I love locost 7's! ...and I have to believe you are seriously underestimating the final weight of your vehicle.
If you are afraid that it's too light, I've got a Packard Flathead straight 8 with a trans you are welcome to use, weighs more then your estimated total car weight.
On the tire/traction issue, am I understanding it's because of tire patch/psi at contact surface? Larger tire patch equals less psi at the contact area.
Whoa..That makes wayy too much sense! So when I replace the coil-overs on the greaseslapper I want as light a spring as I can without the rear bottoming out on every bump I come across. In other words, the compramise on spring size will be toward compliance rather than stiffness. Changing weight isn't the answer.The sprung weight will pick up the unsprung weight if the suspension is too stiff. That's what makes dirt track cars pull wheelies even though the rear tires are not hooked up. Gotcha! That explains how those little Lotus sevens handle like go karts without getting past the limits of adhesion. The relitivly soft suspension ALLOWS the wheels to stay planted.
Yes, BUT a big Buick unloading the rear still can have more weight on the rear than the light car does under the same braking. The brakes in question were not designed for that particular weight and geometry, so it has almost no chance of being right by accident. He could luck out -- it's easy to test it on some sandy or wet pavement to see if the fronts lock first. You can regain control by lifting your foot for a split second in that case, but if the rears lock you can be pointed in random directions real quick. Rear lock up is a major problem, on 4 wheels or two, and you need to address it no matter how heavy or light the car. Newly built rods are always at risk.
Yes, and yours is one of them... Lower weight means better performance in braking, cornering, and acceleration. Unless there are other factors messing it up. Like hydroplaning, the balance of the car and/or suspension setup, or aerodynamics.
NO, NOT really. We were only discussing braking, had he asked about cornering or acceleration or anything else I would have answered differently, but he didn't. As for braking, given the parameters of the proper components for the weight of the vehicle, it is generally correct that the braking distances will be fairly equal for a light and heavy vehicle. Of course in the real world, brake systems are regularly not sized properly, tires sizes are all over the board etc, but in the context of theory, I will stick by my answers at this time
Your answer gives a pretty good indication of what's going on, without telling the whole story. If it did, cars would not be able to get past 1G, and even a good street car on decent street rubber ( like say, a '80s Porsche or better ) can do that. And Racers wouldnt be gutting their Racecars and putting big Rubber on it. The Stopwatch doesn't lie....
Understand that I am a proponent of lighter is better and was relatively amazed at what others were saying regarding weight and braking. That is why I explained that the forces of inertia and traction were linear and therefore the light vehicle will stop as well as the heavy one, and vice versa, with all other factors being equal.
No. They are close to linear. But not completely Linear. If they were, even a simple Swaybar would be useless as a tuningdevice for under/oversteer..
Again you are speaking cornering not braking. But to answer that, Anti Sway Bars do NOT change the weight of a vehicle, they attempt to distribute that weight differently to each corner of the car thereby reducing the probability of overcoming the slip angle of the tire that is on the outside of the corner, while adding weight to the inside tire to increase traction on it. There are also companies, Like Alfa Romeo that did not buy into the entire sway bar concept, instead relying on soft springs to keep the body roll from affecting the weight transfer as much - and it worked up to a certain load level.
I'm talking about acceleration. And as far as I know, braking is in fact acceleration ( negative acceleration ) The laws of physics dont change because a car is trying to speed up, slow down or go around a corner. A swaybar is a crude device. Its a spring, without any damping of its own, that increases the unsprung weight of a car. But even with all that, it works... Overcoming the slipangle is a breakaway point. A swaybar works through the whole range.
When you guys going to get into high and/or low roll centers and front/rear combinations of them and how they affect handling and also different moments of inertia,and how it affects stability/agility which was only hinted at earlier?
i say finish it THEN weigh it! that will get you what you want to know and some fun driving it if it in fact is TO light(thats a first,used to "Damn trying to move 4000lbs!")
I dont mind that this has strayed a wee bit off topic. I would use the term drifted but that might be construed as a cornering comment. It's good to have a discussion like hotroddon and metalshaps are having. We all learn by it.
The one in the middle weighs 310 Kilo - it has an all aluminium 602cc flat twin engine, transmission has an ally case and the chassis is a combination of 25mm diameter tube front subframe and a 360 degree glassfibre structural tub molding. It has had one wheel and its associated suspension mechanism removed to add lightness (a la Colin Chapman) ;-) If this weighs 310 kilo I'd sure like to know how anything with an iron V8 could weigh just a little more than that. Let me know how you've done it.
