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why don't cars have bigger wheels/tyres? Answered

yeah, why don't they have bigger wheels? currently car tyres are about 60 -80cms high. so why not have tyres that are say 120cms or more. more road grip. more components could be stored in it -i.e. for electric vehicles-motors or for reverse breaking-etc.



The tire noise would be higher, there would probably be more friction, and the cost per tire would probably go WAY up.

I was just wondering how would the wheel size affect a vehicle like a soapbox derby car where the only power is from gravity pulling the vehicle down a hill

It just isn't worth the overhead to produce, ship, store, and maintain.  remember that tires aren't made from soy or recycled plastic bags.  Unsprung vehicle weight is the name of the game.  (efficiency)

Loads of reasons... Aesthetic reasons for one, then there's the materials costs of making larger wheels, they're also harder to turn because they'll weigh more. Along with all this larger, heavier wheels would increase fuel consumption somewhat and take away acceleration. Space issues are another reason, the wheels take up space that could be used in the body for other stuff like people, along with the issue of keeping a giant spare wheel.

Larger wheels make for BETTER acceleration (look at any drag-racer for proof). Smaller cars with poor acceleration tend to have tiny wheels. Few cars have full size spares, lots have 'mini donuts' or 'run flat' tires. When was the last time that the wheel well was in the way? Most car bodies are hollow over the wheels, and interior space wouldn't change much with a larger tire-and if it was a problem, the designers would just push the tires out a bit.

I'm talking in terms of actual weight further from the wheel, larger wheels do allow for more grip to accelerate with on drag racers, in terms of everyday cars there's no need for the extra weight which makes it harder to accelerate because you have to accelerate a much larger mass... The boot or trunk usually is made smaller or more awkward by wheel wells, if designers did just do that people carriers would have wheels out the side...

The difference in weight between a 14 inch geo's tires and an 18 inch truck tire is not going to affect practical amounts of acceleration because of weight-unless you notice that having a passenger slows you down? Or a full tank of gas? Never seen a truck with duelies (double tires on the back axle to carry more weight)? Would an extra 4 inches or so around the wheel well make a car 'unsellable' because of 'lost' trunk space? All of your reasons assume that designers start from a blank slate each time they design a car-they don't. Everything is affected by the current market, which is the result of past car designs.

I suppose none of those are big concerns, not enough to affect it, what you brought up about pre-existing designs is probably the reason, it's about the accepted version of design really. Cars do in general look like cars, they have accepted body shapes and configurations, there's not that huge a deviation from the norm really.

To add to yours, it would take more energy to turn the wheel, but it would go farther, so it would be like starting in 2nd gear

"Larger wheels make for BETTER acceleration (look at any drag-racer for proof). Smaller cars with poor acceleration tend to have tiny wheels." Apples and oranges. Larger wheels/tires are not responsible for a drag cars' tremendous acceleration. The supercharged, nitrous-injected beasts of engines in those cars are responsible for that. One reason drag cars have large wheels to handle the speed found at the end of a race. A larger wheel will be turning slower than a smaller wheel given they have the same tangental velocity. Slower angular velocity means less centrifugal force, meaning the tires are less likely to shred. Smaller cars with poor acceleration, or economy cars, typically have small displacement engines. Economy is key with these cars, and low production budgets call for small, inexpensive wheels. Unless, of course you were thinking of width and not diameter.

Then why the small wheels in the front?

for less drag (air drag) and weight, those cars need front wheels ONLy to steer, very very very lightly, thus no need for a wheel that can take 90 degree turns at 100 mph for example

So your car will do a 90 degree corner at 100 without rolling? Sweeeeeeeeet-can I watch? Can I? Can I? Pleeeeeeeease?

nah dont take it litteraly i was exaggerating on purpose... but TRACK cars can take sharp turns at high speeds without rolling... i dont really know what part of my point was so hard to understand that you had to reply that way and i dont understand why the attitude towards my comment, see that "be nice" comment policy thing below your post, its there for a reason, id appreciate it if you replied in a respectful maner as i did, and if i failed to do so then i apologize for it

