The microscopic irregularities in the road mesh with the irregularities in the rubber like teeth in a gear.
Yeah... In a way it can. This car weighed about 770Lb It did fine on 8 1/2" fronts & 11" rears ( hillclimb compound), but was undriveble on 11" fronts & 13" rears ( roadtrack compound ) There just wasn't enough mass & friction to get those tires up to operating temp...
So far, all of the examples have been given in optimal conditions. Yes, a lighter vehicle will stop faster than a heavy one.....on a glass-smooth surface, but not on a rippled blacktop roadway. Bounce will severely change all of the aforementioned dynamics. Remember, we're not talking about strictly salt flats racing. If this will be on America's highways and byways, it will NOT be adhering to classroom physics. It will be obeying the laws of crappy roads combined with classroom physics. Yes, a heavier vehicle will exert its mass etc....blah blah blah, (mass X beer minus the square root of the hypotenuse of my sister's bra, X pi) but all of that must be taken with a grain of salt when said mass bounces off of a rock, pot hole, log, dead skunk, etc. Also, a heavier vehicle, when stopping, tends to 'mash' the tread of the tires downward, creating a larger patch of tire connecting with the road. Let's face it, I'm not smart enough to figure out all the variables, but I've had an empty truck trailer bounce its ass off behind me and take forever to settle down, where a full one would only grind lazily to a stop. THAT is just experience talking. I'm sure the laws of physics took a holiday at that moment. Ya, know...just for me.
I looked at trying to build a 1000# car with a Duratec but went with Pinto and reworked an old 2x3x3/16 frame. Going for light weight concentrating on unsprung weight I planned on www.chuppshotrods.com/html/pricing.html for 1-1/2" x 0.188" front axle and his quarter elliptic rear suspension. Might be heavier than coil overs, but has the look. Alfa Romeo 105 has a 4.10 posi disc braked aluminum centered rear that has a banjo look. Without a lot of power look at Hoosier or M/T ET Front tires all around. 26" or 27" for rears are only 13# each, 22" or 24" for front are 7# or 11#. Use 4 bolt Mustang aluminum spare wheels to match 4 x 108 Alfa rear bolt pattern and get same for Chupp's Wilwood fronts.
I don't think there is any way it can be too light. Motorcycles, Formula 1 cars, road racing bicycles, examples of very light with either wide or narrow tires. Peter
I've asked this before on a couple of related threads... why isn't there a good guilde or chart available from the tire mfgs for recomemded tire widths versus vehicle weights? I'm mostly interested in general safety / performance in all all season driving. It sure would be nice to start your build with wheels / tires that are the most appropriate and safe - then worry about looks / fads. Never got a good answer... Too hard? Gary
I know having a light curb weight is good and all but getting too light can work against you. My cousin's 1950 Studebaker pickup body sat on a dodge truck short wheel base frame with a stock 318. Even though it was a truck probably making it heavier than a car it didn't get traction for shit. Everytime he would try to go for a good takeoff it would just sit there and spin the tires. I would suggest going for a heavy engine and try to figure a way to add a little bit of weight here and there.
Some tyre makers are more helpfull than others with regard to information, All tyres have a load rating which tells the max the tyre will hold up, but in terms of what width works best with what load, too many variables for any kind of chart. Found this; 660lbs street legal with a 0 to 60 of under 3 seconds, called a Roadrazer, 175 bhp four cylinder Looks a little like Ed Roth style ( or is that just me )
That is easy, the production car people do a lot of work on this. You will not find skinny tires on a 6,000 Lb SUV, and you will not find 10" wide rims on a Japanese econo box. If it weighs only 1,000 Lbs, four motorcycle sized tires would probably be about right. And there is some pretty high performance bike rubber out there to choose from. And there is no reason at all that a light vehicle will ride any worse than a heavy vehicle (vertically), provided the suspension rates, and unsprung weight are reduced in proportion. That probably means wire wheels and very soft springs, but it could glide along like a Cadillac, provided there is sufficient suspension travel and the wheel diameter is large enough to cope with really large bumps. But ride rate is not the whole entire story. Very light vehicles often are fairly short and narrow, so it will pitch and roll more on bumps, even with very soft springs. It is vehicle size and polar moment that give it stability, not just weight. A very small light vehicle could probably benefit from a high polar moment. In other words fit the heavy items to either end of the chassis, rather than in the middle to reduce pitching on bumps. And fit the wheels as far apart as possible to give maximum track and wheelbase for best ride and stability on bumps.
well most street bikes have 2 tires and weigh less than 1000 bls, and stop pretty good.you want to build a car that weighs 1000 lb and it has 4 tires .and the problem is?
