13 Jan 2008

Tires:

Tires are the most important – and most frustrating – decision during new car design. Nearly every suspension design parameter is related in some way to tire choice. I’m owing to stay away from hard-to-find 13″ street tires so it means going larger, to 15″ if not 16″ or even 17″. I’ve spent weeks going back and forth between brands, trying to settle on a size that everyone will be able to find, both now and over the life of the book. This very likely means going to 16″ or 17″ to guarantee some non-obsolescence. Yes, larger wheels and tires have a higher polar moment of inertia, weigh more, and cost more. On the other hand is the possibility of simply not being able to find what I specify, so the former outweighs the latter.

Before people jump up and down saying that it’s easy to find 13″ and 15″ tires, well yes, and no. Sure they’re out there, and they’ll continue to be for some years; the problem is the compounds. For as light a car as is being designed, high mileage tires are neither needed nor desired. This thing’s not going to driven in snow or rain (much) so all-weather tires aren’t wanted (besides, it’s a sports car). We need what tirerack.com calls “Ultra Performance Summer Tires”. This greatly cuts down the list of contenders, and even the list of high performance 15″ tires is getting thin, about how it was with 13″ tires when I designed Kimini. Note that this only applies to street tires, NOT race tires. For the track, getting 13″ and 15″ tires is easy, yet that’s not the starting point of this project – it’s going to be street-legal. 14″ tires aren’t mentioned because they never were a popular size and are fading fast, there’s no reason to even go there.

So in an effort to design in some staying power, the tires may be larger. For the moment, my sole concentration is on choosing tire diameter, a primary design concern. At this point, whether the tire’s made for 13″, or 15 – 17″ wheels is immaterial. However, when I read tire data and see that there’s a grand total of only one or two 15″ sizes, the writing’s on the wall.

12 Jan 2008

Spent a few hours carefully measuring a front suspension upright to load the dimensions into WinGeo3. It’s time consuming to find the center of rotation of balljoints. Yes, in the interest of reliability, availability, and cost, I’m specifying stock balljoints at the outboard ends. That makes it easy for the builder to get them from any parts store.

Shocks: Those who read the Kimini book recall my angst over shock selection and pricing. Good shocks are very expensive; I recently saw a new astronomical price for one> shock… $2000. I say unless it comes with topless maidens who install it, I have to wonder what the price gets you. Maybe it includes having an F1 champion fly in and drive your car. Anyhow, I’m wondering once again how I’m going to deal with the expense. The shocks, by necessity, must have adjustable ride height and adjustable valving, preferably being double-adjustable.

In the back of my mind has been to use sportbike motorcycle shocks. It’s nothing new; people have been using them in Locosts for a while now, though many builders are clueless about spring rate versus installation rate. They change the springs to make it all work, then wonder why they can’t set the shock valving the way they want. Anyhow, new bike shocks are also expensive, too, BUT, many bike owner remove them when they upgrade the suspension. That’s excellent news for us because they end up very cheap on Ebay. As a comparison, the Koni shocks on Kimini are about $500 each, plus a $50 spring. The price of a used sportbike shock and spring is $40-$50. Yes, about 10 times cheaper. This is a huge reason to consider them even if they aren’t perfect. Heck, the saved money can easily pay for the entire drivetrain! Bike shocks can> work in a car; the secret is to use them as-is, without changing spring rates. That’s because the shock valving is made to work with a specific spring rate; so as long as it remains unchanged, it doesn’t care what it’s installed in.

This brings us to the next topic, whether to mount the shocks in the traditional outboard position, with the outer end on the lower A-arm,
or to use pushrod suspension. The traditional position is simple, easy, light, and easy to adjust. Using pushrods means more joints, a
pushrod, rocker-arm, and potentially burying the shock inside the body where it’s hard to access. Pushrod suspension came from Formula One where they had to get the shock and spring out of the 200mph air blasting over them. It allows putting them just about anywhere, which is important due to underbody airflow management. We have no such problems! However, many people think pushrod suspension is cool (and it is) but is the added complexity worth it? No… and yes. Technically it’s not, and completely silly, adding unnecessary complexity and making adjustment a potential pain. BUT, what overrides these objections is the $1800 we save. It means we have to compromise our “technical reasoning” on a cost basis.

This reminds me of something Dave Norton (Shrike designer) said about push-rod and rocker-arm suspension, “Just because you CAN design something doesn’t mean you Should design it.” He was referring to the added complexity versus what it does for performance. I have to agree.

Because of the complexity I had no intention of using pushrod suspension until I found how inexpensive motorcycle shocks are. Due solely to pricing, it’s probably the way to go. It does mean adding two rod-ends and a rocker-arm bearing. The one problem with designing in specific motorcycle shocks (and writing a book that uses them) is that over time, that particular unit will become hard to find. To offset this, I’ll choose one from a popular (therefore, common) which will hold off the obsolescence for a long time. Lastly, the ride height adjustment on the shock is unusual, using a ramp-type ride height adjuster instead a threaded collar. This could present a problem, BUT, push-rod suspension lends itself well to adjusting ride height elsewhere, by changing the length of the push-rod. So consider the decision made – probably.