BTW everyone is focusing on the weight of the tires, but it has to do more with the increased "torque" needed to move a wider diameter of wheel... you see there is a thing called "angular momentum" (im not sure the translation is correct tho) wich increases with the "lever length" (in this case the radius of the rim), automotive engineers take estetics into account that is true but the guys who design the engine, transmission, differential etc... design an engine for those tires and or viceversa bcuz the balance between torque, car weight, car acceleraton and top speed requires those tires, thinking that bigger tires have better performance is a common misconception among people, because it sort of makes sense, but there is a reason why it hasnt been implemented yet and its not politics or esthetics..

What's critical in this case is that a gas engine has a 'sweet spot' for power and the transmission has to be designed for that. A go kart has to start with a spin out because it has a direct transmission and a slow start would stall the engine. IFF (If and only if) the power train stays the same, a slightly larger wheel will perform better-but be pushing the envelope of safety built into the calculations for the power train. Which still doesn't answer the question of why tires are the size that they are. Tires have been in the same size range since the original cars were built. Why? Perceived market. Things stay the same-in this case because the people laying down the cash had their perceptions of 'what looks right' solidified 20 and more years ago.

By small, do you mean narrow or short? Looking at the front wheels, they are still quite tall, almost if not just as tall as the rear wheels. There are narrower because: a) less mass to accelerate b) braking is usually reserved for the parachute. The traction under braking afforded by a wide front tire is therefore redundant. c) aerodynamics(kind of a stretch)


My point is that passenger cars aren't designed for best operating efficiency as so many here point to. Cars are designed to sell, and what sells this year is close to what sold last year-with a few exceptions (VW bugs being one). Taking that back, and realizing what and where the auto industry started, wheels are still based on bicycle tires for size.

actually you are getting things mixed up, larger wheels DONT make for more acceleration, and cars with smal small wheels have huge acceleration, However the TOP SPEED is what goes the opposite way, i mean look at it, go karts have a real kick when they accelerate, in drag raciong the wheel size is for a whole set of reasons, larger surface in contact with the asphalt and mos importantly, that wheel size compared to the "engine size" (not dimensional size but powerwise) is like the ratio on a go kart

leverage. take a 2 foot 2x4 and swing it around in a circle. now take an 8 foot 2x4 and swing it around in a circle. which was easier to start and stop?

yeah, but we aren't talking about 8foot wheels. I'm, suggesting that rather than 80cms why not 120cms wheels. bigger wheels for better fuel economy I get what you are saying. but with good breaks then perpendicular motion is a very small problem.

Because the companies would need massive production plants and then it would be pretty hard to carry around a big spare wheel and the time it would take to fix your tyre and would add weight to your car

also think about how the larger tires have more leverage against the brakes, again requiring larger and heavier brakes to stop. A better solution than the 5th gear swap proposal is to change the rearend diff to a more appropriate range. there will always be a trade off between acceleration, top end and economy. I am wrestling that right now choosing the rear gear ratio for my nash project.

So just ignoring for a second all the disadvantages, the only real advantage you gain in my eyes is lower engine rpm at highway speed, witch I can accomplish by swapping out my 5th gear and not radically altering what my car was designed for. I have read that 1 pound of un-sprung rotational mass is equal to ~7 normal pounds as far as the amount of effort required to stop or start it moving by the engine / breaks, so lets say that your 20" wheels weigh 3 pounds more than my 16 wheels , then add another pound per wheel for the bigger disk break that you need just to maintain the same stopping distance. So that's an extra 112 pounds for your engine to cart around, and on top of that you have less room for your engine due to the larger wheel wells. your engine also needs to have more hp than mine to maintain the same wheel HP, breaking distance, and turning radius. Now if I'm making cars I'm going to go with the smaller wheels because its cheaper to produce a car with smaller wheels than one with bigger wheels and comparable attributes. Personally I actually have rimes that are 1" up in size than stock, but I have shorter(less sidewall flex), wider(better traction) tires on the rims maintaining the same diameter/weight. If you have never owned a manual transmission car I'd like to point out you really can feel the difference between having a passenger and not.

