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PostPosted: September 24, 2021, 4:42 pm 
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Miatav8,MstrASE,A&P,F wrote:
It would be interesting to see the westfield specs in vsusp.

according to my sources this is the Vsusp link for westfield (but I can not guarantee it is correct. I think someone gave it more camber); Westfield


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PostPosted: September 25, 2021, 6:23 am 
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Thanks for the link. I understand it may not be an accurate representation of the westfield dims.

For a more direct comparison, I adjusted the static neg camber at the UCA to a 1/2 inch, added the other specs to the chart, converted to customary units, and added a 1/2 inch tire compression. RC moves quite a bit from side to side and is very low with less camber gain, though that may be a good match for the rear.

Westfield?

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PostPosted: September 26, 2021, 4:08 am 
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Miatav8,MstrASE,A&P,F wrote:
Thanks for the link. I understand it may not be an accurate representation of the westfield dims.

For a more direct comparison, I adjusted the static neg camber at the UCA to a 1/2 inch, added the other specs to the chart, converted to customary units, and added a 1/2 inch tire compression. RC moves quite a bit from side to side and is very low with less camber gain, though that may be a good match for the rear.


Heres the source for info locostbuilders.co.uk;
So I think it is not a facorybuilt Westfield.
AdamR20 at locostbuilders.co.uk wrote:
The next one is my Westfield and this actually ties in quite nicely with some of Sam's points (thanks a lot for your input by the way, you're one of the chaps I hoped would pass comment!). The wishbones are nice and long and there is very little RC migration under bump (single or double wheel) or roll in either X or Y directions - but - the camber correction is quite poor, and I found myself having to run huge amounts of static camber to prevent munching the outside edges of the tyres. I ended up over 3.5deg front and 3deg rear and needed more if the adjustments on the car would allow. This obviously impacts straight line grip (both braking and throttle) which is why I wanted something a bit more MX-5-y in terms of camber correction (so I could run less static camber). Using the uprights, diff, half shafts and steering rack kinda nailed down quite a few of the potential 'dots' fairly quickly, so I was left with limited options. Having noticed the RCs migrating around when playing with the MX-5 model I decided to pretty much copy how they acted rather than trying to be clever and using this to control body roll, as I knew it already worked I didn't even consider that Sam but you have just given me some extra stuff to look into I think! Haha.

On a similar subject, I like the car to be pretty compliant as you can probably tell from the wheel rates, in the region of 1.3-1.4deg/g of body roll, so there is actually reasonable amount of wheel movement going on, which is why I've spent a bit of time researching this. Again it comes back to there being no perfect solution as phelpsa said, just the best compromise for you preferences and physical limitations. Looking at it again, I can maybe widen the rear track a little, so the longer wishbones may help keep the RC more static.

Chassis design - I had actually read that it's a good idea to start with rough suspension locations first and then design the chassis around them, which made sense to me, especially as I 'value' how the car drives - especially in the transitions - so much. I figured I could always get the chassis to support the pickups sufficiently, even if it involved a little extra weight. Given the budget I'm setting myself, if it comes in under 450kg, I'll be well chuffed.


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PostPosted: September 26, 2021, 6:32 am 
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From his post, Adam appears to be interested in more camber gain for less static / uneven tire wear (shorter VSA helps), more roll resistance (higher RC achieves this), and a more stable RC.

This tweak checks all those blocks by moving the UCAPs, LCAPs and a shortening the UCA but doesn’t consider the rear RC height: Westfield? Tweak

Sam 68 occasionally contributes here too. There are many on this forum registered on the UK site. FWIW, I forgot my UK password years ago.

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PostPosted: September 29, 2021, 5:04 am 
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I'll keep on posting here.

The front suspension design is as good as it gets.
Quote:
I don’t see the benefit to having a front that handles a lot better than the rear if it can’t be utilized without leaving the road ass-first.

