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Suspension guru needed. Shorter front control arms?


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#1 adrianh08

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Posted 01 February 2020 - 06:48 PM

Need advice from someone who knows more about this than I do. If I get some custom tubular control arms made for my LX k frame, what issues will I face. I want to get both top and bottom arms made 20mm shorter to bring the front wheels in 20mm. Long story short I’ve stuffed up the offsets on the wheels I got made and they are sitting outside the flares. I’ve looked at widening the flares but also want to look at changing the control arms. Will it completely stuff up the steering geometry if I shorten both top and bottom control arms by 20mm to bring the wheels in?
Fixing the wheels isn’t an option and replacing them will cost me about $5k as they are custom billets out of the states. I’d really appreciate some advice here regarding if it is feasible to get shorter control arms made to remedy the problem.

#2 hanra

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Posted 01 February 2020 - 07:30 PM

Sounds like your up for a new set of wheels to me.

#3 arrimar

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Posted 01 February 2020 - 07:43 PM

Can the back of the wheel be machined?

#4 adrianh08

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Posted 01 February 2020 - 07:56 PM

Not enough meat on the wheel hub to be machined. Wheels cost over $10k to get made and land here from the US so I am desperately trying to avoid that scenario. I am trying to find out if 20mm shorter control arms is an option. Certainly enough room inside, it’s more the geometry issues I want to get advice on.

#5 76lxhatch

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Posted 01 February 2020 - 09:03 PM

It can probably be done but I would suggest that its highly unlikely to work well in isolation. At minimum you really need to plot how its going to affect bump steer and camber gain throughout suspension travel and figure out what you need to do to address or minimise any issues. It will have some effect on roll centre too although probably not a big deal, and I'm not sure I'd like to move the steering axis inboard if it could be helped. The different wheel offset is going to make for a larger positive scrub radius which, even ignoring handling concerns, will make tyre clearance at lock worse. Along those lines from what I've seen of your engineering rules you may also run afoul of issues with how this positions the wheel bearings further from the centreline of the wheel.

 

Long story short I think you need to fully understand the implications and do some planning to see how you might work through it, or I guess have someone you trust do it for you.

 

If you're looking at that much money and ways around it just to find an extra 20mm, maybe you should look at flares and body work? You'll still have the scrub radius issue in particular but going a bit wider is otherwise not such a bad thing. Increase the front and rear width to give it some presence! Although I guess that's an engineering no-no too?

 

Or maybe some custom stub axles would allow bringing the wheels in without changing suspension and steering geometry? That would help with the scrub radius too.



#6 axistr

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Posted 01 February 2020 - 09:10 PM

It's amazing how much small changes like shorter arms can effect spring and shock rates. If top and bottom arms are shorter by the exact same measurements and the height of the top and bottom ball joint positions in relation to steering arms and control arms are kept the same as original spec, caster, camber and Kpi should not be effectively change to much. However toe in of course will be effected and you will not get enough toe adjustment without shortening both tie rod bars by 20mm per side. You will need to use a die nut to run up the tie rod bars to compensate the 20mm cut off the bars. You also need to make sure the rack is properly centred. I am not going to guess on the amount but toe out on turns will be effected. And then you will have to get it checked and certified by an licensed engineer. I think the extra cost of the parts Labour and engineering fees will quickly add up and out weigh the cost of the correct rim offsets.

#7 axistr

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Posted 01 February 2020 - 09:28 PM

Bugger forgot about the scrub radius, Kpi should not alter if done correctly but as lx76hatch has mentioned the extra offset will effect scrub radius. The effect of negative scrub radius on the car will definitely be noticeable through extra tram tracking. Positive scrub radius reduces the tram tracking effect and negative magnifys to effect.

#8 dattoman

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Posted 01 February 2020 - 09:31 PM

Or maybe some custom stub axles would allow bringing the wheels in without changing suspension and steering geometry? That would help with the scrub radius too.

 

 

Or depending on the brake setup your thinking of using 

Can you change the hub offset like they used to do using the P76 rotors and bring the wheel away from the guard that way ?

If your doing s brake setup with a floating disc you could make the hub to any offset... just need to pick a disc with reduced height so it doesn't bang into the stub and arms

Caliper bracket location is also a factor

Also caliper clearance inside these wheels



#9 Ando

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Posted 02 February 2020 - 05:31 AM

You should be able to make it work with a combination of things to do;

 

As said above, look into alternative rotor hat height & caliper options.

 

Machine the back of the wheel mount even if it's 3mm or more..whatever can be done safely.

 

Also..split the front flares with a parallel cut & fill with fibreglass etc.

 

More negative camber into the wheels.

If it's a weekend cruiser, then it's more likely tyre's will get old before the tread wears down when considering replacement.

 

Cheers.


Edited by Ando, 02 February 2020 - 05:37 AM.


#10 adrianh08

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Posted 02 February 2020 - 08:10 AM

Based on advice above it appears the P76 rotor on hq stub axles can bring the track in 16-20mm on each side?
If this is the case it will go a long way towards fixing my issue.
I have a full Wilwood set up on torana stubs at the moment but can do without that to save the wheel situation.
I’ve read hoppers stoppers do a P76 rotor in HQ pattern in a kit so I will call them tomorrow. If this set up saves me 16mm or so it would be a great result.
I’ll then just have to work out what brake caliber to use.
Wondering if I could use an adapter plate to run the Wilwood caliper (dependent on rotor thickness)
Certainly hope I can come up with something to pull the wheels in as it is stressing the shit out of me and the cost of having to get two new wheels made would be a nightmare.
I am appreciating all the advice.