Has anyone thought about unsprung weight? a larger tire would probably weigh more and consume more horsepower to go and more braking power to stop, I see this all the time with guys who buy 22's for the SUV and come to me because it won't stop and is all of a sudden slow. note that this effect is also due to the change in gearing that taller 22's create in the original drivetrain.

Well, this is what i think

The strength of anything is based on its cross surface area. For the wheels to support the weight of a car + say 4 or 5 people in it, it has to be strong in the first place. In terms of the laws of scaling, if you scale something up by a factor of say 2, its weight increases by 4 times whereas its strength only increases by 2. This can be seen in an ant and elephant comparison, whereby the ant can carry a few times its own weight while the elephant can't.

The next thing would be the effort required to spin the wheel. if you had gigantic wheels on your bicycle, say 2 meters long, it will be harder to even get it moving. This is due to Torque, which we see in everyday life like your door handles. The longer your handle, the easier it is to push it down and open the door, however, imagine you're the door. the longer the handle is, the harder it is to resist being opened. Thus cars need engines which are as strong as those you can find in sports cars just to keep the car going, which is inefficient.

Hope this helps and i'm just explaining in the POV of physics =D

Only if all things remain the same. They don't. According to that reasoning, tractor and semi tires should be the same size as car tires-they aren't. Penny-farthing, very popular bike, front wheel was 6 foot in diameter, rear about 2 feet.

Tractors and semi truck are different from the consumer automobile. Especially tractors. What is the top speed of a tractor? 15, 20 MPH? (note: this is attributed to the low, low gearing of a tractor, not the wheel size) The wheels on a tractor are wider to prevent the tractor sinking into dirt. Many cars never drive over anything but asphalt. Tractor wheels are tall so they roll through ruts without getting stuck. Tractor wheels are not subject to all the factors engineers must consider with an automobile's wheels. The lateral and linear accelerations typically seen in a car are never seen in a tractor. The loss of strength associated with a larger wheel, negated by adding material, is less of an issue. And the penny farthing has been obsolete for decades. Penny farthings have cranks like a unicycle; for every revolution of the cranks, there is one revolution of the wheel. If a bike with modern wheel sizes (26", 27", 29", 700c) had such a setup, it would be very inefficient and uncomfortable for most riding. 1:1 gear ratios are occasionally seen on trials bikes.

Unfortunately, the previous post (fuggigal1's) was implying that a larger tire would be weaker, I was pointing out evidence to the contrary. And a tractor can have a pretty hefty lateral acceleration when hitting a boulder hidden in mud... The penny farthing was just to poke fun at a physicist trying to make a point : ) A better explanation of the drive would be a tricycle (or Big Wheel) as a unicycle is a mystery to most people : )

so let's screw the idea with the aesthetics of whether large or small wheels are better or worse. might as well say that solar panels look crap on a house so let's not have them. so, issues are -weight of the wheel -strength of the wheel -torque weight and strength I think are relatively irrelevent. most hubs these days are a aluminum or aluminum alloy. -which is light. torque- maybe the issue. sure if you had wheels that had a 1 metre diameter you may be struggling to move if facing up a hill.

Cars don't have to have big wheels OR a big engine to be fast or to handle well. My 87 subaru wagon came from the factory with 13 in wheels and a 1.8ltr engine producing a whopping 73 horse power but that car had alot of torque and would beat most cars off the line .Oh it was a 5 spd with a top end of well over 115 mph.

Cuz we already built the low bridges! :0

It's not all about size (as they say)...

The thing is, all the different aspects have to be taken into account. Bigger wheels would have some advantages, but they would be outweighed by the disadvantages.

