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How stiff can I go on the bilsteins?


turbogrill
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Hi,

 

On our NC Miata we have:

- Bilstein and aftermarket OEM style springs

- Thick front sway

 

Our setup has a little too much roll. An other option would be to do stock front sway and somehow figure out aftermarket non-OEM springs that are stiffer.

 

How do I know how stiff I can go before I get too much under damping? Has anyone tried stiff springs with the typical Bilstein shocks?

 

My current springs are the stiffest OEM style springs I have found

 

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If you reduce the size of your sway bar you'll need to increase the shock damping to compensate for bumps while cornering.

 

A sway bar links the suspension together side to side. This includes the shocks, so effectively increases the damping available for a singe wheel bump. Increasing the sway bar diameter adds effective spring rate to the outside wheel while cornering, somewhat the same as increasing individual spring rates but without changing the suspension frequency.

 

There will be compromises to consider when increasing effective wheel rates with springs or bars to control roll that may help you decide which path to follow. First would be to see if one method would be more likely to address your problem with your present roll stiffness.

 

You'll have to decide which way to go but I typically favour the Big Bar/Small Spring (BBSS) route for stockish cars.

 

 

 

Edited by mender
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Good question!

 

Its wearing a little to much on the edges and we can't get more camber. You also see the car rolling a little and you can feel it.

 

It does push a little but that is fine and not sure how I can fix that. Rear sway is stock.

 

Car definitely handles well, maybe not best but better than most cars. We used to have coil overs and the car handled amazing (would be EC).

One of the big difference is that the springs are way softer now.

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2 minutes ago, turbogrill said:

Good question!

 

Its wearing a little to much on the edges and we can't get more camber. You also see the car rolling a little and you can feel it.

 

It does push a little but that is fine and not sure how I can fix that. Rear sway is stock.

 

Car definitely handles well, maybe not best but better than most cars. We used to have coil overs and the car handled amazing (would be EC).

One of the big difference is that the springs are way softer now.

 

A few thoughts.  If it pushes now, a stiffer sway in the front will probably make that worse.  A stiffer sway in the back will loosen you up so maybe try that.  If some of your drivers aren't used to driving a loose car they may not like that.  No way to get more camber at all?  I am sure you have tried everything, but that seems like one place to keep looking.  But, as you asked in initial post, you may be able to go a little stiffer on springs and not overdrive the bilsteins.  Seems like there should be some pretty good info out there already on that.

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1 minute ago, Burningham said:

 

A few thoughts.  If it pushes now, a stiffer sway in the front will probably make that worse.  A stiffer sway in the back will loosen you up so maybe try that.  If some of your drivers aren't used to driving a loose car they may not like that.  No way to get more camber at all?  I am sure you have tried everything, but that seems like one place to keep looking.  But, as you asked in initial post, you may be able to go a little stiffer on springs and not overdrive the bilsteins.  Seems like there should be some pretty good info out there already on that.

 

The solution to the problem is to get coilovers, there are a million cheap and good alternatives for the NC. But that would be EC. .

 

What about stiffer sway in front and play with tire pressure to reduce the push? Or would that just make the car handle worse (but feel faster).

Also for an endurance race I am not to concerned with a little push. I have the thickest OEM sway in the rear.

 

But it feels like the car could be even faster with less roll.

 

(car is fast as it is, we have other issues that causes us to not podium every race. But it's always fun to fiddle with the car).

 

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47 minutes ago, Burningham said:

 

 A stiffer sway in the back will loosen you up so maybe try that.  If some of your drivers aren't used to driving a loose car they may not like that.  No way to get more camber at all?     But, as you asked in initial post, you may be able to go a little stiffer on springs and not overdrive the bilsteins. 

Do you have as much caster in the front as you can get? that will increase camber in turns.

If you want to increase rear bar stiffness make brackets to shorten the leverage arm of the bar.

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4 minutes ago, gundy said:

Do you have as much caster in the front as you can get? that will increase camber in turns.

If you want to increase rear bar stiffness make brackets to shorten the leverage arm of the bar.

 

 

Hmm....could I just drill into the swaybar? similar to how an adjustable swaybar is.

 

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we ran a 95 m edition that in the old speed vision series....every  race a couple of brothers from California would beat us...we heard they used 600 lbs on the corners...so we did ...they still beat us ...we heard they went to 900 lbs on the corners...so we did , they still beat us , we heard they went to 1100 lbs on the corners ,yes they still beat us .....the car never handled any worse is all I can say..

