How to make your modified Lotus more safe to drive! - LotusTalk - The Lotus Cars Community
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post #1 of 12 (permalink) Old 10-10-2018, 10:49 AM Thread Starter
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How to make your modified Lotus more safe to drive!

So many of us on LotusTalk have a beautiful Lotus sports car, and naturally you want to care for your investment. Many of you won't let other people drive your car because you fear the worst happening.. they don't know how to drive the car properly or maintain control and they wind up in an accident. You probably don't like to even think about it, but this could happen to anyone, even YOU. Our high performance cars (especially after engine mods/upgrades!) require more traction and stability than a standard vehicle does, as it is built with the intention of going higher speeds and accelerating faster than the average vehicle.

One of the main ways you can improve your vehicle's traction and stability at higher speeds is modifying the body of your car to cut through the air and direct wind where needed, so that your car manipulates the air it's driving through instead of the air manipulating the car, which can lead to one of those undesirable accidents. Typically a car will come directly from the auto manufacturer with aerodynamics designed intentionally to handle the power that the car makes from the factory, but when you start making modifications, your car will need some help aerodynamically to have more fun, while still maintaining a safe driving experience!

There are many different easy options other than having a body shop modify the actual body of your car, which can include front-end splitters, rear-end spoilers, and rear-end diffusers. Splitters go under the front bumper of your car and mount to the chassis/frame for rigidity under high air pressure. Splitters use air flow to push down the front end of your car (increase "downforce") to enhance traction in the front-end of your vehicle to improve braking and handling performance. Spoilers mount to your bonnet/trunk in the rear of your car (sometimes chassis/frame mounted through the rear bumper) and use air flow to push down the rear end of your car and improve traction so the drivetrain of your car can put down that additional power you're putting out with less slipping of your tires.

Splitters and Spoilers do a great job of improving downforce, but downforce is negated by "lift". Lift comes from the inevitable air that flows underneath your car. At higher speeds the air pressure is significant to the point where it will start to lift your car off the ground, and if you continue to increase speed, this lift can eventually cause you to lose enough traction that you could spin out or entirely lose control of your vehicle. This is why diffusers were invented! Diffusers mount under the rear bumper of your car and direct air through channels called "elements" so the air shoots out of the back of your car instead of lifting it off the ground. Diffusers reduce "lift" and rear-end air swirl which causes drag, and can slow your car down, reduce efficiency of your engine, and reduce stability and traction at higher speeds!

Stay safe our there when modifying your vehicle and improving the performance of your engine! It is imperative to have supporting mods not only for your engine, but for the body of your car so you can keep your engine running properly, and keep your entire car on the road!
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post #2 of 12 (permalink) Old 10-10-2018, 11:18 AM
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I somewhat agree with this post, if you race the car, but Lotus already made the street cars pretty much as safe as possible with the lack of front camber, super light front wheels (resulting in crazy understeer), massive rear camber and sticky tires with very little braking force there. Unless you're at speed, I can't see the front splitter/rear spoiler/rear diffuser combo making much difference, even in concert.

You're welcome to show some real-world numbers though.

2006 Exige
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post #3 of 12 (permalink) Old 10-11-2018, 03:07 AM
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aero isn't that effective at low speeds making no difference at all.

the elise is rather neutral handling wise. driver training would help the nervous as in what to do and not to do in a lightweight mid engined car and how to collect it safely if it steps out of line. ..

all you would achieve with more aero is making a high speed accident that much worse when it does let go.
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post #4 of 12 (permalink) Old 10-11-2018, 06:57 AM
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Quote:
Originally Posted by difflow View Post

Lift comes from the inevitable air that flows underneath your car. At higher speeds the air pressure is significant to the point where it will start to lift your car off the ground, and if you continue to increase speed, this lift can eventually cause you to lose enough traction that you could spin out or entirely lose control of your vehicle. This is why diffusers were invented! Diffusers mount under the rear bumper of your car and direct air through channels called "elements" so the air shoots out of the back of your car instead of lifting it off the ground. Diffusers reduce "lift" and rear-end air swirl which causes drag, and can slow your car down, reduce efficiency of your engine, and reduce stability and traction at higher speeds!
Lift largely comes from the top surfaces. The bottom is actually going to be a little lower than atmospheric on a smooth underbody car, so it is the fast air over the top that creates low pressure, and this creates an upward pressure differential. Downforce is also often called negative lift since the two are not separable into where they come from.

Diffusers were invented because you are trying to get fairly low pressure air from under the car to meet higher pressure air behind it from where the air has reversed. This is called an adverse pressure gradient because air prefers to flow from high to low, not low to high. The diffuser creates a more gradual transition that makes this more stable. This is where the drag reduction comes from. The downforce comes from the venturi effect between it and the ground. More air flowing under the car is great when you have a good underbody since this amplifies the venturi effect (until it starts to choke).

