Wow...and all this time I just thought old, narrow tracked, front engined
English cars naturally pushed (NASCAR term) in right corners!
Sent from my iPhone
> On Sep 19, 2015, at 11:21 AM, "Marcel Van Mulders"
> <van.mulders.marcel@telenet.be> wrote:
>
> Barry,
> The cross weight 2% off is a lot and should be avoided. It should be very
> nearly to 50% with the driver on board. So forget about the goal that the
> left front wheel and the left rear wheel should have the same load.
> About Schroedar's explanation : that is right when the car has very much
> power (more power understeer out off a corner because of the faster
> acceleration when the inner wheel has more load/less traction loss( better
> load distribution on the driven wheels)). A simpler explanation with that
> weight distribution for our less powered cars is the left front wheel being
> more loaded than the right front wheel(when the car is at rest), hence more
> understeer in a corner to the right than in a corner to the left. Maybe we
> have to accept understeer in slow corners but it can be equal left and
> right, when the cross weight is 50%, driver included.
> Most circuits are clockwise, so most corners are to the right : moving
> weight to the right is always a good thing. Battery, fire exstinguisher and
> fuel tank should be as far to the right as possible. I've moved the complete
> body of my car(TR4A) an inch to the right in respect to the chassis :
> without driver, the left weight is equal to the right now and the front to
> rear is 50.2% whith 25 litres of fuel.
> This is all only an opinion of course, without pretending that it is correct
> or important!
> Marcel
> -----Oorspronkelijk bericht-----
> Van: Fot [mailto:fot-bounces@autox.team.net] Namens Barry Munson
> Verzonden: zaterdag 19 september 2015 6:12
> Aan: 'FOT'
> Onderwerp: [Fot] TR3 Weights
>
> Amici - With the recent string discussing weights and currently dealing with
> a TR3 which understeers in hair pins and decreasing radius corners (right
> turns being the worst) but is neutral and very controllable in high speed
> corners, left or right, I took the opportunity at a recent event to explore
> the weight distribution on the TR3 and using the data try to determine
> whether I had a tire issue or there was something inherent with the weight
> distribution that was contributing to the understeering problem.
> First a bit of background. The car is a 1959 TR3A that I use as my daily
> driver in the summer and it takes me a day to convert it to racing
> configuration. The weights below are for the car in its racing configuration
> but includes the battery in its stock position, heater, windshield wipers,
> headlights and front and rear bumpers. The car has a complete TR6 front
> suspension (2 deg. neg. camber, 3 deg. pos. castor, 1/32 toe-in), TR6 comp.
> front coils and comp. rear leaf springs and a 7/8 anti-roll bar.
> Static weight, ie no driver, but with 5 gals. of fuel is 2009 lbs.
>
> LF - 564 RF - 518
> LR - 462 LR - 465
>
> Front wt. - 1082 53.9%
> Rear wt. - 927 46.1%
> Left wt. - 1026 51.1%
> Right wt. - 983 48.9%
> Right Cross wt. - 980 48.8%
>
> I include these weights more for information than anything else since the
> more relevant weights are with the driver and all his equipment in the car.
>
> With the driver and equipment the total weight was 2221 lbs.
>
> LF - 638 RF - 515
> LR - 547 RR - 521
>
> Front - 1153 51.9%
> Rear - 1068 48.1%
>
> Left - 1185 53.4%
> Right -1036 46.7%
>
> Left Cross wt. - 1159 52.2%
> Right Cross wt. - 1062 47.8%
>
> So what does this mean and how do I interpret it especially considering the
> understeering problem that I'm dealing with. Well that's not easy. I'll
> include a couple of quotes to see if that clarifies the issue - or maybe
> not......
>
> From Per Schroedar, Grassroots Motorsport - " ....Left cross weight >50% the
> car will likely understeer in a right hand turn because right rear tire
> carries more load so the car drives off the right hand turn better. But in a
> left turn the opposite occurs and the handling is worse. In almost all cases
> the loss of corning performance in one direction is greater than the gain in
> the other direction." Not sure that I completely understand this.....
>
> From Dennis Grant, Autocross to Win, Farnorthracing.com -
>
> "Adjusting corner weights is one of those things that is part of your
> baseline setup, but finding any sort of agreement on just how to set corner
> weights is next to impossible. It seems everybody has their own favourite
> formula and magic sequence.
>
> I'm no different.
>
> My method takes as a given that your car is, being production based, almost
> certainly left side and front end heavy, thanks to the packaging of the
> driver (offset left) and the engine/transmission (offset front). There are,
> of course, exceptions, but for the majority of us, the physical distribution
> of weight inside the vehicle is asymmetrical - and so then will be the
> corner weights.
>
> No amount of twiddling spring perches or cranking down on load bolts can
> compensate for 200+ lbs of driver offset 10 inches left of the vehicle
> centreline. Unless there is a corresponding mass in very nearly the same
> location (in plan view) the corner weights will be offset left.
>
> So then, the question becomes how to best minimize the effects of the
> asymmetric weight distribution. If we have to live with it, at least we can
> reduce the effects and keep things reasonably balanced.
>
> Unless you only have left turns to deal with, you don't want to talk about
> "cross weight" or "wedge". Those can be helpful in setting up a car that has
> purposeful lateral static weight distribution bias because all turns are in
> the same direction, but we don't play that game. It doesn't help at all that
> most electronic racing scales sold in North America are intended for the
> roundy-round guys and so will happily show you cross weight like it was the
> magic ticket - it isn't.
>
> Instead, I like to set up a car so that it has equal left weight front and
> rear; that is, the portion of the left side weight on the front wheels is
> the same as the portion on the rear wheels, by percentage. If the car has
> 52% front left weight, then it should have 52% rear left weight. Why? So
> there's no diagonal bias and no static twisting moment. It seems to keep the
> car more predictable."
>
> OK, using Grant's thought process and his Corner Weight Calculator here's
> what the TR3's corner weights would look like:
> Take 23 lbs out of the left front and right rear and add 23 lbs to the right
> front and left rear which would give you the following distribution -
>
> Left Front - 615.2 Right Front - 537.8
> Left Rear - 569.8 Right Rear - 498.2
>
> Front Left - 53.34%
> Rear Left - 53.37%
>
> Left - 1185 53.35%
> Right - 1036 46.65%
>
> Left Cross wt. - 113.0 50.11%
> Right Cross wt. - 1108 49.89%
>
> Hmmmmm need to think about this.........
>
> Barry.
>
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