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Adjustable rear geometry for haynes roadster?
Lew The Machine - 17/9/14 at 09:56 PM

Ok, so I'm about to start cutting steel for my rear wishbones and i realise I only have camber adjustment on the rear!

Two questions...

1. How important is adjustment at the rear?

2. What's the best way to achieve this?

Here's my current design....
(Green circled bits are staying, red circled bits need changing... Possibly)






Any feedback is welcome!

rdodger - 17/9/14 at 10:15 PM

Being able to adjust rear toe is handy. It's difficult to build it with tight enough tolerance to set it without adjustment.

I have it on mine via a cammed bolt on the inner lower wishbone (similar to how MX5 wishbones adjust though my bolt is from a Ford). It adjusts enough to give me a tad of toe in. Alternatively a rose joint on the upright would do it.

Lew The Machine - 17/9/14 at 10:28 PM

That's exactly what I was thinking, I know I'd be annoyed when I took it for alignment and they told me one side was 1mm out haha! Have people done similar mods on their cars? I'm thinking of changing all 3 outer links with rose joints!?

ettore bugatti - 17/9/14 at 10:31 PM

Ah, you found the diff.

Here a JBA Falcon IRS with a rosejoint for toe adjustment
http://youtu.be/cRD1jIoBkE4?list=PLOD18N_fBFiNJuXU5HSJY4j4flVYUuXJ1

I would add some more mounting point on the upper suspension mount on the chassis (like the coilovers) so you can optimize the geometry for the specific application.

How is your IRS assy mounted to the ladder frame?


[Edited on 17/9/14 by ettore bugatti]

ashg - 17/9/14 at 10:34 PM

I put rose jointed rear lower wishbones on my roadster. It allowed boss racing to setup the car perfectly to fractions of a mm

AdrianH - 17/9/14 at 10:43 PM

The old fashioned method was to shim the hub mounting.

Washers if way out, generally thin (a few thou) strips of brass or tin.

Adrian

snapper - 18/9/14 at 05:36 AM

My Robin Hood uses the full Sierra rear end so the only option ( until I replace with Haynes set up) is camber wedges
I bought these off here a while back
Oval racer boys use washers under the hubs on Sierra and Granada

Ben_Copeland - 18/9/14 at 06:27 AM

I'm doing what Ash did, but gonna rosejoint all the joints top and bottom. I didn't put the rear wishbone brackets on my chassis so I don't know how accurately installed they are. It's a pain to get the wishbones in so I'm assuming not very accurately aligned.

Lew The Machine - 18/9/14 at 06:46 AM

I don't really fancy shimming, plus it's not necessary considering I can change the design to avoid it!

I've already changed the design of the rear upright once (now a 5mm laser cut and bent plate using 106gti calipers) so another change is no problem!


quote:
Originally posted by ashg
I put rose jointed rear lower wishbones on my roadster. It allowed boss racing to setup the car perfectly to fractions of a mm


Do you have any photos of said rose jointed wishbones?

Cheers for all the input guys! It's nice to get options of people who've been through the same process haha!

Lew The Machine - 18/9/14 at 07:07 AM

quote:
Originally posted by ettore bugatti
Ah, you found the diff.

Here a JBA Falcon IRS with a rosejoint for toe adjustment
http://youtu.be/cRD1jIoBkE4?list=PLOD18N_fBFiNJuXU5HSJY4j4flVYUuXJ1

I would add some more mounting point on the upper suspension mount on the chassis (like the coilovers) so you can optimize the geometry for the specific application.

How is your IRS assy mounted to the ladder frame?


[Edited on 17/9/14 by ettore bugatti]


Haha yeah I found it! Big thanks for pointing me in it's direction!

What do you mean by add some more mounting points? To change the shock angle?

The IRS will have a "male" box section piece both sides which slides inside the "female" ladder chassis.

It will all be braced to the rollcage/spaceframe so it's not going anywhere, the only problem I'm having is torsional stress throughout the length of the chassis, hoping to sort that with more bracing though haha!

