rear suspension ratios

[edwin veal]

i have heard socket and rik talk many times about different shock ratios for different suspension designs and how they afect performance
i dont really understand some of the theorys but would like to
if anyone understands what im talking about and could shed some light on this it would be great
thanks
edwin

[RCOH]

It is my understanding that ratios are detemined by shock stroke & rear wheel travel.

for example my bike has 5.3 inches of travel & uses a 2.25 inch stroke read shock therefore my suspension ratio is 2.35/1 or my rear wheel moves 2.35 inches for every inch that the shock compresses.

But i may be terribly wrong, so i await someone to either correct me or congratulate me :wink: :)

[S.]

i have heard socket and rik talk many times about different shock ratios for different suspension designs and how they afect performance
i dont really understand some of the theorys but would like to
if anyone understands what im talking about and could shed some light on this it would be great
thanks
edwin

RCOH is correct about what the shock ratio is, basically to get an overall ratio you divide the amount of travel by the shock stroke. For example, an 8" travel bike with a 2.75" stroke shock, you get a ratio of 8/2.75 = 2.91:1

The ratio affects basically how much force is put into the shock for a given force applied at the axle. The ratio varies throughout the travel on ALL bikes - the way it does this is known as the "shock rate". A rising shock rate (progressive) will have a higher leverage ratio in the beginning of the travel, and turn into a lower leverage ratio as you move further into the travel. A falling rate is the opposite; lower leverage ratio to begin with, moving to a higher leverage ratio. "Linear" rates don't exist as such, but they're commonly used to describe ratios that don't vary much through the travel (ie not enough to make a significant difference or be perceptible).

A higher leverage ratio means that more force is put into the shock for a given force at the axle, and this affects both the spring rate and the damper curve. The higher the ratio, the higher weight spring you'll need, and the more damping you'll need (and a lower ratio is obviously the opposite). In theory, ideally you'd want a fairly low ratio (the closer to 1:1, the better) to put less stress on the damper (and the chassis itself), but this just doesn't work because it means you need a huge shock (imagine a shock that was the length of a fork) which is also unnecessary weight, but using a higher ratio is possible due to high quality dampers which can take massive amounts of force before being damaged or blowing seals.

If the ratio is too high, you'll blow the shock up quickly (which is the main argument FOR lower ratios) because too much stress is being placed on it - this is the main issue people have to consider when making aftermarket linkage plates and stuff to get more travel. If it's too low, you can get an overdamped ride, but with any decent shock you can adjust the compression and rebound anyway, so that isn't as much of a problem.

Hope that helps!

[Rik]

imagine a shock that was the length of a fork
Imagine a Manitou frame ;)

[edwin veal]

man you guys rock!
thanks heaps for the info
there maybe a few more questions as i look into a few things further
what would be the maximum leverage ratio that most comon shocks would be able to deal with?
thanks again
edwin

[nicklouse]

taking the travel and the shock stroke to give the sus. ratio is a simplistic approach but is accurate enough for most purposees.

as we have pivots in the sus. systems things are not linear! for instance the first 1" of wheel movement and the last 1" of wheel movement may use more or less shock travel.

have a look at http://www.mtbcomprador.com/pa/english/

[S.]

man you guys rock!
thanks heaps for the info
there maybe a few more questions as i look into a few things further
what would be the maximum leverage ratio that most comon shocks would be able to deal with?
thanks again
edwin

Shocks are designed around a 3:1 ratio, 3.5:1 is about as high as I would say is anything like safe (even that's too high for my liking), but some bikes (eg old Rocky Mountains) run 4:1, which is definitely way too high.

[Disco]

The original Merida Missions came out before the Specialized epics and offered a 1:1 Ratio and hence used really low compression shocks (less frame stress.. shock lasts longer etc) well worth a look out of interest and in fact (if it wasnt for Specialized being a slightly bigger name) should have generated a lot more popularity! The Merida Mission was the first dually to win a WC XC Round/Champs?? *Not sure which.

**Actually they now offer a 5" Travel Trail riding version! 8) **

Little Mike

[petri]

but some bikes (eg old Rocky Mountains) run 4:1, which is definitely way too high.[/quote]

What RM are u talking about?

[S.]

but some bikes (eg old Rocky Mountains) run 4:1, which is definitely way too high.

What RM are u talking about?[/quote]

The original RM6s (not sure if the later ones were the same) had 6" of travel from a 1.5" stroke shock.

[edwin veal]

so would a 3.3:1 ratio be too high do you think?
what brands make a 3" stroke shock?
the other thing is what is the maximum spring weight that would be safe to use on a rear shock?
thanks
i remember why i love farkin soo much

[nicklouse]

The original Merida Missions came out before the Specialized epics and offered a 1:1 Ratio and hence used really low compression shocks (less frame stress.. shock lasts longer etc) well worth a look out of interest and in fact (if it wasnt for Specialized being a slightly bigger name) should have generated a lot more popularity! The Merida Mission was the first dually to win a WC XC Round/Champs?? *Not sure which.

**Actually they now offer a 5" Travel Trail riding version! 8) **

Little Mike

just a correction here. Meridia is bigger than Specialized! Meridia owns about 50%,give or take 1%, of specialized.

[edwin veal]

the other thing is
what was wrong with the higher leverage ratios?
what ever went wrong with the rm's that you were talking about?
wouldnt the leverage ratio be the chainstay legnth by the travel rather than the shock legnth by travel?
feel free to jump scream and throw computers to the floor if i am wrong which is a possibility

[S.]

so would a 3.3:1 ratio be too high do you think?
what brands make a 3" stroke shock?
the other thing is what is the maximum spring weight that would be safe to use on a rear shock?
thanks
i remember why i love farkin soo much

3.3:1 should be ok, if the shock is good quality, in good condition, not sideloaded by a flexy frame, and you use the correct weight spring (ie not excessively soft). There isn't really a safe max spring weight to use; a guy on Hcor.net had a 1050lb spring on his Foes Zigzag with no issues.

the other thing is
what was wrong with the higher leverage ratios?
what ever went wrong with the rm's that you were talking about?
wouldnt the leverage ratio be the chainstay legnth by the travel rather than the shock legnth by travel?
feel free to jump scream and throw computers to the floor if i am wrong which is a possibility
Higher leverage ratios put too much stress on the damping circuits (not that they are very prone to damage, but if you do it's $$$ to fix) and more commonly cause the seals to blow (aka blowing your shock), which will generally leave you without damping pretty quickly. The RM6s (and RM9s) were renowned for their rediculous shock rates, the RM7 wasn't good but wasn't as bad either. The RM6/9s were well known for blowing shocks up (although they were also some of the first "freeride" bikes and supposedly tended to get ridden at least as hard as pretty much everything else).

The leverage ratio isn't the chainstay length by the travel, because using linkages can drastically change the ratio without doing anything to the chainstay length :)