This thread provides input to people looking to buy rear suspension for the RC51. The insights are from lots of research, analysis & experience. Add as you wish.
Note that price discussions are based on the North American market. Places such as Europe, Australia & Asia, may have significantly higher prices for both used & new rear shocks. With this, many world wide RC51 owners buy from North America. No matter what you choose, consider the following.
Aftermarket rear suspension - Consider buying new
When buying an aftermarket rear shock for the RC51, I suggest to strongly consider buying new. The RC51 is fairly unique because we can buy a new triple adjustable top of the line HO204 Ohlins rear shock from Mike or Dan at Kyle USA for only around $950 plus shipping. The shock is specifically built for the RC51. It is fully loaded with adjustable high & low speed compression damping, rebound damping & ride height adjustability... as well as hydraulic preload adjustability. That is a great price brand new, plus it has a two year warranty & is sprung for your weight. That price from Kyle USA is also better than buying an Ohlins shock for many other model bikes (often 50% better), further showing its value. Additionally, Ohlins is the gold standard of suspension with full street & race cred & a worldwide race win history. Ohlins has the best resale & brand recognition... for a reason.
Don't use any experience with other bikes to estimate new or used shock pricing for the RC51. A used Ohlins shock for $850 may be a great deal for an R1 but it is NOT a great deal for the RC51.
Another thing to consider is that when you buy new you can start a relationship with a business. Building a relationship with a shop or business can lead to price discounts on products & service. Do that, spend some money, talk to the owner & ask for discounts after you've shown some repeat & continued buying. Shops & businesses usually reward return & long-term customers. You may save a lot more money over the long term by buying some things new & building a relationship with a shop than buying something used.
The full Ohlins HO204 spec sheet can be found here. You may need a google account to access & download. https://drive.google.com/file/d/0B5J...it?usp=sharing
Check my next post below for even more detailed information on the Ohlins HO204.
There are a variety of other new shock options for the RC51 in North America or elsewhere (Ohlins, Penske, Elka, WP, Maxton, Nitron, Wilber, etc). If buying new, I recommend using the Kyle USA Ohlins HO204 rear shock as the gold standard (see earlier) to judge all other new shock prices. And make sure you compare feature sets. Not all shocks have all the features.
Buying a used aftermarket rear shock
If buying used, off to the marketplace you go. I've seen many high-priced used rear shocks on the market for the RC51. Be careful price-wise when buying used rear shocks.
First, make sure the shock is for an RC51 application. It would be disappointing to get the wrong/mislabelled shock.
Look at the brand next. Different brands & types have different resale values. I've had some of the lesser known brands with success. But resale of lesser brands is poor. OTOH Ohlins is considered to be the best by the masses with the highest resale. Penske is next, followed by the rest (Fox, WP, Elka, Race-Tech, etc). IMO all these choices are good products, but one shouldn't be paying used Ohlins HO204 prices for used Fox twin clicker or Race-Tech shocks.
What type of rear shock is for sale? The top of the line shocks such as the HO204 Ohlins from Kyle USA go for around $950 NEW & are triple adjustable (high speed compression damping, low speed compression damping, rebound) with ride height adjustment & hydraulic preload as well. That's fully loaded. There are shocks sold with less adjustability. The Penske 8981 is only double adjustable for example (it only has general compression damping with no separate high & low speed adjustment) with no hydraulic preload. A lower optioned used shock should cost less. Does the shock have ride height adjustability? If not, that is a notable hit to used resale value. Also, a piggyback shock is the best design (than remote reservoir for example).
Rear shocks wear over time & need service. This should be factored into the price. Service costs can be in the $100-$150 range, plus consider the additional two way shipping costs.
Note that aftermarket rear shocks have more linear springs on them so it's very important to get a rear shock set up with the proper spring for your weight. Buying a correct spring can be around $75 plus shipping. Then you need to find & pay someone to install it or buy the tools to install it.