I'm used to drive "light weight" rwd cars with slippery rear end. (the whole point of having a Opel Ascona B with a 2,4l engine :lol: )

The De dion tube will I make from a seamless 2,5" tube. walltickness would be around 0.078 to 0.09" I think.
It will be quite hevy with brakes etc. Will the Ford sierra differensial keep up with inboard brakes?

So, questions;
- The rear rollcenter must be higher than the front?
- The orginal DAX has a 3link, its also a oppertunity to have a 4link on the car. But then I need a panhard rod or wattlink.
- Will a watt link give me the oppertunity to move the rollcenter of de dion axle, and what is best, having it static for the axle, or the car?
A panhard rod rollcenter will according to my assumptions have half the travel as a wattlink (half the axle and half the car), but move the axle sideways in the travel. (We used to lower the car so the rod was straith with the ground and cut it down so the axle stood in the middle again. It gave more controll when oversteer.)
-And what is the best compromise? 3link, 4link panhard rod, 4link watt link.


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PostPosted: September 29, 2021, 9:58 am 
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Inboard brakes are tougher on the axles and joints plus the brakes are more enclosed affecting cooling. Heat transfer to the area (diff, fuel tank, etc) must also be considered.

It will be much lighter than a solid axle for sure. I think a three link would be close to the weight of an IRS depending on how the IRS is designed.

The rear RC should be higher for more roll stiffness at the rear. If you want to make roll stiffness adjustable, I suggest using adjustable anti-roll bars instead of altering RC height for tuning.

The best compromise to me would be a three link with the large A frame upper and two single trailing arms (dax rush style), watts if a four link. I’d stay with outboard brakes.

I would duplicate the Dax axle and links as closely as possible for a bolt on but using the irs axle of your choice.


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PostPosted: October 1, 2021, 6:08 pm 
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The conventional redesign of the front suspension looks to be well in check. Regarding the CC&AR side of thing, while at one point I did create a spreadsheet that could analyze CC&AR geometric movements, you could just as easily get perfectly functional results simply by spending a some time working with cardboard and push-pin models. I promise, it's not rocket surgery.

I'm in agreement that the unsprung weight of a De Dion vs IRS is not inherently enough different to be concerned about.

As with any other solid axle design, watch out for significant roll steer... Especially roll oversteer.

For conventional (non-triangulated) 3-link or 4-link rear suspensions, there's really nothing wrong with either Watts or Panhard. Depending on how it's mounted, Watts can be set up to hold the roll center stable with respect to the ground, or the sprung mass. Most recommendations are to keep it stable with the sprung mass when reasonably possible. As noted, the Panhard effectively splits the difference on roll center movement, and works fine too. Panhard does have some lateral movement, which is less problematic than it's often made out to be.

If you do a conventional 4-link, regardless of Watts or Panhard, as you figure out the geometry I'd recommend having enough convergence between the upper and lower links to prevent the binding that comes with an inherently over-constrained system. This is mostly of concern when using rod ends.

A triangulated (a-frame, etc) 3-link is easiest analyzed as a triangulated 4-link, so that's what I'll refer to it as from here out.

One thing I remember from my CC&AR analysis is that it has an unusually high roll center for an independent suspension sports car, which works as well as it does due to the way it create anti-jacking forces. The roll center for a triangulated 4-link is based on the height of the convergence point of the triangulated links. In this way, a triangulated 4-link with the top links triangulated at the chassis would make sense for the CC&AR suspension, balancing the roll axis with the the high front roll center. However, in going with a conventional front suspension utilizing a much lower roll center, I would recommend sticking with a bit softer of a roll axis. The lower roll center of the "Satchell Link" configuration of the triangulated 4-link, with the lower links triangulated at the chassis instead, would be the direction I'd be looking from a functional standpoint. If you're going to go through the time and effort of refabricating the front suspension mounting scheme, you might as well do it right and follow suit with the rear suspension.

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