Dazed1 wrote: ↑08 Oct 2017, 17:11
henry wrote: ↑08 Oct 2017, 12:00
The rules specify that wet tyres
may be
max 680mm dia vs 670 for dry. So it is possible, but not prescribed, that the unloaded radius of a wet tyre is 5mm greater than a dry.
But what happens under load? Do they have the same stiffness? If wet tyres are less stiff then the 5mm would soon disappear. Stiffness will be affected by construction and inflation pressures. Does anyone know how they vary?
So at speed the plank may or may not be higher or lower. I don't know which.
I do know that from around 240kph up they rub the plank along the ground, zero clearance. if you deflect the t-tray 5mm at the point of contact it must resist with minimum 4000N. The leading edge of the plank is chamfered, up to 8mm at 30°.
So if the leading edge of the plank encounters standing water it will ride up on it like a hydrofoil. Every mm it is raised will reduce the load on the front wheels by around 800N. My estimate is that the load on the front axle at that speed is around 8000N. So 8mm would just about reduce the front axle load to zero. Aquaplaning.
8mm is quite deep water, but as well as the static water on the track the tyres have been carefully engineered to throw water at the front of the plank.
I don't know whether the plank is the sole problem for running on inundated tracks but I think it is quite feasible that it contributes.
So then what is the total area of the front of the plank that encounters water compared to the total area of the tread of the two front tires? I assume the tire patch would be a greater area, and I assume if the tires start rising on the water, the plank would rise along with them. It is just hard for me to believe the plank is the culprit.
The tyres and the plank are potentially very different in their interaction with the standing water.
The plank is 300 mm wide. The whole of that profile encounters the water and the vast majority of the water has to go between the road and the plank. Only at the edges can it go sideways. The area is small, 300 wide by 15 long, but the water pressure is potentially high.
The front tyres are each between 365 and 380 wide. As slicks their width is 250% of the plank width and so would be much more likely to contribute to aquaplaning, since like the plank water is less likely to be able to go round rather than under the surface.
Rain tyres however are very different. The individual tread blocks are designed with voids around them so the individual block, perhaps 20 - 30mm wide, can squeeze the water into the void and prevent it going between the tyre and the road. So whilst their aggregate area is much greater than the nose of the plank the effect of the water will be much less. The tyres rely on the downforce to provide the load on the individual tyre block so they can do the work of squeezing the water into the tread voids.
You raise a good point about the interaction between the tyre and the plank. However I think it may work the other way round. As the plank rides up on the water it will lower the load on the tyres and so reduce their ability to squeeze the water out. So the plank can make the tyres more susceptible to aquaplaning.
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