26 replies to this topic

[Ali_G]

Could somone please explain to me how Toe is used in the suspension set up of a car.

I have a fair idea what it is but I just don't understand its usage.
Also, do F1 cars acctually use it ?

Niall

[AdamLarnachJr]

Toe is used for steering angles etc. etc. Im sure you already know what toe in and out is for... example... the Dogde Viper has a good amount of toe in, as it rolls down the road the forces push the tires outward, thus aligning them directly ahead at high speeds = less mechanical friction = more speed... on a FWD vehicle its the oppisite, there is toe out, and the driving force will pull the wheels inward.

[Scoots]

Toe out also makes a car much quicker to turn, but adversely affects stability. Auto-X cars often use toe-out.

[desmo]

Toe-in/out as the term is widely used is only a measure of the relative steering angles of the front wheels when the steering wheel is at center. Ackermann geometry will in part determine the toe at all other steering wheel positions.

[Ali_G]

I always thought that the wheels should be perfectly aligned parallel to each other. Otherwise you could have steering problems and excess wear on the wheels.

Wouldn't it also put strain on the suspension and cause more friction between the ground and the tyres.

Niall

[Scoots]

Originally posted by Ali_G
I always thought that the wheels should be perfectly aligned parallel to each other. Otherwise you could have steering problems and excess wear on the wheels.

Wouldn't it also put strain on the suspension and cause more friction between the ground and the tyres.

Niall

As in all design toe-in and toe-out are compromises. If you set toe to 0 the wheels will be pushed into toe-out when the car is moving.

Toe-in makes a car more stable in a straight line, increases tire wear, and makes the tires a little more resistant to following irregularities in the road. This is the most common setup on road cars.

Toe-out makes a car less stable in a straight line, and increases tire wear. This is not-common.

0-Toe is not possible without a suspension with no flex whatsoever. If you set toe to 0 when you are stopped what will happen at 10kph? at 40kph? at 100kph? hard on the brakes? Now you have toe-out and an unstable car.

Most cars come from the factory with enough toe-in to make sure the car never goes to toe-out, just like they come from the factory tuned to understeer rather than oversteer ... it's safer and leads to fewer lawsuits.

-S

[AdamLarnachJr]

As stated toe is needed for many things, most important would be your toe out during a turning radius, if you have a common point somwhere you will have a 90º angle running through the rear axles and two different angles running through the front axles, each one running through a different wheel. One wheel must turn slower (inner) than the other (outer) when turning, hence the need for toe out.

Toe is also important for a vehicles thrust line alignment, which toe can affect... ever seen those cars going down the road sideways... aka doglegging? Thats a problem with toe being out of whack, if the centerline of the vehicle is not parrallel with the straight ahead position you have a thrust line problem, much the same as a tracking problem.

Its a very important angle, just as many others that arent mentioned like SAI, tracking, thrust line, caster, etc. etc.

[Fizzicist]

Interesting post that last one.

When new the Hillman Imp, as a cost saving idea had unequal length track rods. One was of fixed length and the other was adjustable so naturally the toe wasn't parrallel.

Not a great idea but it didn't affect the handling - a sorted Imp will out corner a mini on poor surfaces.

[AndreasNystrom]

In computer games, it makes the car steer much better on twisty circuits. So i guess it does the same in real life more or less. It also affects speed and acceleration.
It also makes the car more stable on straights.

the latest computergames (F1 2002 from EaSports) have lots of setups for the car. Even the third spring . pretty fun to experiment with to see what it does with the car.

[Evo One]

It's rare that I have seen so much bullshit on one thread

Toe-in improves turn in at the expense of straight-line stability whereas toe-out improves straight line stability at the expense of turn in.

Generally, front wheel drive cars tend to run toe-out and rear wheel drive cars run toe-in but this is not always the case - mostly it depends on how much flex there is in the suspension bushes.

[Scoots]

Originally posted by Evo One
It's rare that I have seen so much bullshit on one thread

Toe-in improves turn in at the expense of straight-line stability whereas toe-out improves straight line stability at the expense of turn in.

Generally, front wheel drive cars tend to run toe-out and rear wheel drive cars run toe-in but this is not always the case - mostly it depends on how much flex there is in the suspension bushes.

Are you sure you don't have that backward?

[AdamLarnachJr]

FWD vehicles front axles will pull the toe inwards, hence the reasoning for toe out, regular road forces would push the wheels outwards, but the mechanical force on the axles overcomes that... see my post above.

[Scoots]

Makes sense Adam, but that's only under power right?

[AdamLarnachJr]

I'm not 100% sure on that, but I think thats a negative. It's really hard to put into words at the moment, its 95 degrees out and I just got done diagnosing a misfire on my Z28... I myself am not running on all cylinders ifyou know what I mean, ill try and find some good info on it and post it tomorow.

[Evo One]

Originally posted by Scoots


Are you sure you don't have that backward?

