'84 Bronco II
El Chingón
I know, leaf springs are for poors
Now that I've got that out of the way, how about some discussion on what makes for a good "go-fast" leaf spring suspension? The discussion doesn't need to pertain necessarily to my unique situation, but I need to figure out what I am going to do for my rig.
I am building an early Bronco for the Ultra4 4600 stock class with the primary intention of racing King of the Hammers and am required to keep leaf springs in the rear. I am planning on running the longest shocks that are allowed; 14" of travel set up for a roughly even 7" up and down. I can do whatever I want with the leaf setup, but the axle location can only move up to 3" (I am planning on going 2" back with it), and the leaf spring must be capable of supporting the weight and locating the axle on their own (no 4-links with double shackle leaves, transverse setups, or anything crazy ).
Shackle and Spring Mounting Configuration
The Bronco uses a factory tension shackle setup which I want to stay with since it helps keep arch in the springs with a spring over setup at maximum compression, and is more "stable" than a compression setup. I know a lot of desert guys go spring under to combat axle wrap and help keep arch in the spring at full bump, but I think I will be fine with the tension shackle arrangement and a traction bar unless someone can convince me otherwise. Obviously clearance is at a premium racing the Hammers on 35" tires, so I am pretty opposed to going spring under.
Spring Length and Center Pin Offset
The factory Bronco springs are 48" long with a centered pin, and I don't think 48" long springs are going to last very long with 14" of travel. I want to run longer springs since with additional length the springs will see less stress for a given displacement (better fatigue life). Longer springs will be more prone to axle hop, but that's where the traction bar comes in. It looks like I can move the shackle hanger ~7" back on the frame, which along with moving the axle back ~2" would give me ~29" from the centering pin to the rear eye. I think I am probably going to have to get custom springs made because I am not aware of any good off-the-shelf options that are fairly long with 29" on the long side between the centering pin and the spring eye.
With the forward spring mount in the stock location, that would make for 53" long leaves which still seems on the short side, but I can move that mount as well and I don't have any major limitations on where I can put it. If I move the front mount forward enough to have a centered pin, that would give me 58" long leaves. I've heard that you shouldn't run the long end of a leaf forward because it will give you really bad axle wrap, but does it matter if you have a traction bar? Are there any other undesirable side effects that would arise from having the centering pin offset to the rear (long side forward)? That would allow me to run even longer springs, which may be unnecessary if shorter spring would suffice, but perhaps there is an off-the-shelf option I could run backwards if it would be non-issue. Is there a rule of thumb for spring length relative to travel for reasonable durability?
Leaf Spring and Shackle Geometry
I noticed people tend to use fairly aggressive shackle angles (~45º±) on crawlers with fairly flat springs to get a lot of droop, but what kind of shackle angles are ideal for going fast with a good amount of up-travel? How about for tension shackles? It seems in a tension arrangement, the shackle angle is a lot less critical than a compression setup since inversion isn't really an issue. How about shackle length? I know more travel requires longer shackles, but what is the relation between travel and shackle length? of course spring arch will have a large affect on this relation since more heavily arched springs will grow more under compression. Long shackles will create issues in a compression configuration (more lateral axle movement); although this seems like less of a problem in a tension arrangement, but still an issue.
I've noticed most factory setups place the forward spring eye significantly lower than the rear eye; even in compression shackle arrangements. What effect does this have on suspension behavior? Is this something I might want to change if I move my forward spring mount?
Leaf Spring Construction
It seems leaf packs using lots of thinner leaves rather than fewer thicker leaves are preferred for performance/custom applications. The claim is that they ride smoother/better, but from what I've read at the expense of more weight for a given load capacity. Is that true generally speaking? If so, is the weight difference significant or even worth caring about? Regardless, it seems there is a practical limit to the number of leaves you would want in a given pack.
Military wraps are obviously a good idea as a safety in the event of a main spring failure, but I've noticed many performance springs only have a military wrap on the forward spring eye like these Deaver Ranger Race packs:
Is there a reason not to wrap both ends? Does the shackle end just see a lot less stress?
It seems like wider leaves would increase the roll stiffness and thinner leaves would promote roll. The original Bronco springs are 2.25" wide, is there an argument to go wider or narrower? I know 2.5" seems pretty common, and 3" seems to be used almost exclusively in heavier trucks.
Reverse eyes will allow for more arch at a given compression height, but are they weaker? It appears most Deaver packs have a normal eye forward and a mid eye at the shackle end. Any pros/cons for different eye configurations other than the amount of arch they create for a given spring height? How much arch should I be shooting for, and can you have too much? I know for longevity you don't want your spring arch inverting during travel, and ideally you should still have some arch even at maximum compression.
I've asked a lot of different questions and touched on several topics, so I don't expect someone to answer everything at once, but hopefully it got the ball rolling and will lead to some interesting discussion. My goal for this thread is to be helpful for anyone designing a leaf sprung suspension, although I am primarily focused on rear suspension for the purposes of this thread. I am hoping if nothing else to become a bit more educated on what I might want/need before calling up spring companies and figure out what I need to do for my build
Now that I've got that out of the way, how about some discussion on what makes for a good "go-fast" leaf spring suspension? The discussion doesn't need to pertain necessarily to my unique situation, but I need to figure out what I am going to do for my rig.
