Random Aerodynamic Oddity of the Day Thread

[RedDevil]

Originally Posted by Bicycle Bob

"Knowing and understanding" can pave over huge logical gaps. There were still tenured professors teaching about ancient animal migrations via "land bridges" when all the younger ones had adopted continental drift.

I don't like to be asked for academic proof when I describe my own experience and provide a logical explanation.
But I will welcome any academic proof that waylays my explanation, if you can find it.

I've said enough, it may make sense to you but if it does not so be it.

[kach22i]

Originally Posted by RedDevil

4WD cars roll more smoothly over speed bumps than 2WD cars do. But in winter I'd rather have 2WD with snow tries than 4WD with all season tires. And you lose about 10% in FE.

Winters in SE Michigan are marked by many freeze/thaw cycles, perhaps the most in the world. This accounts for many of our pot holes and results in a very slushy winter. Our roads spend most of the winter being wet as a result of excessive use of salt (cheaply mined locally).

Snow ties are designed to grip and hold snow, the snow on snow bond accounts for snow tire traction.

All Season tires, rain tires and mud tires conversely are designed to remove water from the grooves and fling it out of there, thereby preventing hydroplaning (or mud sliding).

Snowy Winter = Snow Tires

Wet Winter = All Season Tires

Just say'n not all winters are the same.

Originally Posted by RedDevil

The wheels going over a speed bump travel a greater distance than the wheels on a flat surface.
When they are not driven they temporarily speed up, forced forward by the mass of the car. But the driven wheels don't speed up much as they are connected to the engine, which tries to maintain its revs and has a large rotational mass anyway - so the car has to slow down a bit; especially on the upslope.

With 4WD this effect is spread over 2 axles, so when the front wheels hit the bump and slow the car the rear wheels resist the slowing down and force the car over, and likewise when the rear wheels climb the bump the front wheels will pull it over.

There are formidable speed bumps where my parents live, and when my dad bought a Subaru the way it kept going at steady speed over those speed bumps was the thing that impressed me most.

With a velomobile there is very little rotational mass in the wheels, even the driven one. If it also has smooth wheel travel it could float over speed bumps as if they were hardly there.

Interesting theory, but isn't torque on the wheels an important factor?

My rear wheel drive biased AWD Infinity G37X Coupe (automatic) has torque vectoring AWD and prior to having the worn tires replaced I was able experienced their correction on a wet road - it works well. The AWD launch is exceptional, takes off like a big cat on all fours. One thing I can say, it is exceptional over bumps, but that might be because it is just as much a luxury car as a sports car.

Just saying it is perhaps the torque on the wheels you are noticing.

If I recall correctly the Geo Tracker 4WD I drove for 20 years, in 2WD over railroad tracks the rear end would lift a little, but in 4WD it stayed planted and was more stable. Maybe it was the torque to the front wheels? It was a stick shift and I usually slowed down and coasted with the clutch depressed, so I don't see how it could be torque. Wish now that I could go back in time and test out an A to B comparison.

Originally Posted by RedDevil

There are formidable speed bumps where my parents live, and when my dad bought a Subaru the way it kept going at steady speed over those speed bumps was the thing that impressed me most.

Perhaps it is the type of AWD the Subaru uses that makes a difference.

Subaru Employs Four Distinct Types of AWD Systems
https://www.qualitysubaru.com/symmet...-explained.htm

Torque vectoring
https://en.wikipedia.org/wiki/Torque_vectoring

As technology in the automotive industry improves, more vehicles are equipped with torque vectoring differentials. This allows for the wheels to grip the road for better launch and handling.

I've skimmed a couple of articles touching on Torque Vectoring, (example), and ride comfort seems to be overlooked compared to stability and other performance issues (handling).

As far as academic papers, the last sentence in the following synopsis looks promising.

2016
A comparison on optimal torque vectoring strategies in overall performance enhancement of a passenger car

Among the torque vectoring differential strategies, stationary clutch in handling and four-wheel drive in fuel consumption as well as ride comfort have better operation and more enhancements.

