Theory: Giant wheels/brakes could stop vehicle on ice?

Reply

  #1  
Old 04-17-06, 01:46 PM
DaVeBoy's Avatar
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: Mar 2006
Posts: 1,665
Theory: Giant wheels/brakes could stop vehicle on ice?

I promised this thread, yesterday.

For years I have been baffled at why you can't be racing down the highway, hit a patch of ice, and simply brake to a stop on the ice. You can't. You will go into a skid. Have you ever tried to figure out why? I have.

I *believe* it is due to the fact that brakes are puny. With puny brakes...to get the car to stop on dry pavement, you have to push on the brake pedal hard. But *then*, when you hit the ice, the hard pressure you are applying will easily lock up the brakes on ice.

But, if you had giant wheels with great big rotors and pads, this would only need to exert a fraction of the pressure. So *then* when you hit the ice...due to the fact you are not exerting the forceful pressure, it will reduce the probably of going into a skid, and rather simply brake the vehicle to a halt without lock up.

In theory, the larger the wheels/brakes, the least likely it would go into a lockup/slide.

I have noticed now some sporty cars that have 18 inch wheels and I wonder if car manufacturers are realizing this, and hence making this revision.

Then again my theory could be wrong?

What do you think? And if I *am* right...why in the heck have we been driving around on 13 and 14 inch wheels instead of 3-footers!!?
 
Sponsored Links
  #2  
Old 04-17-06, 02:18 PM
majakdragon's Avatar
Member
Join Date: Jul 2003
Location: N.E. Arkansas
Posts: 7,827
The ONLY way your theory would work is if the tires were big enough to span the dry/ice free areas. Ice is ice. It's slippery. Anti-lock brakes don't stop you from sliding on ice. My opinion: Larger tires and wheels are a deal made with the tire manufacturers.
 
  #3  
Old 04-17-06, 02:18 PM
Forum Topic Moderator
Join Date: Oct 2002
Location: Hamilton County, Ohio
Posts: 4,287
That's what ABS brakes are for. Still, you have to factor in the coefficient of friction involved.

An idle mind is the Devil's playground.
 
  #4  
Old 04-17-06, 07:19 PM
Member
Join Date: Dec 2001
Location: nc
Posts: 616
Have you priced tires lately? Large tires are a lot more expensive than smaller tires.

I suppose you could modify your vehicle and install bulldozer tracks for great traction but you probably wouldn't be able to race down the highway on those.

Originally Posted by the_tow_guy
You have got ENTIRELY too much time on your hands!
 
  #5  
Old 04-18-06, 02:55 AM
Member
Join Date: Dec 2001
Posts: 2,538
that is why most vehicles have antilock brakes to help the vehicle stop on slick surfaces like wet pavement or snow without skiding out of control, by using sensors on each wheel the abs computer can monitor the wheel speeds and see if one locks up and relieve brake pressure to the wheel that has locked up.
vehicles often slide around on ice and many times it has nothing to do with the brakes or if they are even applied before finding the ditch or some other object to stop the vehicle from sliding.
 
  #6  
Old 04-19-06, 10:49 AM
Member
Join Date: Feb 2005
Location: Michigan
Posts: 335
the size of the brake rotor and pad and a lower pressure, does the same thing as a smaller rotor and pad with a higher pressure. You still are creating a negative acceleration either way. Bigger tires would increase the surface area between the road and rubber therefore increasing the coefficient of friction to the road, however the larger the tire, the larger the centrifical force, so it would take a larger engine, trans and brakes to go along with the bigger tires to have similiar performance. so bigger tires mean bigger bill at the pump.
 
  #7  
Old 04-19-06, 04:29 PM
DaVeBoy's Avatar
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: Mar 2006
Posts: 1,665
Originally Posted by zzzz1486
the size of the brake rotor and pad and a lower pressure, does the same thing as a smaller rotor and pad with a higher pressure. You still are creating a negative acceleration either way. Bigger tires would increase the surface area between the road and rubber therefore increasing the coefficient of friction to the road, however the larger the tire, the larger the centrifical force, so it would take a larger engine, trans and brakes to go along with the bigger tires to have similiar performance. so bigger tires mean bigger bill at the pump.
Per your first sentence...the very thing you say is in defiance of the rationale I provided. (But therein lies the crux of the matter: Who is right?)

MY reasoning is that by reducing the pressure you need to stop on dry pavement..that once you hit ice and try to stop and apply the same pressure, the skidding effect will be reduced because you are applying less pressure. I do believe there will be a difference where by reduced pressure the wheels can be slowed without without causing lockup. Don't get me wrong though: Lockup can occur anyway. It's just that it would take more to cause it, like slipperier ice, or harder braking.

If there is more surface area on the road ( a negative aspect you point out) from bigger tires, then make the wheels bigger and the rubber smaller and harder, to equalize. That is how that sports car I saw, was. Haven't you seen those narrow band tires that are out now, with those fancy cut-out chrome (no hubcap) wheels?

A bigger bill at the pump? How much bigger, I wonder?, especially if the tires/wheels were engineered like I said. And could there be other benefits like a smoother ride? Or, what about a "flywheel effect", where once the car got up to speed , it would be more easier for it to sustain the speed?

I keep mulling over, though, the reason you give at the onset and this is the very thing I have gone back and forth over, in my head over the last number of years, as I just am not entirely certain that a bigger pad/rotor/less pressure will equate to the same skid problem if compared to smaller pad/rotor/more pressure. I keep thinking that it is the *pressure* that means something when you hit the ice.

I may actually have to conduct an experiment to satisfy my curiousity.
 
  #8  
Old 04-19-06, 04:42 PM
DaVeBoy's Avatar
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: Mar 2006
Posts: 1,665
Originally Posted by bejay
that is why most vehicles have antilock brakes to help the vehicle stop on slick surfaces like wet pavement or snow without skiding out of control, by using sensors on each wheel the abs computer can monitor the wheel speeds and see if one locks up and relieve brake pressure to the wheel that has locked up.
vehicles often slide around on ice and many times it has nothing to do with the brakes or if they are even applied before finding the ditch or some other object to stop the vehicle from sliding.
I'm not so sure that anti-lock brakes accomplish the same thing. By releasing the brake pressure may not be the answer as much as applying less pressure throughout the braking.

This is how I got started, envisioning my theory: What I did was, I pictured myself in a four wheel buggy without a motor; just a simple wagon-like contraption with wheelchair-like wheels I could easily grab and squeeze. I said to myself, "Isn't it possible to just start squeezing the wheels with my hands and have the carriage come to a stop without my squeezing to cause the wheel to stop (lock up) in my hand while I go skidding across the ice?

And I have remained befuddled over this ever since...not believing that there is not someway to simply allow you to squeeze your way to a controlled stop, quite quickly.
 
  #9  
Old 04-19-06, 05:15 PM
majakdragon's Avatar
Member
Join Date: Jul 2003
Location: N.E. Arkansas
Posts: 7,827
One of the reasons you have a really hard(to the point of almost impossible) time stopping on ice,is that ice offers NO traction. Rubber slides on ice, wood slides on ice,metal slides on ice, YOU slide on ice! Without some sort of traction to slow your momentum you will slide. It doesn't really matter if you are on skinny wheels,fat wide wheels, high off the ground,low to the ground,flat on the ground,1 pound or 1 million pounds! It WILL slide on ice because there is no traction to slow the momentum of a moving object! Studded tires(now illegal in most places) dug into the ice to give traction. This is what helped stop the momentum of the moving object. Someone please correct me if I am wrong.
 
  #10  
Old 04-19-06, 05:20 PM
the_tow_guy's Avatar
Group Moderator
Join Date: Feb 2001
Location: SW Fla USA
Posts: 11,515
Okay, lets get the science and physics right. Nothing slides ON the ice; it slides on the thin film of water that's created when the weight of the item on top of it causes a very slight melting of the ice itself.

THAT should keep the discussion going for a while!!!
 
  #11  
Old 04-19-06, 09:18 PM
Member
Join Date: Feb 2005
Location: Michigan
Posts: 335
good one tow guy
 
  #12  
Old 04-20-06, 04:02 PM
DaVeBoy's Avatar
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: Mar 2006
Posts: 1,665
Originally Posted by majakdragon
One of the reasons you have a really hard(to the point of almost impossible) time stopping on ice,is that ice offers NO traction. Rubber slides on ice, wood slides on ice,metal slides on ice, YOU slide on ice! Without some sort of traction to slow your momentum you will slide. It doesn't really matter if you are on skinny wheels,fat wide wheels, high off the ground,low to the ground,flat on the ground,1 pound or 1 million pounds! It WILL slide on ice because there is no traction to slow the momentum of a moving object! Studded tires(now illegal in most places) dug into the ice to give traction. This is what helped stop the momentum of the moving object. Someone please correct me if I am wrong.
You are all right. My theory is wrong. I played around with a hard plastic disc in my hand, on my slippery arm rest while I was watching tv last night after I left my posting grounds here at my friends house... and I could tell from rotating it across the arm rest and then squeezing the outer edge of it, how it would 'skid' no matter how soft I applied the pressure.

Yet, even as I was observing this, I have this mental block where I just can't get it into my head that there is no way to simply slow a vehicle down in the way that you can when you hold a model car and slow it down on a slippery surface. Maybe the only way that would work is by a reversing rocket engine? I kinda doubt that anything mechanical linked up to the wheels, including engine braking, would work, if everything got slippery enough. Even engine braking would probably lock it up, eh?
 
  #13  
Old 04-21-06, 05:11 AM
the_tow_guy's Avatar
Group Moderator
Join Date: Feb 2001
Location: SW Fla USA
Posts: 11,515
Originally Posted by DaVeBoy
mental block
Good choice of phrase, Dave. LOL
 
  #14  
Old 04-21-06, 04:23 PM
DaVeBoy's Avatar
Banned. Rule And/Or Policy Violation
Thread Starter
Join Date: Mar 2006
Posts: 1,665
It's rather odd how someone like me is into diagnosing various problems and manages to do so quite successfully, and yet, there are these things, like pondering over something someone else might know the answer to, correctly in 2 seconds, where it takes me years for it to sink in.....

Another such thing for me is when someone says something like Tracy is the niece of my grandmas uncle who married Bob's stepdaughter. Those types of things.
 
  #15  
Old 04-30-08, 01:27 PM
Member
Join Date: Apr 2005
Location: Royal Oak, MI
Posts: 222
Somehow I ran across this searching for something else, and with apologies for bumping an old thread, I just found it something that my instincts make hard for me to not respond to.

Larger brakes don't equate to faster stopping. Any size brake pad and rotor, in the case of disc brakes, or brake shoes and drum, in the case of drum brakes, that can lock a wheel is capable of stopping a car as fast as any other size of brake.

Larger tires do not mean a higher coefficient of friction.

Strictly speaking, a larger brake disc or drum means a greater rotational inertia, which is one of the things that needs to be overcome to bring a car to a stop, but relative to the inertia of the vehicle, it's not generally a first order effect - particularly when you consider a to b changes. For dynamic simulation by mathematical formula, you can't really neglect the effect, but for practical consideration, it just isn't a question... Although it might be if you're talking about going to a 3' rotor.

ABS might not be as good as a driver capable of modulating the brakes right at the edge of the traction circle, but even for someone with that ability, it's hard to beat ABS with power brakes because the power assist takes away the feel a driver would need while the ABS has constant input as to individual wheel speed from sensors installed at each wheel, and computers are always going to have better response times than drivers.

I find tires to be a fascinating subject. How they work is that the weight you put onto the tire results in a certain amount of the tire contacting the ground. A rigid cylindrical solid and a rigid surface would result in a point, or if both were perfectly cylindrical and flat respectively a line, but because the tire is flexible, it is a contact patch.

As your tire rolls, the rubber is constantly being deformed and relaxed as it conforms to the flat shape of the road in the contact patch and then returns to its round tire shape. On the inside surface, when the tire is just rolling, it means the rubber is compressed and on the outside surface where the rubber changes from round to flat, it is stretched. As the rubber moves towards the center of the contact patch, the geometry tends to want to compress the rubber because it approaches the center of the tire and its "instantaneous circumference" becomes smaller. However, being rubber, it resists this because such compression would require it to slide on the ground

That's generally what rolling friction is.

Traction of a tire gets more interesting. On the "front" of the contact patch you have rubber pushing on the rubber of the contact patch trying to compress it while on the "rear" you have rubber pulling on the rubber of the contact patch trying to stretch it. Where the external forces on the rubber exceed the adhesion of the rubber to the road, the rubber slides. The more traction you are trying to gain, the more of the rubber that is sliding until the entire contact patch is sliding.

On a perfect surface, larger tires achieve larger contact patches and have higher potential to generate traction.

On wet surfaces, though, larger tires work against you because there is more contact patch to keep the tire "afloat" on the fluid between the tire and the road. Enter tread design, which will do more for traction on ice than drag racing slicks.
 
Reply


Thread Tools
Search this Thread
Display Modes
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -7. The time now is 09:30 AM.