I think I understand the problem from a weight per wheel load perspective, but what I'd really like to get at is contact patch(es) vs weight / weight distribution. Obvioiusly, a wide tire will support a light car, but it will hydroplane far easier not to mention be uncessarily heavy. Conversely, a too-narrow tire that will still carry the required load may not have even the optimum tire patch for even "normal" driving / cornering of an OEM car. Given that we rodders almost always start a build / choose rims n tires for looks rather than real world realities, I just thought it would be neat to at least have a known, bottom estimate for real world situations before we start building our fantasy cars. Could it be just as simple as knowing rim / tread width / contact patch versus wheel load? Factor in track? Wheel base? Front / rear weight distribuiton? One other question... motorcycle tires have such a tiny contact patch (and aren't motorcycle tires basically designed more so they run more on their sides versus vertically?), so... why would you choose them for the front wheels on cars (except perhaps the fronts on drag cars, land speed cars and soap box derby racers?). When I see them on hot rods... I just shake my head in amazement. Thanx, Gary
proportioning valve, it limits the pressure to the rear brakes under heavy braking, this stops the rears from locking up and the back end taking on a life of it's own. you can tget them reasonable from places like summit,but the problem is if you have a diagnol braking circuit with a dual master cyl, this means left front right rear, right front left rear on split circuits, you will have to source an OEM one, the split braking circuits are a good safety item,no one will ever know about. prevents both of the fronts or both of the rears from failing at once,this could make your car take off in different directions,depending on which failed. the split circuit means you have a much better chance of keeping control.
Very wide flat tires have a few problems. First they may not always stay completely flat on the road as the body rises and falls, or rolls, on it's suspension. It helps if the vehicle is very low, and has a very wide track (like a proper open wheel race car). But a very light practical road car, may be relatively skinny and tall for packaging reasons. Fitting very wide tires to a tall skinny vehicle with a soft suspension that rolls a lot cornering, is not going to work too well, even in the dry. In the wet it will be absolutely diabolical. Bike tires are ideal BECAUSE they work at funny extreme camber angles, they are actually designed to do that. The round section also disperses water pretty well. And they are light weight, have a low rolling resistance, exactly what is needed. They also have suitably high speed and performance ratings, and the load ratings will be about right too.
By the time you add a transmission, heavy rear end, and strengthen everything enough so it does not break, it will be right back to being a a very heavy car.
O/k here is a fully road registered car that weighs 1,005 Lb. It has 245 Hp and accelerates to 100 Mph in well under seven seconds. And it does not need a bloody great cast iron V8 engine to do it either. It also stops and goes around corners faster than just about anything else on wheels. http://en.wikipedia.org/wiki/Ariel_Atom <a
Contact patch area is weight divided by tyre pressure. Idealy it's nice if the front and rear pressures are not hugely diffrent. As a ball park, I would go with 1" of width for every 100lbs wheel load minimum. Where a tyre touches the blacktop the surface bends to create the required contact patch to hold up the weight against the pressure of air inside. So while motorcycle tyres are much more barreled than car tyres the area of the contact patch still is the same for the same tyre pressure, however since motorcycles are fairly light they are often available in softer compound, so they are not such a crazy choice as first seems. You are right that starting a design with the tyres is the way. Certainly I have always started by looking at the wheels and tyres I want to be able to use, and working out how much set back, chassis length etc is going to be needed to suit, but I admit this is my first time building a road going hot rod, and I guess hot rod builders come at things from a diffrent angle. While things like the Ariel Atom and Roadrazer are amazingly light, and thier motorcycle four cyclinder units produce amazing power for thier size, but I guess a V8 is still where it's at for this site. So how light can a car be with one in ? I have serious thoughts about making the engine/gearbox the 'spine' and saving frame weight that way while still keeping the 'look', various people have pointed out that engine blocks are not meant to carry 'chassis' loads - but when your engine is iron a half inch thick you got to figure it's fairly stiff compaired to any frame I could make to bolt it into.
I can add only the examples of a few vehicles that I have actually weighed: 'T', 350/TH400 = 1900# '69 Cadillac Hearse = 6500# '75 Moto Guzzi 850 + sidecar = 650# '81 Citroën 2CV6 = 1350# And, FWIW, they all stopped very well, save the Goose wanted to turn left whilst stopping quickly...non-braked third wheel. Cosmo
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