Rear shock placement

[blazer4corners]

If you start from scratch on your rear suspension what is the best placement for shocks .stagered one in front of the axle ,one behind.both behind the axle tops leaning towards each other . Shocks behind the axle staight up and down.Or shocks in front of the axle tops leaning towards the front of the car.Now the car will be used for heavy steet abuse.mainly for handling maybe some track time at Mid-ohio if they have open track days Oh its a S10 blazer with a 358 sbc and 200-4r thanks in advance for your help

[yody]

just don't put them at more than a 30 degree angle, shocks like being placed vertically but obviously they will have some angle in them due to mounting confiments. i think if you aren't using leaf springs there isn't as much of a need for staggered shocks.

[awr68]

I was told 20* is optimum...so that is what I did......

[yody]

shocks work the most "effective" when placed perpendicular to the motion of travel, so 20 degrees would most likely not be optimum. probably around 90% effective, according to herb adams you also want the shocks placed as close to the wheels as possible, try to keep them vertical if possible when mounting. Also i am pretty sure staggered shocks are only for leaf spring type suspensions. Anthony-maybe 20 degrees is optimum due to your moutning constraints/suspesnions packaging. or that is ideal with your spring rates?

[awr68]

Don't know...it's what jp told me to do???

[yody]

well he is a pretty smart guy, so there must be a reason, maybe the reason is that i am wrong?!!

[blazer4corners]

thanks guys i didnt there was that much "science" involved with shock placement

[Norm Peterson]

You could work up some justification for staggering the shocks on a coil sprung axle if you're using soft OE bushings in the links (arms), which could permit some unwanted axle rotation (side view). But for full benefit, the shock bushings would then have to be fairly rigid.

shocks work the most "effective" when placed perpendicular to the motion of travel

Absolutely. Note that "perpendicular to the motion" in roll could be several degrees off the vertical if, say, the rear roll center is below axle centerline height.

Norm

[blazer4corners]

Thanks Norm i was hoping you would chime in.

[jannes_z-28]

The rate of the shock and colioverspring are dependent of the angle they are mounted in. If you mount it in 45 degrees you need twice the rate to handle the load. Think about it, how much load could it carry if it was at 90 degrees? None!

The rate is also dependent on the relationship of cars centerline to the wheel distance compared to the distance between the axle shock mount and the wheel. So if the shock is mounted half way between the wheel and the cars centerline you will need twice as strong shock/spring.

It is the simple mechanics of force calculation.




Jan

[yody]

yes, that is why i stated to put it towards the wheels as far as possible. because the wheel is what is going to be going over bumps and so forth and is the very farthest out part of your suspension that will recieve the load from body roll etc.. so the farther out towards the wheel the more it is dampening.

[awr68]

So with all this said it doesn't sound like I have to redo anything but possibly increase the spring rate if needed...is the correct? I hope.

[yody]

looks like you can just turn up the stiffness on the shock some to compensate, i dont' think it is that big of a deal in your case, tuning the shocks to how the car handles will have the greatest effect.

[parsonsj]

20 degrees, eh? Oddly enough, mine are at about 20 degrees.

I do understand that all other things being equal, shocks should be mounted so that they are effectively vertical against the expected motion. So shocks that are designed for going around corners should be angled some, since the body will roll. Both Anthony's and my car have a roll center below the axle centerline, so some angle is to the good.

The effective rate of the shock is the cosine (or is it sine?) of the angle away from its expected best working angle, so a shock at 20 degrees is somewhere around 95 % effective as a shock at 5 degrees.

Also factor in that you want the shock as far out as possible on the bottom end, and that it needs to be properly mounted inside the frame rail on the upper end. Finally, for best tuning ability, a longer travel shock is usually a better bet than a short version.

Add all that up with Morrison's 4 bar setup (which both Anthony and I run) and 20 degrees from vertical is a good all around compromise.

jp

[Matt@RFR]

So which would you rather have:

The bottom of the shocks as far apart as possible but with an angle to clear the frame

OR

Shocks mounted vertically but further inboard

[awr68]

Thanks for the post jp, I was a little worried...that might explain the sleepless night...yep, I'm back to having those...they tend to go hand and hand with progress on the car.

[parsonsj]

Great question!

I'm gonna go dig up Herb Adams. I believe he said as far apart as possible with the bottom of the shock pointing at the tire contact patch.

jp

[awr68]

I remember that too...and when I was laying mine all out it was real close...let us know what you find.

[parsonsj]

OK, I lied. Adams is silent, other than to say that tuning is important. Duh. Carroll Smith in Tune to Win is also silent.

But my man Steve Smith says unequivocally to mount the rear shocks at 15 +- a few degrees from vertical in Paved Track Stock Car Technology.

My guess is that the angle isn't really as important as other things like rate, geometry, dampening, asb diameter, etc.

jp

[Norm Peterson]

Just a couple of out-of-the-box thoughts because there has to be more than just two options here . . .

Locate the frame rail inside the design shock top mount location instead of vice-versa. Once you get all of the rear axle locating links picked up, the frame mostly just supports the fuel tank, trunk load, and rear bumper. Properly braced/gusseted, a couple of little lateral kinks way back there shouldn't hurt overall chassis stiffness.

Use bellcranks to regain the motion lost to the cosine effect.

Norm