I'm quite sure:

I have tested extensively with both front wheel drive and four wheel drive cars - lap times were always better with slightly more toe in that the maximum factory setting. The cars were more nervous and didn't feel quicker but the results showed otherwise.

It may be that rear wheel drive cars behave differently.

[Group B]

Have to agree with Scoots here: at least in the world of rc racing (scales 1/8 to 1/12, both rwd & 4wd) it's definitely and categorically the other way round. A small amount of toe-in (especially rear) is used to help make the car track straight at high speed, but too much toe-in will make it difficult to turn as well as reduce the overall top speed because of tire scrub. Sometimes a small amount of toe-out can improve steering response, but generally little toe-in is the popular overall balance.

Haven't played much with fwd though, so as has been said already, that could be deifferent.

[AdamLarnachJr]

RC Racing!?

Did you know that if an ant was 10 feet tall it couldn't stand up?

[Group B]

My apologies for making a contribution, I wasn't aware that the laws of physics change with scale.
It's totally beyond me why so many people around the world hate stereotype Americans and see them as stupid, loud, arrogant and obnoxious adam.

[AdamLarnachJr]

WOW! Is it amazing how things can be interpreted. Group B, I meant no ill attitude towards you personally and what I said was merely a joke, if thats too much I'm sorry.

However, after doing alignments for about 6 months and having manufacturers specs in front of me every single day, the above is what I have come to experience. RC Racing is a bit different, you have much lighter vehicles with forces on them that are not proportional to their road going brethren, that was where the 10 foot ant came in, its a scientific fact.

[Group B]

Ok, fair enough - I read it as being condescending and dismissive, but a jokes a joke. I'm not going to claim to fully understand the physics behind the results you, I, scoots and others have reported -I'm just telling it as it is in my experience. As a point of "halfway house" curiosity has anyone got any experience of go-kart setup?

[desmo]

Seriously I thought that vehicle dynamics for a four wheeled vehicle would be largely independant of scale, and thus the same underlying theories would hold for a 1/12 RC and an F1 car. I cannot recall reading that vehicle dynamics are scale dependent to any great degree. In karts we ran a small degree (2-4mm) of toe-in, but honestly only because that is what the recommendation of the chassis maker was rather than through empirical testing or understanding the pros and cons of differing settings.

[VAR1016]

Group B confrims my FWD experience, but again as EVO one says, suspension design and media also have a part to play.

The Lancia Fulvia, properly engineered with long double-wishbone suspension specifies toe-out at the front, whilst the dead axle at the rear has toe-in to ensure directional stability (the tail of the car is relatively light). However the car responds well to parallel tracking at the front; steering and turn-in are sharper. I suppose it should be added that the (1600) Fulvia runs 3 degrees of caster and 1 degree negative camber. The reduction in toe out adds a welcome lightening to the steering!

On the other hand the (FWD) FIAT 128s were specified to have toe-in at the front (Macpherson struts, lower arms and anti roll bar doubling as location) The rear is also toed in (transverse leaf, struts and lower wishbones).

VAR1016

[Fizzicist]

Having spent a good few years racing RC cars at 1/10 scale, I can confirm with Groub B that these little beasties respond in exactly the same manner to suspension set up changes as a full scale car - the laws of physics don't change with size.

I used to race RWD and 4WD buggies and generally found that a little toe in and plenty of negative camber on the fronts and near neutral on the rears of a RWD buggy resulted in great handling and very sharp turn in with the back planted on the ground.

4WD responded well to neutral toe on the front and a small amount of toe in on the rears for stability.

this is all very distant memories though - about 12 years minimum!

[Scoots]

The "Laws of physics" may not change with size, but the forces sure as hell do! I've dealt with RC cars and they are MUCH more static in their suspension dynamics than any road car. While the responses are similar in general, they are not identical.

[AdamLarnachJr]

One major factor that might give the RC/F1 comparison some level versus regular road cars is bushings, something I failed to think of when comparing the suspensions. Road cars typically use rubber or urethane, RC and most race cars use solid or none. That could explain similiar setups, but as I said, the forces cannot be scaled.

[Yelnats]

I see that the general consensus is that toe in increases straight line stability and this matches my experience with alignment but has anyone given consideration why this is so? My theory is that when a car is displaced from a straight line by an external force such as an off camber road the effect will be to place more load on the tire on the low side of the vehicle which will also be the direction that the car is being displaced. Since that tire is pointed in the opposite direction i.e. toward the uphill direction it will tend to steer the car back on line more than it's mate which has now been unloaded proportionatly.

[AdamLarnachJr]

That would actually have more to do with caster. I remember Cadillac had a huge lawsuit in California (famous for our ridiculous "crowned" roads) because people would fall asleep at the wheel and end up in an accident... geez I wonder why!? However the plaintiffs won the lawsuit (only in America man:() by saying that Cadillac should have compensated for the "crowned" roads. Thus if you look up Caddy specs on an alignment machine, you will see they have more caster one side than the other.

Its stupid I know, but hey?