1) How does the tyre design change the lightbulb effect? The lightbulb effect is always going to be present to my knowledge as the tyre manufacturer has little control over the inflated shape, and the bead width must always be narrower than the widest point of the tyre, or the tyre blows off, so the wheel designer can't really get rid of it either (but can hide it with wider external widths). I actually just wrote about this in the other thread that just started on rim internal width: viewtopic.php?f=3&t=176111#p1883694Jaisen wrote: ↑Tue Aug 13, 2024 4:59 am1) Regarding the lightbulb effect it will be heavily tire dependent. If the 28mm tire was designed around a modern 21mm rim there is likely to be little to no lightbulb effect and you will get good integration between the rim and tire. If the tire was designed based on older standards using 19mm or god forbid 17mm rims, yes the effect will be more pronounced. Unfortunately, even though there are design standards set by ETRTO not all manufacturers follow them strictly.Nereth wrote: ↑Tue Aug 13, 2024 4:26 amYeah so if we want to know about bike-in-frame, one of the most interesting bits of data I had in my first post was on the system6 whitepaper, which had the Knot64 wheels designed specifically for it. I would SUSPECT, then, that those wheels were tested inside a bike (a system6).
These are 32mm external wheels (21 internal), that turned out to be faster with 23s than 25s, (probably equivalent to 24 and 26 todays, since those were GP4000 SII and those blow up big compared to todays tyres).
So on the one hand, if you lose aero going from 23 to 25, you'll probably see an even bigger loss going from 25 to 28 (for one because the 23 to 25 is 2mm and 25 to 28 is 3mm, and for two because the "lightbulb" effect is probably nonlinear and hits you harder as you get larger). However, on the other hand, the difference in that test betwen 23s and 25s was tenths of a watt. So even with 25-28 being larger than tenths of a watt, it's not clear that it's more than, say, a watt.
This is all a little hazy once you look into the details to make the comparison, but it's still some of the best comparative data I can think of for wheel-in-frame. It might be indicative that tyres/wheels make less difference inside a frame (which leads us to optimise Crr instead) and maybe the guys selling wheels know that, but don't want to say it because it makes the improvements from their latest fancypants wheels less sellable to us.
Another piece of data that we do have is that the colnago V4rs that tour tested with 30mm tyres on Enve 3.4s. One of the worst performing bikes in terms of Aero that you can imagine. How much of that is caused by the frame? How much is caused by the shallow depth wheels? How much is caused by the wide tyres? Speculatively, I would guess that a *lot* is caused by the tyres/wheels, and a lesser amount by the frame. This is simply based on looking at a lot of their results, very few frames seem to be capable of tanking the results that hard, and the V4RS doesn't look like it's as bad as those. But relatively shallow wheels and wide tyres is the unique feature of that bike in that wind tunnel so I think that's probably to blame for a lot of the unusually bad result.
2) Regarding the V4RS, my conjecture is the tires had little to no impact. In the white paper I posted up thread from Hunt the 30mm WAM tires on the Enve 4.5s had little to no aero drag penalty vs 28mm WAM tires which is a common config in Tour Magazin tests. The frame and shallow wheels are the clear outliers all things considered from my point of view. Same with the Cervelo R5 which tests extremely slow.
2) I actually was thinking about that paper last night, because I still hadn't read it. I still plan to. Eventually. I should probably use the time I spend posting to do some learning instead
