Festiva Chassis Dynamics

[F3BZ]

In the world of exotics, it seems that a mid engined car with 50/50 (or 25/25/25/25) weight distribution is pinnacle. maybe that applies to RWD or AWD. in your opinion, if you could hypothetically have up to 100% of the vehicles weight on or beyond the front wheels of our cars, what do you think would be near an optimal and safe weight distribution for a road course driven festiva?

[Advancedynamix]

In the world of exotics, it seems that a mid engined car with 50/50 (or 25/25/25/25) weight distribution is pinnacle. maybe that applies to RWD or AWD. in your opinion, if you could hypothetically have up to 100% of the vehicles weight on or beyond the front wheels of our cars, what do you think would be near an optimal and safe weight distribution for a road course driven festiva?

We are working on that. 100 percent isn't ideal unless you have a gyro stability management like a segway vehicle, but as much weight on the front wheels as possible is optimal on a FWD vehicle.
The rear wheels do very little on a FWD vehicle and weight over them actually acts to spin the car in circles under hard cornering. Weight forward of the front axle stabilizes the chassis and helps with driving and cornering grip ( but ultimately, any weight is counter productive, so try to keep things light).
RWD platforms do work better with weight on the rear wheels, but any more than 50% will make the car hard to drive at 10/10 of the limit. Ask any Porsche race driver.
AWD cars also benefit from weight forward designs. Both Subaru and Audi have had great success with front weight biased AWD cars.

After a few years of testing, and playing around with these light FWD cars, I'm convinced that the old 50/50 mid rear platform is inferior in many ways to a lightweight fwd car. In street trim, my B6t Festiva would out corner even the mighty Lotus Exige with it's ideal chassis configuration. I watched one slide off the track in my rear view mirror as the driver attempted to follow me into the carousel at firebird Main coarse. Apparently the Festiva can carry more speed into corners than the Lotus, even with less tire under the car. The two cars were nearly identical weight and HP, but the Lotus was no match for the Festiva.

[F3BZ]

Festiva Chassis Dynamics

interesting. thanks for your input. the 100% was a "hypothetical" limit but mathematically impossible. just wondered how close to that would be ideal. my build goal will require the engine be moved forward as much as practical and my old school magazine thinking was that it would hurt handling so this is good news. now it brings up other questions. i wonder how much this affects the contribution of the rear brakes if the rear of the car is unloaded by the fulcrum?, effect of a heavy front end. do you use an adjustable proportioning valve? or as silly as it seems, if they don't contribute much, could the rear brakes and their unsprung weight be removed? not on a street legal car of course.

[Dragonhealer]

interesting. thanks for your input. the 100% was a "hypothetical" limit but mathematically impossible. just wondered how close to that would be ideal. my build goal will require the engine be moved forward as much as practical and my old school magazine thinking was that it would hurt handling so this is good news. now it brings up other questions. i wonder how much this affects the contribution of the rear brakes if the rear of the car is unloaded by the fulcrum?, effect of a heavy front end. do you use an adjustable proportioning valve? or as silly as it seems, if they don't contribute much, could the rear brakes and their unsprung weight be removed? not on a street legal car of course.

Excellent questions! And I'll leave it for Charlie to reply, but here is a datum point: stock Festiva on corner scales with the rear seat and rear hatch assembly removed has 70.7% of the weight on the front axle. I had hypothesized a 77%/23% as ideal, but that may fall short of the optimum, we are working to find out!

[Advancedynamix]

So far, the stock rear brakes and brake bias seem to work well. The biggest problem that we've seen is the rear ends tendency to hydroplane in wet conditions. This is why I suggest narrow, deeply treaded tires on the rear of a lightened and engine swapped Festiva when driven in the rain. This seems to solve the problem.

[bhearts]

How do the front wheels compare in weight on Pedro?

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[TominMO]

So far, the stock rear brakes and brake bias seem to work well. The biggest problem that we've seen is the rear ends tendency to hydroplane in wet conditions. This is why I suggest narrow, deeply treaded tires on the rear of a lightened and engine swapped Festiva when driven in the rain. This seems to solve the problem.

Would this apply well in both wet and dry conditions on the street? I.E., if I'm running my 165/55-14s on front, would the car corner better in wet conditions with skinnier 155/80-13s that had a deep tread? Especially given that they would be S or T-rated. I'm thinking the same tires as on the front would still be better for dry.

