ADVrider

ADVrider (http://www.advrider.com/forums/index.php)
-   The perfect line and other riding myths (http://www.advrider.com/forums/forumdisplay.php?f=23)
-   -   Twin shocks vs. monoshocks? (http://www.advrider.com/forums/showthread.php?t=974512)

SloMo228 04-30-2014 06:26 PM

Twin shocks vs. monoshocks?
 
Maybe this is the wrong forum, but I'm interested in hearing people's thoughts on the differences between an old-school twin shock and a modern monoshock rear suspension. Assuming you could somehow have two otherwise identical chassis, one with a monoshock swingarm, and the other with twin shocks, and the shocks/springs themselves are of equal quality and appropriately set up for the rider, what are the inherent advantages/disadvantages of each?

Are there any handling (or other) advantages to a twin shock swingarm, or are bikes which have them simply designed that way for aesthetic or perhaps economic purposes?

I'd like to hear some people's ideas about this.

NJ-Brett 04-30-2014 07:06 PM

Dirt bikes or street bikes?
Its hard to get 12 inches of travel out of the dual shock setup.
On the street, twin shocks make it easy to adjust for added load, and the shocks keep bags out of the rear wheel, otherwise the single shock setup likely has some performance advantages but uses up space.

Moronic 04-30-2014 08:04 PM

Consider how it would work if you replaced the monoshock on a "modern" rear end with twin shocks mounted in the same place.

What difference would that make? 1: More parts. 2: Probably more static friction (stiction) from using two small seals on two small diameter shafts rather than one big seal on one big shaft.

But probably, looking only at performance, not much difference at all.

So, looking purely at the choice of one or two shocks, the main advantages of the single shock seem to be space efficiency, cost efficiency and serviceability.

Okay, but twin shocks on a monoshock chassis wouldn't be an old-school twin-shock suspension. So let's look at the question from the opposite end.

How would it work if you replaced the twin shocks on a traditional twin-shock bike with a bigger single shock just on one side?

In fact plenty of bikes these days are built like this, and some makers (e.g. BMW) were doing it in the '80s. The advantages of the single-shock set-up will be exactly the same as in the former case: space efficiency, cost efficiency, serviceability.

However ... in order to use the shock just on one side, the swingarm and its pivot on the frame have to be stiff enough to carry the significant torsional loads generated by having the load on the tyre resisted by a single component that is offset several inches to one side of the tyre.

On a twin-shock bike, that torsional loading is balanced by the torsional loading from the shock on the opposite side. So ... one manufacturing advantage of the twin-shock set-up is that you can get away with a less robust swingarm.

As suggested above, there are also design and serviceability advantages to running the shocks either side of the wheel (or on one side) rather than in front of the wheel: it frees up space between the tyre and the engine, and shocks placed there can be (much!) easier to remove and adjust.

IMO that just about sums up the theory. What about the practice?

In practice, the main advantages of the single shock chassis tend to be improved stiffness and a better shock (as it is cheaper to build one big shock than two little ones). The cost of upgrading the single shock will be lower also, to similar performance levels.

A secondary advantage is that some chassis designs run the single shock through a progressive linkage, which allows a single-rate spring to act like a progressive-rate spring - at the cost of placing a bunch of small bearings in some of the grittiest spots on the bike. :1drink

scootrboi 04-30-2014 09:25 PM

kind of an old idea
 
The rear wheel comes off like a car wheel. That is what I like.https://farm9.staticflickr.com/8496/...8a29a8_z_d.jpg

RFVC600R 04-30-2014 10:19 PM

Sorry to go off topic, but is that the bike you spent 42 years on?? :ear Good job man, I hope to have my XL half as long as that.:clap

Moronic 04-30-2014 10:35 PM

Quote:

Originally Posted by scootrboi (Post 24062213)
The rear wheel comes off like a car wheel. That is what I like.

Nice one. You can't do that with trad twin shocks. :lol3

JohnCW 05-01-2014 12:19 AM

Quote:

Originally Posted by SloMo228 (Post 24060960)
Maybe this is the wrong forum, but I'm interested in hearing people's thoughts on the differences between an old-school twin shock and a modern monoshock rear suspension.

A monoshock has the significant advantage of allowing a longer rear suspension travel.

Moronic 05-01-2014 01:20 AM

Quote:

Originally Posted by JohnCW (Post 24062701)
A monoshock has the significant advantage of allowing a longer rear suspension travel.

Perhaps ...

http://nachtflug.smugmug.com/KTM/198...3V/0/O/KTM.jpg

Rucksta 05-01-2014 03:06 AM

Some may find this article interesting
 
http://www.carbibles.com/suspension_bible_bikes.html


Look for
Motorbike suspension - back end.

about 1/3 down

scootrboi 05-01-2014 06:01 AM

chain in oil bath
 
]
Quote:

Originally Posted by Moronic (Post 24062471)
Nice one. You can't do that with trad twin shocks. :lol3

https://farm9.staticflickr.com/8243/...33575a_z_d.jpg The chain drive monoshock swingarm design is from 1951 and was used on all Heinkel scooters and minicars. Changing wheels on the back takes a few minutes, and a spare is mounted under the luggage rack.

DAKEZ 05-01-2014 07:31 AM

Quote:

Originally Posted by NJ-Brett (Post 24061283)
Its hard to get 12 inches of travel out of the dual shock setup.

THIS ^^^^ [burp]

Rgconner 05-01-2014 07:48 AM

The Vespa put everything into the swingarm in '47. More unsprung weight, but also allows for a monoshock.

Front is built like a nosegear, so it is also monoshock. (well, mono SPRING on the early models)
Quote:

Originally Posted by scootrboi (Post 24063691)
]

https://farm9.staticflickr.com/8243/...33575a_z_d.jpg The chain drive monoshock swingarm design is from 1951 and was used on all Heinkel scooters and minicars. Changing wheels on the back takes a few minutes, and a spare is mounted under the luggage rack.


cccolin 05-01-2014 08:25 AM

this is relevant to my interests. would like to do a conversion to dual shocks for aesthetic reasons but hadn't considered the extra cost. hmm

SloMo228 05-01-2014 08:37 AM

What's been posted pretty much sums up what I expected, though I never thought there would be a difference in suspension travel. Makes sense, though. The single shock is usually mounted far forward of where dual shocks would be, so the shock doesn't require a full 12" stroke to get 12" of suspension travel due to the lever effect of the swingarm.

One plus of dual shocks that I liked on the ZRX I owned was that not having the single shock allowed for a pretty big storage area under the seat. It was very handy when using the bike as a commuter.

NJ-Brett 05-01-2014 09:57 AM

Yes, there are also two setups for single shock, a small shock with a linkage in front of the rear wheel, and the early setup like my xt200 has, a giant shock under the seat and gas tank.
That takes up all the space on a bike, the battery was put in a small box mounted behind the motor and in front of the rear wheel.

Twin shocks gives lots of room under the seat.


Times are GMT -7.   It's 03:55 AM.

Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014