<img src="http://yoda.densan.ca/kmr/bikes/andreas1.jpg">
<img src="http://yoda.densan.ca/kmr/bikes/andreas2.jpg">
<img src="http://yoda.densan.ca/kmr/bikes/andreas3.jpg">
<img src="http://yoda.densan.ca/kmr/bikes/andreas4.jpg">

Bought it off AndrewTO for well, it was cheap.... didn't come with a shock but it did come with the titanium bolt hardware. Fortunetly it came with the reducer hardware to fit a fox shock so if and when I find a good deal on one in the future, I can easily swap it in to replace this NOS DNM Backdraft shock I've had kicking around for a few years. Its not a bad shock per say, but its almost as heavy (409g) as some coil shocks I own. One thing going for it is the length (7.5") and stroke (1.75") fit nicely into the shock compatibility range for this model year (2001). Another downside was I had to spend over 2 hours fabricating the reducer hardware to get the shock to fit the frame properly. In any case, if I did the math right on the leverage ratio of the swingarm this should give about 4.5" of travel. Now to just decide how I'm going to build it.

That's a nice frame! Is it polished or brushed? It should have 5.25" of travel, which will match a 130 or 140mm fork nicely. It has a small seat assembly. I would run the shock mount all the way to the top. Have fun with that!!

I measured the initial leverage ratio out as 2.7 to 1, I know its a rising rate design as the swingarm arcs the angle the shock actuates at changes slightly but how much I haven't crunched the sin/cos math on yet.

It was the brushed finish but two hours with the rags and polishing paste and voila....

I thought they were 3:1 ratio.

I know I've read that number for the frames, but never on the old MC website or literature... its usually been mag reviews where they go "its about a 3 to 1 ratio" or something without any math to back it up. With any singlepivot cantilever beam you can easily determine the leverage ratio of the actual beam itself by simple math. Distance from axle center to shock eyelet center divided by distance from eyelet center to pivot center. On my frame is 17"/6.5" = 2.615. On a 2002 Specialized BigHit SPEC (that's the single-pivot lower model one they used to have) its 19.25"/9" = 2.139.

Now that specialized comes equipped with a 2.25" stroke shock and claims 5.5" of wheel travel. Now obviously the stroke x the beam ratio (2.25x2.139 = 4.8") isn't the only part of the equation involved. What's missing is that the angle the shock is anchored at between the beam and the frame acts like a lever also just as the straddle cable and yoke angle did with cantilever brake arms and the math is essentially the same to figure out the leverage ratio effect of that shock angle but I'm rather out of practice at doing it but I did do some measuring if someone else wants to crunch the figures.

Now I measured the angles on the two frames and forms basically a 70 degree angle on the san andreas and 65 degrees on the bighit and that's without any preload. As the shocks compress the angles increase (as the swingarm kicks forwards) and this has the effect lending a rising rate to the design. You really need two people and a built bike (both my frames are bare right now) to measure the angles and different points of compression, or deflate/remove the springs and move them by hand but the point is the same. Determine the angles and use a calculator and some sin/cos division and you can figure out the ratio at different points of the shock stroke.

Anyways the simpler method is to put the bike in a stand, measure the distance the axle is above the ground, then remove the shock spring (or deflate if an air shock), and pull upwards on the swingarm to maximum compression and measure the distance the axle is above the ground again. This gives you the vertical wheel travel at least (the actual wheel travel will be greater as the axle is moving in an arc, on these frames its swings upwards and forwards). I just measured the San Andreas out to 5" exactly using this method (so 2.857 ratio). You can also take measurements at different points of shock compression if you wanna see how the ratio changes. You can do this with a friend as you stand the beside the bike, then sit on it to the normal rider weight sag position measuring the axle height above the ground each time. If your friend weighs more/less than and the bike is set to your weight, have him sit on it and you can get another set of measurements to determine how quickly the leverage rate ramps up.

As an aside, i dug up some old reviews in MBA and the 1996 R-Series had a 1.25" stroke shock and claimed 4" travel (so that's more than 3:1). A 2000 review of a DHS which is essentially what mine is with a Rockshox Sid XC air shock of 1.5" stroke and claimed 4" travel again (a 97 review with the MC Aftershock of unlisted stroke claimed 4.25") which puts it about a 2.66 ratio. Again these numbers come down to minor variations in shock angles, the swing arm may have changed a bit since the early days, and well... the phases of the moon and the "new math" of MBA writers.

All I know is Mountain Cycle claimed my '96 San Andreas has 1.5" stroke and 4.5" of travel and my newer version, which I think is an '03, claimed 2" stroke and 6" of travel.

Yet the very one mba reviewed in 96 was given as 1.25 stroke and 4" travel. Either they rounded up the wheel travel or something else is going on. The 1.5" stroke for a 1996 era shock is also rather unusual. Few shocks back then were made with that much stroke.