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Old 07-26-2009, 11:59 AM   #1
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Default TC design question

Why is it the top mounting holes are always higher on the rear shock tower compared to the front? Is the extra shock travel on the rear really necessary?
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Old 07-26-2009, 01:08 PM   #2
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Because thats the way companies designed them.
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Old 07-26-2009, 02:54 PM   #3
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Just a guess but I think it's so the shock can be stood more upright to allow for a stiffer rear suspension not for the travel. Once a shock starts to get laid down the arm has a mechanical advantage over it so it seems softer.
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Old 07-26-2009, 06:04 PM   #4
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Just a guess but I think it's so the shock can be stood more upright to allow for a stiffer rear suspension not for the travel. Once a shock starts to get laid down the arm has a mechanical advantage over it so it seems softer.
I was always told its the opposite. The more a shock is layed down the stiffer and more progressive the damping becomes. I'm confused now
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Old 07-26-2009, 08:05 PM   #5
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I was always told its the opposite. The more a shock is layed down the stiffer and more progressive the damping becomes. I'm confused now
No, the more they are leaned in, the softer they are and the more lateral grip you have. The more stood up they are the stiffer they are
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Old 07-26-2009, 08:06 PM   #6
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I was always told its the opposite. The more a shock is layed down the stiffer and more progressive the damping becomes. I'm confused now

On a touring car the closer to the wheel the shock is, and the more inline with the motion of the lower arm, the harder the spring will appear to the wheel, and the more dampening.

On a pancar, the more angled the shock is (again, making it inline with the motion of the pod) the firmer the shock/spring. More parrallel will soften it.

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Old 07-26-2009, 08:27 PM   #7
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Guys, hes not asking about shock angle. Hes asking why most TC's have higher rear shock tower holes than the front. Basically, whats the purpose of the higher rear shocktower and the extra shock extension that comes with it?

It depends on how the weight is distributed in the design of the car, and roll center. If the car is weighted 50/50 F/R and L/R, then it could be argued that equal length shocks and identical shock towers F/R could be used, versus one thats weighted more to the rear (and/or spread out moreso left to right) that might require the added leverage a taller rear shock tower and rear shocks further from the centerline of the chassis when compared to the front, would provide over chassis weight transfer control. This is a very general explanation tho.

Roll center and shock extension are entirely separate discussions...
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Old 07-27-2009, 02:16 AM   #8
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It's because the rear shocks are usually mounted further out on the arm, so the tower needs to be higher to allow full suspension compression.
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Old 07-27-2009, 04:22 AM   #9
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It's because the rear shocks are usually mounted further out on the arm, so the tower needs to be higher to allow full suspension compression.
Which doesn't really answer the question but it changes it to "why do manufacturers mount the shocks further out on the arm on the rear"?

But I think you're wrong anyway. The further out on the arm you have the shock, the less angular arm travel you need before the shock is fully compressed. Just imagine for an arm sweep of 10 degrees for instance how far the shock shaft will travel if attached near the suspension inboard hinge and how much if it was attached to the outer end of the suspension arm.

My personal opinion is that manufacturers allow for softer rear suspension and lower ride height on the rear which seems to be a more stable setup for TC cars. Both these require more suspension travel be accomodated hence the raised rear suspension bridge.

And I think it is indeed necessary to have more rear suspension travel allowed than front for most of it is used when entering in a corner under brakes which would probably mean rear inner tire would come off the ground if there was no serious downtravel allowed.

Of course it doesn't matter much if you're an adept of "point and shoot" driving style school.
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Old 07-27-2009, 04:48 AM   #10
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Which doesn't really answer the question but it changes it to "why do manufacturers mount the shocks further out on the arm on the rear"?

But I think you're wrong anyway. The further out on the arm you have the shock, the less angular arm travel you need before the shock is fully compressed. Just imagine for an arm sweep of 10 degrees for instance how far the shock shaft will travel if attached near the suspension inboard hinge and how much if it was attached to the outer end of the suspension arm.

My personal opinion is that manufacturers allow for softer rear suspension and lower ride height on the rear which seems to be a more stable setup for TC cars. Both these require more suspension travel be accomodated hence the raised rear suspension bridge.

And I think it is indeed necessary to have more rear suspension travel allowed than front for most of it is used when entering in a corner under brakes which would probably mean rear inner tire would come off the ground if there was no serious downtravel allowed.

Of course it doesn't matter much if you're an adept of "point and shoot" driving style school.
Well, you may think I am wrong - I KNOW you are wrong!

Starting of with the shock mounting position - why is it like this? Mostly it is just following the accepted design. You can get almost identical handling effects by using a more inboard mounting position and a stiffer spring/damper setting. There are a few mechanical reasons why the suspension works more consistently with with an outboard mounting though

Secondly, the rear of the typical touring cars is not softer - it is stiffer. Because of the outboard shock mounting, the wheel rate is a lot stiffer at the back end.

Thirdly, if the mounting point is further out on the arm, it will also will be higher up at full compression. To retain the same shock angle at full compression, the mounting point on the tower must also be higher.
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Old 07-27-2009, 05:32 AM   #11
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Originally Posted by sosidge View Post
Well, you may think I am wrong - I KNOW you are wrong!

