flex?

[usmcruiser]

Why is it that a SOA 40 will flex so much better than a SUA?

There is the same ammount of weight on the spings, it is not like the springs automaticly strech when you put the axel under it.

This has been in the back of my brain for a while and I can't figure it out.


*edit*

Is it because there is possibly more up travel so it allows the opposite side to drop more?

 

[65swb45]

Try a thread search on 'sprung' weight vs unsprung weight.

 

[usmcruiser]

okay thanks.

 

[bustanutley]

Basically it comes down to leverage against the spring and the arc the spring has to travel in side to side of the vehicle. SUA the spring has to bend side ways quite a bit, this binds the spring. When the spring is on top of the axle this effect is minimized leaving the spring to work closer to an idealized situation of traveling strictly up and down. If you do a geometry analysis on the two situations you will find that the axle will actually have more leverage against the spring in a SOA setup based on angles. Another consideration is that the u bolts now work to de-arch the spring rather that to keep its arch.

 

[Mace]

Basically it comes down to leverage against the spring and the arc the spring has to travel in side to side of the vehicle. SUA the spring has to bend side ways quite a bit, this binds the spring. When the spring is on top of the axle this effect is minimized leaving the spring to work closer to an idealized situation of traveling strictly up and down. If you do a geometry analysis on the two situations you will find that the axle will actually have more leverage against the spring in a SOA setup based on angles. Another consideration is that the u bolts now work to de-arch the spring rather that to keep its arch.

Huh???

under droop you are working to "arch" the spring no matter where the axle resides..
You have the same effective contact patch (the U bolt plates) if you are SO vs SU..


If you think about where the axle is mounted in relation to the springs you have your answer. When you place the axle under the leafs you will have 5 or so " of lift.
The amount of Droop remains the same as if you had the stock springs SUA. But that 5" makes a big difference at the tire. Now, if you get a set of 5" SUA lift springs you can have reasonable droop but honestly, for a given length spring to achieve a 5" lift you have to lose a bit of down trevel. the springs can only arch a certain amount. With a mounting point above the axle you will have more droop because the spring is at an almost flat orientation at rest. Vs the lift spring being very arched..

Make sense?

 

[Cryptic]

I agree with Mace. The axle is still unsprung regardless of whether above or below the spring. There is a small increase in leverage by soa axle position. Mostly the advantage is room for uptravel on a comparably soft flat spring. For a lift spring to keep its arch under the truck it has to be stiffer. Droop/max arch will be similar for the same length of spring.

 

[tobydog]

Most of the flex is due to limber stock springs being able to be used.

 

[usmcruiser]

That is why I am using old 60 and 55 spings.

 

[DocB]

I wonder why toyota didn't produce these trucks with SOA in the first place? The mini trucks are SOA. On a rig designed for what the 40 is designed for, SOA just makes more sense to me.