longer wheelbase and longitudinal transfer problems

[Hondanisti]

http://www.autosport.com/news/report.php/id/57361

http://www.autosport.com/news/report.php/id/57407

When I first drove the car I was massively struggling with locking the rears and rear stability among other things. We worked bloody hard in the last two months to try and resolve the issues....

...you can't hit the brakes hard. You have to be careful and you start adjusting the brake bias to the front and then you start locking up the fronts. Then you end up having both at the same time.


The areas are the unstable rear end under braking and a basic lack of downforce compared to Ferrari and McLaren, people like that, and BMW and Renault definitely.... a lot of it is the aero of the car. Under braking we are struggling with stability, which means you lose out in confidence because you can't brake where you want to.

At the start of the lap I was getting understeer because the tyres were not up to temperature, then later in the lap I was getting oversteer as the rears were going off, which just shows the issues that we have.

I had a problem right from the start with the car bottoming out much more than it has been at any other point over the weekend.

if the front tires are too cold and the rear tires are blistering too fast and you have braking instability and bottoming out while still in a straight line on a bumpy track and not at turn in trail braking, then your problem with a longer wheelbase is one of :

http://www2.ee.ic.ac.uk/cap/publication ... lt_pap.pdf

http://en.wikipedia.org/wiki/Car_handling



pitch angular inertia

center of gravity location (as it relates to the distance to the axle)

spring rate of tire itself

suspension damping coefficient

Honda with the longer wheelbase hasn't figured out the effect of the sidewall construction spring rate effect of these new Bridgestones and put in countermeasures for them at the damper systems or hasn't sorted out the pit angular inertia behaviour of their car.

Rear braking lock up is brake bias related. They're using too much rear bias to fix a bad handling problem and its costing them straightline braking stability.


They have a lot of work to sort out systematically at Malaysia with finding what the root cause of this is and then getting that fixed before they then sort out the aero and braking problem integration. Hopefully the new rear suspension geometry/damping will fix the problem.

[Hondanisti]

Craig Scarborough:

I think Ferrari have gone longer car for one or two reasons

Firstly for a larger fuel tank, as the new tyres will encourage longer stints.

Secondly the longer moncoque gives more space for aerodynamics, as both weight and CofP have moved forwards this year making the front wing work will be critical.

The different wheelbase will not unduly affect weight distribution, every team has told me they can achieve the forwards weight bias with just Ballast and without having to alter the layout.

perhaps Honda's center of Pressure isn't moved forward enough ?

[pyry]

if they have rear downforce problems moving the center of pressure forward is not a very optimal solution

[Hondanisti]

do you think they're problem is insufficient rear downforce ?

it appears from the quotes that they have rear instability under braking and it's not certain that the problem is aerodynamic only.


I've been trying to tease that out.

This isn't to say that everything stated publicly is meant to be correct or intentionally to misdirect or mislead.


if you take what they say at face value, I get the impression that it's chassis dynamics and aero.

[ginsu]

yes, i think its about time we look at why the RA107 is so much slower than the RA106. They changed a few things, one of them is the location of the steering rack. They moved it from being in-line horizontally with the position of the stub axle/spindle to the top of the knuckle in-line with the upper wishbone.
For one, that increases the loads that are fed through the steering arm because you have a much shorter lever arm. This is pretty significant.

R107


RA106


You go from having essentially the radial distance from the center of the wheel to the inside of the wheel rim. (13" dia, I believe), so you have a 6.5" lever arm. What is the max length for a lever arm at the top of the knuckle? I dunno, but probably less than a couple inches. So, at least, you have a change in force by 3:1...3 times as much force, and they don't look to have redesigned the steering system. This means parts could be flexing a lot more than they intend it to. The complaints about the car being nervous under braking, well, there's 5g's of force, so five times the weight of the car is loading those front wheels and that front steering. Just the change in the location of the steering rack alone could account for most of the complaints.


RA107
Dimensions

* Overall length: 4700mm
* Overall height: 950mm
* Overall width: 1800mm


RA106

Overall Length 4675mm
Overall Height 950mm
Overall Width 1800mm
Front Track 1460mm
Rear Track 1420mm
Wheel base 3140mm

Now, we know the wheelbase is actually longer on the RA107, but I don't think we know how much. But, if the car is 25mm longer, than the wheelbase can't be much more than that.

Increased wheelbase will actually help with stability by reducing weight transfer and pitch frequency. Unfortunately, unless certain heavy items are relocated this is going to move the center of gravity backward.

And, as it has been said, the increase in length and wheelbase has very likely moved the aerodynamic center of pressure up a bit farther on the car.

If the center of pressure and the center of gravity are farther away from each other, than obviously the effects are going to be increased because the pitch moment is greater. The car will be more pitch sensitive, i.e. nervous under aerodynamic transients. So, this also helps explain some of their complaints, as braking is when the c_of_p is moved as far forward as possible.

So Honda obviously now know what they have done, unfortunately they may be only able to 'patch' up the car and they might actually want to redesign it, instead.

[jaho101]

Wasn't Honda's philosophy with the new design to create faster air going under the car so they could have better airflow to the diffuser? Their set-up doesn't look too good anyhow, they should have gone for something more traditional.

[Timstr]

The wheelbase dimensions published by Honda are conflicting with statements from Fry.

BAR/H 004 - 3050mm
BAR/H 005 - 3140mm
BAR/H 006 - 3140mm
RA-106 - 3140mm
SA-07 - 3135mm

Nick Fry said in an interview with autosport.com that they had increased there wheelbase in two steps, as they were on the shorter end of the scale compared to other teams.

The first step was introduced at the Turkish GP IIRC. The second step was with the RA-107.

This leads me to conclude that the published figures should be taken with a grain of salt.

Although I think the SA-07 figure is the actual wheelbase length of the RA-106 introduced in Turkey last year.

[Belatti]

Still nothing seems to work for Honda!!!

[modbaraban]

Can the moderator unite these 2 topics, please?

viewtopic.php?t=4530