Mr C - 18/9/14 at 07:30 AM

If you can change the design I would make a "Z" wishbone. Basically an A frame from the the forward hub mounting point rose jointed at the hub end, to both chassis points, then a turnbuckle with L/R handed joints from the rear hub mounting point connecting to the A frame just forward of the rear chassis mounting point.

Camber Dave - 18/9/14 at 07:37 AM

A detail perhaps, but I would mount the antiroll bar droplinks as far outboard as possible.

That way it will be more effective with a light gauge bar.

Slimy38 - 18/9/14 at 08:56 AM

I've probably come into this a bit late, but both the ARB and coilover mounting seem wrong. With the forces they will apply, having them in the middle of a tube seems like a bad idea? I'm guessing there is a reason why the coilover is mounted mid wishbone rather than on the top of the upright as per the original Haynes design?

Lew The Machine - 18/9/14 at 09:16 AM

quote:
Originally posted by Mr C
If you can change the design I would make a "Z" wishbone. Basically an A frame from the the forward hub mounting point rose jointed at the hub end, to both chassis points, then a turnbuckle with L/R handed joints from the rear hub mounting point connecting to the A frame just forward of the rear chassis mounting point.


Similar to the "JBA Falcon" design that ettore bugatti posted? It does seem to be quite a popular design for rear lower wishbones!

Does anyone have a good source for ordering rose joints? (and possibly a spec sheet for them so I can do some 3D work before I order them)

Lew The Machine - 18/9/14 at 09:23 AM

quote:
Originally posted by Slimy38
I've probably come into this a bit late, but both the ARB and coilover mounting seem wrong. With the forces they will apply, having them in the middle of a tube seems like a bad idea? I'm guessing there is a reason why the coilover is mounted mid wishbone rather than on the top of the upright as per the original Haynes design?


Definitely not too late... No metal was harmed in the making of this design ;-)

The ARB mounts are still floating, and the connection from them to the wishbones via droplinks can still be changed!

Good question about shock position, again it's not confirmed but I've seen it done that way on other rear ends so thought it wouldn't be a problem? The reason for having it low down was to avoid having to fabricate a relatively heavy duty shock mount at a high level, I thought I'd try and utilise the rear wishbone & diff mounting frame for as many purposes as possible!?

loggyboy - 18/9/14 at 09:35 AM

Similar looking wishbones on a IRS striker - showing adjustable mounts. (albeint limited to increments of 0.5 x the thread pitch)


Lew The Machine - 18/9/14 at 09:53 AM

That looks EXACTLY like the design I looked at when doing mine, only difference being that has holes in the side of the upright!? Weight saving?

loggyboy - 18/9/14 at 09:57 AM

quote:
Originally posted by Lew The Machine
That looks EXACTLY like the design I looked at when doing mine, only difference being that has holes in the side of the upright!? Weight saving?


Standard Raw design, but yes, I would expect that's the reason.

Lew The Machine - 18/9/14 at 10:11 AM

quote:
Originally posted by loggyboy
quote:
Originally posted by Lew The Machine
That looks EXACTLY like the design I looked at when doing mine, only difference being that has holes in the side of the upright!? Weight saving?


Standard Raw design, but yes, I would expect that's the reason.


What brakes are you using on that?

Are there any cad files available for those uprights?

looks like a good quality build!

loggyboy - 18/9/14 at 11:21 AM

That's actually 2 builds, top one is mine, which has sierra disc hubs and carriers. The 2nd is a chap called Mikes whose using the Golf rear brake setup that will mount to the 2 extra holes on the upright, that used the sierra drum hub carriers.
The uprights are Raw supplied, so I doubt a CAD file is readily available unless some one has drawn up their own.

mikeb - 18/9/14 at 11:23 AM

Nothing wrong with Shimming it, but its a pain to change once set if you want to change to a different set up.
If you have the time rose joint it.

ettore bugatti - 18/9/14 at 06:37 PM

quote:
Originally posted by Lew The Machine

What do you mean by add some more mounting points? To change the shock angle?

The IRS will have a "male" box section piece both sides which slides inside the "female" ladder chassis.

