# Talk:Circle of forces

## Too simplistic

A lot of this is far too simplistic. There are many factors that affect the ability of a vehicle to make effective contact with the road surface. Friction is not all of the story as the ability of a tire to match the contour of the surface over which it is travelling is arguably more important. The suspension characteristics are very important in this respect. For example worn shock absorbers can be disastrous to road holding capability.

The following all have an impact:

• Tire construction
• Alignment
• Tire Pressure

As noted, the consequent force is a sum of vectors and it can not be correct that both vraking or acceleration have the same resultant vector, indeed applying more power to a front-wheel drive vehicle can assist cornering.

Four wheel drive vehicles are usually not able to corner faster than other vehicles and indeed fast cornering is one of the major causes of roll-over. Even moderate cornering speeds can cause significant loss of applied force on the inner pair of wheels due to the high centre of gravity.—Preceding unsigned comment added by Rjstott (talkcontribs) 07:26, 25 April 2004

Circle of forces does not automatically show why four wheel drive cars can corner more quickly than two wheel drive cars. In fact I'm not even sure four wheel drive cars can corner faster. When cornering all you want the tires to do is corner, all four wheel drive cars do is give you more traction, this is not cornering. So during cornering all the four wheel drive is doing is very little except adding weight. There are obviously lots of sub arguments to this such as slip angle, rolling friction, limited slip differentials, power distribution, weight transfer and when to apply power out of a corner and steering input. The list is almost endless. One thing is however certain. Four wheel drive is better under acceleration (for as long as you have power to loose traction) but once you are up to speed the gains become much more subjective.—Preceding unsigned comment added by 137.82.113.236 (talkcontribs) 21:49, 15 February 2005
Part of the reason that four-wheel-drive vehicles cannot corner faster than rear-wheel-drive vehicles is that that the maximum traction provided by the front wheels must be shared between acceleration and steering, whereas all of the front wheels' traction may be used for steering when all of the car's power is transmitted through the rear wheels.
Four-wheel-drive is more stable through corners, but not faster.—Preceding unsigned comment added by 129.86.163.246 (talkcontribs) 19:20, 18 March 2005
AWD is faster through corners because the drive force (Fx) is shared more equally between wheels. Increasing Fy reduces the lateral load limit (Fx) as shown by the traction circle. Obviously when cornering with no drive required, there is no difference between AWD and 2WD but generally some drive is required to maintain cornering speed - especially at racing speeds. The drive system for ultimate grip is one which distributes the drive to each wheel in proportion to the load on that wheel (torque vectoring). Significantly higher cornering speeds are possible with such a system. — Preceding unsigned comment added by 131.181.251.130 (talk) 01:52, 3 March 2015 (UTC)

## Tyre or vehicle

Trying to apply the circle of forces model to the vehicle as a whole has lead to vague and inaccurate conclusions in this article and the discussion above. The circle of forces model applies to an individual tire. This article should focus on that aspect alone. There should then be a higher-level article that incorporates the circle of forces, along with vertical load transfer and other effects, into a general overview of handling.

It also confuses the issue to mix in discussions of driving technique and vehicle configuration at this level. That seems to have lead to the injection of opinion and speculation not supported by the article up to that point.

The circle of friction article should also use a consistent set of definitions and conventions so that slip angle doesn't confuse the issue. Some of the existing article (as of this date) and the discussion above seems to orient the friction circle with respect to the wheel, i.e. with the acceleration-braking axis in the plane of rotation of the tire. That might make some intuitive sense from a driver's point of view, but it makes the explanation confusing. Under that convention, acceleration appears to add to the cornering power. (At the extreme, with a 90-degree slip angle, acceleration becomes the only force available for cornering.) The normal, engineering convention is to define the circle of forces such that the acceleration-braking axis is always tangential to the path of the tire, not in the plane of rotation of the tire. The article should use that convention, then link to an article on slip angle to clarify the effects of cornering drag, etc.--Tedd 22:05, 27 Mar 2005 (UTC)

## SUV or 4WD

Let's not confuse SUV with four wheel drive. You don't have to roll over when using 4WD. There have been 4WD formula one cars and Indy cars.

