Spetz

I'm just wondering, what yields more side grip, a lower CG or higher CG (and ulimately lower or higher car)?

With softer springs my car has more side grip, and wondering does this mean that a higher car that likes to roll more will have more side grip than a low car?

And then taking roll out of the equation, lets say one car with 20mm of ground clearance rolls at 5 degrees, and then the same car lowered to 10mm ground clearance and suspension changed so that it also rolls 5 degrees, which would have more traction?

Thanks

oneofakindtrini

i have nvr heard of this theory b4. this wekend i shall put it to the test. but raising the car will offset the center of gravity. then throwing off your adjustments to your tie rods. ( camber or caster). it may not be worth it.

Spetz

Of course I meant doing a wheel alignment after so nothing changes

The way I see it is more roll = more weight on the outside tyre
And higher CG = more leverage to roll

GYNAIKAS

Generally it's better to have weight transfered to all 4 wheels. Weight transfer needs time to happen and there's no way to achieve something like that unless you use great camber angles wich has many other disadvantages. Keep your car low.

tonykalil

My Feedback: (14)

Hey Spetz,

It sounds like a good theory, but in reality, the grip you gain on the outside tire is lost to the grip you lose on the inner tires. As you force more weight down on the outer tires, some energy is lost to heat that can never be regained. It is very small, but still measureable. It is this reason that all race cars (track cars) try to keep the car as level as possible. Also, as you corner, you want the weight distributed in a balanced manner so that you can set a car up in the corner. If you apply power or brakes, you always run the risk of upsetting the car which is going the maximum possible speed through a corner. For this to happen, the car must be at its maximum level of adhesion, and for this, all of the tires must be working to their best ability.

I hope this helps,

Anthony

Spetz

I realise that taller + softer might mean you can't change direction quickly, it gets out of balance easily etc etc
But for sheer side grip, is taller better?

I am running my car at standard height... and considering lowering it by about 5mm or so

rc rock

what is standard height. a good place for a car your size is 7-14 mm any more and it will push less should be alright if you don't mind loosing the abbility to go over rocks and bumps

Spetz

It's about 25mm now
I've dropped it to 17mm before by changing the shock hook up point on the LCA but it gripped less (though I realise this also made the suspension stiffer)

ziggy12345

I always wondered why F1 cars look like double decker buses

Spetz

Have you been using your crackpipe again?
I don't see how an F1 car looks like a bus... a double decker no less

oneofakindtrini

isn't that why cars are lower in the front? when turning the outside wheels will have more weight on them so in turn more grip.

tonykalil

My Feedback: (14)

For sheer grip, keep your car as low as possible, with the exception of clearance for the condition of your street. You might remember me saying that I run some of my cars high and soft, but it is definately not for grip. For grip, you need all four tires placed as firmly as you can get them. Raising the ride height makes the car transfer weight off of the inside tires, and you can never regain that lost grip even with the added grip of the outside tires.

By the way, I think the F1 bus comparison is referring to the rule passes a few years ago that mandated a "plank" on the bottom of the car to interrupt a flat and low sidepod. It was an idea to slow the cars down. It unfortunately raises the ride height of the cars, however, on the other hand, he may be referring to the fact that Double Decker busses are very low to the ground?? Your guess.


Trini, cars are lower in the front mostly for stance. The "performance stance" of a lower front ride height comes from drag racing cars that needed to transfer weight to the rear tires. In the late 50s and early 60s, drag cars were actually totally raised about 1 foot (see altered drag cars) to transfer the most amount of weight to the rear tires when accelerating. All real race cars have at most 1/2 degree of drop in the nose. This is to allow the bottom of the car to act as a diffuser, which increases downforce. With street cars, the disturbed bottom can't use any air to ant benefit, but lowering the nose sure looks cool!

The balance of the car has a little to do with ride height, and much more to do with roll centers. Roll centers are the theoretical axis upon which the car roll, or transfers weight. It is determined by the angle of the suspension arms. A live axle has its roll center dead center. A high Center of Gravity can be made competetive if the roll centers coincide with the high CG. That is how those race trucks in Europe corner so well. But lowering a car too much will cause the suspension arms to force the roll center below the surface of the road, and the car will not corner at all! This is a huge problem with 5.0 Mustangs. Kids lower them, and then they expect them to handle great - but instead, they plow, or push through corners. This is why smart kids get drop spindles, which lower the ride height, but leave the suspension geometry alone.

The same translates to our RC cars. Making sure the angles of the upper suspension arms is correct is a very important factor when setting up your RC car.

ziggy12345

I thought this joke was obvious........

Double decker busses have a high centre of gravity and F1 cars have a low centre of gravity. If a high centre of gravity gives you more grip F! cars would look like double decker buses, but they dont so.......................

