RF shock.

[keeks]

I got some great answers to a post a while back about bottoming out the rf shock using a 2 piece lower. ie: lower shock mounting position on the one piece.

My question is, can you get the same shock travel back by raising the upper mount position? Or will this mess up front end geometry and cause other problems?

The upper mount is buggered anyways, so I was thinking about raising it when I weld the new one on.

[jrkracing54]

I got some great answers to a post a while back about bottoming out the rf shock using a 2 piece lower. ie: lower shock mounting position on the one piece.

My question is, can you get the same shock travel back by raising the upper mount position? Or will this mess up front end geometry and cause other problems?

The upper mount is buggered anyways, so I was thinking about raising it when I weld the new one on.

Not sure what chassis you are running but I'm pretty sure Outpace makes one piece lowers for the right front that lower the shock mount to help with this exact problem. Hope this helps. John 1*

[charcoal01]

Don't raise your rf shock mount. You're changing the spring table and with affect the handling of the chassis.

[Matt49]

The wheel does not know where the upper shock mount is. It only feels force in one direction. The only thing you can possibly change my moving the upper shock mount is the angle. More angle will result in less wheel rate.
Moving the lower shock mount can change angle and/or motion ration. Motion ratio is the distance between the lower shock mount and the control arm heim on the frame divided by the distance between the ball joint and the control arm heim on the frame. The bigger the motion ratio, the higher the wheel rate.

The only reason there is any angle in the shock/spring on A-arm suspended cars is to make it so that the angle changes as little as possible in its travel.

Motion ratio has a huge effect on wheel rate. Understanding that math behind it helps a bunch.

[keeks]

Thanks everyone. Matt49, great info. I love math. But this whole front end geometry is overwhelming. I need to start a work book I think. :)

[hucktyson]

The only man on this planet capable of answering this question is none other than Brian " Gay " Gray !!

[Matt49]

The only man on this planet capable of answering this question is none other than Brian " Gay " Gray !!

Please take this bullsh!t back to the gossip section where it belongs.
If you have a beef with Brian Gray, I suggest you call him. He's not a hard person to find or get in touch with. Why don't you man up and give him a ring or stop by his shop?

Personally, I don't know him outside of 4m and don't need to. I know he has some ideas that I think are interesting and some that I think are crazy. But nothing constructive comes from injecting this type of rhetoric into a thread that could be very informative to those wishing to learn about their race cars.

There used to be MANY more intelligent minds that posted in this tech section. Posts like this are the reason many of them have found better things to do.

[hucktyson]

My problem with him is that he spews his absurd BS on here acting like he has a shop full of 5 figure checks hanging on his walls. Guys come
On here looking for legit advice and he feeds them non stop nonsense which can possibly cause them to get discouraged and quit all together . Morons like him posting are a cancer in the sport we all love.

[jedclampit]

If the intent here is to raise the top shock mount, up, to allow for more travel before bottoming out the shock, then it will change the chassis's Leverage, move the botttom down with a mount relocation......

My tooscents!

[HEAVY DUTY]

Raising the top mount should make it harder for the weight to get over on the RF, same as if you raised the RR shock mount

[Brian Gray]

the nonsense? really. ask some of the people that come to my business for help racing if i feed them nonsense. my credentials speak for itself. they wouldnt keep comming back for nonsense.

i wasnt going to weigh in on this one because there are so many opinions about shock mounting but here is what i know and when i design a front end or rear for that matter this is the physics i refer to.

the car only knows what happens at the tire with that said the angle the shock is mounted at will surely effect the wheel rate so yes you could move the mount up without changing handling. as far as the leverage goes that is relative to CG center of gravity and the roll center location. i know of teams that have played with the so called spring table but there is no evidence to show this effects the handling of the car.

look at it like this if you have a rope and you hang a 10 lb weight from it. no matter where you attach the weight you still have 10 lbs plus the rope at the attachment point.

weight transfer is only relative to the length of the moment arm in the suspension. shock mountings will not change that.

now if thats misinformation i'm sorry . and btw if im always so wrong you can always present the facts that prove it!

[MasterSbilt_Racer]

There is no question spring table matters on the non- independent rear of the car. The front, I am not so certain.

[bb14]

Changing from the top shock hole to the lower shock hole on a Rocket changes the spring rate but according to Rocket not enough to worry about. I had this same question when running high camber with the A-arm hitting the shock. I called Rocket for a solution and was told that a lot of teams are running in the lower hole. The main thing to remember is that you will lose shock travel when doing this. You need a different lower. You can do the math to see the difference and adjust around it.

Maybe the added leverage is why they do this??? I doubt it but a thought!

On another note I believe Ruhlman offers a new shock mount that requires welding.

[Brian Gray]

yes in the solid axle rear of the car the shock mounting points would change some things since they have influence on rear roll center.

[latemodels4life]

My problem with him is that he spews his absurd BS on here acting like he has a shop full of 5 figure checks hanging on his walls. Guys come
On here looking for legit advice and he feeds them non stop nonsense which can possibly cause them to get discouraged and quit all together . Morons like him posting are a cancer in the sport we all love.

