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Thread: weight balance vs. aero balance

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    Senior Member slodrew's Avatar
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    Default weight balance vs. aero balance

    If a car has perfect 50/50 balance and the suspension is set up so the car is neutral and then you put a big wing on the back of it without doing anything to increase the down force on the front of the car, how does it benefit the car? To me it doesn't make sense. It seems like it would disrupt that perfect 50/50 weight balance and make the car push..

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    Since when is 50/50 (Fr/Rr) perfect?
    But to answer your question, I have experimented with that very question in the past and arrived at the conclusion that as long as you don't get greedy with too much rear downforce, you will go faster with a wing even without anything in the front.
    Last edited by Blackbird; 08-11-2015 at 08:08 PM.

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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by slodrew View Post
    If a car has perfect 50/50 balance and the suspension is set up so the car is neutral and then you put a big wing on the back of it without doing anything to increase the down force on the front of the car, how does it benefit the car? To me it doesn't make sense. It seems like it would disrupt that perfect 50/50 weight balance and make the car push..
    You are correct. I'm going to simplify a little, but a wing over the rear axle adds grip to the rear without taking it from the front.

    A wing on the trunk adds even more grip to the rear, but does so by stealing some from the front in the bargain. Try pushing on the trunk of your die cast car and watch it pop a wheelie.

    You can try to balance this with springs, but it will affect your low speed handling.

    A spoiler can also reduce drag.
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    *Loves Racing* Fabman's Avatar
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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    Quote Originally Posted by robburgoon View Post
    You are correct. I'm going to simplify a little, but a wing over the rear axle adds grip to the rear without taking it from the front.

    A wing on the trunk adds even more grip to the rear, but does so by stealing some from the front in the bargain. Try pushing on the trunk of your die cast car and watch it pop a wheelie.

    You can try to balance this with springs, but it will affect your low speed handling.

    A spoiler can also reduce drag.
    To take it a step further, a wing connected directly to the uprights adds all the grip you can ask for without the need to compromise low speed grip, but has been banned from racing for decades
    As for restoring balance (with a typical application), it really depends on how many Lbs. of downforce you're really adding.
    500 Lbs at top speed?
    You're definitely going to need to re-tune the suspension
    100 Lbs at top speed?
    Might not need change much at all...

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    And just a quick comment on the weight balance - rear weight bias is preferable for road racing.
    The question is how much and that it debatable.
    But, don't get too hung up if you're not reaching your perfect world scenario weight bias, the reality is that in any front engined car there's more weight to remove from the back than from the front, it's just the nature of things.

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    Not Certified Slow SDSUsnowboards's Avatar
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    Quote Originally Posted by Blackbird View Post
    Since when is 50/50 (Fr/Rr) perfect?
    But to answer your question, I have experimented with that very question in the past and arrived at the conclusion that as long as you don't get greedy with too much rear downforce, you will go faster with a wing even without anything in the front.
    This. My MR2 has a weight distribution of about 44F/56R. I added a rear wing and my times dropped dramatically.
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    BMW Master bawareca's Avatar
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    Once I added an effective wing my car started pushing at high speed even though I had a decent splitter. After I destroyed the splitter I put the AOA to almost zero and the lap times (at BW) went up ~1 sec. Then I decided to play and removed the wing completely and the lap times went up ~5 secs. The car was sliding on ice thru the faster corners. So, in my experience, rear aero bias is better than no wing at all.
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    Overcooker F@ck's Avatar
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    I had to look up the ban of wings mounted to wheel uprights that Moti mentioned. F1 banned it because it resulted in some nasty crashes.

    Why is this?

    Discussion from here: Rear Wing Position. - Forum - F1technical.net

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    FWD racecars with 60/40 weight distribution are faster with wings.

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    Senior Member robburgoon's Avatar
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    Drivers often like a car to have a slight push at high speed, and be a little loose at low speed. A wing on the back can help get you to that behavior.
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    Kam
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    Quote Originally Posted by robburgoon View Post
    Try pushing on the trunk of your die cast car and watch it pop a wheelie.
    While a simple concept to convey, I've always understand aero to be far more complicated...

    For instance, simply pushing on the back of a car does raise the front a bit... but what about when the car is moving with the air pushing the front of the car far more than the rear?

    Ultimately, it's about balance. But, I'm not an aerodynamicist.
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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by Kam View Post
    but what about when the car is moving with the air pushing the front of the car far more than the rear?
    I'm not really sure what you're asking. If air is pushing the nose down, it sounds to me like you have some front downforce.


    It's possible that the lift that the average car generates is aft of the center of mass. If that's the case, that might help explain why so many claim their car likes a mild wing with no other changes... but I'm just speculating now.

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    *Loves Racing* Fabman's Avatar
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    Something to consider:
    Downforce is parasitic and rises exponentially with the cube of velocity. The faster you go, the more aerodynamic drag, and in a big way.
    Lets say a car traveling at 40 mph requires 20 horsepower to overcome aerodynamic drag. The horse power required to propel that same car would rise to 160 hp at twice the speed (80 mph).
    So before you add that sprint car wing to the top of your Miata, consider how much more horse power it's going to take to overcome the parasitic losses just to maintain your current straightaway speed. In short, I think the smart money says "Just enough" downforce to balance, but not enough to Balace. Haha...

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    Senior Member JulioG's Avatar
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    Yes, wings create drag in exchange for downforce. But, you can have your cake and eat it too. Flat bottoms, rear diffusers can reduce both lift and drag.

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    *Loves Racing* Fabman's Avatar
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    Aerodynamics is a big topic....Just wanted to insert a little reality check in there. Carry on.

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    Kam
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    Quote Originally Posted by robburgoon View Post
    I'm not really sure what you're asking. If air is pushing the nose down, it sounds to me like you have some front downforce.
    What I mean is, the example of pushing on the rear of a static car isn't completely representative of what's happening when you only add a rear wing. Why? Because the front of the car will have some front downforce and won't "pop a wheelie".
    I may be pointing out semantics, but having seen that example used several times before and used poorly (or incompletely).
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    Senior Member slodrew's Avatar
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    Concave undertray technology.. I'm thinking it's better to be sucked down than pushed down.

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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by Kam View Post
    What I mean is, the example of pushing on the rear of a static car isn't completely representative of what's happening when you only add a rear wing. Why? Because the front of the car will have some front downforce and won't "pop a wheelie".
    I may be pointing out semantics, but having seen that example used several times before and used poorly (or incompletely).
    It's still good enough. Hang the wing far enough off the rear bumper, and you'll get a wheelie.

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    http://www.trackhq.com/Banners/yellowsitesponsor.gif Blackbird's Avatar
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    Quote Originally Posted by Fabman View Post
    Something to consider:
    Downforce is parasitic and rises exponentially with the cube of velocity. The faster you go, the more aerodynamic drag, and in a big way.
    Lets say a car traveling at 40 mph requires 20 horsepower to overcome aerodynamic drag. The horse power required to propel that same car would rise to 160 hp at twice the speed (80 mph).
    So before you add that sprint car wing to the top of your Miata, consider how much more horse power it's going to take to overcome the parasitic losses just to maintain your current straightaway speed. In short, I think the smart money says "Just enough" downforce to balance, but not enough to Balace. Haha...
    This is obviously track and power dependent, take Sonoma and ACS as polar examples.
    Sonoma - no real straightway, no high speed sections, lots of elevation changes and corners where downforce is everything.
    ACS - so much WOT action, most of which where wings won't help low and medium powered cars, and cutting drag pays big dividends.
    Last edited by Blackbird; 08-12-2015 at 01:33 PM.
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