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I think you would be better off creating an SLA front suspension rather than the double ball joint set-up.

 

Alternatively, have you considered putting narrower front wheels / tire on the car and using longer lower control arms to push them out to the width of your fenders.  You would of course have to relocate the top of the strut outboard by a distance similar to the added length of the lower control arms.  The factory LCA is ~11.3 long center to center.  You currently have 15x14 wheels with essentially a 4" backspace.  I would go to a 15 x 11 with a 5.5 inch backspace and make some LCAs about 16 inches center to center.

 

Which ever avenue you pursue, I am watching eagerly and would be willing to provide any help I am able.

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That's an interesting idea Dan, but I'd have several problems:
1. The cage is built to support the stock strut tower, and I'd be moving it over quite a ways.

2. Car would be way wider than it needs to be
3. Don't really want staggered tires. Always had issues getting the front end to hook up, and that's going to be exacerbated with narrower front tires
4. Tie rods will interfere with the wheels. Possible that a 16 x 10 or better, a 16 x 12 might work, but one of the reasons I went with the 15x14 is the easy availability of the FA tires

5. Doesn't really fix the scrub radius issue. Obviously would be less with a narrower rim, but might still be 4" if I couldn't do the 5.5" backspace.


I like the dual ball joint thing because it could potentially be easy to implement, we'll see what the computers say.

If the dual ball joint doesn't work and the car doesn't hook up with my new tires then I think I'll go one of two ways; either SLA or go to a 3" flare and run a 15 x 11 with the 275/35/15 Hoosier or 16 x 12 if I can find an appropriate slick to fit.

 

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That's a really interesting option, thanks. How would one go about figuring out which spindles to try? Assuming some Nissan stuff would have the same bolt pattern so might be able to bolt the existing suspension up to it, thinking would need new front brakes, or at least new caliper brackets. I know Nissan used the Set 2 and Set 6 bearings up through the 300ZX, so that part might be the same if I stayed Nissan.

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Take a look into my build and you get an idea. Wheel bolt pattern is same as S30, mine has 5-lug with more options with wheels.  

 There are plenty of aftermarket spindles, so you can play almost everything with them. And ofc. control arms, brakes, etc.

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Posted (edited)

I checked it out and it's easy to see why the scrub is reduced. This actually looks like a pretty easy solution. I'm guessing there is a 12.2" Wilwood setup for an S13 that's readily available too.

Still want to see what can be done with the dual ball joints, but thanks again, very helpful!

 

DSCF0534.JPG

Edited by JMortensen

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I looked at your build as I am looking into different front suspension options.  Is the added front track width from your custom control arms or is the s13 just wider? It looks like you reangled the steering arms on the knuckles, how is that holding up, I have always been nervous about welding cast pieces.  The only other write up of a s13 swap I found was on zilvia, he used a rhd skyline rack for due to swapping the knuckles to front steer, are you still on the s30 rack? How is bump steer with it. Sorry for the thread jack.

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3 hours ago, caperix said:

I looked at your build as I am looking into different front suspension options.  Is the added front track width from your custom control arms or is the s13 just wider? It looks like you reangled the steering arms on the knuckles, how is that holding up, I have always been nervous about welding cast pieces.  The only other write up of a s13 swap I found was on zilvia, he used a rhd skyline rack for due to swapping the knuckles to front steer, are you still on the s30 rack? How is bump steer with it. Sorry for the thread jack.

I think the added width is tires and wheel offset which brings with it a horrible scrub, hence the thread looking for solutions which the dual ball joint potentially offers. If it works, tie rod outer points and their attachment at the knuckles would need to be located correctly to allow proper Ackerman and zero or minimize bump steer (assuming things are correct on the inner points to start with). Caster shouldn't really be affected. Dynamic camber probably would at least a little but maybe not enough to cause issues. I'm intrigued by the possibilities. Advantages to SLA or strut would be similar.

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On 7/6/2018 at 7:23 AM, 74_5.0L_Z said:

I think you would be better off creating an SLA front suspension rather than the double ball joint set-up.

 

Alternatively, have you considered putting narrower front wheels / tire on the car and using longer lower control arms to push them out to the width of your fenders.  You would of course have to relocate the top of the strut outboard by a distance similar to the added length of the lower control arms.  The factory LCA is ~11.3 long center to center.  You currently have 15x14 wheels with essentially a 4" backspace.  I would go to a 15 x 11 with a 5.5 inch backspace and make some LCAs about 16 inches center to center.

 

Which ever avenue you pursue, I am watching eagerly and would be willing to provide any help I am able.

While I believe your are right in the "ideal" setup and intend to go that route on my car (it's a mess up there from multiple impacts and rust plus the engine swap so all the structure is getting replaced anyway.) For that to really work correctly wheels large enough to hold the whole outer end would be needed and a full inner structure with all new arms, rack, knuckles, coilovers, etc. Would be necessary. A build like this where the existing setup is already there and very sound - tearing the whole front end apart for a complete redesign is probably not worth the effort. At best the entire upper structure has to be redone most likely lowers and rack too.

