madmog
Club Retro Rides Member
Posts: 1,153
Club RR Member Number: 46
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Sept 27, 2022 17:58:22 GMT
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Is there a rule of thumb or formula to determine the optimum weight reduction of a car? Or to put it a slightly different way, is there a weight reduction at which performance decreases because there isn't enough mass to push the tyres into the tarmac and they start slipping too soon? Or is that theoretical weight less than is physically possible?
Thinking of something like that Smart Hyabusa that seems to be too light for its power
and conversely the 2cv which weighs very little but grips really well because of soft suspension and skinny tyres.... and perhaps lack of power too
would something heavy being lightened reach a point where suspension would need to be softened and tyres narrowed to increase grip?
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Last Edit: Sept 27, 2022 17:58:41 GMT by madmog
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Sept 29, 2022 8:27:41 GMT
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Depends what car you start with and how much weight you are prepared to remove from it. I've looked into this a fair bit and if we exclude suspension, brakes, wheels and tyres, you have to be brutal to make meaningful weight savings. Remove seats, dash, door cards, headliner, spare wheel, carpet, sound deadening, replace glass for lexan, lightweight battery etc.
The Internet says removing 8.5kgs gains yiu 1 horsepower in terms of power to weight ratio.
I think where the weight is removed from also counts. Removing rear seats and spare wheel from the boot can be balanced out by moving the battery from the engine bay to the boot.
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Sept 29, 2022 8:46:32 GMT
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At a very high level the lighter the better but there are some caveats, you need to at least maintain and ideally lower the vertical centre of gravity by removing weight from higher up in the vehicle and you also need to aim for a neutral front to rear distribution. With a significant weight reduction you will need new suspension settings and the optimum tyres will probably be ones with a softer compound.
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stealthstylz
Club Retro Rides Member
Posts: 14,834
Club RR Member Number: 174
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Sept 29, 2022 12:03:45 GMT
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The position of the remaining weight is most critical I've found, whilst getting the car as light as possible. The heaviest bits left always tend to be the engine/gearbox, driver and fuel tank. I've only dealt with FWD hatches really so you're pretty stuck with engine position, so it's usually driver as far back as possible and fuel tank and battery as low as possible on the opposite side of the car.
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slater
Club Retro Rides Member
Posts: 6,390
Club RR Member Number: 78
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Sept 29, 2022 18:03:58 GMT
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would something heavy being lightened reach a point where suspension would need to be softened and tyres narrowed to increase grip? In theory the former could become the case. The lighter the car the lighter the spring rate needed. However most cars are so softly sprung to start with in reality you would probably only reach that situation in some kind of off road rallying discipline where you need a far softer setup than road use. Narrower tyres would only apply if that car was unable to work them hard enough to get tyre temperature. At the end of the day lighter is better. The idea that you need weight to 'push the tyres into the road' is completely. flawed at the level of fundamental physics. In a straight line you loose due to the extra energy needed to accelerate it and round a corner the laws of inertia will beat you. |
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Sept 29, 2022 22:38:17 GMT
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become the case. The lighter the car the lighter the spring rate needed. However most cars are so softly sprung to start with in reality you would probably only reach that situation in some kind of off road rallying discipline where you need a far softer setup than road use. Not even then, contrary to what many think off road dakar/safari, etc cars run pretty stiff spring rates, they're just lifted the CoG so much they look like they roll around a lot. Generally you're gonna be running 2-3x the ride frequency of a road car. |
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Generally speaking in Motorsport you simply strip as much weight out as you possibly can. However as has been said its important to distribute remaining weight where you can properly. Hence why Batteries and extinguishers get mounted behind seats, co-drivers are sat really low down in cars etc. When I was racing my Ef we did stop taking weight out fo the back as it would have become to floaty.
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madmog
Club Retro Rides Member
Posts: 1,153
Club RR Member Number: 46
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...The idea that you need weight to 'push the tyres into the road' is completely. flawed at the level of fundamental physics. In a straight line you loose due to the extra energy needed to accelerate it and round a corner the laws of inertia will beat you. Could you expand on this please, I don't fully understand. When I was racing my Ef we did stop taking weight out fo the back as it would have become to floaty.[/quote Is this a matter of balance or total weight? If you took all of the weight out of the back but could somehow also remove the same weight from the front (magical polystyrene engine) so that the car was rebalanced would you have a floaty back and front or would the floatiness go away? |
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...The idea that you need weight to 'push the tyres into the road' is completely. flawed at the level of fundamental physics. In a straight line you loose due to the extra energy needed to accelerate it and round a corner the laws of inertia will beat you. Could you expand on this please, I don't fully understand. In laymans terms, although grip does increase with additional weight, it doesn't increase fast enough to offset the additional forces that that additional weight produces. The issue you see with small cars and big power is they tend to be pretty limited on what tyres they can fit. I suppose the approach would be 'more power, less weight (with one eye on distribution), until you reach the limits of driveability on the biggest stickiest tyres you can fit'*. Those 'limits of driveability' will end up being variable on a whole host of different things from torque curve to driver skill to throttle pedal resolution, so it's a pretty moveable feast that you tend not to get anywhere near until you're putting turbo Hayabusas in Smart Cars. |
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