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Slick tyre aero effects


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#1 NRoshier

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Posted 23 March 2021 - 05:52

I was thinking of underfloor aero the other day WRT racing cars and the effect of tyre aerodynamics. Clearly the tyre meeting the tarmac means that the air has to go either side of the wheel and thus would squirt (for want of a better word) to either side of the tyre. The air going inboard would probably have some velocity, particularly as the car gains speed. This would seem to then have the potential to affect underfloor aero, as the air is 'squirting' into the volume you want to eventually go under the car. I recall that F1 combated this back in the 1990's, but have sportcars or DTM cars attempted to control this, or is it simply not an issue on an enclosed wheel car?



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#2 desmo

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Posted 23 March 2021 - 14:58

I swear I read a technical paper in fluid dynamics that dealt with this exact subject but it was many years ago.



#3 Charlieman

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Posted 23 March 2021 - 16:08

In the days before ground effect, the air adjacent to the sides of tyres was known to be important. F1 teams with experimental capacity ike McLaren tested rear wing location, brake ducts, cooling and the like when aero rules were more relaxed. Designers have tried to use squish or squirt effects from tyres (eg 1980 F1 Ligier with extractor venturi) and it has become significant since CFD expanded experimental possibilities. Squirting air around a venturi or diffuser (extraction effects) could be as useful as pushing air through one. I recommend the recent book by Adrian Newey.

 

Designers have been aware of the problems of tyre generated air movements for sports cars and land speed record cars since the first fully enclosed wheel designs. It's seriously difficult to keep wheels on the ground, hence early experiments with ground effect on the Auto Union LSR car in the 1930s. Sports prototype over body aerodynamics -- and its relationship with under body aero -- is less discussed than F1 but it seems terrifyingly complicated to me.



#4 NRoshier

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Posted 06 April 2021 - 01:10

I've read Adrian's book and enjoyed it. It's interesting, but does not go into the details in great detail.



#5 Charlieman

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Posted 07 April 2021 - 10:50

I saw a photo last night of the 1978 Ferrari 312T3 which featured turning vanes adjacent to the rear wheels. The Ferrari Flat 12 limited air flow at the rear of the car but vanes were one of the tricks used on the T3 and T4 Ferraris to improve sidepod downforce.

 

The 1985 Lotus 97T appears to be the first car to use bargeboards or turning vanes by the front wheels. The car worked well but vanes were not used on its successor. Can anyone point me to technical discussion of the design process at Lotus?



#6 Kelpiecross

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Posted 08 April 2021 - 06:19

Probably beside the point a little - but Jack Brabham found with his new 3-litre car in the mid-sixties that  its max speed was actually  noticeably  slower than the previous 21/2 litre car.  Apparently he  put this down to the wider tyres  on the new car having more aero drag than the previous car with  narrower tyres

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#7 Greg Locock

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Posted 08 April 2021 - 09:37

I was idly looking at the various estimates of CD and CL for rotating wheels, in Katz, I think it was. Flaky numbers r us.



#8 desmo

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Posted 08 April 2021 - 14:00

I've read Adrian's book and enjoyed it. It's interesting, but does not go into the details in great detail.

Any book written by an author under the threat of onerous NDAs will probably disappoint in predictable ways.



#9 Ali_G

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Posted 11 April 2021 - 12:25

Read today that part of the move from 13 inch to 18 inch rims is to reduce tyre deflection which has a significant effect on aero.

Surely the effect of moving to the larger rims couldn’t have such a huge effect.

I thought the biggest change would be the reduction in unsprung weight?

#10 Bikr7549

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Posted 11 April 2021 - 14:51

I thought the biggest change would be the reduction in unsprung weight?

 

I would think it is just the opposite, if the same type of wheel is used. There is simply more metal involved.

 

For wet racing conditions we used to use steel wheels to mount the rains, with the thought being that the extra weight made the suspension a bit softer. Well, actually the real reason for the use of steel was simply the cost, but...


Edited by Bikr7549, 11 April 2021 - 14:52.


#11 Ali_G

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Posted 11 April 2021 - 20:11

I would think it is just the opposite, if the same type of wheel is used. There is simply more metal involved.

For wet racing conditions we used to use steel wheels to mount the rains, with the thought being that the extra weight made the suspension a bit softer. Well, actually the real reason for the use of steel was simply the cost, but...


I thought the new alloy wheels would be much lighter than rubber?

#12 GreenMachine

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Posted 11 April 2021 - 21:25

Read today that part of the move from 13 inch to 18 inch rims is to reduce tyre deflection which has a significant effect on aero.

Surely the effect of moving to the larger rims couldn’t have such a huge effect.

I thought the biggest change would be the reduction in unsprung weight?

 

Sidewall height. 

 

Larger diameter rim (wheel), smaller (proportionally) sidewall = reduced flex.



#13 Fat Boy

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Posted 12 April 2021 - 19:58

Any book written by an author under the threat of onerous NDAs will probably disappoint in predictable ways.

I'll be open in mine, but I don't know 5% of what Adrain does. At least every team that I've signed anything with has already gone teats up, Lol!

 

It'll probably be less of a book and more of a pamphlet...or maybe just a couple pieces of notebook paper...with crayon scribbles.



#14 Fat Boy

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Posted 12 April 2021 - 20:00

Sidewall height. 

 

Larger diameter rim (wheel), smaller (proportionally) sidewall = reduced flex.

I'm sure the sidewall deflection is a big deal, but let's not neglect the additional real estate for brake discs.



#15 DogEarred

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Posted 12 April 2021 - 20:06

Some years ago it was a difficult area to map accurately in wind tunnels.

 

Tyre properties could not 'scaled down' accurately.

 

More recently, tyre companies have put in the effort (by way of financial bribes from the wealthier teams, no doubt) to manufacture more realistic tyres with the correct 'squish' properties.

 

It's an important area.