First of all, it's a matter of material mass/strength. Take a stick that is 3 feet long and try to break it over your knee. Assuming you didn't pick a really strong stick, you should be able to do it pretty easily. Now take a stick the same diameter but only 1 foot long. Trying to break that will be much harder because you won't have the same leverage. It's the same with metal--if you have a larger diameter wheel, you face the flex and strain that comes from bending over a much larger distance. The only answer to this would be to put more material to support that strain, and that gives you two more disadvantages.

You would need to spend more to use that much more material, and that means cars would cost more to make and, therefore, to buy. The other problem is that more weight means more fuel consumption for acceleration. So while you may get better handling, you would use a horrible amount of fuel while in traffic or driving in a city.

There are steps being taken to address some of the things you've mentioned, though. For example, it is possible to get wheels that are wider (for increased grip) made from lighter materials, but they are more expensive (you generally have to buy them afterward, not with the car. Also, there are rims that have thinner tires now as well. This helps because it reduces weight (strength per weight of rubber is much less than metal), and less flexibility gives a more direct feel on the road (or so I hear, I've never driven on those tires).

I do agree that some new vehicles, especially electrics, have wheels so small they do look a bit ridiculous. But especially with the capacity of electric vehicles to run for any length of time, weight is a premium because less weight = more carrying distance per charge. Aesthetically, I think that an 18-20 inch (45.7-50.8 cm) is generally ideal for a normal passenger car, but even then, there are times when those wouldn't work very well either.

Plus, there is the matter of leverage - it requires greater power to start off, accelerate and brake with larger wheels, even if they re the same mass as smaller wheels.

But you get better gas mileage because it takes less engine effort to maintain speed (fewer rpm per kph). And, as tyre size increases, surface area available for disk brakes increases and your brakes would work better with the same pressure. It's one of those 'it's always been that way' things : )

You get better gas mileage when you don't brake. But weeeeeeeellllll, if you live in a modern area you more or less brake every few blocks if you aren't on an expressway. So the gas mileage doesn't really become better, since much more force is required to get it turning again after you braked. And then again.

Yes, though the advantage really depends on your driving environment and habits. For example, I live in Southern California, US so heavy stop-start traffic is a fact of life. In that case, the added benefit of higher-speed efficiency is lost. That is why there is no universal answer to the problem.

The problem is that the marketing department designs the outside and THEN the mechanical designers get the plans and can make calculations.

That's true of any industry...though, in some cases it proves beneficial. For example, the Apple guys sitting around a table thinking, "How small can we make this new iPod?"

Or rather, "How can we exclude MMS, Video Shooting, and C+P from a smartphone?"

No, it would be the same, it would take more force to complete one wheel rotation, but the one rotation would take the car farther, that is what a transmission is for, it would be like driving in 2nd or third gear when you are in first, the only advantage i can think of is longer tire life

yeah dragsters have big meats on the back but they also run 1000HP+ engines. with special transmissions and they rebuild the engines after every run or two. Also they consume huge amounts of fuel. I would imagine that the reason why tires are the size they are is because Mr. German engineer and his team have figured out the best size to go with todays engines, transmissions, drivelines and applications. BUT LUCKILY. they know there is people out there with money that can spend extra money on gas and bigger wheels and well thats what aftermarket parts are for.

Then why hasn't tire size changed more than a few inches in diameter over the last 150 years? Width has changed for more traction, sidewall depth has changed, but basic outside diameter hasn't changed much.

when you have bigger tires it takes more energy to turn them so that would lead to more emissions and fuel which in the end result to more money even if you have the most efficient car in the world the tires eventually would wear out the transmission and screw up the steering and brake which could eventually lead to engine failure trust me they have done test and surveys and anything that could possibly happen i used to wonder the same thing so don't feel embarrassed

larger wheels wold help with increasing mileage but the larger a wheel is the harder it is to turn. this wouldn't be a problem normally but when it comes to towing or going up a huge hill it could be problematic

It mainly has to do with SAE (Society of Automotive Engineers). They decided long ago to standardize everything in the automotive industry to simplfy manufacturing and inventory. For an vehicle of a certain size, weight and power, there is an optimum size for tires that is the most efficent and cheapest to make.