Hucky it sounds like you are explaining your self. whats up with that. P.S. Cant wait to see you race

[Matt49]

The tire contact patch feels one thing and that is wheel rate.

The only "leverage" that the chassis has is dependent upon the VCG and the roll center and that is not influenced AT ALL by the upper shock mount on an A-arm suspension. PERIOD.

On an A-arm suspension, the only thing you can do with shock mounting is influence the wheel rate by changing the angle or the motion ratio (and motion ratio is only changed by moving the LOWER shock mount). You cannot change the roll center. Mount the top of the shock 10 feet in the air and the roll center of the car doesn't change. The wheel rate will be the same, therefore the handling will be the same.

For an A-arm suspension:
wheel rate=(motion ratio)squared times spring rate times the cosine of the shock angle.

Motion ration is the distance between the lower shock mount and the inner lower control arm mount divided by the distance between the lower ball joint and the inner control arm mount.

And by "shock angle" we're talking about the angle between the line that the shock travels and a line perpendicular to the ground.

Hint for those that don't follow the math: motion ratio is WAY more critical to wheel rate than shock angle.

Weight transfer calculation is more complex but with respect to the car itself, it only involves VCG and roll center. On an A-arm suspension, neither of these are influenced by shock mounting position.

If anyone would like to dispute these facts, I look forward to seeing the math that explains it.

[hpmaster]

Dang a post with facts, logic, supporting statements, not trying to sell me some BS part or impress me with unsubstantiated "fact", sans personal attacks and personal theory's. You win yourself a fruit cup!

[fastford]

I moved my upper mount up one inch when I first started playing with a bump stop, it helped my car tremendously by allowing more rear steer, really helped when I picked up the throttle

[HEAVY DUTY]

I still believe that moving the upper shock mount has to effect the spring rate a little. If the car is just in compression, it wouldn't matter, but in roll, the upper shock mount is moving sideways.. If the car is rolling around a point, using a clock for example, and the center pivot that the hands move on was the center of gravity. If the shock mount was at 1 oclock, the force would be pushing out on the upper shock mount. If the upper shock mount was at 3 oclock, the weight would push straight down on the upper mount.Although moving the mount an inch or two wont make much difference, but moving it down 6 or 8 inches will. Part of the reason a modified uses so much stiffer springs than a late model is the height of the top of the spring, but most is because of the motion ratio.

[Matt49]

I still believe that moving the upper shock mount has to effect the spring rate a little. If the car is just in compression, it wouldn't matter, but in roll, the upper shock mount is moving sideways.. If the car is rolling around a point, using a clock for example, and the center pivot that the hands move on was the center of gravity. If the shock mount was at 1 oclock, the force would be pushing out on the upper shock mount. If the upper shock mount was at 3 oclock, the weight would push straight down on the upper mount.Although moving the mount an inch or two wont make much difference, but moving it down 6 or 8 inches will. Part of the reason a modified uses so much stiffer springs than a late model is the height of the top of the spring, but most is because of the motion ratio.

Yes moving the upper shock mount in or out changes WHEEL rate (not spring rate) due to the shock angle change. But just moving it up and leaving the angle the same doesn't change the wheel rate at all.
Three things and three things only affect wheel rate on an a-arm suspension:
Spring rate (linearly)
Motion ratio (exponentially)
Shock/spring angle (a function of the cosine of the angle)

At the angles we're dealing with (around 20 degrees) an angle has a pretty small effect on the wheel rate.
For example:
400 pound spring with 14/19 motion ratio and a shock/spring at a 20 degree angle gives you a wheel rate of about 204 pounds/inch.
Changing the shock angle (using the upper mount) to 15 degrees or 25 degrees changes the wheel rate to 210 pounds or 197 pounds respectively.
But move the shock angle to 25 degrees by moving the lower shock mount out 2 inches and you're up to a 257 pound wheel rate.
Moral of the story is that motion ratio is far more critical to wheel rate than shock/spring angle.

The front shocks do not affect a cars ability to roll other than in the wheel rate they provide. The motion of the a-arm suspension is dictated by moment center only. The suspension does not "know" the angle of the shock.

Now rear suspension on a late model is a whole different story. The shocks/spring locations play a part in the roll center, the wheel rate, and the roll rate. But like I said...whole different story and I'm still trying to figure out the math on it.

[Bubstr]

Yes moving the upper shock mount in or out changes WHEEL rate (not spring rate) due to the shock angle change. But just moving it up and leaving the angle the same doesn't change the wheel rate at all.
Three things and three things only affect wheel rate on an a-arm suspension:
Spring rate (linearly)
Motion ratio (exponentially)
Shock/spring angle (a function of the cosine of the angle)

At the angles we're dealing with (around 20 degrees) an angle has a pretty small effect on the wheel rate.
For example:
400 pound spring with 14/19 motion ratio and a shock/spring at a 20 degree angle gives you a wheel rate of about 204 pounds/inch.
Changing the shock angle (using the upper mount) to 15 degrees or 25 degrees changes the wheel rate to 210 pounds or 197 pounds respectively.
But move the shock angle to 25 degrees by moving the lower shock mount out 2 inches and you're up to a 257 pound wheel rate.
Moral of the story is that motion ratio is far more critical to wheel rate than shock/spring angle.