[Advancedynamix]

Would this apply well in both wet and dry conditions on the street? I.E., if I'm running my 165/55-14s on front, would the car corner better in wet conditions with skinnier 155/80-13s that had a deep tread? Especially given that they would be S or T-rated. I'm thinking the same tires as on the front would still be better for dry.

This does apply to the street as well. I usually run no wider than a 165mm tire on the street on all 4 corners because the Festiva doesn't have enough weight to effectively utilize a wider tread patch on typical roads.
In wet or snowy conditions your 155/80-13 tires will work better on the rear. The front of the car may be a different story. You'll have to test it to see.

[TominMO]

This does apply to the street as well. I usually run no wider than a 165mm tire on the street on all 4 corners because the Festiva doesn't have enough weight to effectively utilize a wider treat on typical roads.
In wet or snowy conditions your 155/80-13 tires will work better on the rear. The front of the car may be a different story. You'll have to test it to see.

Not planning on the Festy ever seeing snow again, especially with salt or brine on the road. So probably I'll just go slower in the rain on the tires I have on there now. The Aspire is my four-season car; I have brand new snows (155/80-13 Bridgestone Blizzaks) mounted on Aspire steelies for it, should we get some heavy snow here. In the garage, swap 'em all in ~10 minutes.

[fastivaca]

I run 155/80-13s on all four corners in the winter. I've had no problems with getting stuck (unless I'm doing something stupid) and can make it where a lot of all/four wheel drive vehicles seem to be traction challenged.

I've been running 185-60's in the summer but my current set will be ready for replacement soon. I make go to something a little narrower based on Charlie's suggestion above. Will be keeping the 13"x5" wheels though.

[Advancedynamix]

Not planning on the Festy ever seeing snow again, especially with salt or brine on the road. So probably I'll just go slower in the rain on the tires I have on there now. The Aspire is my four-season car; I have brand new snows (155/80-13 Bridgestone Blizzaks) mounted on Aspire steelies for it, should we get some heavy snow here. In the garage, swap 'em all in ~10 minutes.

With a good tread depth and a typical car weight (for a festiva) you probably won't notice any problems. Tweak is easy to drive in the rain, and doesn't get tail happy on the street, even with the frontward biased weight. I was running 185/45-15 Nankang tires on Tweak without any issues on the street. The new owner replaced those with 165/45-15 Federal Formoza tires and he likes them better. His wife and him choose to drive Tweak (181hp/180ftlbs B6t swap) over their stock engine Festiva in the rain. Both cars have 165/45-15 federal tires, but Tweak has more weight over the front wheels and hooks up much better in the rain and is more stable and predictable. Both cars have the same adjustable coilovers as well, but the stock engined car has lighter springs in the front (Tweak has 180lb, Nastiva has 120lb) because of the lighter front end.

The most noticeable hydroplaning situation I've personally seen and felt was on a BP swapped Festiva with a frontward mounted engine, no interior, no rear hatch and 195/60-14" Falken Azenis 615K tires. This was at MSR in Houston under moderate rain. The rear of the car would drift on every corner at speed, and I almost spun several times. It was a fun challenge, but made me very aware of something I hadn't considered. The light rear end will hydroplane easier.
With More negative camber and narrower tires in the rear, the car would have been much more stable. The test car had stock camber settings in the rear.

[Advancedynamix]

How do the front wheels compare in weight on Pedro?

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I haven't had Pedro on the scales yet. We were going to do it the last time I was at the track and we must have forgotten. The difference is night an day on the track however. Pedro doesn't "turn in" nearly as quickly as Tweak, and tends to push more through the corner. This also could be partly due to the front compression dampening being to stiff on Pedro because the shocks are set lower than their optimal ride range. Also, the tires are a different size on Pedro, but I've run both cars on the same track with Nankang NS2 tires.
Pedro feels wonderfully balanced at the limit on street tires however, where Tweak would really overwork street tires and had more of a tendency to want to spin around in circles after the tires got hot. Pedro is much easier to drive at 10/10.

[jawbraeka]

Is that any help?

[bhazard]

Are those lengths in mm?

[Advancedynamix]

That's neat! Thanks. Good resource to have.