Indeed there are lots of factors to consider and some situations greatly favour 4WD. For the F1 experiments, the 4WD cars did not deliver the goods. At the time the front tires were small compared with the rears and it's possible that since the tire development and the car development were (and still are) closely linked that the 4WD cars were the odd fish and were not a good compromise. At Indy, again it wasn't a fair comparison and in those days an advantage could have been reduction in rear tire wear. This leads to the crux of the force circle vs 4WD vs 2WD relation, as I see it.

The front tires in cornering have a slip angle, naturally, to develop the lateral force which causes rotation of the car mass. The rear tires do not develop a slip angle until after the front tires do and the car has begun rotation. This slip angle and force generated in the front tires is not directed square to the car centerline; it appears partially as drag. This is why cars slow down when weaved side to side and in corners. By applying some driving torque to the front tires, the front tires can pull the front end into the turn and therefore need less slip angle. The driving force vector is at an angle into the turn and contributes to turning, requiring less lateral force of the tire. This also reduces drag and has the potential to make a car go faster. But not necessarily.

However, this does not violate the force circle rule. You can't get the front tire to develop the same cornering force as before; it still degrades cornering force when driving / braking force is applied. You see this pretty quickly in a 2WD car if you are in a strong "push" already and have to hit the brakes. You go straight on into Hard Objects. The question is whether your car can take advantage of the 4WD driving torque: can it do with less cornering force at the front? Arguably in rallying where power is excessive and grip is low, front wheel drive and 4WD have been very successful and all the world championship rally cars are 4WD. This is also due in part to straight-line acceleration, perhaps in very large part.

Certainly you can't take a pavement racing car that's balanced as a 2WD car and just plug 4WD onto it and get something better. At the least it has to have changes made, and the 4WD doesn't turn the tires into magical devices.--Alec Mar 28 05

## Help Needed With Graphic

--Tedd 16:44, 28 March 2006 (UTC)

We really need to either get that image back or rewrite the article! Brian Jason Drake 11:36, 4 April 2006 (UTC)

Text identical to http://www.reference.com/browse/wiki/Circle_of_forces - Leonard G. 00:58, 29 June 2006 (UTC)

Cast your eyes just a tiny bit further down to the statement which seems to state quite clearly that they copied it from Wikipedia. I can't see any suggestion of a copyvio. Brian Jason Drake 04:42, 10 July 2006 (UTC)

## I am an Art-teest...

Hey, I drew up a new graph in Adobe Illustrator, based on what I could understand from the article... Hope it's right!

Yes, it's correct and also a big improvement over my original diagram. Thanks very much for adding it. --Tedd 01:14, 18 November 2006 (UTC)

## Racetrack (game)

The circle of forces is fundamental to the paper-and-pencil game called Racetrack. Should it be linked in a "See also" section here?--Noe (talk) 09:14, 18 February 2008 (UTC)

Actually the concept of circle of forces has no relevance in the Racetrack game. There is no maximum resultant velocity restriction in the game, in fact the game takes no consideration at all of either a maximum resultant velocity or force. I will remove the reference until someone provides a valid reason for it's inclusion. --118.92.152.19 (talk) 00:39, 5 January 2011 (UTC)
As stated in Racetrack (game), there is a limit on the magnitude of the force (or acceleration, which ignoring units and constants like the mass is the same). This defines a circle.
Combined with the restriction that moves must be to grid points, a radius of at least 1 but less than squareroot 2 gives the 4-neighbour rule, and a radius of at least squareroot 2 but less than 2 gives the 8-neighbour rule.
I revert the removal.
-- (talk) 14:02, 5 January 2011 (UTC)