 

Longer lower arms should help but bring all the same issues and more. This double joint idea is simply a long virtual arm. Advantage would be getting the effective long arm without messing with crazy brake/hub/knuckle offsets or maybe impossible parts. Potential disadvantages I see are extra leverage on the steering to move the compounded outer end and not sure what the thing would be like dynamically. Just thinking out loud here, hopefully the discussion helps anyone considering this myself included.

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On 7/7/2018 at 12:19 PM, JMortensen said:

I checked it out and it's easy to see why the scrub is reduced. This actually looks like a pretty easy solution. I'm guessing there is a 12.2" Wilwood setup for an S13 that's readily available too.

Still want to see what can be done with the dual ball joints, but thanks again, very helpful!

 

DSCF0534.JPG

Very nicely done! I really like the sway bar implementation and will "borrow" that idea if I can make it happen. Clean quality work. I'll enjoy following your build TUME.

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Posted (edited)
1 hour ago, jpndave said:

I think the added width is tires and wheel offset which brings with it a horrible scrub, hence the thread looking for solutions which the dual ball joint potentially offers. If it works, tie rod outer points and their attachment at the knuckles would need to be located correctly to allow proper Ackerman and zero or minimize bump steer (assuming things are correct on the inner points to start with). Caster shouldn't really be affected. Dynamic camber probably would at least a little but maybe not enough to cause issues. I'm intrigued by the possibilities. Advantages to SLA or strut would be similar.

My control arms are very slightly wider than stock, but yes, the main thing is the 15 x 14 wheels. I was surprised at the relative lack of difference that rack position had on Ackerman. When I set up the ps rack I had to move it forward. Prior to that I had a manual rack which I moved backwards as far as possible. Moving the stock rack back about 1.5" yielded another degree or two of angle change at full lock, so in the normal driving zone had almost no effect. Moving the new rack forward about 2" from stock basically turned it into a parallel steer car. 

As you say, the dynamic characteristics is the interesting variable. I don't know if there is a way to get this setup to have better Ackerman characteristics or not, and bumpsteer was pretty well managed before, so it will be interesting to see how that works out. I did have a friend with a 510 who went from stock knuckles to ones that were bent for Ackerman and the turn in on his autocross car was vastly improved. I'd like to have more Ackerman if possible, but I think it's really hard to do with the stock spindles.

Cary has been super busy but is thinking he'll have something modeled in a couple weeks.

Edited by JMortensen

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Posted (edited)

Ackerman itself is pretty simple to sort. The other thread had some good posts and "Chassis Engineering" has a great write up on it as well as the rest of the chassis. I have and have read a bunch of them and Herb Adam's is hands down the best for basics. Carroll Smith's series is next on the list for advanced stuff. All the rest are a few good points here and there all IMO as a disclaimer. I'll see if I can get a chance to post some of that basic information. I highly recommend Adam's book as a must have for basic understanding from this stuff to cage design and chassis stiffness. Not a how-to but all the sound basic theory to get you there. 

 

You'll have to watch as steering points get moved for ideal Ackerman to not upset bump steer. Up and down doesn't really matter on the Ackerman just getting it right in relation to the kingpin pivot line relative to the center of the hypothetical rear axle. So a line from outer steering joint through kingpin pivot ideally lands at the center of the rear differential (if it's centered) outboard is less that ideal past center is more. Slow speeds I think "perfect/ideal" is the goal. Other applications might mess with it to band-aid issues. I wiil design for center of rear or ideal which minimizes scrubbing any tire for turning a different radius as both front tires are now turning the same angle as vehicle travel. If you start to push, get loose or drift that is no longer true since the car isn't turning the same as steering. If the car is going to spend a lot of time with one of those conditions setting Ackerman to match conditions is possibly a better option. 

 

If I can time to get that program loaded up entering the points would be simple enough.

 

I'd probably start with the lower arm coordinates then move to the arm location to optimized Ackerman and steering.

 

Hopefully the program will show any dynamic changes. Steering effort issue will likely be try and see but with the power rack will probably be a non-issue for you. I'm not planning on a power rack so it could be a problem for me. 

Edited by jpndave

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I've got Adam's book. I actually ended up with a roll cage that was inspired by the balsa testing he did. Fig 12-14 on p90 if you're interested. I thought Staniforth's Competition Car Suspension had more info on how much to use and why, but YMMV.


In any event, here is the thread where I showed what I measured when I moved the rack back and forward, used longer and shorter steer knuckles, etc: 

 

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Posted (edited)
17 hours ago, JMortensen said:

I'll have to go through Staniforth's book again with a fresh set of eyes. In his defense it was one of my last reads and after Adam's Basics and multiple Smith advanced books much seemed redundant.

 

I'll review the link thanks for posting it up. 

Edited by jpndave

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