Spetz

Ziggy don't worry I sensed the sarcasm, but I thought it was funnier to pretend I didn't. Considering Tony got confused from my post and thought you were serious

Tony,
What you say makes sense but by that theory it means 0 body roll is best yet obviously body roll generates grip.
And I thought that if the car was higher, it acts like a level/pulley system where it can load even more weight on the outside tyres

I know, this pretty much contradicts racing cars but I am sure there is a difference in scale that can't be accounted for

nitrohead5300

oneofakindtrini

so basically by raising the car. your goal is for when your make a turn. more downward momentum= more weight onto the tires= more grip. is that what your gettin at?

tonykalil

My Feedback: (14)

Hey Trini,

I think you get what he is gettin at, it is just a flawed theory. The amount of grip that 2 tires can generate is less than the amount that 4 can generate. Because rolling to the outside would lessen the grip on the inside tires, the net effect (or total amount of gripping force) is less than a level car would generate.

Spetz, body roll does not generate grip under any circumstance. What it does, is preload the tire sidewall, so that the slack is taken up and the tire can impart the greatest force to the car. On my Porsche (real car), the tires can only go in one spot on the car. That means that you can not rotate them. The right front must always go on the right front, and the left rear...etc. The tires are designed to "roll in". This means that if you roll the right tires down the street by themselves, they will naturally follow a left curve. This is to pre-load the tires so that the sidewall is always loaded, and a steering input can quickly be converted into a turn.

It is obviously less practical to do this on most street cars, so they go with symetrical tires, and generate body roll. But race cars want zero roll. Transferring weight means that you have to transfer it back again, and engineers want the CAR to change direction, not its WEIGHT.

The main difference in RC cars and scale cars is the toe in of the front end. RC cars almost always have the front wheels toed out. This is only for one reason, and that is to make it go as straight as possible. The effect of preloading the tires goes out the window here, since the tires are preloaded the WRONG WAY. They do this because almost every RC car steering geometry is incorrect. When you push the wheel up, most tires turn in a little more due to the tie rod being at a different angle to the roll center. This causes the cars to oversteer in corners - when the car enters the corner, it compresses the suspension, which turns the wheel more than you intended. This causes a chain reaction that loads the suspension even more and turns the wheels even more.

If you want to run with toe in - like a real car, flip the ball end to the other side of the spindle so that when you compress the suspension, the wheel does not oversteer.

This will give you a crisp handling car that still tracks straight.

Like I always say, it is all in the setup.

ziggy12345

Ok let me explain

You are talking about 2 things that effect grip, The roll centre and the centre of gravity

The roll centre is a point above the suspention that the car roll around. By altering the geometry of the links etc .. you change change its height. If the roll centre is high the car will transfer less weight over to the outside in a corner and if its low it will transfer more weight and so improve grip.

The centre of gravity is the weight of the car at a given height. The CofG position rolling around the roll centre gives you the roll moment. (force x length) Its the size of the roll moment that determines the weight transfer

You can have the roll centre high or low but the CofG must be as low as possible.

Cheers

Spetz

Tony so you're saying the best traction is from no body roll at all?
But in which case why do you stiffen an end up to give grip to the other end?

Also, since softening my suspension it's clear that the car has plenty more grip

I'm not saying the more body roll the better, but I'm saying that it seems like some body roll is good

tonykalil

My Feedback: (14)

Ziggy, you are right on. However, sometimes, you do not have the luxury of a low CG, so you just adjust your roll center up to accomodate it. So long as you are not keeping the roll center too far under the CG, you will have a vehicle that perfoms well.

Spetz, if I understand your question correctly, I assume you are asking why you would alter the stiffness of the sway bar on the front or rear. By adjusting the stiffness of one end of the car, you actually affect the opposite end. If you want the car to turn in sharply, you stiffen up the rear sway bar. This is because when the car goes into the corner, the front will set into the corner with (as equal a weight as you can get) on both tires (assuming no sway bar). However, the rear inner tire is lifted, because it is essentially linked to the outer rear tire, so you are "picking up" the inner rear, and causing the rear to have less grip. This is just an extreme, as no real race car would run just a front or rear - you balance the stiffness of both sway bars to control the balance of the car. Many race cars actually have adjustable rear sway bars to allow better turn in during the race.

The reason you are getting better grip with a softer setup is because all of the tires are now allowed more contact with the road. If the suspension is too hard, the wheels will skip, or bounce over the texture of the road, and you will have minimal grip. It is almost like running an F1 car over a track of closely spaced speed bumps. The car would rarely touch the ground, however, a regular street car with compliant suspension would allow the tires to soak up the bumps, and keep them placed on the pavement much better.

If you run soft springs, stiff shocks, and stiff sway bars, you will have the best basher setup that you can imagine. Make sure the suspension has alot of jounce, and rebound, meaning that the car settles half way down on the springs when you set it on the ground.

This has been the principal behind every Lotus suspension. Colin Chapman was a brilliant engineer, and he came up with this formula. The cars were stiffly shocked and had massive sway bars, but they always had soft springs. This also allowed the cars to take less punishment since most of the bumps in the road were converted to heat through the shocks (yep, that is what they actually do) instead of transmitting the forces into the chassis.

I hope this helps

Spetz

Actually I got rid of any downtravel from the car because it would lift off oversteer a lot. Once I got rid of it, it really helped the handling

What you say make sense but I didn't really understand the swaybar thing. By your theory the best traction is with 0 body roll, but isn't that a contradiction to stiffening the opposite end to get more traction/grip?

jkgreen06

great info bump