I know you just recently took over, but you should really have an expert review your statements since you are going to be seen as an expert by many.
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post #5 of 12 (permalink) Old 10-11-2018, 06:26 PM
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It would be cool if a thread started with some well-researched information we could use as a springboard for an interesting discussion. I hate having to start from rebutting errors and refuting widely-held misconceptions. It’s usually a losing battle and a waste of time.

@difflow - That thing you labeled as a spoiler is actually a wing. Spoilers block or redirect airflow, wings make lift and drag.

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. . .
because air prefers to flow from high to low
. . .
The first clue something is wrong with your physics is when inanimate objects are given agency. Air doesn’t “prefer” to do anything, just like a moving object doesn’t “want” to keep moving.

I’m not an aeronautical engineer, but I’ve designed and built plenty of model aircraft using the same technology that enables full-scale aircraft flight (while accounting for a much higher Reynolds number). This is the same flight regime that a wing on the back of a car operates. A lot of the things @difflow posted strikes me as more marketing hyperbole than science. If your post was an advertisement, then great job!!!!!!!!!! (Especially with the exclamation points!) But it is probably lacking in accurately describing some basics about lift, drag and airflow management. The explanations posted by @cyow5 are better, but still incorporate some-long held misconceptions about lift and how it is generated.

For a more rigorous discussion, @difflow could benefit from someone well-educated in vehicle aerodynamics to help write something about the role of a diffuser. There are several books available on the matter - consulting one of those and re-writing the first post in this thread would be a good starting point.

And just for fun, here are some guys who thought they understood vehicle aerodynamics:

Glen

2011 Lotus Elise SC

Last edited by Glen; 10-12-2018 at 03:43 AM. Reason: composition
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post #6 of 12 (permalink) Old 10-12-2018, 03:36 AM
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Simon McBeath has authored several books on vehicle aerodynamics. Here is an article he wrote about Exige testing and here is one of several books he’s written. I just ordered this book to read.

Glen
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post #7 of 12 (permalink) Old 10-12-2018, 03:53 AM
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Quote:
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Simon McBeath has authored several books on vehicle aerodynamics. Here is an article he wrote about Exige testing and here is one of several books he’s written. I just ordered this book to read.

Glen
That book is extremely recommended. I have read it twice now. I tried to make sure that I was just regurgitated what he had said, but in simplifying an entire book down to one paragraph then there must be errors of omission and simplification.

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post #8 of 12 (permalink) Old 10-12-2018, 07:32 AM
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. . . but in simplifying an entire book down to one paragraph then there must be errors of omission and simplification.
That’s a great point. This topic is far more complicated than “make your Lotus more safe to drive.” It deserves a discussion that accurately highlights what is known and can be predicted with some accuracy and what requires testing to get it right. If Difflow is doing some testing of their new products, I’m sure a lot of people would be interested in that process and the results.

Glen

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post #9 of 12 (permalink) Old 10-12-2018, 11:54 AM
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I've got Simon's rear wing on my car.

** save ~10 lbs gain 1 hp ** EQ: Y=(190*X) / (1984-X) where Y is (HP) and X is (lbs)

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post #10 of 12 (permalink) Old 07-02-2019, 11:48 AM Thread Starter
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Thanks for the feedback!
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post #11 of 12 (permalink) Old 07-02-2019, 01:43 PM
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Quote:
Originally Posted by Glen View Post
It would be cool if a thread started with some well-researched information we could use as a springboard for an interesting discussion. I hate having to start from rebutting errors and refuting widely-held misconceptions. It’s usually a losing battle and a waste of time.

@difflow - That thing you labeled as a spoiler is actually a wing. Spoilers block or redirect airflow, wings make lift and drag.



The first clue something is wrong with your physics is when inanimate objects are given agency. Air doesn’t “prefer” to do anything, just like a moving object doesn’t “want” to keep moving.

I’m not an aeronautical engineer, but I’ve designed and built plenty of model aircraft using the same technology that enables full-scale aircraft flight (while accounting for a much higher Reynolds number). This is the same flight regime that a wing on the back of a car operates. A lot of the things @difflow posted strikes me as more marketing hyperbole than science. If your post was an advertisement, then great job!!!!!!!!!! (Especially with the exclamation points!) But it is probably lacking in accurately describing some basics about lift, drag and airflow management. The explanations posted by @cyow5 are better, but still incorporate some-long held misconceptions about lift and how it is generated.

For a more rigorous discussion, @difflow could benefit from someone well-educated in vehicle aerodynamics to help write something about the role of a diffuser. There are several books available on the matter - consulting one of those and re-writing the first post in this thread would be a good starting point.

And just for fun, here are some guys who thought they understood vehicle aerodynamics:
https://m.youtube.com/watch?v=g8XxQkXCmsU

Glen
Yannick executed a nice backwards 1.5 flip but botched the landing.
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post #12 of 12 (permalink) Old 07-04-2019, 02:25 PM
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You can make your modified Lotus safer with consistent and continuous driver education. Its the cheapest and most effective step you can take to enjoy our cars.
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