so i wouldn't worry about scrapping an MR2, there's plenty more of them about than escorts or sierras
Hi all,
I've been plotting a self-designed and built middy for what seems like a million years now but I've decided to stop procrastinating and get
on with doing it.
But - choosing a donor is difficult! I want to keep costs down and avoid wrecking rare cars if this takes off and some kits get sold.
- Do people think it's wrong to choose a donor like a 306 GTI6, Fiat Coupe Turbo, Alfa 145, MR2, I think they'd give great engines but is it
frowned upon to encourage scrapping of 'saveable' and potentially future classic donor cars? Obviously it's not huge numbers but
still..
- In terms of upright selection, there's very few FWD cars with uprights that could be used as is, due to moving the front hubs engine and box to
the back, therefore needing some free-wheeling front hubs for the middy kit car. An MR2 would be ideal as it already has this layout, a good engine,
and the uprights are suitable for adapting to double wishbone design, but would people buy the MR2 donor and think 'I like this, why bother with
a kit car that has no roof, heater, etc.?' Sevens are good cause they came from taking a reasonable engine from a pile of rusty poo (Rotten
Sierra's and Escorts) but a middy with a nice engine is likely to need an 'interesting' donor to provide its innards. Looking at Sylva
Riot/J15, maybe a lot of people might be put off and want to look for more power than the fiesta engines it's based on?
- From a commercial point of view, is it preferable not to expect punters to have to buy a second set of front uprights and hubs, then strip another
set of CVs to fill the bearing holes in the front hubs? This adds lots to the costs really but necessary to achieve a matching bolt pattern.
Excuse the essay but I get really bored at work so this is more hoping to kick-off a discussion about mid-engine kit design in particular upright
choice than any definitive answers!
Nick
MR2 donor has many plus points as you rightly say.
I have a 3SGE engine in my car, albeit in RWD configuration.
Up to 173 HP standard or 178 if it is a JDM engine like mine.
If that's not enough there's always the 200+ Turbo variant.
Plenty of aftermarket kit for the 3SGE too.
It wouldn't be too worried about scrapping an MR2. They're not exactly scarce. There should be a decent enough supply of accident damaged
ones anyway.
You'll have to compete with Ferrari 355 wannabes though!
Geoff.
If you want to sell the kits you may may to compromise on the donor for more readily available ones
i'm sure theres plenty of rusty scrap MR2s too. besides, personally, i'd much rather have a mk2 escort (as per the locost book) over a MR2,
but thats me so i wouldn't worry about scrapping an MR2, there's plenty more of them about than escorts or sierras
One thing to consider, how many kit cars carry spare wheels? In that case, why worry in the front stud pattern is different to the back, it doesn't matter if you can't fit the spare to any particular corner, if you haven't got a spare anyway.
quote:
Originally posted by interestedparty
One thing to consider, how many kit cars carry spare wheels? In that case, why worry in the front stud pattern is different to the back, it doesn't matter if you can't fit the spare to any particular corner, if you haven't got a spare anyway.
I'm in the same situation (but with no intention to build kits for purchase) and I'm seriously considering MR2 turbos as donors. The problem being the price of them - 1.5K for a scrapper at the moment.
Obviously you have the same choices as all the 7 builders but this assumes you depart from the one donor idea but saying that virtually no kit is a
true one-donor vehicle! With parts and upgrades coming from many sources.
Building a midi myself I’ve gone from pillar to post on this decision, originally thinking I’d go with MX5’s, cheep, easily available, designed for
double wishbones and with suitable rears from the same vehicle. Lots of people have used these for both 7 style cars and midi’s so this is a well
trodden path.
For several reasons, some of them cosmetic, like building is an exo-car and I wanted the steering rack higher and more out of sight under the front
cowl, some because of my own geometry decisions like wanting the lower wishbones as low as possible and parallel to the ground. Anyway long story
short I’m making my own!
Originally I started penning a tubular fabricated design that I posted some pictures of here, however the design requires quite a few turned parts and
being round the jigging during fabrication was not so easy. Currently I’m working on a more angular fabricated/folded version, I’m basing it around
the rear stub axle from a micra which is a very compact part with a simple bolt fixing. I hope to have some pictures and a mock up done next week that
I’ll share here.
One final caveat to the above, when you start laying out your own design it’s very easy to aim for perfection, I’m beating myself up constantly trying
to get perfect angles and scrub radius close to near zero, all packaged as neatly as possible based around joints and bearings that are easily
available. I have to keep reminding myself that; cortina, mx5 and triumph uprights all very successfully used on high performance specials are nowhere
near theoretical perfection, with all the compromises that need to be made there is no such thing!
Morning all. Just a small question on scrub radius as mentioned above. I am by no means an expert but I was under the impression that some scrub was
necessary/desireable in order to create some 'feel' in the steering.
