bennjamin
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| posted on 20/8/16 at 09:59 PM |
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MX5 rear subframe and suspension use on smaller car- trim width and maintain geometry ?
Hey everyone
I am researching using a miata/mx5 rear end on my honda S600 build.I intend to use a F20c or similar motor.
This is to replace the existing chain drive or live axle option. I am basing this rear end off similar builds in RWD minis , other small convertibles
etc.
The front end is acceptable but I am open to suggestions !
HERE
is an image of the design (sitting upside down)
So , school me abit about using another cars subframe + IRS setup....
1.Using an entire MX5 rear end - If the suspension is kept as is and the carrier area of the subframe is simply cut and narrowed to suit , will this
keep the geometry ?
2.The honda S600 rear tracking is 1128mm and the mx5 (1st gen ) is 1430mm. Pending wheel offsets and widths I can narrow the subframe 151mm either
side of center and shorten the driveshafts to suit and it should be a good start right ?
Ill shoot some more questions about this soon
thanks for any input ! Ben
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bennjamin
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| posted on 20/8/16 at 10:06 PM |
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*edit
My aim is for the Honda to be a little lighter and alittle more power , but equal or better handling than a 1st gen MX5.
[Edited on 20/8/16 by bennjamin]
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Doctor Derek Doctors
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| posted on 21/8/16 at 07:47 AM |
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It sounds like quite a logically Locost idea, it might be worth checking if any other Mazda's had the same CV/splines joints but were narrower
trackr so you wouldn't need custom driveshafts.
Instead of chopping and welding the original subframe using it as a template to make a new narrower version might be better as the one I had was quite
crude.
If you are going down that route would the simplest option be to use the entire MX5 drivelibe with a shortened propshaft and PPF? It's not F20c
power but it would still be quick and fun. It would be the quickest route to getting the car on the road.
Annoyingly I have just chucked a surplus MX5 rear subframe in the tip.
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Doctor Derek Doctors
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| posted on 21/8/16 at 07:51 AM |
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Was just thinking about Geo' narrowing the frame and keeping the same wishbones to give a narrower track won't drastically affect the geo,
I think the notabke blhange would be to slightly lower the roll centre. But seeing as how you are using the Geo' in a completely different car
it's going to feel totally different anyway.
Designer and Supplier of the T89 Designs - Single Seater Locost. Build you own Single Seater Racecar for ~£5k.
Plans and Drawings available, U2U or e-mail for details.
Available Now: The Sports Racer Add-On pack, Build a full bodied Sports Racer for Trackdays, Sprints and Racing.
www.t89.co.uk
www.racecarwings.co.uk
callan@t89.co.uk
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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Sam_68
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| posted on 21/8/16 at 08:58 AM |
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Apart from lowering the static roll centre, it can potentially screw up dynamic location of the roll centre (ie. the roll centre moves about
significantly as the suspension moves).
This in turn means that the weight transfer is shifting about as the suspension moves during cornering, which can make the car feel rather unpleasant
and squirrelly.
You may get away with it, but personally I prefer to do a proper suspension analysis (using one of the readily available geometry programs) to ensure
that the roll centre remains constrained to within a couple of millimetres of the same position relative to the sprung mass, throughout its working
range.
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britishtrident
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| posted on 21/8/16 at 11:54 AM |
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300mm = 1ft is a huge reduction in track I can't see the Mazda final drive casting with its wide mounting lugs fitting in, a Sierra or
Freelander diff casing might be a better candidate. However it isn't clear from your post if the car is the live axle or the rare chain driven
trailing arm version, if live axle really it might be best to leave the axle geometry alone. Honda are of course famous for using anti-clockwise on
many older models so it would just be matter ensuring the axle rotation is the correct to match the engine.
If you really want to go IRS you could go Locost style IRS or the simpler Strut or Semi-Trailing arms. You might even have room for a de Dion.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Sam_68
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| posted on 21/8/16 at 12:44 PM |
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Sorry Bennjamin... I only half read the original post, so I didn't really register that it was you and your S600 we're talking about (it
is indeed the chain driven trailing arm arrangement we're talking about, BT).
I really shouldn't be replying on forums that early on a Sunday morning... my brain doesn't get into gear until about mid-day! 
I Agree that you'll have some fairly serious packaging problems, with the Mazda diff and subframe, in a car as small as the S600.
I'd definitely be looking for the easy option of a suitably narrow live axle, if I were you.
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britishtrident
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| posted on 21/8/16 at 01:01 PM |
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Ford Anglia 105e axle would be an option for a clockwise engine.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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Sam_68
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| posted on 21/8/16 at 01:11 PM |
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Or MG Midget: rear track is 1138mm, versus the Honda's 1128mm (Anglia is 1162mm).
More modern stuff like the little Japanese vans and Jeeps might be worth checking, too.
Invert the axle, if the engine spins the 'wrong' way?
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bennjamin
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| posted on 22/8/16 at 01:59 AM |
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Thanks for the replies everyone.
I need to put this through a program or a scale image to work out more sense.
I have advised my fabricator and he agrees about using the standard subframe as a template for a tubed narrowed replacement. This should give more
room for the OEM diff or an alternative.
FYI this car came as a chain drive setup - the later S800 came with a 4 link but is impossible to find parts for. So I'd thought to give it a
IRS end similar to the front.
Lets see how it goes. Will keep you updated !
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