Where to put ballast?

amk · 04-01-2005, 11:10 PM

I need to add about 20kg of ballast to the car for a rally. One mechanic says put it in the passenger side foot well (low and between the wheels) another mechanic says put it forward of the petrol tank (low and even out the front rear weight bias).

Where would you put it?

350HP930 · 04-02-2005, 04:11 AM

Passenger footwell. That way it balances out your weight, is forward, but not far enough forward to add a lot to the car's rotational inertia.

Bill Verburg · Bill Verburg's Garage

Quote:

Passenger footwell. That way it balances out your weight, is forward, but not far enough forward to add a lot to the car's rotational inertia.

Exactly!

Wil Ferch · 04-02-2005, 03:48 PM

I guess I would generally agree.... but would temper the answer by first finding out the baseline values of the car...what are the individual corner weights before you think of adding anything???

From this, having a high or low moment of inertia notwithstanding....you'd have a better idea of where the "fixed amount" ( 20 kg) of ballast should be placed.

I would offer the view that getting the car inherently better balanced, would (maybe) be of more benefit than if the additonal weight added to get this balance...is far forward or in the cabin.

Wil

Tyson Schmidt · 04-02-2005, 03:53 PM

For off-road rally, I'd put it out front. (higher polar moment=more stable, balanced, and oversteer/understeer more available to the driver.)

For tarmac, then passenger's footwell, or bottom of smugler's box.

amk · 04-02-2005, 06:02 PM

Thanks guys.

The corner balance is currently very good, can’t remember the exact figures (my mechanic keeps a track setup log book for the car). We are going to re-visit the corner balance while fitting the lead weights.

For the rally my navigator will be sitting next to me, he weights about 5kg more than me so that’s 25kg extra on his side if we put the weights in the foot well.

The mechanic who did the cars suspension and takes care of corner balancing and alignment is very good. Everyone who drives the car comments on how chuckable and predictable it is. So this guys got a few points on the board. He wants to put the weights in the foot well to avoid rotational inertia… but he specializes in track cars not rallying.

The other mechanic is part of our team for the rally, he’s navigating in another car and we are sharing a support crew. This guy has a lot of experience at a national level as a navigator and setting up rally cars, a lot of it in dirt rallies. Last year they came second outright in Classic for Targa Tasmania. He thinks we should put the weight up front and low, in front of the petrol tank… but we’re doing a tarmac rally not a dirt rally.

Dilemma, dilemma…

I guess so far I’m leaning toward the passenger side foot well… assuming we can still achieve a good corner balance… or maybe above the centre tunnel behind the driver foot rest…

350HP930 · 04-02-2005, 07:00 PM

The lower the better. If you will be carrying a passenger then I think adding some lead sheeting to the top of the front pan near the steering rack would be a good alternate location.

Bill Verburg · Bill Verburg's Garage

Since there will be a navigator, why not split the difference, lead sheet would be easier to place on the drivers side.

Like Tyson said the further forward the higher the polar moment the slower the yaw and pitch rate will be, generally I like less than stock but that is personal and depends on the course traveled over.