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Replacing Dampers With Coilovers...?

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Kane

Did you have any success with this Ash?

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petert

Parry has mastered this. He runs 23mm TB's plus 650lb springs. You'd have to ask him how it's mounted however.

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welshpug

23's are pretty bloody stiff as they are! circa 220 lb wheel rate.

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petert

He's got 500+ lb total wheel rate. So have I now.

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Rippthrough

Is the formula just 3-1 then?

So a 600lb spring is 200lb at the wheel?

No, it's worse, those saying 100lb/inch=300lb/inch aren't doing their suspension calcs correctly - if the bottom mount moves 1/3rd of the wheel travel then not only do you have only 1/3rd of the distance (remember a spring is rated for force/distance), you also only have 1/3rd of the leverage (the force bit).

 

So a 900lb/inch spring at the shock becomes a 100lb/inch wheel rate.

This is why when I was developing the Fox rear dampers I only ever sold them as torsion bar assisters, never replacements.

 

I don't think it's quite as bad as 3:1 though, I'll have to check but IIRC it's nearer 2.5 or so but varies a fair amount through the travel.

Edited by Rippthrough

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A1AXX

Another Resurrection!

 

I just ordered Avos today.

 

I am running 19mm TBs (110lb/in) 

 

I ordered 12" Avos, 600lb springs and dampers revalved to suit & spherical ends.

 

To add to this, the reason I have done this is because of the availability of proper heat treated 24mm tbs! At lease a 600lb spring is a 600lb spring!

 

 

 

Edited by A1AXX

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A1AXX
On 2/13/2016 at 12:39 PM, Rippthrough said:

No, it's worse, those saying 100lb/inch=300lb/inch aren't doing their suspension calcs correctly - if the bottom mount moves 1/3rd of the wheel travel then not only do you have only 1/3rd of the distance (remember a spring is rated for force/distance), you also only have 1/3rd of the leverage (the force bit).

 

So a 900lb/inch spring at the shock becomes a 100lb/inch wheel rate.

This is why when I was developing the Fox rear dampers I only ever sold them as torsion bar assisters, never replacements.

 

I don't think it's quite as bad as 3:1 though, I'll have to check but IIRC it's nearer 2.5 or so but varies a fair amount through the travel.

Trying to make sense of this..

 

Regards the 205, if wheel moves 3" and the damper moves 1", The ratio is 3:1 right?

How does a 900lb spring become 100lb at the wheel?! 

Did you mean this as an example? IS the rate actually 2.5:1 then?

 

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wicked

Interesting topic; do you have any clue on the damping rate of those Avo's?

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welshpug

unless you are limited by regulations I would go straight for an upright 1-1 damper, far simpler to get right.

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A1AXX
On 04/12/2017 at 2:25 PM, wicked said:

Interesting topic; do you have any clue on the damping rate of those Avo's?

I realised a few minutes ago what I’m missing!

 

The torsion bar itself still needs to be damped!

 

It is going to add about 300 lb to the 600lb Spring at the high damper.

 

I have just emailed avo to correct the valving!

 

 

Edited by A1AXX

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A1AXX
On 04/12/2017 at 2:53 PM, welshpug said:

unless you are limited by regulations I would go straight for an upright 1-1 damper, far simpler to get right.

Yea I want to keep it standard in case of regs, can modify after if necessary and they will be easily sold if I can prove it works!

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A1AXX

Avo has already damped to suit! 

 

Nigel knows what I’m trying to achieve so valved accordingly 

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petert

As I said earlier, 650lb coil overs works very well with 23mm torsion bars. We changed the upper mount, in order to improve the spring position. Attached is the file I sent to the plasma cutter. Hopefully you'll get the idea. Here is a link to a recent race where you can see for yourself how successful it is. I wouldn't have turreted my car if I new it was going to be that good.

 

 

 

 

Screen Shot 2017-12-07 at 2.45.43 PM.png

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wicked

Nice solution Peter! Will that work with standard length dampers? (bilsteins)

 

Edited by wicked

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A1AXX
20 hours ago, petert said:

As I said earlier, 650lb coil overs works very well with 23mm torsion bars. We changed the upper mount, in order to improve the spring position. Attached is the file I sent to the plasma cutter. Hopefully you'll get the idea. Here is a link to a recent race where you can see for yourself how successful it is. I wouldn't have turreted my car if I new it was going to be that good.

 

 

 

 

Screen Shot 2017-12-07 at 2.45.43 PM.png

Epic idea that on the brackets.

 

from the pic it looks like it locates into the original damper hole, and also the rear beam mount for support, so no need to risk to the tin plates! And also the damper sits more horizontal.

 

Good work, I will have to do the same, I didn’t think of it at all.

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petert
On 12/7/2017 at 7:14 PM, wicked said:

Nice solution Peter! Will that work with standard length dampers? (bilsteins)

 

Credit should go to Adrian Wuillemin. His idea, I just made it happen. I guess the CC distance would be approx. 15mm longer?

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petert

Here you go.

coil over mount.jpeg

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Rippthrough
On 04/12/2017 at 12:54 PM, A1AXX said:

Trying to make sense of this..

 

Regards the 205, if wheel moves 3" and the damper moves 1", The ratio is 3:1 right?

How does a 900lb spring become 100lb at the wheel?! 

Did you mean this as an example? IS the rate actually 2.5:1 then?

 


Okay, lets go with your numbers.
You move the wheel 3 inches, your mount moves the 900lb/inch spring by 1 inch - from the 3:1 ratio
 So, that's 900lb of load on the mount, which, because it's 3:1 and you're dealing with leverage, is 300lb of load at the wheel.
 But the wheel has moved 3 inches.
So it's 100lb/inch at the wheel.

 Which is why those running huge rear spring rates with the bars disabled - and then advising everyone it's fine to run big springs + bars, or massive bars - are wrong, because their wheel rate is far lower than they realise, and they're telling other people to use rates 2-3x higher than what they're actually using.

Using Peterts' numbers above just as a quick working example with some quick 'beer mat' approximations - 650lb/inch springs on 23mm bars, with a ~2.5 ratio, the spring is only adding approximately 50% to the spring rate that the 23mm bar is already providing.
 So it's pretty much the same rate as switching from the 23mm bars to 24.5mm bars.
 Not even close to the 500lb/inch+ wheel rate mentioned earlier.

As a more hilarious example, if you take out the torsion bars completely, and just run on a spring in the rear damper position, you'd need well over1000lb/inch springs just to match the 23's.

Edited by Rippthrough

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