11 Jan 2008

I realize I haven’t described what Midlana looks like. While the details are still squishy, it’s basically a Lotus Super Seven with the passenger compartment pushed forward enough to allow a transverse drivetrain behind the driver. It’s not original (what is?) as there’s one manufacturer in England (Sylva) that produces one now, the Riot. Will Midlana be a knockoff of that, no, though all these cars are a knockoff of something. No, it’ll be its own thing, but will use commonly available composite so the builder has little or no messy, stinky composite work to do. It’s going to be “buildable”, easy to maintain, and inexpensive.

Thanks for all the comments regarding seat placement, sorry I couldn’t respond to everyone separately. I think I’m going to stick to the traditional side-by-side placement. It’s a combination of reasons: routing the seatbelts, not getting undue attention from safety inspectors, motor vehicle registration people, and later, cops, and, being able to hear, say, a driving instructor. From a selfish point of view, it’ll be much easier to get it through registration in California if it looks like a “normal” car. Then there’s the “too different” aspect; I’d like this car to be something people <i>want</i> to build, and the center seating might be a bit much. I know I’ll never make everyone happy, but alienating a huge group right off the bat’s probably not a good idea!

Engine choice: The builder will have a decent-sized bay to install whatever they want (with limits). Everyone has access to different engines due to differing budgets and regional availability. Then there’s form factor. There are many transverse FWD drivetrains out there, all with similar layout; that’s the type that Midlana will accept. Of course there are other engines like the Subaru flat-four: low, light, with a “real” transaxle. The problem is that the transmission tail shaft sticks out quite far past the axle centerline. That’s of no consequence if the car’s designed for it, but it’s not. A transverse layout is shorter, front to back, which packages much nicer, and there’s the rub. There are far more transverse drivetrains out there than Subaru drivetrains, so I didn’t want to force builders to use only one engine brand. (Technically the engine bay could be made large enough to fit everything on earth, that it gets out of hand. This is the consequence of following a cookbook; you’re stuck with the designer’s vision).

10 Jan 2008

I have a question for you: if you had a choice of building a car with two seats side-by-side, or two seats, one behind the other, which would you choose? In the first case, the car could be considered more “sociable”, in that you can easily talk to and see each other. This is important, but I’m not sure how much. I mean, how many people do you Really give rides to? Does your spouse Really love riding in the car, or is it more to be polite and put up with your crazy hobby.

Or, do you compromise the social aspect of it by putting yourself front and center, like driving a “real” race car. Also, the car wouldn’t have to be all that much longer since the rear passenger’s feet could straddle the front driver’s seat. There’s no pesky driveshaft tunnel to fool with, so that’s not an issue. Hmmm, something to think about, but I’d like comments either way. I think I know the answer, that it’s just a bit too “different”, but I’d like you to consider what you get (as a driving experience) before discarding the idea).

It suddenly hit me today that unlike Kimini, where I did anything I wanted and didn’t care what anyone said, now I have to care what people think. It’ll take some readjustment, having to listen to what people want! Or do I say, “This is how it is, take it or leave it.” That doesn’t do well to sell books with that kind of attitude.

Let me know. Of course, none of this is going to happen unless I find a drivetrain.

9 Jan 2008

Just this morning I was very, very close to getting a great deal on pistons and rods for my chosen engine. Then, I started thinking about it all and canceled the deal, but let me back up and explain. I preface this with, once again I’m going mid-engine.

My brother, who’s using the GM supercharged 3.8l V6 in his Stalker, of course thinks that it’s the no-brainer obvious choice. I said there aren’t decent transaxles for it, and adapting one to it seemed silly, but he said with enough effort I could make it work. Exactly… I don’t want to reinvent the wheel when there are already FWD drivetrains waiting to be used, and not really heavy one’s either. I’m comfortable with Honda engines, having built Kimini using a Honda H22A1. Because of the awesome aftermarket support, both in parts and forums, I’ve decided to stick with them.

