Rear Suspension - Mono Shock vs. Dual Shock

From my personal experiences I've come to feel that bikes I've ridden with monoshock are less subject to wallowing in hard turns. This could be more a factor of the improved frame designs that reduce flexing, though.



I'm certainly no expert, but it seems logical that a dual shock setup has the liability that one shock is going to compress differently than the other no matter how carefully you try to tune them. Monoshck eliminates any possibility of an imbalance between the two.



Another advantage would appear to be weight saving.



All this in addition to FrankS1's comments about the ability of monoshock systems to allow the design of variable rates.

I agree that a spring/shock unit acting through linkage offers better tuning opportunities, and is certainly one reason for use on race bikes. Of course, for 99.9% of the bikes with mono shocks, nobody will ever even consider replacing the linkage.



I think the biggest reasons for chosing one or the other are:



1) Image -- do you want the bike to seem modern or retro? A mono shock on a Triumph Bonneville just wouldn't seen right, same for a Harley Sportster. Dual shocks on a new sportbike would seem equally out of place. Of course the Harley Softtail is also a Mono shock dictated by styling considerations more than performance.



2) Packaging, as mentioned, is a big factor. Where does the designer need the exhaust pipes to run? Will dual shocks get in the way of saddle bags, etc?

Assuming that the swing arm has the level of torsional stiffness that modern handling standards demand, it should not matter if the two shocks are tuned alike -- hell, there are quite a few monoshocks that work just like dual shocks with one shock removed (obviously requiring a stronger spring/damper).



When I used to race my old SR500, with a welded on swingarm brace, I often deliberately used different springs left and right. I only had two different rates to chose from, and if I wanted something between these rates, using one of each allowed me to split the difference.



On older bikes, the swing arms had the torsional strength of overcooked noodles, hence the recommendations to be sure to set preload etc equally. On any modern bike, I cannot believe that any imbalance within the entire range of adjustability could effect handling (of course the resulting overall spring and/or damping rate would do so).



I think the wallowing you note is likely a function of the fact that more performance-oriented bikes tend to use monoshocks, thus they have more rigid chassis and generally more attention given to suspension tuning.

Single Sided Swingarms

Clearly there is no performance advantage to single sided swingarms. It seems intuitively obvious that for a given amount of material (= weight), a double sided swingarm will have greater torsional stiffness. Note that Ducati have gone back to the double sided swingarm for the 999 for this reason.

Single sided swingarms have a couple of possible advantages that have led to their (limited) use:

1) Facilitates tire change -- important in endurance racing where quick pit stops are important, also probably of interest to touring bike riders, hence the use by BMW and Goldwings.

2) May facilitate exhaust routing -- this was a factor in the Ducati 916 series. Part of the reason for the funky muffler on the 999 is to compensate for the unequal pipe lengths dictated by the rew routing required.

3) it looks "trick" and high-tech.

For shaft drive bikes, I suspect that the shaft housing etc required anyway is already heavy enough that it is close to being stiff enough anyway, so there may not be much weight penalty, and in any case, the designers are not that worried about cutting every possible gram from the weight of such bikes.

For chain drive bikes, the system has an additional disadvantage in that chain adjustment requires an eccentric adjuster, that changes ride height and suspension geometry with a chain adjustment.

In my opinion, they are kind of like single sided forks that have been used in a few cases (I think mostly on scooters, and a few mountain bikes) -- they are a cool technical novelty -- it is neat to be able to do it, but why, other than to show off your technical prowess.

Still, I do think that the single sided swingarms on 916, VFR and Honda Hawks do look pretty sharp.