The front shocks do not affect a cars ability to roll other than in the wheel rate they provide. The motion of the a-arm suspension is dictated by moment center only. The suspension does not "know" the angle of the shock.

Now rear suspension on a late model is a whole different story. The shocks/spring locations play a part in the roll center, the wheel rate, and the roll rate. But like I said...whole different story and I'm still trying to figure out the math on it.

Good post, So as long as you keep the shocks lower attachment point in the same position, Moving the top attaching point to change the angle, will change the wheel rate, but not in a linear curve, so many degrees for so many pounds. It starts off small and grows as the angle gets greater.

I take it, the angle we are talking about would be measured off the lower control arm? If so would the roll over of the chassis have any effect on this angle and would you do your calculations after the chassis took a set or on level?

I was taught that up to 15 degrees was not worth worrying about and the angle was figured off the lower control arm with a set in the chassis. When you go over that 15, it changes more quickly. But you have the math.

Ever experiment between changing wheel rate with this method and say wheel spacing? I realize, that's what they make adjustable shocks for, but I sometimes am not sold on increasing dampening to increase wheel rate and still getting contact compliance. Sorry mind is wandering on what if's.

[Matt49]

Good post, So as long as you keep the shocks lower attachment point in the same position, Moving the top attaching point to change the angle, will change the wheel rate, but not in a linear curve, so many degrees for so many pounds. It starts off small and grows as the angle gets greater.

I take it, the angle we are talking about would be measured off the lower control arm? If so would the roll over of the chassis have any effect on this angle and would you do your calculations after the chassis took a set or on level?

I was taught that up to 15 degrees was not worth worrying about and the angle was figured off the lower control arm with a set in the chassis. When you go over that 15, it changes more quickly. But you have the math.

Ever experiment between changing wheel rate with this method and say wheel spacing? I realize, that's what they make adjustable shocks for, but I sometimes am not sold on increasing dampening to increase wheel rate and still getting contact compliance. Sorry mind is wandering on what if's.

Correct in your first paragraph. Like you said, the angle change has a non-linear effect and doesn’t make much difference until you get pretty steep because we are dealing with a cosine curve that starts flat and is at maximum slope at 90; but it doesn’t take a straight line to get there. A lot of folks think that since a spring laid all the way over would end up providing no effective rate then a spring laid half way over must provide half the rate. But that’s just not the case. That’s where the trig comes in and in this case cosine of the angle is the correct calculation. Google “cosine table” for a good look. The math is sort of answered for you there in terms of where the change in angle starts to really change the cosine value. Or Google “cosine curve” for more of a graphical view.

The angle you measure is actually the angle of the shock relative to a line perpendicular to the ground where 0 degrees is straight up and down. Obviously if shock angle changes during travel, this would have an effect on the dynamic wheel rate. But wheel rate is relative to the ground which is why we’re measuring against the ground. The wheel doesn’t know that the chassis is moving and rolling. It only knows that it’s feeling some weight.

If you wanted to measure the shock angle relative to the ground (90 degrees being straight up and down) you could do that to but just use the sine of the angle in the wheel rate equation. Example the cosine of 70 degrees is equal to the sine of 20 degrees etc.
Wheel spacing doesn’t change wheel rate on an A-arm suspension. You can space the wheel out three feet and it still feels the rate felt at the lower ball joint. I will add a small but relatively unimportant caveat to this: Camber change produces a bit of a secondary motion ratio but it isn’t enough that it makes much difference at such small scrub radiuses.

I know this part doesn’t make sense at first but imagine the following scenario:

You’ve determined your wheel rate and you decide to put a big 10’ long cheater bar on the snout of the spindle to see what it feels like way out there. Assuming no camber gain, you’d feel the exact same wheel rate at the end of the cheater bar as you would at the lower ball joint. You aren’t generating any leverage against the lower ball joint with the cheater bar because the upper ball joint is pushing back against you and you’re moving in the same up and down line as the wheel would be just further away. There’s nothing to torque, you’re only moving something up and down.

Now introduce a ton of camber gain into this. Let’s say you generate 10 degrees of camber gain with 2 inches of ball joint travel. Your 10’ cheater bar now moved a little over 20 inches but your lower ball join only moved 2 inches! Obviously you’ve got less rate at the end of your cheater bar than at your ball joint. But this is an extreme example of camber gain and REALLY extreme example of offset. Bring these things back to normal racing parameters and they don’t have much of a net effect. But fun stuff to think about for sure :-)

[Matt49]

Sorry for the long-windedness on this stuff. But understanding wheel rates are very important when it comes to understanding why some cars like softer or stiffer springs on some corners. Everybody gets caught up in roll center (which is very important) and effective wheel rates don't seem to get discussed very much.

[Ghopper]

I think Matt49 has explained this subject well.

I only want to add that on an independent frontend you should package the coilovers for your necessary stroke and clearance from other parts. The final Wheel Rate, as mentioned spring rate measured from the wheel, can be achieve by adding whatever spring is necessary to meet your target.


Ghopper