Longer Wheelbase vs Narrower Tires

[Jersey Tom]

It is nowhere near as simple as that.
Moving mass forward or back and the result will depend firstly on how much mass and how far it is moved.
You can provoke either oversteer or understeer from either action.
On type is loaded the other is unloaded and this is the problem with high DF cars, it also depends on the center of DF up until full mechanical effect takes over at lower speed.

I can't think of an example where moving the CG forward would result in anything other than increased understeer.

[autogyro]

Also the RB pitches much better than the other cars.
It seems to keep a very low ride height and plank clearence without dragging and yet is still capable of pitching enough to increase the DF effect into corners.
Another result of geometry and as you say getting the CofG and its height exactly correct.

[autogyro]

It is nowhere near as simple as that.
Moving mass forward or back and the result will depend firstly on how much mass and how far it is moved.
You can provoke either oversteer or understeer from either action.
On type is loaded the other is unloaded and this is the problem with high DF cars, it also depends on the center of DF up until full mechanical effect takes over at lower speed.

I can't think of an example where moving the CG forward would result in anything other than increased understeer.

It would be an extreme working a set up out of a very badly understeering design caused by a rear weight bias with the CofG way low at the rear.
An unlikely starting point I agree.

[marcush.]

It is nowhere near as simple as that.
Moving mass forward or back and the result will depend firstly on how much mass and how far it is moved.
You can provoke either oversteer or understeer from either action.
On type is loaded the other is unloaded and this is the problem with high DF cars, it also depends on the center of DF up until full mechanical effect takes over at lower speed.

I can't think of an example where moving the CG forward would result in anything other than increased understeer.

the F1 cars of the last years cried for more and more front weight shift but yet allmost all cars ate the rears due to loads of oversteer ?

also there is the possibility of understeer because of underworking the front tyres..which could be helped by a wheight shift forward,right?

[sundevil]

It is nowhere near as simple as that.
Moving mass forward or back and the result will depend firstly on how much mass and how far it is moved.
You can provoke either oversteer or understeer from either action.
On type is loaded the other is unloaded and this is the problem with high DF cars, it also depends on the center of DF up until full mechanical effect takes over at lower speed.

actually, it is that simple. like i said, "all else being equal" (holding all other variables constant), simply moving mass toward the front tires will provoke understeer in a four-wheeled, rear-wheel drive road car. yes, the characteristics of a Formula 1 car can be altered by changing the aerodynamics, but that is not the question of this thread. and i was responding to a specific post that stated that moving mass forward will provoke oversteer. this was incorrect, and a fairly important point withing the discussion of wheelbase, weight distribution and tire size.

[Jersey Tom]

+1 to sundevil

[marcush.]

so the tyre stiffness /stiffness split front rear does NOT play a part in this ???
thaT looks too simple to me ,and why is Brawn regretting Bridgestones decision not to reduce front tyre stiffness more with the reduction in contact patch...?

[autogyro]

so the tyre stiffness /stiffness split front rear does NOT play a part in this ???
thaT looks too simple to me ,and why is Brawn regretting Bridgestones decision not to reduce front tyre stiffness more with the reduction in contact patch...?

+1
I also disagree.

[Holm86]

It is nowhere near as simple as that.
Moving mass forward or back and the result will depend firstly on how much mass and how far it is moved.
You can provoke either oversteer or understeer from either action.
On type is loaded the other is unloaded and this is the problem with high DF cars, it also depends on the center of DF up until full mechanical effect takes over at lower speed.

actually, it is that simple. like i said, "all else being equal" (holding all other variables constant), simply moving mass toward the front tires will provoke understeer in a four-wheeled, rear-wheel drive road car. yes, the characteristics of a Formula 1 car can be altered by changing the aerodynamics, but that is not the question of this thread. and i was responding to a specific post that stated that moving mass forward will provoke oversteer. this was incorrect, and a fairly important point withing the discussion of wheelbase, weight distribution and tire size.

Sorry guess i was wrong. I thought it would work the other way round.

[Jersey Tom]

so the tyre stiffness /stiffness split front rear does NOT play a part in this ???
thaT looks too simple to me ,and why is Brawn regretting Bridgestones decision not to reduce front tyre stiffness more with the reduction in contact patch...?

Not following you on this.

If the only change being made on a vehicle is moving the CG location fore or aft.. with regard to pure cornering balance, forward = more understeer, rearward = less understeer. There's no immediate example I can think of where this won't be the trend.

Whatever issues Brawn or whoever had with the old Bridgestone tires could have been any number of things. Wouldn't be surprised if it had to do with forward load transfer sensitivity and the fronts become way too positive for the rears under braking (trailbrake / brake-in-turn oversteer). Load transfer produces the opposite shift in balance that a CG shift will generate.