I am building an early Bronco for the Ultra4 4600 stock class with the primary intention of racing King of the Hammers and am required to keep leaf springs in the rear. I am planning on running the longest shocks that are allowed; 14" of travel set up for a roughly even 7" up and down. I can do whatever I want with the leaf setup, but the axle location can only move up to 3" (I am planning on going 2" back with it), and the leaf spring must be capable of supporting the weight and locating the axle on their own (no 4-links with double shackle leaves, transverse setups, or anything crazy ).
Shackle and Spring Mounting Configuration
The Bronco uses a factory tension shackle setup which I want to stay with since it helps keep arch in the springs with a spring over setup at maximum compression, and is more "stable" than a compression setup. I know a lot of desert guys go spring under to combat axle wrap and help keep arch in the spring at full bump, but I think I will be fine with the tension shackle arrangement and a traction bar unless someone can convince me otherwise. Obviously clearance is at a premium racing the Hammers on 35" tires, so I am pretty opposed to going spring under.
Spring Length and Center Pin Offset
The factory Bronco springs are 48" long with a centered pin, and I don't think 48" long springs are going to last very long with 14" of travel. I want to run longer springs since with additional length the springs will see less stress for a given displacement (better fatigue life). Longer springs will be more prone to axle hop, but that's where the traction bar comes in. It looks like I can move the shackle hanger ~7" back on the frame, which along with moving the axle back ~2" would give me ~29" from the centering pin to the rear eye. I think I am probably going to have to get custom springs made because I am not aware of any good off-the-shelf options that are fairly long with 29" on the long side between the centering pin and the spring eye.
With the forward spring mount in the stock location, that would make for 53" long leaves which still seems on the short side, but I can move that mount as well and I don't have any major limitations on where I can put it. If I move the front mount forward enough to have a centered pin, that would give me 58" long leaves. I've heard that you shouldn't run the long end of a leaf forward because it will give you really bad axle wrap, but does it matter if you have a traction bar? Are there any other undesirable side effects that would arise from having the centering pin offset to the rear (long side forward)? That would allow me to run even longer springs, which may be unnecessary if shorter spring would suffice, but perhaps there is an off-the-shelf option I could run backwards if it would be non-issue. Is there a rule of thumb for spring length relative to travel for reasonable durability?
Leaf Spring and Shackle Geometry
I noticed people tend to use fairly aggressive shackle angles (~45º±) on crawlers with fairly flat springs to get a lot of droop, but what kind of shackle angles are ideal for going fast with a good amount of up-travel? How about for tension shackles? It seems in a tension arrangement, the shackle angle is a lot less critical than a compression setup since inversion isn't really an issue. How about shackle length? I know more travel requires longer shackles, but what is the relation between travel and shackle length? of course spring arch will have a large affect on this relation since more heavily arched springs will grow more under compression. Long shackles will create issues in a compression configuration (more lateral axle movement); although this seems like less of a problem in a tension arrangement, but still an issue.
I've noticed most factory setups place the forward spring eye significantly lower than the rear eye; even in compression shackle arrangements. What effect does this have on suspension behavior? Is this something I might want to change if I move my forward spring mount?
Leaf Spring Construction
It seems leaf packs using lots of thinner leaves rather than fewer thicker leaves are preferred for performance/custom applications. The claim is that they ride smoother/better, but from what I've read at the expense of more weight for a given load capacity. Is that true generally speaking? If so, is the weight difference significant or even worth caring about? Regardless, it seems there is a practical limit to the number of leaves you would want in a given pack.
Military wraps are obviously a good idea as a safety in the event of a main spring failure, but I've noticed many performance springs only have a military wrap on the forward spring eye like these Deaver Ranger Race packs:
Is there a reason not to wrap both ends? Does the shackle end just see a lot less stress?
It seems like wider leaves would increase the roll stiffness and thinner leaves would promote roll. The original Bronco springs are 2.25" wide, is there an argument to go wider or narrower? I know 2.5" seems pretty common, and 3" seems to be used almost exclusively in heavier trucks.
Reverse eyes will allow for more arch at a given compression height, but are they weaker? It appears most Deaver packs have a normal eye forward and a mid eye at the shackle end. Any pros/cons for different eye configurations other than the amount of arch they create for a given spring height? How much arch should I be shooting for, and can you have too much? I know for longevity you don't want your spring arch inverting during travel, and ideally you should still have some arch even at maximum compression.
I've asked a lot of different questions and touched on several topics, so I don't expect someone to answer everything at once, but hopefully it got the ball rolling and will lead to some interesting discussion. My goal for this thread is to be helpful for anyone designing a leaf sprung suspension, although I am primarily focused on rear suspension for the purposes of this thread. I am hoping if nothing else to become a bit more educated on what I might want/need before calling up spring companies and figure out what I need to do for my build