Trailing arm vs semi trailing arm

[LockedupXJ]

Well i did a search and a google search and i cant seem to figure out what a semi trailing arm is? I know what a trailing arm is but i cant figure out what a semi trailng arm is, That said which is better?

[bdkw1]

Hear comes the debate agian......

Trailing arm has the pivots at 90* to the wheel and has no camber gain in travel.

Semi-trailing arm has the pivots angled slightly to produce camber gain on uptravel.

[yoshi]

Originally Posted by bdkw1

Hear comes the debate agian......

Trailing arm has the pivots at 90* to the wheel and has no camber gain in travel.

Semi-trailing arm has the pivots angled slightly to produce camber gain on up travel.

he meant no camber gain...

[masterfabr]

Most builder/suspension designers prefer semitrailing arms due to the advantages of the camber gain to handling.

[Engineer]

Is it really for the camber gain/loss, to improve handling, or is it to reduce the amount of plung on the axle when you have longer travel? I always assumed it was to take care of the plunge issue. Can a straight trailing arm, and 18" of travel work with a 930 CV without plung issues?

Thanks

[bdkw1]

Plunge will be the same for both styles given the same arm/axle lengths.

[masterfabr]

Originally Posted by Engineer

Is it really for the camber gain/loss, to improve handling, or is it to reduce the amount of plung on the axle when you have longer travel? I always assumed it was to take care of the plunge issue. Can a straight trailing arm, and 18" of travel work with a 930 CV without plung issues?

Thanks

Most agree camber gain improves handling.

[jumpin jellybean]

man thanks for more info I really need to get cracking on reading all about the differnt things to build front ends and such keep up the good info guys need to go get asprin now my head hurts

[rowycoracing]

Originally Posted by Engineer

Is it really for the camber gain/loss, to improve handling, or is it to reduce the amount of plung on the axle when you have longer travel? I always assumed it was to take care of the plunge issue. Can a straight trailing arm, and 18" of travel work with a 930 CV without plung issues?

Thanks

Like BK said plunge is equal but with camber change you do get a small benefit on the outer CV because it doesn't have to flex quite as severely at full bump. That doesn't give you more overall travel for a given type of CV and suspension lay out because the inner CV is still limiting but it may reduce wear on the outers a bit.

[Engineer]

Originally Posted by bdkw1

Plunge will be the same for both styles given the same arm/axle lengths.

Sorry, but plunge will not be the same. If you are looking at the rear of the car, with a trailing arm, the wheel goes straight up and down. The higher and lower the wheel goes the farther it gets from the tranny CV. With a Semi trailing arm, the wheel moves in an arc. This is why the camber change occurs. But when the suspension goes to full bump and the most camber is present, the wheel didn't go straight up and twist, it followed the arc. The wheel moves towards the center of the car as it goes above and below centerline. This is going to reduce the amount of plunge on the semi-trailing design. Because the wheel moves in and out, you inevitably also get toe change with the semi-trailing arm.

Another factor that affects the amount of plunge is the location of the wheel cv behind the tranny cv if your looking at the side of the car. If at full droop, the wheel cv is directly below the tranny cv, and after following its arc upward (around the trailing arm pivot), the wheel cv is behind the tranny cv, this will help reduce the amount of plunge. This affect will be present on both trailing and semi-trailing arms. I assume this is why when people make long travel trailing arms they make them longer and wider.

I am not saying that you might not end up with the same amount of plunge from the two different designs, just that if everything else stays the same (arm/axle length) then I don't believe plunge will remain the same.