Spring rule ID/OD question

[turbogrill]

Hi,

 

The rules says springs are 0pts if:
"Maintains the exact same ID/OD measurements as the OE spring (+/- 0.25”) when measured at the midpoint and at each end of the spring"

 

Does this mean that ID/OD both needs to be (+/- 0.25"). So the ID can be -0.25 and the OD can be +0.25 (or vice versa or any other combination)?

 

Let say my spring is (MD=Material Diameter):

ID: 5 inches

MD: 1 inch 
OD: 7 inches (5+1+1)

 

So I can fit any spring as long as both of these are true:
4.75 < ID < 5.25

6.75 < OD < 7.25

(Here are the Moog springs in an excel sheet if anyone is interested, https://docs.google.com/spreadsheets/d/1XLkGtwQCwXLToD-MIMerlNNfQm2GSiq8llu649uusUk/edit?usp=sharing )

 

 

 

 

 

[TimS]

I believe the diameter rule is talking about the spring itself not the wire sized of the spring. Rule is so you can’t use a 2.5” race spring in place of a barrel style OEM spring. You can have larger diameter spring wire if the spring is the same dimensions over as the OEM spring. 

[turbogrill]

1 hour ago, TimS said:

I believe the diameter rule is talking about the spring itself not the wire sized of the spring. Rule is so you can’t use a 2.5” race spring in place of a barrel style OEM spring. You can have larger diameter spring wire if the spring is the same dimensions over as the OEM spring. 

 

They mention both OD and ID. Does both of them need to be with the range?

 

Or is it good as long as OD or ID is within range. 

 

For instance I can find a thicker spring from a truck that fits within the ID requirement. But the OD would be 0.25 bigger. 

[atxe30]

Just now, turbogrill said:

 

They mention both OD and ID. Does both of them need to be with the range?

 

Or is it good as long as OD or ID is within range. 

 

For instance I can find a thicker spring from a truck that fits within the ID requirement. But the OD would be 0.25 bigger. 

have you tried Swift springs? I *think* they make some barrel springs and they def can give you spring rates you are looking for....

[turbogrill]

7 minutes ago, atxe30 said:

have you tried Swift springs? I *think* they make some barrel springs and they def can give you spring rates you are looking for....

 

They do make Miata lowering springs but they are too soft. Or you meant have them make custom springs for me?

 

[TimS]

I believe keeping the spring visually similar and close to the dimensions is what is looked at. Lots a Miata Champcars so I’m sure there is a special set of springs people use

[atxe30]

i think the whole point is to keep you from just swapping in coil-overs.... (a quaint concept in the current era.....).....

[turbogrill]

1 hour ago, atxe30 said:

i think the whole point is to keep you from just swapping in coil-overs.... (a quaint concept in the current era.....).....

 

I just don't want someone with a caliper DQ my win because my $60 Ford Bronco springs are 0.26" smaller/larger than the Miata springs

 

Edited December 27, 2021 by turbogrill

[TimS]

Quarter of an inch should pass any post race inspection 

[turbogrill]

After some thinking it has to be the ID or OD that matter. Not both.

 

If they write ID/OD that means ID or OD. I think that is how to interpret the english language, it is not ID and OD.

 

Same as him/her means him or her

 

case closed.

 

thanks 

 

[wvumtnbkr]

It is both.  It means your spring can't be larger than  .25" larger diameter than stock.  

 

It also means it can't be .25" diameter smaller than stock.

 

That's the window you need to work within.

[turbogrill]

2 hours ago, wvumtnbkr said:

It is both.  It means your spring can't be larger than  .25" larger diameter than stock.  

 

It also means it can't be .25" diameter smaller than stock.

 

That's the window you need to work within.

 

That makes the most sense, I just managed to interpret the rule slightly different.

 

 

 

thanks.

[enginerd]

On 12/27/2021 at 6:21 PM, turbogrill said:

After some thinking it has to be the ID or OD that matter. Not both.

 

If they write ID/OD that means ID or OD. I think that is how to interpret the english language, it is not ID and OD.

 

Same as him/her means him or her

 

case closed.

 

thanks 

You may be technically correct but I don’t think a situation where this distinction could matter would ever come up. It would take a reduction in wire diameter to meet one size requirement but not the other. Almost any spring which meets the ID +/- 1/4 would also meet the OD +/- 1/4

 

Edit: Actually if you went up in wire diameter you could be safe on ID and not on OD. 

Edited December 29, 2021 by enginerd