Z Cars Rear Suspension Info
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sidewinder
On the Road
Joined: Wed Aug 11, 2010 9:27 am Posts: 621 Location: Sheffield GTM: Libra
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Z Cars Rear Suspension Info
Does anyone have official fitting instructions for the Zcars rear arms setup? Or any technical design info however small.
I'm thinking about creating something similar and am looking for any info that might help. Contacted Zcars themselves and they can't/won't supply any info.
Like how high up the tub wall is the pivot point, is it just at the same point as the OE lower arm pivot? The Z also don't seem to have any facility for altering toe in/out/straight after setting the track via the rose joints?
My initial idea is to create a similar L arm but use pillow joints like the RDM arms (I think exposed rose joints for a road car a terrible idea) and also use an MGTF (or F) upright bolted to the end to remove the need for bespoke bearing housings and brake mounts which need to be spot on.
Other thoughts are make it solid like Z or do a tubular trellis box style like OE? Make it from aluminium for lightness?
I'm no suspension geometry expert, but can do some simple flat cad things and have em laser cut and professionally welded so i aim to design the thing within the limits of my know-how and available resources - hence some of my initial design choices. Also this is intended for a road car, not interested in creating ultimo stiffness track weapon etc.
_________________ 2000 GTM Libra 1.8VVC 145BHP
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Thu May 11, 2023 10:41 am |
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sanzomat
GTM Nirvana
Joined: Sun Oct 19, 2014 10:10 pm Posts: 1138 Location: Bristol GTM: Spyder
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Re: Z Cars Rear Suspension Info
https://www.teamgtm.com/node/14700I'm assuming you've looked at all the images in this thread on Team GTM. I think it just fits to the bottom set of trailing arm mounts. My understanding was that track is set using spacers between the rose joint and the bracket sides and toe is set by screwing in/out the rose joints from the trailing arms. Doesn't look like you can alter toe without taking the bolt out of the rose joint eye. I'd be interested to know how much service life the rose joints are giving on those that have Z cars. The bigger, top quality ones are presumably not too bad but even then I'd have thought 3-4 years and they'd be FUBAR? Having said that I've changed my mk1.5 land rover track rods ends twice now so about every 5-6 years. I recall speaking to a guy with a yellow Libra at Stoneleigh (maybe 2017?) who had made his own Z-cars esque trailing arms. He stopped on the Kitnet pitch as his crank pulley had come off! If he is still around then it would be worth finding out how he went about it?
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Thu May 11, 2023 11:49 am |
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sidewinder
On the Road
Joined: Wed Aug 11, 2010 9:27 am Posts: 621 Location: Sheffield GTM: Libra
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Re: Z Cars Rear Suspension Info
Thanks Sanz, no i've not seen those as i'm not seemingly be registered on TGTM. I've applied so will have a look if approved.
Yeah i prefer the pillow joints as on my mk2b arms cos they are sealed.
_________________ 2000 GTM Libra 1.8VVC 145BHP
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Fri May 12, 2023 2:27 pm |
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Spider
Looking like a GTM
Joined: Sat Oct 22, 2016 12:41 am Posts: 154 Location: Brisbane Australia GTM: Spyder
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Re: Z Cars Rear Suspension Info
The Z cars design is good from a stiffness/strength aspect. Because it is a single trailing arm it will need torsional stiffness in the X axis (car longitudinal axis). The original wishbones are very floppy on that axis. IMO a good height for the pivot is about 120mm above the bottom of the rear bulkhead (on a Spyder - I assume Libra is the same.) I think that is about 18mm above the axle height. I went through the process of designing (mostly) a "better than Z cars" semi-trailing-arm alternative.
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Mon May 15, 2023 5:27 am |
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Phil.1380
Part built GTM
Joined: Mon Oct 19, 2020 7:27 pm Posts: 64 Location: Lincoln, UK. GTM: Libra
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Re: Z Cars Rear Suspension Info
Spider wrote: stuff Spider wrote Mate, you redesigned the redesign ?? With proper analysis and modeling ?? Respect !! Phil.
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Mon May 15, 2023 9:17 pm |
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Spider
Looking like a GTM
Joined: Sat Oct 22, 2016 12:41 am Posts: 154 Location: Brisbane Australia GTM: Spyder
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Re: Z Cars Rear Suspension Info
The Z-cars rear is a pure trailing arm design - pivot axis runs side to side and horizontal (zero camber gain, zero roll steer and roll centre at ground level). Zero camber gain means the wheels roll over with the chassis in a corner which is the wrong way. Also if you dial in some static negative camber, the pivot axis now slopes down towards the centre of the car which lowers the RC below ground level and also produces some roll steer in the wrong direction (oversteer).
Almost nobody uses this setup - especially in a RWD - preferring a semi trailing arm design. I settled on 10 degrees axis angle in plan view and 2 degrees in front view. I can't remember exact numbers but RC is well above ground, there is useful camber gain, and roll steer is in the right direction.
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Tue May 16, 2023 4:27 am |
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sidewinder
On the Road
Joined: Wed Aug 11, 2010 9:27 am Posts: 621 Location: Sheffield GTM: Libra
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Re: Z Cars Rear Suspension Info
Thanks for your info Spider. I found this interesting https://www.autozine.org/technical_scho ... sion21.htmRelatively easy to understand. Does anyone have an email address for teamgtm, my membership conf. mails just keep bouncing?
_________________ 2000 GTM Libra 1.8VVC 145BHP
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Tue May 16, 2023 3:17 pm |
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Spider
Looking like a GTM
Joined: Sat Oct 22, 2016 12:41 am Posts: 154 Location: Brisbane Australia GTM: Spyder
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Re: Z Cars Rear Suspension Info
That article explains trailing and semi-trailing systems well. A couple of errors though.
1. Adverse camber in corners leads to lower (rear) grip which is oversteer not understeer.
2. Pivot angle for common semi-trailing systems ranges from zero (trailing arm suspension) to about 20 degrees. Not 50 - 70 as stated. High performance and race vehicles tend towards the lower end ie 10 - 12 degrees.
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Tue May 16, 2023 10:04 pm |
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