[RedDevil]

Winter tires have softer rubber and cut-up notches, so they will stay in contact with the road when temperatures are below freezing and conventional tire rubber becomes too hard to deform to match the road surface.

All season tires are better in the rain, but true winter tires will still have adequate grip.
In snow or on sheet ice grip levels drop enormously, and then the winter tires perform way better.
Even though my winter tires are not optimal 99% of the time, they still allow me to drive my car in a normal way, and when the cold sets in they won't leave me stranded.

As for speed bumps my point is that a speed bump, having slopes, increases the surface of the road over a certain horizontal distance so the wheels that go over the bump rotate faster than the wheels that do not.

If the diff between the front and rear axle is open (in a 4WD) then the wheels on the bump will resist going over the bump less than they would do in a 2WD, as the revs in the engine only rise half as fast. The torque on the drive shafts will increase somewhat, but as the diff is open so does the torque on the wheels on the flat, so, whatever resistance the wheels meet on the bump is countered by extra forward force on the other axle. Very smooth indeed.

If the diff is locked all wheels keep turning at the same speed; the wheels on the bump do cover a greater distance however, so there will be some friction then and the car will slow down a bit as energy gets wasted.

Come to think of it, I've noticed some very weird behavior in 4WD cars taking tight turns like crab-like movements, snap understeer or oversteer even at low speeds.
I believe in those cases the central diff locked up; as the front wheels travel a greater distance through the turn, the wheels will rub and once slipping will not regain grip easily. Add ABS not getting what is happening and doing something odd and the mess is complete. I saw one WRX slide sideways to the berm while moving slowly with no revving, leaving everyone perplexed.
The road may have been moist but definitely wasn't slippery.

[cRiPpLe_rOoStEr]

I didn't feel so much difference to FWD cars when I drove a 2010 Subaru Impreza, yet I tended to drive it more carefully than my father did.

[RedDevil]

This weekend the Formula 1 Dutch GP will be held again at Zandvoort, after an absence of 36 years.
Drivers and fans alike are enthusiastic about the track, as it is notoriously difficult with quick successions of sweeping corners and now even two steeply banked corners to alleviate the lack of long straights to aid overtaking.

The track shares its winding characteristics with the circuit in Suzuka, Japan for one reason: Both were designed by Johannes ("John", "Hans") Hugenholtz.

John did not only design racetracks however.

Besides circuits he was involved in the stillborn projects of the Dutch "Barkey" car (1948) and the "Delfino" (1989), the latter based on the Alfa Romeo Alfasud chassis and drivetrain.

I could not find Barkey but at least the Delfino is documented:
https://www.alexmiedema.nl/2020/08/0...erlandse-auto/

Translation:
Prototype Delfino

Design: J.R.Th. Hugenholtz
Construction: E.W.B. Cars
Interior: P. Jansens
Paint: Sikkens Autonova
Tires: Pirelli

- flat four cylinder engine
- 1712 CC
- 118 HP
- 5 gears
- Cd coefficient: ~0.19
- fuel consumption: over 20 km per liter (> 47 mpgUS) at 120 km/h (~75 mph)

[cRiPpLe_rOoStEr]

Since the Alfa Romeo 145 and 146 were fitted with either that very same boxer engine mounted longitudinally or some transverse inline-4, it would be quite interesting to see how such different layouts would influence the aerodynamics of that prototype.

[cRiPpLe_rOoStEr]

The rear of this Brazilian Chevrolet Monza looks quite clean aerodynamically-wise.

[kach22i]

https://forums.pelicanparts.com/pors...stitute-2.html



1970 Fiat
Abarth TCR 1000 Berlina Corsa

https://revsinstitute.org/the-collection/fiat-abarth/

[freebeard]

I like it. I could see the Bonneville spoiler and wide-body rocker panels on my Superbeetle.

Not the red front bumper.

[freebeard]

justacarguy.blogspot.com/2021/09/there-must-be-reason-this-photographer.html

I saw this by Arthur Radebaugh and was instantly reminded of this: