if 4 are good, 6 has got to be better, right?

[Pulsar]

It will be much more stable, and you shouldn't run into any cases of understeer, so it should track pretty much where you point it. It should help coming out of corners as well, letting you go full throttle a bit quicker.

I'm not sure, but they might be using narrower and a bit smaller tires than they otherwise would. The second set definitely seems to be smaller. I am surprised they didn't make them smaller still to help with the aero. If you look at the designs they had before, it seems they were going for that, so I don't know what the deal is.

Its probably pretty lightweight, it looks like a typical fiberglass bodied barebones car. It probably only added maybe 300-400lbs, which it could still be competitive in power to weight with plenty of cars if its 3500 lbs or so.

Actually, something like this would've made sense for something like the Veyron.

And exactly how do you figure it's not going to run into understeer? Contact area is only slightly related to friction - in fact "ideally" surface area isn't related to frictional force at all. I'll direct you to some of the most basic frictional formulas out there:

Friction Force = u (coefficient of friction determined by material and surface texture) * Normal force (weight).

This will have a minimal impact, if any, on friction in the front of the car. If you want to reduce understeer, change your weight distribution to affect your normal force, or break harder through the beginning of the turn to transfer more weight to the front tires.

 

[RichUK]

 

[slashbinslashbash]

Theoretically, the size of the contact patch won't change at all. Pressure = Force / Area. The Force (weight of the car on the front axle(s)) stays the same. Assuming a common inflation pressure in the tires (say 30psi) the Area must stay the same as well. So instead of having, say, a 10 sq. in. contact patch per tire, you will have 2 tires each with a 5 sq. in. contact patch. In other words, each tire will deform less against the ground (assuming same tire diameter and width). (Pulling these numbers out of my ass, but you get the idea.)

This car looks... interesting. I don't see the real benefit of the 6 wheels, but just thinking about the driving dynamics, it could have some interesting side effects. For example, I am wondering how donuts would work in this car... and really any other situation when the rear of the car has broken loose while the front is still providing traction. More stable? Less stable? Easier to do donuts? Harder maybe, or even impossible?

 

[GoatMonkey]

I have my doubts about how well this will work. They are going to have to prove that this is better with track numbers. If they're going to bring back crazy racing car ideas of the past, they should have gone with the Chapparal sucker car.

 

[dawp]

my opinion is that it brings in extra unneeded complexity. an alignment is probably be a royal pain in the ass.

 

[Throckmorton]

And exactly how do you figure it's not going to run into understeer? Contact area is only slightly related to friction - in fact "ideally" surface area isn't related to frictional force at all. I'll direct you to some of the most basic frictional formulas out there:

Friction Force = u (coefficient of friction determined by material and surface texture) * Normal force (weight).

This will have a minimal impact, if any, on friction in the front of the car. If you want to reduce understeer, change your weight distribution to affect your normal force, or break harder through the beginning of the turn to transfer more weight to the front tires.

This isn't your high school physics class. This is the real world. More contact patch means more traction, because the tire is a soft material conforming to a rough hard surface. More contact patch means more bumps interlocking with the rubber.

 

[darkswordsman17]

And exactly how do you figure it's not going to run into understeer? Contact area is only slightly related to friction - in fact "ideally" surface area isn't related to frictional force at all. I'll direct you to some of the most basic frictional formulas out there:

Friction Force = u (coefficient of friction determined by material and surface texture) * Normal force (weight).

This will have a minimal impact, if any, on friction in the front of the car. If you want to reduce understeer, change your weight distribution to affect your normal force, or break harder through the beginning of the turn to transfer more weight to the front tires.

Well, yeah you can still get it to understeer. There is more weight and it is balanced across 4 tires so there's better weight balance. Should help with making braking more stable (limit brake dive), reduce instances of lockup (by using more brakes should need less braking per wheel, as well as if one wheel locks up there's 3 others still steering). It should also oversteer less. In general, it should track (as in go where you steer it) better.

That's not to say you can't match or better it with a 4 wheel car.

 

[JCH13]

This isn't your high school physics class. This is the real world. More contact patch means more traction, because the tire is a soft material conforming to a rough hard surface. More contact patch means more bumps interlocking with the rubber.

To a certain extent you are right, but over most of the usable load range of the tire it behaves in the more "ideal high school physics" way until the tire-road 'interlock' is saturated. Even at or over saturation the tire grip is still dependent on normal force.

The only way to get an appreciably bigger contact patch is to run a lower tire pressure, regardless of the width.

I think the reason why people think that wider tires get more grip is that softer compound tires are usually wider so that there is more total tread area on the tire so it won't wear out as quickly. On other automotive forums I see people make the claim "man, my 235mm tires grip so much better than the stock 215mm tires!" (I have generalized this). They don't consider that they went from completely trashed OEM tires with 600 tread wear to UHP summer tires with 140 tread wear. They just think the tire is better it's because it is 20mm wider, not because it's a brand new tire with a much stickier tread compound.

 

[ShawnD1]

I think the reason why people think that wider tires get more grip is that softer compound tires are usually wider so that there is more total tread area on the tire so it won't wear out as quickly.

High school physics says surface area doesn't matter. All that matters is the coefficient of friction. In a lot of cases this is true enough.

When we get out of high school physics and start dealing with real world physics, things like material strength creep in. Let's try a thought experiment. What would happen if your car had tires as wide as bicycle tires? The coefficient of friction is the same, weight of the vehicle is about the same, so it should stop just fine, right? Not quite. As you would guess, the bicycle tires would be totally shredded because the rubber is not strong enough to hold together under those kinds of forces. With wide tires that have really high surface area, tires will either work or they will skid. If you have skinny tires, they either work or they shred to pieces.

 

[JTsyo]

That just looks wrong for some reason.

 

[JCH13]

High school physics says surface area doesn't matter. All that matters is the coefficient of friction. In a lot of cases this is true enough.

When we get out of high school physics and start dealing with real world physics, things like material strength creep in. Let's try a thought experiment. What would happen if your car had tires as wide as bicycle tires? The coefficient of friction is the same, weight of the vehicle is about the same, so it should stop just fine, right? Not quite. As you would guess, the bicycle tires would be totally shredded because the rubber is not strong enough to hold together under those kinds of forces. With wide tires that have really high surface area, tires will either work or they will skid. If you have skinny tires, they either work or they shred to pieces.

Your "thought experiment" presumably changes several variables of the situation at the same time: tire width, tire pressure (by the nature of calling it a "bike tire"), and possibly even the construction of the tire (for the same reason). This is not a proper comparison. You can only change one variable for a proper thought experiment. In this case, changing tire width, will only change the shape of the contact area, not the size of contact area, nor the strength of the rubber, nor its coefficient of friction (which is a function of said contact pressure). In the real world this change in shape may have second or third order effects on grip, but we're talking negligible changes, <1%, in most situations.

While I can appreciate (sort of) the point you're trying to make, that material strength does matter in the real world, in typical ShawnD1 fashion you take a small part of a post, out of context, make a wild exaggeration, and then find something wrong with it. I mentioned that wider tires do indeed wear at a lower rate than narrower tires. I acknowledged that the "hs physics" approach did not adequately represent the true behavior of a tire over all load ranges. It is a close approximation given the proper bounds (which does not include bike tires being used on a car).

 

[Howard]

http://www.eng-tips.com/viewthread.cfm?qid=102250

http://www.imazda.com/forums/showthread.php?t=8875

premise 1: the maximum allowable slip angle determines maximum static grip
premise 2: a wider tire experiences a lower slip angle for the same load
theory: wider tires have more grip due to lower slip angles

 

[JCH13]

http://www.eng-tips.com/viewthread.cfm?qid=102250

http://www.imazda.com/forums/showthread.php?t=8875

premise 1: the maximum allowable slip angle determines maximum static grip
premise 2: a wider tire experiences a lower slip angle for the same load
theory: wider tires have more grip due to lower slip angles

A wider tire will develop more grip at a lower slip angle, but it will also have a lower maximum slip angle. So while a wider tire may respond faster (because it develops more grip at a lower slip angle) it will reach it's limit at a smaller slip angle with an end result of similar performance. At least that's how I interpret it.

Read the 4th post in the eng-tips forum, by Evelrod, where he tested two very similar tires. The narrower tire was faster by 1-1.5 seconds per lap.

FWIW: http://www.fromsteve.net/node/12
A good article describing slip angle (though I can't see the graphs).

The next page also talks about tire grip. The coefficient of friction decreases as more load is applied in a non-linear fashion as we have been talking about. Though the simplistic physics version still works (approximately) over relatively small variations (no, it won't work for bike tires). This article confirms what most drivers know to be true: weight transfer sucks! The article explains (quite well) how sway bars work too.