DESIGNING MY OWN CROSSBAR! need help

[xxae07xx]

so ive been wanting to do this for a while just havent had the time but i want to make my own crossbar just bc i dont wanna pay 400 for it. i was going to use the top rear seatbelt bolt holes just like the miracle bar but then instead of the lower seatbelt holes, i was gonna cross over down to the top of the struts...and then maybe tie the two struts together....since everyones always going on about how useless the nitto bar without triangulation is...any input and design help would be helpful. thanks

[ozmdd]

Are you trying to create a harness bar, or are you trying to stiffen the chassis, or both? Do the existing x-braces use the upper seat-belt mounts?

[xxae07xx]

stiffness and yes they do. i thot u had one of those

[lilredrocket]

So might argue that even with tying in to the rear shock tower is useless because the shocks are mounted in rubber. But hey I'm all for you trying this out. Custom FTW!!!!

[Cosmonaut]

so it this an actual design process or copying other designs?
im would assume that the reason they are priced as such would be to cover engineering cost and R&D.
if it is a custom design what areas of the structure are you looking to brace?
oh and when done right, Custom FTW!

[xxae07xx]

im not sure what you mean. i have been sitting around drawing, measuring and brainstorming for a while if thats what you mean by design process and i was looking at miracles when i saw that most go from top rear to strut towers. so the idea is based on existing bars, just bars that arent for our cars

[lilredrocket]

we don't have struts in the rear they are shock towers that is why the crossbar for our cars is different than the other ones on the market

[blacksandiegovitz]

Originally Posted by xxae07xx

im not sure what you mean. i have been sitting around drawing, measuring and brainstorming for a while if thats what you mean by design process and i was looking at miracles when i saw that most go from top rear to strut towers. so the idea is based on existing bars, just bars that arent for our cars

No it does not bolt anywhere nere the strut towers. The top bolts to the seat belt holes and the bottom bolts into the holes that the backseat bolts into. It also has a floor bar that ties the lower all together. I also added a megan c-pillar bar to the top for looks . Pic of my ride for reference

[ozmdd]

Originally Posted by xxae07xx

im not sure what you mean. i have been sitting around drawing, measuring and brainstorming for a while if thats what you mean by design process and i was looking at miracles when i saw that most go from top rear to strut towers. so the idea is based on existing bars, just bars that arent for our cars

I think you're mixing two different bracing points that aren't going to work together. The shock towers are probably not going to work with the x-brace, but who knows. This is the reason they spend a bunch of money on CAD-CAM modeling to identify what will happen when you re-direct stress and forces within the chassis. You might be able to cross from opposite-side seatbelt upper mounts to the shock tower, but you might end-up flexing your body in undesireable ways.

In general, if it hasn't been done before, you probably need some engineering knowledge or be willing to guinea-pig your car.
Can you post a picture of the design you're wanting to emulate? That will help a lot in determining if it is compatible with our suspension/body design.

[cali yaris]

One of the benefits of the cross brace as it is is vertical suppression. Your suspension does more work with the cross brace installed. If it were at an angle (going to the rear shock towers), this effect would be reduced or nullified.

The other benefit is twist flex of the upper body, side to side. I don't know how this would be affected by angling the cross brace, but I'm pretty sure this would be reduced as well.

At any rate, you won't get any benefit by actually tying it to the top of the shock; as previously posted, that is mounted on rubber. You'd have to find a way to mount it to the tower around the shock.

Check out Rob323's (something like that) full cage on his rally car for ideas on how and where to mount it.

[tk-421]

Good luck with the design! Just in case you're still not 100% set on a crossbar format, you might be interested in something like this instead:
http://www.yarisworld.com/forums/sho...6&postcount=13

And if you end up going for it, make two and I'll buy one from you!

[Sabretooth]

If you can make it less than $400 and works better than what we already have, make 3...lol

[Sabretooth]

Well all the guys who built cages so far, havnt actually mounted them on the rear shock tower, they are mearly welding to the unibody before the shock tower, this is the case for Rob323's Rally car and the China Touring Championship Yarises that were made.

So I think your in for a bit of trial and error finding how to mount onto the shock tower.

[xxae07xx]

http://img17.imageshack.us/img17/384...lecrossbar.jpg

this is what i was gonna build mine like but if its a bad idea, and from all the input it seems to be, then i will just build a replica of the miracle available for our cars

[Sabretooth]

That actually connects the shock towers, or at least it appears to, could just bolt to the area around it, like most our strut braces do...also that is another Miracle Cross Bar, lol

Its all how good you are a fabricating and if you can weld decently...

[xxae07xx]

yes i know its a miracle bar....i googled them to find that image....thats why i said earlier that most miracle bars attach at the towers...but its cool. apparently my idea was faulty and i will do something else

[Sabretooth]

Build a harness bar ;)


Use the old bolts from the Front Seatbelts, then attach it to there, with guide bars meeting at the base where the back seats would fasten.

Just needs a small area for the harness to fasten

[rob323]

Originally Posted by Sabretooth

Well all the guys who built cages so far, haven't actually mounted them on the rear shock tower, they are mearly welding to the unibody before the shock tower

Yep, if the dropkick that did our cage had done it as we had asked, it would have attached directly in front of the top of the shock, not over on the wheel arch.


Luckily for us, the rear torsion beam suspension design (with shocks, not struts) means that it's not a problem and still works as it was originally intended to work.

So I think your in for a bit of trial and error finding how to mount onto the shock tower.

Echo's have a semi decent mounting point on the top of the shock tower (between the shock tower and the sides), does the Yaris? If so, use that.

But, you say you want to stiffen it. What do you want to stiffen, and in what direction?
The typical cross braces (from upper seatbelt points to floor etc) stiffen the upper rear of the body to the floor pan, but that means it puts more torsional forces on the floor pan (which is where your rear torsion beam mounting points are).
We did not attach to the upper rear part of the body to anything for 2 reasons.
1 - We don't care if that area flexes as it doesn't affect suspension geometry or anything else.
2 - We would prefer for that area to flex by itself rather than transferring those forces to the floor pan and making the floor pan have to work harder to resist them.

(off topic - I found a surprising amount of play in the rubber bushes in the top of the rear shocks and I expect the Yaris would be the same (Take a trim off and bounce the car up and down and have a look). We swapped them for much harder durometer and larger bushes on our competition shocks. There is no play left in the rubber now, the shocks now have to do all the work.)