My experience is certainly that excessive scrub radius is a bad thing. Steering too heavy and kickback from bumps involving just one front wheel but
is zero scrub a good thing?
Orton, your upright design sounds very interesting,look forward to seeing some pics. Does the bolt pattern match your rear hubs (mx5?)?
On the scrub radius thing, I've read elsewhere and seen on Formula Student cars that 0-10mm is ideal. But depends on what's achievable with
the hardware you have.
I think MEV provide their own front upright, does anyone know what bearings they use?
quote:
Originally posted by MikeCapon
Morning all. Just a small question on scrub radius as mentioned above. I am by no means an expert but I was under the impression that some scrub was necessary/desireable in order to create some 'feel' in the steering.
My experience is certainly that excessive scrub radius is a bad thing. Steering too heavy and kickback from bumps involving just one front wheel but is zero scrub a good thing?
quote:
Originally posted by GRRR
Orton, your upright design sounds very interesting,look forward to seeing some pics. Does the bolt pattern match your rear hubs (mx5?)?
On the scrub radius thing, I've read elsewhere and seen on Formula Student cars that 0-10mm is ideal. But depends on what's achievable with the hardware you have.
quote:
Originally posted by Neville Jones
quote:
Originally posted by MikeCapon
Morning all. Just a small question on scrub radius as mentioned above. I am by no means an expert but I was under the impression that some scrub was necessary/desireable in order to create some 'feel' in the steering.
My experience is certainly that excessive scrub radius is a bad thing. Steering too heavy and kickback from bumps involving just one front wheel but is zero scrub a good thing?
Don't start that one again Mike!
The amateurs believe(from threads like this) that some scrub gives what you say. Professionals design for zero scrub(due to kickback and a few other problems caused), and accept the barest minimum that can be staisfactorily tolerated. High speed racecars certainly zero. Just imagine what kickback at 200mph would be like!
Cheers,
Nev.
Surely some feedback is desirable, e.g. on my road car it's easy to tell when one wheel is losing grip through the feel through the steering.
On another note, is kpi at the rear irrelevant due to no steering?
I don't think race car geometry has much place on a road car driven at reasonable speeds
More important would be robustness and ride quality (given the terrible quality of the roads just now) plus lifespan of components like joints that
should last more than a few thousand miles unlike the use of rose joints etc which are perfect for a race car but not so for the reality of road
use
Also is the long term availability of spares as kit cars tend to last a lot longer than their production car donor
[Edited on 11/2/11 by Mr Whippy]
This is something that I need to read-up on... can anyone recommend any good sources of information?
I think for a any new 'sporty' kit it is important to consider track day use because while the average enthusiastic driver wouldn't
notice subtle geometry issues, a few professional opinions sating 'awful geometry for track use' for word to spread and the customer to go
somewhere else with a reputation of good track performance, even if they don't need/use it.
Maybe an unfair comparison but remember the Stratos with awful handling on Top Gear? I doubt that helped their sales much!
Back to stub axles, the micra stuff looks ok, and I noticed golf mk2/3 gti stubs come with caliper mounts on the stub already too. I'd be
worried about designing an upright strong enough to hold it all together tho.
[What about a road car?]
With the exception of a couple of specific cars, most road cars would be designed with zero scrub in mind, but maybe not in the final design due to
packaging, and production parts being utilised.
Some fwd cars have been designed with negative scrub, with the aim in mind of combatting torque steer. Not sure how that worked out in practice.
This is one of the areas where the engineering offices do battle with the 'stylists'. Change the wheels and tyres, or even just tyre
profile, and all your hard worked design and numbers go out the window.
As I put, design with zero in mind, and suffer the minimum that can be tolerated in the compromises.
The 'feel' that everyone talks about, usually comes from castor.
Cheers,
Nev.
Just be aware that Calliper mounts fix calliper position, calliper position fixes disc position, disc position fixes wheel mounting face (without
custom discs and hubs). Everything I’ve looked at so far puts everything too far outboard meaning you’re fighting every other aspect of the upright
design to get the rose joints out far enough to minimise scrub. The good thing about the micra stub-axle is it is so short – only 90mm from the
mounting face to the very end and ony 60mm from the mounting face to the outside face of the bearing the extra 30mm is threaded to take the nut.
I’ve a couple of cunning ideas to reduce the length still further but I’m waiting on an odd size of box section before I can finalise everything. I
hope to have a cad model finished over the weekend end and some mock up pic’s done next week. I don’t see calliper mounting as any real problem
Check this open source design http://locostusa.com/forums/viewtopic.php?f=26&t=6376
quote:
Originally posted by ZEN
Check this open source design http://locostusa.com/forums/viewtopic.php?f=26&t=6376
Posted Here
http://locostbuilders.co.uk/forum/3/viewthread.php?tid=150531&page=1