At what point would you draw the line on maximum tire diameter?

[Hummina Shadeeba]

With larger tire diameter resulting in better aerodynamics for any given tire volume

I thought a smaller wheel was more aero because the shorter spoke or whatever circling over the top creates less drag. The smaller wheel spoke is going faster though.


Cool vehicle. A couple things I suspect though: vision out looks awful, i wouldnt feel safe in a crash no matter what they did and they’re trying to make it safer seems extra weight

 

[ebike4healthandfitness]

I thought a smaller wheel was more aero because the shorter spoke or whatever circling over the top creates less drag. The smaller wheel spoke is going faster though.

I was referring to just the tire itself. Notice I used the words "for any given tire volume"....so the smaller diameter tire presents a larger frontal area for "any given tire volume".

Now as far as drag from spokes and nipples goes, yes a smaller diameter rim travels at a higher rpm for any given road speed.....but the actual drag at the level of the spoke nipple isn't any worse for the small diameter rim than it would be for a larger diameter rim. This because the speed at which the nipple travels through the air is still the same at X road speed as it would be if the nipple were on a larger diameter rim. What helps a smaller diameter wheel of X amount of spokes at X spoke thickness and X spoke bracing angle is the fact the spokes are shorter. So the small diameter rim of the same spoke count (and same spoke bracing angle) as a larger diameter rim comes out slightly better as far as aerodynamic drag goes.

 

[Hummina Shadeeba]

"for any given tire volume"....so the smaller diameter tire presents a larger frontal area for "any given tire volume".

I remember long ago thinking I was aero on my skinny 18mm road tires and now they often use mid 20s on aero wheels and the frontal area doesn’t seem to determine aerodynamics, but having a smaller wheel does.


So same speed of the nipple on a small or larger wheel makes sense thanks.

 

[ebike4healthandfitness]

I remember long ago thinking I was aero on my skinny 18mm road tires and now they often use mid 20s on aero wheels and the frontal area doesn’t seem to determine aerodynamics, but having a smaller wheel does.

When you say "smaller wheel" are you referring to differing effective rim diameters at the same bead seat diameter? (e.g. An aero 700c rim will have a smaller effective rim diameter than a typical low profile 700c rim)

If so, then this is something different than what I was referring to which is comparing different tire diameters (As a starting point consider 32" x 2.00" vs 20" x 2.00" tire. If both are on the same internal width rim and have 100 aspect ratio the 32" tire would have 67%* greater tire volume. Therefore in order for the 20" diameter tire to have equivalent tire volume as the 32" x 2.00" it would have to be much wider than 2.00". The math works out that the larger diameter tire has a smaller frontal area when it's tire volume is the same as a smaller diameter tire. This is why larger diameter tires at the same tire volume as a smaller diameter tire have better aerodynamics.)

*67% rather than 60% because the calculation is done with the average of the inside and outside tire diameter rather than just the outside tire diameter. Therefore the calculation is 30/18 for 67% rather than 32/20 for 60%.

 

[Hummina Shadeeba]

When you say "smaller wheel" are you referring to differing effective rim diameters at the same bead seat diameter? (e.g. An aero 700c rim will have a smaller effective rim diameter than a typical low profile 700c rim)

If so, then this is something different than what I was referring to which is comparing different tire diameters (As a starting point consider 32" x 2.00" vs 20" x 2.00" tire. If both are on the same internal width rim and have 100 aspect ratio the 32" tire would have 67%* greater tire volume. Therefore in order for the 20" diameter tire to have equivalent tire volume as the 32" x 2.00" it would have to be much wider than 2.00". The math works out that the larger diameter tire has a smaller frontal area when it's tire volume is the same as a smaller diameter tire. This is why larger diameter tires at the same tire volume as a smaller diameter tire have better aerodynamics.)

*67% rather than 60% because the calculation is done with the average of the inside and outside tire diameter rather than just the outside tire diameter. Therefore the calculation is 30/18 for 67% rather than 32/20 for 60%.

Id like to summarize what I understand you wrote:
for aerodynamics the smaller effective rim diameter the better.
The smaller frontal area the better.
———-




The larger the tire volume seems to be assumed better, and that’s understandable for suspension. Could kind of cheat and make a disk wheel with no spokes and fill the hollow of the wheel with air and run tubeless. Has that been done? I can imagine no drawbacks.

other than ur wheel exploding. And going to have to be heavier. But for getting the most aero and best suspension..in theory. Or maybe it would barely be noticed. What pressure would it have to be?

 

[ebike4healthandfitness]

The larger the tire volume seems to be assumed better, and that’s understandable for suspension. Could kind of cheat and make a disk wheel with no spokes and fill the hollow of the wheel with air and run tubeless. Has that been done? I can imagine no drawbacks.

other than ur wheel exploding. And going to have to be heavier. But for getting the most aero and best suspension..in theory. Or maybe it would barely be noticed. What pressure would it have to be?

I think that is a great idea and no I haven't seen it done before.

Since your effective volume becomes much larger the pressure increase from an given tire deflection will be much smaller. In cases where you were trying to control maximum tire deflection from impacts you would want to inflate to a higher pressure. Nice thing is that even with a higher inflation pressure the change in pressure from impacts would be much smaller.

P.S. You could even apply this idea to deep V section rims. Simply attach spokes to rim in a way that doesn't lead to communication with the tire's pressurized air volume. One example of attaching spokes in this fashion would be Kineo tubeless spoked rims.

 

[Hummina Shadeeba]

I think that is a great idea and no I haven't seen it done before.

Since your effective volume becomes much larger the pressure increase from an given tire deflection will be much smaller. In cases where you were trying to control maximum tire deflection from impacts you would want to inflate to a higher pressure. Nice thing is that even with a higher inflation pressure the change in pressure from impacts would be much smaller.

P.S. You could even apply this idea to deep V section rims. Simply attach spokes to rim in a way that doesn't lead to communication with the tire's pressurized air volume. One example of attaching spokes in this fashion would be Kineo tubeless spoked rims.

If using a deep profile rim and it were filled with compressed air supporting the tire I don’t see the advantage. The pressure wouldn’t increase as much with tire deflection but i don’t think it changes much normally, and even if increased less I don’t see that reducing rolling resistance or giving better suspension.

 

[ebike4healthandfitness]

If using a deep profile rim and it were filled with compressed air supporting the tire I don’t see the advantage.

If a disc wheel filled with air gives an advantage wouldn't a 80mm deep V section rim filled with air also give a advantage? It would just be a smaller advantage right? (i.e. still an advantage, just not the full sized advantage)

 

[Hummina Shadeeba]

If a disc wheel filled with air gives an advantage wouldn't a 80mm deep V section rim filled with air also give an advantage? It would just be a smaller advantage right? (i.e. still an advantage, just not the full sized advantage)

What would be the advantage of either?