There are a few mechanical reasons why the suspension works more consistently with with an outboard mounting though

Secondly, the rear of the typical touring cars is not softer - it is stiffer. Because of the outboard shock mounting, the wheel rate is a lot stiffer at the back end.

Thirdly, if the mounting point is further out on the arm, it will also will be higher up at full compression. To retain the same shock angle at full compression, the mounting point on the tower must also be higher.
Not sure what makes you so confident. (actually I was just trying to go easy on your ego. Your initial statement makes very little sense and it's just plain wrong).

But let's investigate what has been said.

"There are a few mechanical reasons why the suspension works more consistently with with an outboard mounting thou"

If this is not an off the cuff comment and you do indeed know any of these reasons then I am pretty sure everybody would appreciate to hear it. I think that's what the initial question was asked for. If not, then I am not sure you've supported your initial assesment of my analysis compellingly enough.

"Secondly, the rear of the typical touring cars is not softer - it is stiffer. Because of the outboard shock mounting, the wheel rate is a lot stiffer at the back end."

Secondly, that is just plain wrong. Real or scale all my cars have stiffer suspension on their front ends. If you didn't read carefully the first time, here is my initial statement:

"My personal opinion is that manufacturers allow for softer rear suspension"

Not talking about wheel rate (I don't know what that is) or anything else.

Thirdly, if the mounting point is further out on the arm, it will also will be higher up at full compression. To retain the same shock angle at full compression, the mounting point on the tower must also be higher.

So we agree after all.
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Old 07-27-2009, 05:42 AM   #12
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Quote:
Originally Posted by sosidge View Post
Well, you may think I am wrong - I KNOW you are wrong!

Starting of with the shock mounting position - why is it like this? Mostly it is just following the accepted design. You can get almost identical handling effects by using a more inboard mounting position and a stiffer spring/damper setting. There are a few mechanical reasons why the suspension works more consistently with with an outboard mounting though

Secondly, the rear of the typical touring cars is not softer - it is stiffer. Because of the outboard shock mounting, the wheel rate is a lot stiffer at the back end.

Thirdly, if the mounting point is further out on the arm, it will also will be higher up at full compression. To retain the same shock angle at full compression, the mounting point on the tower must also be higher.
For once I fully agree with sosidge.

It's actually a combination of the shocks being mounted more stood up and further out on the arm, which means that for a same vertical travel of the wheel, the piston moves a lot more at the rear than at the front. This is the reason why the rear end is stiffer in both damping and spring rate than the front.

As for the effect of standing up or laying down the shocks, well it goes like this:

With the way our TC are designed, as the suspension compresses, the damping and spring rates seen at the wheel always increase, this means it gets stiffer as it compresses.

A more stood up shock will show stiffer damping and spring rates, and at the same time these will change little as the suspension compresses, giving it a more linear feel.

A more laid down shock will show softer damping and spring rates overall, but the difference in stiffness between extended and compressed will be greater due to a greater variation of the angle of the shock in relation to the arm.

This is why front shocks are laid down more than rear shocks, and why we're generally using stiffer springs and thicker oils in the front.
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Old 07-27-2009, 05:45 AM   #13
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Originally Posted by niznai View Post
Not sure what makes you so confident. (actually I was just trying to go easy on your ego. Your initial statement makes very little sense and it's just plain wrong).

But let's investigate what has been said.

"There are a few mechanical reasons why the suspension works more consistently with with an outboard mounting thou"

If this is not an off the cuff comment and you do indeed know any of these reasons then I am pretty sure everybody would appreciate to hear it. I think that's what the initial question was asked for. If not, then I am not sure you've supported your initial assesment of my analysis compellingly enough.

"Secondly, the rear of the typical touring cars is not softer - it is stiffer. Because of the outboard shock mounting, the wheel rate is a lot stiffer at the back end."

Secondly, that is just plain wrong. Real or scale all my cars have stiffer suspension on their front ends. If you didn't read carefully the first time, here is my initial statement:

"My personal opinion is that manufacturers allow for softer rear suspension"

Not talking about wheel rate (I don't know what that is) or anything else.

Thirdly, if the mounting point is further out on the arm, it will also will be higher up at full compression. To retain the same shock angle at full compression, the mounting point on the tower must also be higher.

So we agree after all.
If you don't know what wheel rates are then I'm sorry but you should look it up before anything as it is the base of everything that relates to suspension settings.

Once you understand it everything will be clear.
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Old 07-27-2009, 05:55 AM   #14
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Rear shock towers also appear to be wider than the front too, which will have something to do with how the suspension reacts. It should make the car more stable/predictable.

A common modification for the tc3 was to use the rear shock mount on the front also, for this very reason, to make the car more drivable.

However, the original question is nothing to do with that...
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Old 07-27-2009, 06:04 AM   #15
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Originally Posted by tc3team View Post
Rear shock towers also appear to be wider than the front too, which will have something to do with how the suspension reacts. It should make the car more stable/predictable.

A common modification for the tc3 was to use the rear shock mount on the front also, for this very reason, to make the car more drivable.

However, the original question is nothing to do with that...
It's wider as a result of the pickup points in the arms and the shocks angle, nothing else.
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