Let me start off by saying I
really like what you're trying to accomplish, and think you have the beginnings of a great design on your hands!! I also very much applaud your effort to give the car a certain nostalgic feel and character. However, as with any early development model, there are a number of areas of concern as well.
esp42089 wrote:
Total width at rear tires is ~58"
Measure again. Based on the posted images of your model, even the front wheels are in the 60" ballpark across the outsides of the tires. The rears are closer to
68. Not that this is a problem, especially if you like your elbows, but just a point of accuracy. To get a 58 inch width, with a 38 inch frame, and nearly 9 inch wide tires, would leave you with ~1" of elbow room between the inside of the tire and the frame.
esp42089 wrote:
Between the fast rack and the big wheel, it should be precise without being too twitchy, all the while feeling very old-school.
If by "old-school" you mean "extremely heavy", they you're probably right.
esp42089 wrote:
Tires are the most common size in the world: 225-45-17.
Good choice, and good on you for making this an early decision.
esp42089 wrote:
Why not use a lever on the shifter?...
...The hand clutch may actually help with this as hands are more sensitive than feet, so 1" of travel isn't a problem....
...I'm told those triple disk 5.5" clutches have very very short strokes from engaged to disengaged and that on a street car the clutch becomes an on/off switch. My hope is that this behavior works to my favor on a hand clutch because a couple inch stroke is all that could be managed. I'm thinking I need to call around and see what the manufacturers say. Maybe a motorcycle clutch like below would move enough fluid to actuate the clutch, because that could be a pretty workable solution.
Yes this style of setup can work great with a bike clutch in a bike engined car, no it will not work worth a damn with a racing clutch in a car engined car. Pulling a few random numbers from the internet...Lets assume a 9:1 ratio at the very tip of the clutch lever, a .312 in^2 master cylinder, a 1.215 in^2 release bearing, and a clutch that requires 650 lbs to release. This will actually get you down to a 18.5 lb pull at the tip of the lever...However even with a 3" pull, it will only move the release bearing .085 inches. The setup instructions require .170-.230 of air gap between a new clutch and the release bearing, to allow sufficient space for the spring fingers to rise as the discs wear, and that's in addition to the flex in the spring that needs to be overcome before fully releasing the clutch. So while it surprised me by getting the force into an acceptable range, it does so at the expense of travel. And reducing the travel enough to be viable would result in it being too much force to operate motorcycle style with you hand. While hands are more sensitive than feet, they are also much weaker. If you went with a dog-box transmission, you might be able to get away with a parking brake style lever actuation just for getting started...However, nothing about any of this is street friendly. These clutches aren't just an on/off switch from a modulation standpoint, but from a functional standpoint as well. The quickest way to kill one of these clutches is to slip it.
esp42089 wrote:
I'm thinking about a 3-link with a Watt's link for rear suspension
You'll probably want/need a significantly beefier mount/support structure for your center link. It's going to see as much load as:
(engine torque x gear ratio x final drive ratio) /(lever arm length from center line of axles measured in feet)
However, this is also limited to a maximum of the amount of torque that the tires can react against the pavement.
esp42089 wrote:
I've modeled a Hub-to-Hub of 56"
Considering this, in combination with my initial comment on the width of the vehicle, it appears that you modeled the wheels with the wrong offset. By my rough calculations you've modeled maybe a 38 or 40 mm offset in the negative (mounting surface inboard of wheel center line) direction, effectively widening the car. Where as the vast majority of wheels with that size of offset are in the positive (mounting surface outboard of wheel center line) direction...Most often also by a similar amount. So with more typical wheel offsets, expect to lose another ~3 inches of (frightening that you even have to measure it) elbow-to-tire clearance per side. Also, to get a 58 overall width from a 56 hub distance with 225 tires, would require something on the order of an 89mm offset, again in the positive direction.
esp42089 wrote:
Front suspension is not done yet.
Between that and the radiator, I have no idea how you plan to get the engine in and out...Although I suppose the chassis could literally be built (permanently) around the engine.
esp42089 wrote:
For width, the frame is 38" outside to outside edge. I mocked up some cardboard and found that I can sit comfortably next to myself in the car
What about your ability to perform large/quick steering inputs, like trying to catch a bit of power induced oversteer on a short wheelbase car? Seems to me like your passenger would be likely to inhibit this to at least some degree.
esp42089 wrote:
I'm not sure a 4pt harness adds much safety over a lap belt.
Absolutely out of the question if you plan to actually drive this anywhere on the street. Even a minor collision would likely result in moderate to severe injuries. I'm going to go out on a limb and assume that you don't actually think a 2 point lap belt would provide anywhere near the same level of safety as a 4 point harness, and that you are actually intending to refer to 3 point belts. In a production car where you sit further from the steering wheel, a 4 point harness may not add much over an OEM 3 point belt...But when sitting that close to the steering wheel a harness (preferably 5-6 point) is almost a necessity. In fact, as close as that's modeled to the driver, you'd probably still be well served to add a steering wheel pad in addition to being fully harnessed.
esp42089 wrote:
I really prefer the taller, narrower look of Indy cars.
Personally, I think you may be trying too hard to keep the overall package too small...Especially if this is meant to be genuinely enjoyable for you to actually drive, and not just look at while it's parked. Proportions could be kept similar, but merely made more realistically functional. Remember, while computer models may allow you to put 10 lbs of poo in a 5 lb bag, doesn't mean it'll actually work when you try it.