Why are the physical and visual speeds of my custom wheel collider different?

Question

I am trying to make my own custom wheel collider in unity using a sphere cast, but I am having problems with the forwards friction component. The wheels angular velocity is pretty much exactly 6 times higher than it should be. The tyre behaves as it should like this, but the wheel spins too fast as a result of friction. so if the car is on hill, and it rolls down the hill, the friction will speed the wheel up 6 times faster than it should. simply dividing the wheel speed by 6 doesn't work, as the friction goes up drastically, and the car barely moves. I'm not too familiar with this kind of physics, so I don't really know where to begin.

void ApplyForwardsFriction()
    {
        _wheelForwardSpeed = Vector3.Dot(_wheelVelocity, _wheelForwardDirection);

        float rpm = _wheelAngularVelocity *(60 / (2 * Mathf.PI * _radius));
        float slip = -Mathf.Sign(Vector3.Dot(_wheelForwardDirection, _wheelForwardDirection * _wheelForwardSpeed)) * (_wheelForwardDirection * _wheelForwardSpeed).magnitude + (rpm * Mathf.PI / 180.0f * _radius);
        float slipRat = _wheelForwardSpeed == 0 ? 0 : (_wheelForwardSpeed - _wheelAngularVelocity) / _wheelForwardSpeed;
        
        float frictionForce = slip * _forwardsTractionCoefficient * _forwardsTractionCurve.Evaluate(Mathf.Abs(slipRat)) * _suspensionForce;
        _totalForce += _wheelForwardDirection * frictionForce;

        float fricTorque = frictionForce * _radius;
        float wheelAngularAccelRPS = fricTorque / _momentOfInertia;
        float wheelAngularAccelMPS = wheelAngularAccelRPS * _radius;
        _wheelAngularVelocity -= wheelAngularAccelMPS * Time.fixedDeltaTime;
        //_wheelAngularVelocity /= 6;

        float motorAccelRPS = _motorTorque / _momentOfInertia;
        float motorAccelMPS = motorAccelRPS * _radius;
        _wheelAngularVelocity += motorAccelMPS * Time.fixedDeltaTime;
    }

_wheelForwardSpeed is the true speed of the tyre, ignoring the sideways component. _wheelAngularVelocity is measured in metres per second.

These are the physical speeds of the tyre, not the visual mesh being rotated, that is done separately.

I have divided the speed the wheels visually rotate by 6 to get the desired visual and physical behaviour, but it means that the _wheelAngularVelocity is incorrect.

void ApplyWheelPose()
    {
        if (!_handbrakeEnabled)
        {
            float radiansPerSecond = (_wheelAngularVelocity / _radius) / 6;
            if (_leftWheel) _wheelEulers.x -= radiansPerSecond * Mathf.Rad2Deg * Time.deltaTime;
            else _wheelEulers.x += radiansPerSecond * Mathf.Rad2Deg * Time.deltaTime;
        }

        _wheelEulers.y = _originalYRot + _steerAngle;

        _mesh.transform.localRotation = Quaternion.Euler(_wheelEulers);

        _mesh.transform.position = _wheelPosition;
    }

Someone let me know what I'm doing wrong? maybe its not incorrect at all, and I got my units mixed, such that the _wheelAngularVelocity is not metres per second?

_radius is in metres, and _wheelForwardSpeed is in metres per second. ApplyWheelPose() is being called in Update(), and ApplyForwardsFriction() is being called in FixedUpdate(). Thanks.