In theory once air built up behind the bumper it no longer restricted the path of the air passing by it. Fast forward to GTA event. Emilio pullled his bumper mid event along with other mods in order to help aero. Seems to me the whole rear bumper thing has to be re-evaluated.

Didn't someone here or on the big forum do a coast down test with and without a rear bumper?

Edit: Jep, here it is
https://www.miataturbo.net/race-prep...results-80176/

22lb weight reduction. I have seen no data that conclusively shows an aero benefit of any kind.

And it was Moti that insisted on the weight reduction. His idea, not mine.

If that's not reason enough, I don't know what is. However, it's a time attack only option because... well, no bumper.

Right, a nicely concluded 5 year circle thread.

Total removal not an option (road and W2W) and no real evidence to support cut means it'll stay.

Thanks for the updates :)

I have some CFD data on the matter so might as well share the results. Take it with a grain of salt as CFD always...

According to the simulations I've run it seems that removing the bumper or only cutting it would help the flow around the rear of the car substantially. There seems to be a build-up of turbulent flow behind the stock rear bumper which disturbs the flow from exiting under the car and creates pressure under the floor of the trunk which leads to positive lift. Releasing this high pressure turbulent flow by removing the bumper seems to have a very positive 28lbs gain on negative lift. According to the simulations the bumper doesn't seem to create much drag because the turbulent higher pressure flow behind the bumper helps the flow coming under the car to exit under the bumper.

So here are the result from the two simulations. Both were run at 100mph.

https://cimg5.ibsrv.net/gimg/www.mia...0bf013a4b6.jpg


https://cimg8.ibsrv.net/gimg/www.mia...6927d1a2cb.png

https://cimg9.ibsrv.net/gimg/www.mia...648562bb8a.png

https://cimg0.ibsrv.net/gimg/www.mia...65bf7b34e9.png

https://cimg1.ibsrv.net/gimg/www.mia...e0f6abe30a.png

U is in m/s

https://cimg2.ibsrv.net/gimg/www.mia...2980df0146.png

When tested the model was fitted with a splitter in 2 degrees AOA, spats, rear spoiler on the trunk, APR GTC-200 in 5 degrees AOA and larger endplates.

https://cimg4.ibsrv.net/gimg/www.mia...de6fa71aaa.jpg