A lot of this really comes down to what the driver is keying on and bitching about the most. As an example, working with a FSAE team the other weekend... we made a setup change and sent the driver out. He comes back after a lap shaking his head and says the car "oversteers all over." When we sat down and specifically asked what the neutral-throttle apex balance was through a keyhole corner.. the answer was that the car pushed really bad. Mid corner understeer to snap power-on oversteer. Fixable without touching shocks or air pressure.

Just an example though, that you have to really get the whole story of if balance issues are a pure cornering issue, or weight-transfer related, or driving torque related, or what. If we hadn't asked that specifically, we could have easily made the wrong change.

[marcush.]

so .. again .. the vertical stiffness of the tyre is solely a setup issue according to your view then .. compensate with spring and damper to make it work ,it has nothing to do with static weight distribution ?


I came across some weird things with FWD Touringcars cars which had to live with too stiff rear tyres ....but I guess that is not racecars.. [-X ... and will not count..

[Jersey Tom]

I guess I'm just seeing what link you're trying to make between vertical tire stiffness and handling or setup. I think of tire springrate as it's own thing. It plays into wheel rate and chassis force transmissibility to you have so tune springs and dampers accordingly.

Handling is all about yaw response. Tire springrate is not a primary contributor to yaw response. Thus it doesn't go through my brain in terms of an immediate player for pure cornering balance.

Mid-corner balance is relatively straightforward to tune by itself. Things like forward load transfer sensitivity are more "locked in" and dominated by the tires... and IMO damper tuning and such are just bandaids on the real problem.

[marcush.]

I guess I'm just seeing what link you're trying to make between vertical tire stiffness and handling or setup. I think of tire springrate as it's own thing. It plays into wheel rate and chassis force transmissibility to you have so tune springs and dampers accordingly.

Handling is all about yaw response. Tire springrate is not a primary contributor to yaw response. Thus it doesn't go through my brain in terms of an immediate player for pure cornering balance.

Mid-corner balance is relatively straightforward to tune by itself. Things like forward load transfer sensitivity are more "locked in" and dominated by the tires... and IMO damper tuning and such are just bandaids on the real problem.

Tom ,I have to admit this link is more a feeling than hard fact and it may well be that phenomena I experienced had quite different reasons than tire springrate.Actually I´m currently going through all my past experience looking for weird things that could possibly have been influenced or set up by tyre springrate issues..so DaveW really rattled my small cage...

[DaveW]

I can't think of an example where moving the CG forward would result in anything other than increased understeer.

I suspect the issues being discussed have been sorted now, but here is my contribution.

This thread is about changing wheelbase of a be-slicked aero car, rather than (simply) the position of the centre of gravity. Hence, while a simple change in c.g. position (with all else held constant) will have the effect described by JT & Sundevil, the reality is more complex, as autogyro suggested.

Suppose Merc. has a driver complaining of understeer & measurements to show that the front tyre temperatures are lower than ideal. If the wheel axles are moved aft relative to the c.g. (hence moving the c.g. forward), then the front tyres will be "worked" harder, and can therefore be expected to stabilize at a higher working temperature. This will increase front tyre "grip" (up to a point) which is likely to over-power all (or most) other considerations & lead to a nett balance change towards oversteer.

A c.g. shift will, of course, be matched by a centre of pressure shift for an aero vehicle when the wheel axles are moved, which helps my argument, but the argument is still valid for a non-aero vehicle using slicks. Working the tyres correctly is the single most important objective when setting up the suspension of a non-aero vehicle, & it is also important for an aero vehicle. Set-up options in the latter case might be compromised by aero constraints, which explains the importance of being able to adjust c.g. position, & also why a change in tyre specs. can require the c.g. position to be moved.

[Jersey Tom]

I can't think of an example where moving the CG forward would result in anything other than increased understeer.

Suppose Merc. has a driver complaining of understeer & measurements to show that the front tyre temperatures are lower than ideal. If the wheel axles are moved aft relative to the c.g. (hence moving the c.g. forward), then the front tyres will be "worked" harder, and can therefore be expected to stabilize at a higher working temperature. This will increase front tyre "grip" (up to a point) which is likely to over-power all (or most) other considerations & lead to a nett balance change towards oversteer.

Seems like this is "reaching" a bit.. lot of 'ifs' and speculation.. and the temperature effect is surprisingly difficult to sort out with any amount of confidence.

In any event, in my experience a car that has a noticeable balance problem will typically have higher temps at the axle lacking grip. Understeer works the fronts harder than the rears by itself. Tight cars push front temps up and roast them, loose cars push rear temps up.

Beside that.. whatever temp change you get purely from the extra load of shifting the CG forward a couple inches... I don't think you'd even notice it.