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1 minute ago, ablesnead said:

we ran a 95 m edition that in the old speed vision series....every  race a couple of brothers from California would beat us...we heard they used 600 lbs on the corners...so we did ...they still beat us ...we heard they went to 900 lbs on the corners...so we did , they still beat us , we heard they went to 1100 lbs on the corners ,yes they still beat us .....the car never handled any worse is all I can say..

 

You should have gotten to 1200 lbs...

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4 hours ago, turbogrill said:

 

 

Hmm....could I just drill into the swaybar? similar to how an adjustable swaybar is.

 

I probably shouldn't say it but motion ratio changes by the square of the difference whereas the sway bar rate due to location on the end of the bar is a straight lever.

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As I tell everybody that is willing to listen...

 

Check tire temps with a probe and that will tell you what the tires like.  It will help you set pressures and camber.

 

Once you have that, balance the car with swaybar or ride height.  Tire pressure adjustments don't work so well in endurance racing it seems.

 

We usually balance the car with ride height.  (We have adjustable spring perches).

 

If it is a macstrut front end, a bigger swaybar or stiffer spring can actually help the front by maintaining the alignment you have statically.  

 

I believe it was Colin Chapman that said "any suspension will work if you don't let it"...

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3 hours ago, mender said:

I probably shouldn't say it but motion ratio changes by the square of the difference whereas the sway bar rate due to location on the end of the bar is a straight lever.


image.png.29a95ec3fdb99dee0d56e4aea8f03189.png

 

Are you saying that when I am drilling I am making R smaller but also increasing K?

 

Trying to remember anything from high school:

 

endlink_angle = tan-1( drill_distance / endlink_height )

 

K = cos(  endlink_angle  )

R = lever_length - drill_distance

 

Seems like as long as the endlink_angle is not crazy it should be good?

 

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2 hours ago, turbogrill said:


image.png.29a95ec3fdb99dee0d56e4aea8f03189.png

 

Are you saying that when I am drilling I am making R smaller but also increasing K?

 

Trying to remember anything from high school:

 

endlink_angle = tan-1( drill_distance / endlink_height )

 

K = cos(  endlink_angle  )

R = lever_length - drill_distance

 

Seems like as long as the endlink_angle is not crazy it should be good?

 

Look at the other end of the link.

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3 hours ago, shanehutton said:

You don't need to drill the swaybar.  You just need to find a way to move the pickup point and shorten the arm.  Some do it with clamps that go around the bar so perhaps try to find something like that instead of drilling a hole.

Screen Shot 2020-03-23 at 10.07.05 AM.png

 

 

So move the pick up point from the control arm inwards? So move it where the arrow is? 

 

image.png.2e0278b9ad60cca210725bb169df5603.png

 

 

 

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22 minutes ago, shanehutton said:

No.  Move it along the axis that runs from the front to the back of the car. Along that axis, you want to make the arm shorter.

Screen Shot 2020-03-23 at 6.28.44 PM.png

 

That would involve drilling the swaybar.

Figured you could change the pickup point instead. 

 

Should have the same effect, leverage on the control arm instead of the bar 

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1 hour ago, mender said:

That would reduce the effectiveness of the sway bar.

 

Yes, but moving it the other way would work right?

 

.... might be hard from a practical perspective.

So the other option is to move the attachment point on the swaybar.

 

Right?

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2 hours ago, turbogrill said:

 

Yes, but moving it the other way would work right?

 

.... might be hard from a practical perspective.

So the other option is to move the attachment point on the swaybar.

 

Right?

Moving the attachment point toward the wheel increases the motion ratio. 

 

If the arm is 12" long and the present mount is in the middle, the motion ratio is 6/12 or 0.5^2 = 0.25. If the mount is moved 1" toward the wheel, the motion ratio is now 7/12 or 0.5833^2 = 0.34. That increase the effective stiffness of the sway bar by 0.34/0.25 or 36%. Pretty good change by moving the attachment point one inch. 

 

There will be some loss on that due to the new angle of the link but a longer link decreases that. 

 

P.S. The effective attachment point is the centre of the lower heim joint in your picture. Reversing the joint so that the stud is facing inward and using a longer link would give you a noticable change in roll stiffness.

 

You're welcome. :)

Edited by mender
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