Single vs double shear birdcages

[HOG HUNTER]

I am going to be purchasing new birdcages soon. What is everyone's opinion on single vs double shear birdcages?

[cjsracing]

I have double shear now, but I won't lie my favorite birdcages that I have used were the simple BSB #4150's. I am considering going back to them.

[keeks]

I think double shear gives a more even load on the bearings.

[TheJet-09]

^^^ I agree. I used the PPM model this year and liked them. I also like that it's a little easier to move the birdcage end of the link, for indexing purposes, because much like the end connecting to the frame, you're just removing a half inch bolt and sliding the end/spacers up or down inside the birdcage ears. It at least seems easier than threading a 5/8" bolt all the way out, then reattaching.

[Matt49]

If you didn't have a j-bar and had some sort of 0 shaped bar that wrapped around the drive shaft, would the loads on those bearings at each end of the j-bar be any different? The answer is no. Adding a second shear point to the bolt at the end of your radius rod doesn't change how the load is applied to the bearings on the axle unless that single shear bolt is physically yielding (some might argue that it is). Force is a vector and will be felt at the axle in line with said vector, not in line with the material carrying the load.
I'm not saying that a double-shear design isn't better but this stuff about loading the bearings more evenly is a little over blown I think.

[Lizardracing]

With that above.....Smaller/shorter single bolt is less weight than long bolt/spacer.

[HOG HUNTER]

Thanks for all the input! What about the shock mounts, swivel or non-swivel?

[Matt49]

Get the swivel mounts. You really need them on both LR shocks. You can get by without it on the RR but might was well keep it consistent.

[zeroracing]

Matt, one manufacture of race parts is actually advertising on facebook that their O shaped pan hard bar does in fact cause more even loading... I actually think the guy makes nice looking stuff but find it concerning that people believe it changes the loading on the car.

The double shear vs. single could change loading on the cage bearings itself. The moment arm from the barrel to the bolt, in a single shear this is going to cause all of the load to go down a single arm, the single side and into the cage itself. In a double it would travel down each leg. That said I am not sure you would ever see or feel any difference, it is just the vertical loads on the way down.

The double shear offers a much higher bolt strength than the single, Grade 8 1/2" bolt in single shear is about 17,670 and in double is 35,340. But you would probably break the link and heim long before either bolt.

What I like about the double shear is less likely to bend when the car binds up, the single shears i have had fold over or start to twist over time, double shear would be less likely since you are not cantilevered out on the bolt. The single shear causes an eccentric load on the cage which really can torque it back and forth, causing a failure (rare but done it), the double shear removes this cantilever action. This is from the bolt to cage frame to barrel, not in what the car feels overall at the tire. Also a double like Wehrs you don't have to take the bolt all the way out, just loosen and slide up or down.

Matt is dead on you better have swivel mounts or your waiting for failure.

Final note is weight, on our LR i want as heavy as I can get, RR not as much.

[Matt49]

I should have prefaced my loading statement with the assumption that the lateral mounting location of the radius rod was not moving with respect to the bearing location. That is likely not the case in some of the double shear designs which WILL help with load distribution if they get the lateral mounting location close to the "middle" of the bearing contact points with the axle. I think we're saying the same thing. Any fulcrum affect that is put on the ear of a single shear setup due to the bolt length is load being placed on the bearing that doesn't have an ear attached to it.
It's interesting that this topic has come up because I have a birdcage design that I'm pretty fond of but I don't have means of production. I'm buying an entry level CNC milling machine over the winter to make it a reality along with dozens of other things I'd like to make but just can't do on my manual milling machine.

[grt74]

Matt, one manufacture of race parts is actually advertising on facebook that their O shaped pan hard bar does in fact cause more even loading... I actually think the guy makes nice looking stuff but find it concerning that people believe it changes the loading on the car.

The double shear vs. single could change loading on the cage bearings itself. The moment arm from the barrel to the bolt, in a single shear this is going to cause all of the load to go down a single arm, the single side and into the cage itself. In a double it would travel down each leg. That said I am not sure you would ever see or feel any difference, it is just the vertical loads on the way down.

The double shear offers a much higher bolt strength than the single, Grade 8 1/2" bolt in single shear is about 17,670 and in double is 35,340. But you would probably break the link and heim long before either bolt.

What I like about the double shear is less likely to bend when the car binds up, the single shears i have had fold over or start to twist over time, double shear would be less likely since you are not cantilevered out on the bolt. The single shear causes an eccentric load on the cage which really can torque it back and forth, causing a failure (rare but done it), the double shear removes this cantilever action. This is from the bolt to cage frame to barrel, not in what the car feels overall at the tire. Also a double like Wehrs you don't have to take the bolt all the way out, just loosen and slide up or down.

Matt is dead on you better have swivel mounts or your waiting for failure.

Final note is weight, on our LR i want as heavy as I can get, RR not as much.

this was tested in an asphalt car, the pan hard bar or j bar will indeed flex a little while racing the car or under load,now whether its enough to justify or not is the key, the o style will not flex if built correctly, now evening the load on a rear end is all about where it is mounted on the rear end, left to right
off subject, but i thought i would let you guys know why they built them
as far as the birdcages im on the fence, as long as there the wide ones (bearings are spaced out wide) its hard to see the difference, but with the double shear cages you can move the rods from the right or left depending on how you want your 4 bar alignment alot easier

[keeks]

"The double shear vs. single could change loading on the cage bearings itself. The moment arm from the barrel to the bolt, in a single shear this is going to cause all of the load to go down a single arm, the single side and into the cage itself. In a double it would travel down each leg. That said I am not sure you would ever see or feel any difference, it is just the vertical loads on the way down."

Thanks Zero. I was going to reply similarly. Great info Matt.