whats wrong with hair pins?

i got a pm about hairpins being unsafe.

whats the buzz about them?

thanks

 

Briefly... there is an old argument that says you should never use hairpins with a tube axle, that hairpins should only be used with a forged axle. However, the other side of the argument is that in the end, it really doesn't matter.

It has been pretty well covered on the HAMB here:
http://www.jalopyjournal.com/forum/showthread.php?t=280835

 

I don't think they are all unsafe but I have seen some that were unsafe,,too long,too thin a material and poorly designed attachment to the frame.

HRP

 

hairpins with the frame end gusseted are safe , if mounted correctly . the ones with no gusset , IMHO will flex & not safe .. steve

 

well if i were looking for a hair pin setup. what would be the minumin tube o.d., rod/ clevis end and length?

i have a i beam axle

 

I think you've got it a little backwards there... Tube axles are generally thought to only be used WITH hairpins because they have a little give to them. Some folks say that split wishbones are a bad choice for tube axles because they lack the flexibility that the hairpins have. A forged ibeam axle will twist and flex slightly so split bones work well with them.

There's nothing unsafe about hairpins. Unless they're installed improperly.

 

Yep, the good ones are fine,just don't ever use them with a tube axle.Either the axle or the hairpins must flex,and it should be the axle.I-beams twist and tube axles won't.

 

Tube axles should only be used with a 4-bar set-up,because the caster does not change as the suspension travels.You do NOT want your hairpins to be bending all the time,especially chrome hairpins.Since you are using an I-beam,you can use any of the above,or wishbones.

 

When I was first looking at split bones vs hairpins I talked at long lenght with Pete&Jake.
If you actually take a look at a tube axle and its design you see that it will not bend or flex very well at all.............but an I beam, either cast or forged will bend and twist. When using hairpins the axle can not remain ridgid or the hairpin will transfer all of the energy to the attachment point......................which will bend and twist as the hairpins travel in their arc..........................this will crack the frame/attachment point or bend the arms of the hairpins. With that said I have seen split bones/hairpins used with both round tube and I beam axles although I have seen more 4 bar setups with round tube than anything else.
Also while talking about hairpins, I would put a gusset between the bars of a hairpin as have seen to accidents where panic stops have caused the hairpins to bend causing the axle to fold under the frontend of the car...................IMHO