Applying Aerodynamics to Lotus Seven-Shaped Objects

[CBuff]

Applying Aerodynamics to Lotus Seven-Shaped Objects

 

What the Car Teaches You Once You Start Bolting on Bits

 

https://aricstreeter.substack.com/p/applying-aerodynamics-to-lotus-seven?r=2bb48a&utm_medium=ios&shareImageVariant=split&fbclid=IwY2xjawPpi1FleHRuA2FlbQIxMQBzcnRjBmFwcF9pZA80MDk5NjI2MjMwODU2MDkAAR5uYPu176OSu_fnIGlc_pALA3lyBfoOovmG3rgJ7ib7s-9KPizfQO_qv-HVQw_aem_nlr5xgEGaY8T33nY4sdcvw&triedRedirect=true

 

 

[Vovchandr]

A lot to take in there. Somebody with crazy track time like Croc can certainly share his feedback on this article and adding Aero to the brick. 

 

I've considered adding Aero from an aesthetic standpoint and would be unlikely to use it on the track. 

[Scott_]

That was an interesting article.

 

Scott

[NSXguy]

Thanks for sharing!! Thoroughly enjoyed the analysis and reporting! 

[Croc]

A couple of things on this article:

 

1) Aric Streeter is well known to me and is very much worth reading his substack blog.  I don't always agree with his perspective but they are very well written and interesting and challenge your thinking.

 

2) The green car featured in his aero article was for sale last quarter of 2025 - it was listed on the weekly summary on a FaceBook ad.  Have not seen it advertized this year.

 

3) I have seen the results of the MIRA testing and it is complicated.  Aric does a good job in boiling it down for more ready consumption but there are nuances lost in making it simple for the reader.  

 

4) His linking of aero to suspension needing to work together is a core lesson most people miss.  They come along and shove a big wing on a seven and then never modify the suspension.  You have to firm up the suspension to make the car work with the aero effects added.  Even then I am wondering if he did not go firm enough in the front end with the 2.5" dip he discusses.  More information than what he shares would be interesting to think through at deeper level.  Tires have to be rethought, including pressures.

 

5) He expresses his ideas within a construct of aero whereas I have always thought of it and expressed it within the framework of weight transfer.  Nothing wrong with that but sometimes the same ideas can be thought of in very different ways.  

 

6) What is not really discussed in the article is how an effective aero package of a car requires you to profoundly changes your driving style.  You now have to "trust" something you cannot see.  You have to lift the cornering speed to make the aero optimally effective.  Your operating speed range in a car within a corner becomes narrower as you have a minimum speed for aero to work and a maximum speed from the laws of physics.  A lot of drivers cannot make that leap.  I have done it but I do not enjoy it - its a far more intense driving experience plus I find my seat of the pants feel of the car on the limit is diminished/masked.  Its not as much fun - at least for me.

 

7) Aero is should be applied intelligently.  The Lotus 7  was originated in a period before aero.  Why modify it for aero with all the compromises that entails when the smart option would be to go for a later design car of another type that leverages aero more effectively - less compromises and ultimately faster.  This is a wonderful thought exercise but a poor basis for engineering a faster race car.  There are more efficient and arguably cheaper ways to be faster.

[panamericano]

Re @Croc 's point #6.  A friend was mechanic on a Can Am car in the old days.  Big (early)aero.  The driver routinely took a curve at say 100 mph.  He did a cool down lap and had an off at 70.

[wdb]

Then there was the infamous Top Gear episode where Richard Hammond tried his hand at a modern F1 car and pretty much failed to get through the first turn.

[Reiver]

Very interesting stuff.... not a tracker but enjoy when others experiment with their hobby/passion.  

[Marek]

Tough to overemphasize @Croc's comment on the implications of aero to driving style.  In my time engineering for semi-pro and pro teams, this was probably the toughest hurdle for drivers to develop through.  The old driver mantra for aero is, "The faster you go, the faster you CAN go.".  That takes a leap of confidence made even more difficult by the fact that grip from aero load is neither constant or even linear to speed.  And then getting your head around it for a low aero car does not mean easy success with a high aero car.  There were frequent examples of drivers making the move from FF to FF2000 or S2000 (wingless to wings) but then really struggling when moving to high aero cars.

[BruceBe]

Good article, if just a bit oversimplified for easier reading/digestion. A tire does not differentiate between longitudinal and lateral forces - the traction circle is a function of contact patch and normal load on the tire. These cars have high-speed understeer in corners on throttle - a side-effect of the front-end lift he describes. The analysis prioritization of the brake effect vs. cornering is largely a function of the circuit.

 

Inherent front-end lift is why a better rear brake package with proportioning is so effective. The rear can do so much more than the front very early in the brake event - allowing you to be a little more urgent with the pedal (later), getting the speed off a bit (reducing lift), and then the front can really start contributing.

 

Empirically, cars fitted with full windscreens get more front-end lift earlier than those without.

 

Download cars are a different beast, each one of them is a bit unique, and should be methodically and incrementally approached as a driver. With extensive experience in a Caterham/Lola SP/300.R, I can share that the aero effect is very wide ranging.  A lower speeds, it's just an over-sprung car with sticky tires, but you get the hand-of-gawd pushing down on you at 100+mph. And be careful in a draft :-)

 

Cheers,

-Bruce

[CarlB]

Both Croc and Bruce have good points. I think Croc's point about modifying a car designed before aero became important is a very good point. I think one of the best parts of a sevens handling is the soft suspension. It makes the car predictable and makes the tires work better. The article, Bruce and Croc talk about the need to increase the spring rate to compensate for the aero load, but I want to add that the aerodynamic center of pressure moves as the rake of the car changes. Cars with lots of down force wind up with very stiff springs to limit the center of pressure moving back and forth, not just to compensate for the additional load created by the aero. If the center of pressure is moving the oversteer / Understeer balance is moving.