mojo HD with a coil shock? Perfect.
The only downside of a coil shock is its weight. Stock Fox Float RP23 weighs around 300g, Rock Shox Vivid R2C with 400lbs coil without mounting hardware is exactly 1000g, resulting in 700g weight penalty. You can loose 300g by using Titanium coil, but it costs 5 times the price of a steel coil. Because of this, most people dismiss coil shock for trail use. They spent serious money on their light carbon frame, so why would they put so heavy shock on it? It's quite simple, because of how it rides.
When I first swung my leg over my Ibis Mojo HD, I was less than impressed with the Fox Float RP23 and suspension performance. Finding the right pressure was real pita, constantly choosing between small bump sensitivity and bottom out resistance. Slightly higher pressure and it became really harsh with unpleasant spiking in rock gardens. When setup with slightly lower pressure, it gave up its travel way too much easily, bottoming out on every reasonably sized drop or jump. Custom suspension tuning improved it little bit, but it was still not good enough. It took only one ride on a friends Specialized SX trail with a coil shock at a bike bark to plant a thought in my head to try this on my Ibis Mojo HD. World was about to change...
After long research and decision making (more on that later) I've ended up with Rock Shox Vivid R2C with 400lbs steel coil (85kg with gear) and M/M tune. This resulted in exactly 30% sag with one turn of preload. I set the Low speed compression to 3 clicks from fully open and rebound to the middle. The very first thing that surprised me was the lack of pedal bob. I backed the LSC all the way out and pedaling was still perfect. Even in very steep technical section, where you really need to put your power down (I ride 1x9 with 32x34-11t), it felt better than RP23. Another benefit is the absence of a propedal. Yes, benefit. You don't realize how liberating it is to not worry about the fact if you have your propedal on or off until you try it. Combine it with 1x9 or 1x10 and you will find yourself "in the zone" much more often.
I could feel the small added weight the first time I pedaled up the hill, but quickly forgot and never thought about it again after the slope changed and I pointed the bike down the hill. Traction was much better, bike sat higher in its travel and landings were nice and controlled. I ran the same section multiple times to fine tune the shock, but still ended up with LSC fully open. With next service, I'll get the shock tuned to reduce the compression damping, improving the sensitivity even more without compromising the pedaling abilities and getting more usable range on the LSC adjuster.
Ok, I expected it to be better down the hill, but how does it ride on a trail? Another superlatives come to mind, but the only idea is that you have to try it for yourself. If you paid that much for a frame, at least try to find the opportunity to put a coil shock on it. It changed my mind about selling the bike, to flies and mud in my teeth as I am smiling on the bike constantly. The weight penalty is worth it and I can't see myself going back to an air shock anytime soon. I was so much excited about it, that my front Fox Float 36 air fork is already sold and a new Marzocchi 55 RC3 Ti coil fork should arrive the next week. But, won't the bike feel heavy? Not at all, and even if it will, it means that I got weaker and I can solve that by working out more. Also, my bike is supposed to be all about fun, so why spoil it with a bad shock even if it's super light?
Coil shock options
During my research I came across these shocks, some of which I considered buying. Of course, there are more alternatives out there, but I was taking availability, customer service and servicing into consideration here in Slovakia/Europe.
Rock Shox Vivid R2CProduct page: http://www.sram.com/rockshox/products/vivid-r2c Available on Amazon.com from $333 Reasonably priced, reliable, easy to service, easy to setup, good customer reviews. I was little bit worried about the lack of a high speed compression adjuster, but that turned out to be unnecessary. Bottom out resistance is adjusted through 3 different elastomer DropStop pads. Dead simple and effective. Medium one works fine for me. Order from Germany arrived within 3 business days.
X Fusion Vector - HLRProduct page: http://www.xfusionshox.com/en/product/shocks/2012-vector/2013-vector-hlr.html Also reasonably priced with raving reviews. I was already determined to get this shock, unfortunately incompetent dealer for Czech republic and Slovakia turned me off the deal.
Fox RC4Product page: http://www.ridefox.com/product.php?m=bike&t=shocks&p=99301
Cane Creek Double BarrelProduct page: http://www.canecreek.com/products/suspension/double-barrel Available on Amazon from $558, 8.5" x 2.5" (216/63mm) As good as it gets, also expensive, looks really good, especially with titanium coil:) Can also be super complicated to setup, as CC doesn't provide base setting for Ibis Mojo HD (they do it only for DB Air).
Marzocchi ROCO COIL RC WORLD CUPProduct page: http://www.marzocchi.com/Template/detailProdotti.asp?LN=UK&idC=1585&IdFolder=552&IdOggetto=60729 I didn't include BOS, Elka and other because of complicated purchase and service options here.
Shock and mounting hardware size
If we don't take 140mm suspension setup into consideration Ibis Mojo HD takes 216x64mm (8,5x2,5") coil shock. You also have to include new mounting hardware. Proper size for Ibis Mojo HD is 40x8mm for front shock eye and 21.8x8mm for the rear end. This applies for all frame sizes.
Save yourself the money and disappointment and don't buy Titanium coil straight away. Make sure you have the right spring rate with steel coil first. As mentioned above, I weigh ±85kg with gear and 400lbs coil with 1 turn of preload is perfect for me. You can use this Spring calculator, insert all data in the first row and check first 2 fields in the second row, depending on your prefered shock manufacturer. If you end up with more than 4 turns of preload to set the right sag, you will be better off with harder spring.
Very few things can be learned just from reading a book, but this one has opened my eyes and I realized the mistakes I was doing. Well written with great images it's an investment well worth the money. Check it out