A friend of mine who is not big on literature research is talking about starting a scratch build mid-engined full body sports/race car project, and in conversation with him I am reminded of things I have learnt during the process of my build so far.

I note below some of my thoughts on how to approach a project like this. I understand that the below is spelt out in much greater detail in various excellent books and websites and is being discussed on other threads, I post it here as a summarized version. If I had followed these recommendations when I started, I would have saved myself considerable time, hassle and expense.

When starting out at least do the following, in this order:

Decide what the car is going to look like, i.e what body shell, if not original. This also determines wheel base dimension and the width over wheels. i.e determine the wheel positions.
If original body, decide on at least the front and rear track, wheel base can be adjusted.
Decide on what tyres you will use, exact width and profile, and procure if you are serious.
Decide on what hubs/uprights/steering rack you will use and procure/make if you are serious
Decide on what rims/offset you will use and procure if you are serious
Decide on what engine and transmission you will use and procure if you are serious.
Position all above parts on garage floor or build table and sort ergonomics – where do you fit?
If you are going to draw up in cad, finalize the position of all above parts in your model only now.
All the above could be an iterative process, but please complete it BEFORE you start the chassis.

Design suspension – if you are not going to do the research to enable you to do this yourself the only options are:
Get someone else to do it for you
Copy an existing car, strictly only valid if using that cars uprights/hubs/wheels/tyres.
Guess

Once you know where the inner suspension points are, you can design the chassis, to accommodate all above. CAD / balsa model / cut and tack on build table are all valid methods, but best results would be obtained by combining them. Please do not start with a Locost chassis and try to modify it to accommodate a RWD drive train.

Cheers

Fred W B

Fred, just to expand on the ergonomics point - try and find a similar cockpit and take measurements of the relationships of seats, pedals, column and gearshift. Then draw your 'personal space' including head & elbow room and make sure you put this into the mix as soon as you can.

[Edited on 29-10-07 by RazMan]

One other point I would make is to try and build in some adjustability wherever possible. e.g. pedals, steering column, seat position etc. IMHO being able to get a good driving position takes precedance over most other aspects of the car. If you can't get comfy and feel at ease with the car you'll never enjoy driving it.

Since I am a real nerd...

1. I have started by purchasing a seat.
2. Around the seat, I am currently building a mock including pedals, steering wheel and gear lever.

3. Using a gaming wheel, pedals and shift lever, I will use the mockup and spend some hours in front of my favorite racing sim (which means testing the ergonomics for hours on end)

4. Based on input from the gaming sessions, adjust ergonomics and re-iterate.

I would have thought that it would be better to sort the ergonomics first, and then decide on wheelbase; I find it difficult to find space for the pedal assembly when taking the front wheels turning angles into consideration - is this a problem i real life?

For my .002 cents the ergonomics are huge as was already pointed out. Getting the steering wheel and shifter to fall into hand are important as is the brake pedal position relative to the accelerator.

I think that your steps are in order but I want to elaborate on the process. I think that one of the more important things to do asap is ensure that you get the wheel scrub radius not going positive outboard of the wheel centerline. It is so important to get that right as this is how you get good feedback through the steering wheel from the tires and self-centering. I know this because I had to re-design my upright KPI location after I chose a taller tire and threw my scrub radius outboard of the wheel centerline. Once I brought it back 4mm inboard of the centerline, my self-centering came right back and the steering feel was much better.

So at the very outset you must pick an upright design for the front of your car, determine your total rolling radius of the tread, then figure out your scrub radius based from the KPI. That then lets you pick the correct backspacing on the rim. From that point on you don't change the tire diameter unless you re-calculate your scrub radius.

Hope I am not going into too much detail. Since you were just posting a summary, but I think that the scrub radius issue is overlooked a lot and IMHO is really important to a great handling sportscar.

Good points, thanks. Input is welcome, just want to build a thread that can be refered to.

Ringus -

quote:

---

I would have thought that it would be better to sort the ergonomics first, and then decide on wheelbase; I find it difficult to find space for the pedal assembly when taking the front wheels turning angles into consideration - is this a problem i real life?

---

quote:

---

If original body, decide on at least the front and rear track, wheel base can be adjusted.

---

Fred!

Thanks for your input, and sorry for not reading thoroughly enough.

Now waiting for Kiminis "read my book" (which I, btw have done already )

BR,
Ringius

quote:

---

Originally posted by Ringius
Since I am a real nerd...

1. I have started by purchasing a seat.
2. Around the seat, I am currently building a mock including pedals, steering wheel and gear lever.

3. Using a gaming wheel, pedals and shift lever, I will use the mockup and spend some hours in front of my favorite racing sim (which means testing the ergonomics for hours on end)

4. Based on input from the gaming sessions, adjust ergonomics and re-iterate.

---

[

[Edited on 1/11/07 by andygtt]

I'm a nerd - and I'm proud

[Edited on 2/11/07 by Ringius]

I would suggest getting other people to sit in it as well, maybe one really tall person and a short person just to check that if the resulting car HAD to be driven by someone else (for instance, if you sold it in order to finance the Mk 2 version), then that would be both comfortable and safe for them

Really good point. By the time I am done, my sons will probably have their licenses, I they are both seem to become taller than I am.

(currently I THINK I would let them...)

quote:

---

Originally posted by Ringius
I'm a nerd - and I'm proud

[Edited on 2/11/07 by Ringius]

---

quote:

---

Originally posted by andygtt

quote:

---

Originally posted by Ringius
I'm a nerd - and I'm proud

[Edited on 2/11/07 by Ringius]

---

lol, glad you took my comment in good spirit as I have just realised you are not the person I thought I was ribbing (similar advatar).

Not my usual greeting.

---

rumbled

Do you honestly think I'd be nerdy enough to set the seat up with my playstation steering wheel and pedals? Course not.






I used a plastic school chair, a dinner plate and a file box

Would be fun though ,wouldn't it