So over the last six months I’ve been thinking about which drivetrain I’d like use. While Midlana will accept many drivetrains, I still had to pick mine. Naturally I was drawn to the largest 4-cyl that Honda makes, the K24 (2.4l). There are four variations, going in the CRV, Acura TSX, Euro Accord, and USDM Accord. Each has different power levels, with the TSX being the highest, Unfortunately for that very reason, it’s the most desirable and sought after. On the other hand, the Accord, making about 20% less power, is typically about three times cheaper – really. Many people convert these over by adding a better head, changing the pistons, rods, and so on. It wasn’t until today that I started rethinking my whole engine selection. If I get the Accord engine, I’ll have to build the engine before I can use it; that wasn’t the intent at all, I want to drive the car as soon as it’s on its wheels. Then I started adding up the costs of getting a Accord engine to what I want and was surprised that, for the money, I could just go straight to a 200hp TSX engine. It’s a slam-dunk solution; buy it, put it in, and I’m all set. Even better is that when I go forced-induction, zero internal modifications are needed. [that’s what I thought at the time, hah (Sept 2016)]

Of course, don’t expect what I say today to be what I do tomorrow, as I’m full of vague nebulous ideas that come and go all the time. Just because I come up with something doesn’t mean it’s going to stick around, and it can be discarded like yesterday’s Hollywood starlet. On the other hand, I realize people like reading along, following my thought process, be it smart or completely idiotic. Anyway, the more time I spend typing the less I have to work on the design, so I’m off to work on that. I’ll discuss the plan in more detail in future entries.

8 Jan 2008

A kind coworker let me take dimensions off her car’s drivetrain, the make I’m considering using as donor. This is an important step because, even though many engines will fit Midlana, I want to make absolutely sure that mine will fit, too.

6 Jan 2008

Well, vacation has come to an end, though I managed to cross some things off the to-do list: clean the garage, make good progress learning CAD, and added pages to the book manuscript. Also received the suspension design software from Wm. C. Mitchell, along with an amazing suspension book by Rowley, so between these two I’m ready to rock and roll.

Oh yeah, I wore out the little electric RC helicopter, surprisingly, not by crashing it; the tiny plastic gears finally stripped out. So of course I fixed that by buying a bigger helicopter 😉

Looks like, as with Kimini, I’m going to have to buy a drivetrain if I want to know how big it is because no one’s taking the time to help me measure certain drivetrain dimensions. A little disappointing, but as expected. Short of that, I realized that a coworker has one of these cars so I guess I’ll be measuring her… engine.

2 Jan 2008

Got an electric helicopter for Christmas, which is surprisingly capable for the low price. Great fun flying indoors, as long as Cooper doesn’t get at it. From his point of view, it’s a big bug that invading his space!

Spent the day cleaning out the garage, and it’s far more pleasant now,  not stepping on boxes and stepping in grit everywhere. Of course our  trash can now weighs about 250lbs… I wonder if the trash guys will  complain. A clean garage is a vacuum, wanting to be filled with something. I’m working on that.

28 Dec 2007

Ordered WinGeo3 4.03 from Mitchell Software. It’s one of the few (and perhaps the only) suspension software packages that uses force application points instead of kinematic roll centers. I figured out this is a better way to design suspension and will use it to design MidLana’s suspension. It also cleanses my soul – slightly – by finally paying him! See, I had used a very old DOS-based copy of Mitchell’s FreeBody software to design Kimini’s suspension…

24 Dec 2007

Sorry for the lack of updates, things are happening, just slowly. Received the uprights and the steering rack, parts needed before suspension design can start. I also need to choose tires and wheel sizes… not necessarily buying them yet (like I did with Kimini, and have the tires harden for 10 years, but I digress) but a size is needed as they’re part of the overall suspension design. I’m currently deciding between 15″, 16″, and 17″, since I’ve given up finding 13″ street tires.

Started reading up on potential drivetrains; I’m pretty sure I know which one I want. It’s now a matter of finding weight and sizes, which is much harder than it should be.

Learning CAD is frustrating, to me at least. My creativity shoots miles ahead, then stands around waiting for me to use the tools in order to achieve the vision. I don’t blame Alibre Design, I’m just too dumb to know how to use it yet. I don’t have the luxury of using Alibre at work (or any CAD for that matter) so it’s taking a long time to learn.

Instead of making drawings of every tube, there will be one fully dimensioned master drawing. The reasoning is: because metal moves when welded, and tubes are never cut exactly the correct length, exact dimensions are useless. If “Tube 63″ is specified to be exactly 12.48574532″ long, with a 43.2 degree angle, but the space it’s supposed to fit into is physically 12.5” and 45 degrees (due to cut errors and welding distortion), what good are tube drawings? Said another way, having one master drawing means that <i>target</i> dimensions are given, not exact hard numbers. This makes it clear to the builder that while the values are <i>theoretically</i> exact, it’s very likely that the space it’s to fit in won’t match the drawing exactly. That’s okay, and it tells the builder that he can, if he wishes, correct the error then, make up for it later, or just not worry about the slight inaccuracy.

Over the break I plan to clean the garage, as boxes have been creeping onto the floor over the last couple years. Freeing up room gives extra space for, oh, new things. Where Kimini’s going to park once construction starts is something that’ll be dealt with then.

Merry Christmas everyone! Oh, and I have a name for the new car: MidLana. Mid because it’s mid engine, and Lana is our granddaughter’s name. I like the sound of it, and it’s unique on the Interweb… it’ll just take a while before people can remember it off the top of their heads. Hopefully – this time – the car will be done before she’s 10 years old!