It will all be braced to the rollcage/spaceframe so it's not going anywhere, the only problem I'm having is torsional stress throughout the length of the chassis, hoping to sort that with more bracing though haha!


No, more mounting points on the chassis so you change the top wishbone angle (and thus rollcentre height and 'swing arm length'.
I could only find any example of a RC car:


I was thinking that when the subframe was hung underneath the ladderframe leg you maybe could design something like a MX-5 subframe from sheet metal.

Mr C - 18/9/14 at 08:15 PM

Apologies I missed the JBA post. yes similar.. though I would use a turnbuckle and rose joionts at both ends of the adjustable arm. This will alllow you to adjust the toe by slackening off two lock nuts and rotating the turn buckle, rather than having the dismantle the roase joiny and screw it in or out and resaassemble. I'll try and find an image of what I mean.

Mr C - 18/9/14 at 08:21 PM

Found an image, this is looking towards the back of the car.

Lew The Machine - 18/9/14 at 08:48 PM

quote:
Originally posted by Mr C
Found an image, this is looking towards the back of the car.



Yeah that pretty much the kind of setup I was thinking of, the JBA design is limited to adjustment by the thread pitch but using a rotating link bar makes it possible to get it perfect!

Interesting to see those rose joints bolted vertically rather than horizontally? Is there a reason for this?

[Edited on 18/9/14 by Lew The Machine]

Slimy38 - 19/9/14 at 07:39 AM

quote:
Originally posted by Lew The Machine
Good question about shock position, again it's not confirmed but I've seen it done that way on other rear ends so thought it wouldn't be a problem? The reason for having it low down was to avoid having to fabricate a relatively heavy duty shock mount at a high level, I thought I'd try and utilise the rear wishbone & diff mounting frame for as many purposes as possible!?


The shock can be fixed to the lower wishbone, it's more the placement of the fixing? The photos posted above actually show a similar arrangement, but notice how close they are to the upright (pretty much as close as they can get without fouling the upright itself). I think you having yours two thirds along the wishbone, and directly above a heat affected zone (from the horizontal brace) which is already under stress due to no triangulation, is just asking for a break.

Lew The Machine - 19/9/14 at 01:04 PM

Ok so here's my first re-design!

I've left the top joint as a bush but I might change that to a rosejoint too as it don't like the idea of effectively "twisting" when adjusting toe-in/out!?

I may also change the angle of triangulation to sit behind the rosejoint brackets on the diagonal!

I've moved the shock out and closer to centre, this has forced me to decrease the angle it was sitting at... Not too drastically but still!




[Edited on 19/9/14 by Lew The Machine]

Mr C - 19/9/14 at 03:38 PM

Looking good. The second joint was rose jointed on mine to allow the movement. Makes sense to have the triangulation behind the inboard rose joint, maybe move the rose joint further inboard making the turnbuckle longer??

Anyhow good job and loving the CAD work.

Lew The Machine - 19/9/14 at 05:03 PM

quote:
Originally posted by Mr C
Looking good. The second joint was rose jointed on mine to allow the movement. Makes sense to have the triangulation behind the inboard rose joint, maybe move the rose joint further inboard making the turnbuckle longer??

Anyhow good job and loving the CAD work.


Haha cheers, it's my job so it helps to be half decent at it

As soon as I'd modelled the triangulation I knew it was in the wrong place but I was in a rush so had to leave it... The principle seems ok though!?

I think I need to space the bottom of the upright out a bit more to move the rose joints apart and allow the link to mount further inboard like you said, the rose joint was starting to sit on a bit more of an angle than I'd like

Here's some more CAD... can never have too much CAD





Lew The Machine - 23/9/14 at 01:40 PM

ok, Bit more work done on the design (pics to follow)...

Do we like these or are they to be avoided?


http://www.mcgillmotorsport.com/m12-turnbuckle-link-adjustment-210mm-240mm-linkage-12mm-559/


And which rose Joint do i want? They will be M12 but there are 3 types...



http://www.mcgillmotorsport.com/metric-rod-ends-accessories-male-rod-ends-metric/


Never played with rose joints so any warnings/advice you have would be appreciated!

Cheers