#11 Ando

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Posted 02 February 2020 - 08:26 AM

Most if not all of the Wilwood calipers can be narrowed or widened with their middle spacers to suit different rotor thicknesses. 

 

It's a matter of seeing what can be done to solve your track width problem.

 

Good luck



#12 adrianh08

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Posted 02 February 2020 - 09:08 AM

Cheers mate. I am going to make some calls tomorrow to look into the P76 rotor option.
I will lose the large diameter rotors I currently have but that’s ok to get the wheels to work.

#13 neglectedtorana

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Posted 02 February 2020 - 09:45 AM

I have VN Commodore rotors on mine with Wilwood calipers, the VN rotors are 82mm tall where as standard HQ rotors are 72mm tall

Looking at the P76 specs it is only 62mm tall, that's a good start

 

Hope you have success



#14 adrianh08

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Posted 02 February 2020 - 10:42 AM

Thanks mate I am exploring all my options. I’ll let everyone know how I go. Or there will be a very cheap Hatchback for sale with lots of good bits. Just shit front wheels.

#15 Bigfella237

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Posted 02 February 2020 - 12:25 PM

Just back on the original idea for a second... I'd have to look it up again but from memory it's a nightmare to get custom control arms engineered too, you have to have all the materials and welds x-rayed and certified or provide 'typical' samples for destructive testing or something like that?

 

I know it's not a helpful comment in any way but wow... ten grand for a set of rims! I think if I was spending that much I would've quadruple-checked that my measurements were correct first! :o



#16 adrianh08

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Posted 02 February 2020 - 01:44 PM

You’d think so wouldn’t you! I did the measurements off my 4 door which has 17x8 on it plus asked a bunch of people who have 9 and even 10s on the front of their LX and based all my measurements on that. But for whatever reason these buggers sit out half an inch or so more than they should. Hoping I can work it out with flare modifications and some extra negative camber. Maybe up to 3 degrees which I know some guys run. Not ideal for tyres but this won’t be driven much so tyre life doesn’t worry me.

#17 rexy

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Posted 02 February 2020 - 03:01 PM

The P76 front rotor solution is easy and cheap enough. I run them on the front of my blue LJ.

Another potential solution that hasn’t been mentioned is one of the aftermarket independent front suspension setups from waddingtons and others. Probably worth a call to see if there is a potential solution if your others don’t work out. Won’t be as cheap as P76 rotors and widening the flares though!

 

Do the rears fit ok?



#18 adrianh08

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Posted 02 February 2020 - 03:56 PM

Hi mate. Yep rears are ok once I go the wider rear flares which are readily available. I’m going to do some homework on how the IFS could help with bringing the wheels in at all as opposed to just giving better handling and more height options. I need to slightly reduce the track basically. However I’ve stuffed around today with the camber and the flares and am hoping I’m making some progress. Just be a matter if it’s enough or not.

#19 neglectedtorana

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Posted 02 February 2020 - 06:29 PM

Did your custom wheels arrive exactly as you ordered?

Have you measured the new wheels to make sure that the mistake is not part of the wheel?



#20 Cook

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Posted 02 February 2020 - 06:48 PM

Hi Adrian.  I really hope you can get a good result. I have had steel wheel centres re-spaced but understand that that Just most likely isn't possible.  Out of pure curiosity, what wheels/offsets are you trying to squeeze in? Cheers Ron 



#21 claysummers

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Posted 02 February 2020 - 07:17 PM

Not 20mm perhaps, but thought about playing with the hub offset? There may be a hub and disc set that bring the mounting face in.


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#22 claysummers

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Posted 02 February 2020 - 07:20 PM

Sorry just read above and realised this has been suggested already.


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#23 Lazarus

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Posted 02 February 2020 - 07:53 PM

Ring Hoppers Stoppers and CRS and see if they have a solution also. They would have considered a few options when coming up with their kits.



#24 Bigfella237

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Posted 02 February 2020 - 08:07 PM

I think it's just a question of "a p-piece from here... and a p-piece from there"

 

You could gain a few mm from offset bushes in standard control arms, a few from the alignment, half the deficit from the P76 hubs, maybe a few mm machined from the inside of the rim, and the rest from the flares.

 

It's not ideal because it leaves you no wiggle-room on the alignment and you still have a huge scrub radius to deal with, which means heavier steering, a tendency toward understeer, and wheel-to-body clearance problems (because the wheel swings in a bigger arc). And adding negative camber further increases positive scrub radius too, making things worse.

 

But getting within an inch of the standard track measurement will be the biggest hurdle, depending on the rim width of course. The wider the rim, the better off you are in that regard. If you have a pair of 8" rims and a pair of 10" rims, both with the same frontspace, then the 10's will reduce the track by 2" compared to the 8's.



#25 UC308Hatch

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Posted 02 February 2020 - 09:36 PM

Hi Adrian,

Not sure how your Billets are made, but mine are basically a 2 piece construction, a billet center & a rolled outer band, welded at the rear.

Have you considered getting the weld machined out, center moved out to your required offset & re-welded? Worst case you might need new outer bands.....




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