I'm sorry, did you say something, I was too busy staring at that wildly sexy three wheeler in the middle there. Please crate and ship to me immediately, thank you
W O W - Thanks for all the input - I have readded my parts and need to reword my total weight is unsprung weight - 918 lbs using a 2.5 4cyl ( 254 lbs ) - alum 5 speed ( 150 lbs) - 62 lb rad. - body skelaton is 38 lbs - figured 65 lbs for the glass for the body skin - bed metal -31 lbs - bed decking wood 18 lbs- 6 lb gas mini drum - 61 lbs battery - ect ect ect - Pretty sure i have everything added in less fluids - Front axle - 59 ford pick up drum brakes 15 inch rims - rear axle 7 1/4 dodge dart - mono frt spring 1/4 elipt rear springs - Harley Davidson coilover rear shocks - gas ATV coilover frt shocks w/ 400 lb rate springs -- If this is too light I will go to the 225 slant six ( 417 lbs) with 904 auto trany( ? lbs) BUT THANKS FOR ALL THE INPUT - Jaxx
I guessed I missed something, but if you are going to run a slant six and stick in a chrome moly tubular space frame (ala sprint car), I can believe it MIGHT be possible. I. E. 225 slant six goes around 450 or so, early aluminum block about 70 less, aluminum 170 even more, aluminum intake (feather Duster, early super six, or some kind of aftermarket would save another 20 or so, tube headers 20 or 30 more over the cast iron manifold, so it might be possible to get a slant down to 300 to 350 with the right components. Aluminum short tailshaft 833 (overdrive Feather Duster or aftermarket are probably the most common) would drop transmission weight to 70 pounds from the 130-135 of a regular A833 or a 904. 7 1/4 inch rear will go about 80 pounds with 9 inch drums, with rear suspension adding another 30 to 50 pounds depending on what you use. Just a driveline will add another 10-20. Tubular chrome moly frame would weight in about 80 pounds bare. Figuring a not so unrealistic 350 or so for the slant and you're up to 580 so far. Undropped sprint car axle and tubular torsion bar front end setup with aluminum hats and calipers, chrome moly four bar and panhard rod is probably the lightest complete straight axle setup available and would still be at least 100 pounds. Manual aluminum Mopar steering chuck about 10-12 pounds. Early 20s Dodge bucket with aluminum floor would probably be under 100 pounds, but add a windshield and interior and you're talking more like 200-300. Aluminum radiator, track nose (aluminum or glass), and a small fuel tank would add another yet another 50 to 75, and more likely over 100. The lightest wheel/tire combo will add 20-30 pounds a corner. Add in at least another 100 pounds for the misc. (steering column, instruments, brake master cylinder(s), wiring, etc.). Best I can it figured get down to is STILL a tic over 1100 pounds. What components are you using that make you feel the finish weight will be so light?
950 pounds? No weigh! I have nothing intelligent to add. Edit: no, wait I do: It cannot be too light.
Drag racers lighten their cars to accelerate faster. It works exactly the same with deceleration. A light car will decelerate and accelate faster than a heavy one. It's simple momentum. Momentum = Mass X Velocity If you have more mass (weight) you have more momentum, which is the tendency to keep moving. Less weight means less tendency to keep moving. Unless you can change the laws of physics, light cars stop quicker than heavy ones. There's only two things which change the laws of physics. Pride and Beer. Beer can be expressed by the following formula: Momentum = Mass X Velocity X Beer Here's the equation for pride: Momentum = Whatever I say it is.
I've almost driven myself nuts trying to figure this out so i dont think about it anymore, but can a car be too light? I mean, there has to be a point where a car would be too light. what if it weighed (impossible, I know, just for an example) only a couple pounds? You have to have some kind of pressure on the tires to get traction, whether it be through down force (impossible at standstill), or good old fashion weight, right? ughhh its happening again...
I don't believe that weight is possible for a fully equipped road car, maybe a stripped to the bone single seat race car. But anyhow, motorcycles are pretty light and they accelerate and stop just fine. What worries me more about something built really light for the street is fragility. You may start having problems with things cracking and falling off. Things like chassis flex driving over uneven surfaces, and having the doors jam shut if the car is parked on an uneven surface. All the flapping and rattling parts at speed will not feel secure. The lightest car I have ever owned was a Lotus, and it had many problems. A great little fun car but it aged fairly quickly because it was so light and fragile in construction.
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