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-   -   Spring rate on solid axle (http://www.clubcobra.com/forums/all-cobra-talk/148155-spring-rate-solid-axle.html)

teewhite 11-20-2025 01:07 PM
Spring rate on solid axle
 
Hey guys, could anyone offer some clarity on what spring rate I would need.
I've tried to figure this up myself using qa1s site but the rate I get is much less than what I see other people talking about or using.

rear end total: 1050lbs
Unsprung weight: 200lbs (assumed)
Leaves 850lbs (425lbs corner weight)

I'll be using 14" springs, at 30% compression that's 4.2"
425lbs / 4.2 =101lbs spring rate
The coilovers at 30deg. Actual spring value is .87
101lbs / .87 =116lb spring rate

So I'm coming up with 116lb spring rate but I see so many guys on here going with 250 or even 300lb springs on their solid axles, can anyone show me where I'm going wrong with this?

Tom Wells 11-20-2025 02:47 PM
Tee,

Nothing obvious.

Here's my question: is the all-in weight of the rear really 1050 pounds?

Most lightweight (i.e. thin fiberglass, small block etc) Cobra kits come in around 2250-2500 pounds and usually have a rearward weight bias of 52-55%

Also recall your calculation needs to include you, a mostly full tank of gas, all fluids etc.

Springs for race-oriented cars are usually a bit stiffer than for a mostly street cruiser.

Tom

teewhite 11-20-2025 04:42 PM
Quote:
Originally Posted by Tom Wells (Post 1527538)
Tee,

Nothing obvious.

Here's my question: is the all-in weight of the rear really 1050 pounds?

Most lightweight (i.e. thin fiberglass, small block etc) Cobra kits come in around 2250-2500 pounds and usually have a rearward weight bias of 52-55%

Also recall your calculation needs to include you, a mostly full tank of gas, all fluids etc.

Springs for race-oriented cars are usually a bit stiffer than for a mostly street cruiser.


Tom

Thanks Tom, that's the rear weight figured at a 55% bias and my weight added.

teewhite 11-20-2025 04:45 PM
I'll add that the unsprung weight is just an assumption, I don't know exactly what the axle weighs, but it's pretty minimal and qa1 recommended using 200-300lbs

Tom Wells 11-20-2025 05:48 PM
Tee,

Wow! 1050 + 45/55 x 1050 = 1050 + 859 = 1909 lbs with driver and all fluids.

That's maybe what an aluminum 289 would weigh.

Or perhaps it isn't a Cobra?

Tom

teewhite 11-20-2025 08:22 PM
Quote:
Originally Posted by Tom Wells (Post 1527541)
Tee,

Wow! 1050 + 45/55 x 1050 = 1050 + 859 = 1909 lbs with driver and all fluids.

That's maybe what an aluminum 289 would weigh.

Or perhaps it isn't a Cobra?

Tom
Wow Sorry My mistake actually, it was a lawn mower this whole time, thanks bud

Tom Wells 11-21-2025 05:39 AM
Tee,

That's OK.

Grab something from Best Stop and be happy!

Tom


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