If you need to spring and/or service a used shock it will cost you some significant additional money. If you have to add shipping it costs even more. This can add up to $250+ extra to the purchase price of a used shock.
Also I would recommend only trusting a seller's declaration of recent shock service if the seller can provide you with a receipt for the the work.
Add in the condition of the shock overall. Any scratches, missing items, corrosion, damage, wear, etc? The more issues the lower the price should be.
Does the shock come with the original box (this is a big thing if you are going to keep the bike over time, because it makes shipping the shock for future service easy & much less susceptible to damage), installation instructions, set-up guide, etc? Ask for these things. In/Ex-clusion should affect price.
All of these comparisons should be made... because (again) for brand new with two years of warranty you get NEW Ohlins for around $950 plus shipping.
Price thoughts on used aftermarket rear shocks
What do used shock prices come down to? Prices are somewhat personal, but half price of new is a good starting point for used suspension; that means half of $950 (currently) for Ohlins. Then start adding or taking away money depending on the previously mentioned items.
If, for example, a used shock is HO204 Ohlins, cherry, recently serviced or proven low miles, sprung for your weight, & with the box/materials, I could see $700-$750 ish, plus shipping, maybe. Beyond that price (& even at that price) many will pay the extra to buy new.
If for example a used shock is fox, double adjustable, in rough condition, no proof of service nor sprung for your weight, I could see $200 because you could get into it another $200 to $300 before bolting it into the bike.
Some additional notes on buying aftermarket rear suspension
You may want to consider service options when buying a new or used rear shock. After all, a person should service the rear shock every so often. For many people this consideration won't matter as they don't have a local option or they just want the best. For others they may have local Penske (or other major brand) service shop near them. That may tip the balance in choosing a shock. Also rest of world (ROW) RC51 owners may want to consider other ROW manufacturers if they are close to retailers or service shops. FWIW, Ohlins is available and in demand worldwide with their dealer/service network. A used Fox shock may not be the best option for a euro owner.
If buying used see what other rear shocks are on the market for sale. It's bargaining leverage. Check out other forums, ebay, etc. An educated buyer gets better value.
Fox shocks are no longer made; it factors into their used prices.
Race-Tech & Traxxion Dynamics upgraded stock shocks are a good value smaller step upgrade but their used price should reflect that. Many use them on track/race bikes. I've seen the market for used Race-Tech rear shocks somewhere around $150-175$, depending on factors discussed here.
Rework & upgrading of a stock rear shock
The Ohlins source & price discussed is hard to beat for any other new RC51 shock option on the market at this time. But I will mention a value option to those available who want an upgrade at a lower cost. The stock shock can be reworked by various shops with better internals & a linear spring (plus they make the shock serviceable). For example, Race-Tech & Traxxion Dynamics rear shock upgrades are popular choices. If you are interested in this value option ask the forum for recommended service shops as there are a bunch. I've had friends who hot-shoe (top class) track days mid pack with no issues on this equipment. Many people on all types of bikes run Race-Tech & Traxxion Dynamics worked rear shocks with no significant issues. Prices depend on the work needed but can run from $250 to $400 or so. Keep bills!
Stock OEM rear suspension
Stock shocks are a reasonable street use option in my experience. Their progressive spring gives maximum weight flexibility from single to two-up riding. I even have used them in the first season of tracking a bike. And they can be serviced by some shops. Is there room for improvement? Yes, as discussed earlier.
If looking for a used stock OEM rear shock it should be inexpensive. It's a good option if you want to replace a worn out high mile unit. Supply is high and demand is low. Some people even give them away. Without known mileage, I recommend assuming a used shock has high mileage (better to be surprised than disappointed). Also, examine the condition (high resolution pictures, zoom, etc). IMO $50-75 plus shipping is ok on a clean & low/moderate mileage stock rear shock. Ignore high prices often seen on Ebay, as the market will correct if people don't overpay.
That's all. Hope it helps. Good luck with the search & cheers