On top of that, on the 303s the sheer volume of air that they hold due to the width of the 303s vs thinner/older CC's allows you to run at a much lower pressure...

I'll expect that to disappear about the same time people stop replying with posts like, "I don't know if it's more aero or if it rolls faster, but the 'grip' (or 'feel' or whatever subjective quantity) of TireX is AWESOME." I'll say it again, the tire that has been TESTED - empirically - to be the best combination of aero and Crr on the 303 Firecrest is the Continental 4000S. That doesn't mean it's the best tire for every race, but it's generally the best all around match unless you really need a wider tire for some really rough roads.

However, as an aside to you, Tom, I'm not sure that this, "The total air volumes (around the entire tire) of both setups are already so large that the compression at the contact patch has basically NO effect on the air pressure inside the tire." is what people are arguing. At least, it's not what I've heard. What I've heard is that the total volume *allows* for a lower pressure to achieve equivalent volume. Basically, if you were to take a cross section of the wider rim vs. a narrower rim with tire mounted and inflated, the cross sectional area would be larger with the wider rim. As a result, to achieve a given volume of air, you need less pressure. I do not think that I've ever heard someone say that the compression of the contact patch noticeably affects pressure inside the tire. Basically, as you increase rim width, cross sectional area (and obviously the resulting volume from integrating over the rim) goes up.



Make rim wider, cross sectional area goes up, volume gets bigger, less pressure needed to achieve equivalent total air volume.

Well, I will *speculate* that equivalent air volume results in a proportionally equivalent deflection of the tire. And I speculate that to be a good thing.

Please explain to me how my speculation is any more or less well founded than your speculation about tire sidewalls.

However, as an aside to you, Tom, I'm not sure that this, "The total air volumes (around the entire tire) of both setups are already so large that the compression at the contact patch has basically NO effect on the air pressure inside the tire." is what people are arguing. At least, it's not what I've heard. What I've heard is that the total volume *allows* for a lower pressure to achieve equivalent volume. Basically, if you were to take a cross section of the wider rim vs. a narrower rim with tire mounted and inflated, the cross sectional area would be larger with the wider rim. As a result, to achieve a given volume of air, you need less pressure. I do not think that I've ever heard someone say that the compression of the contact patch noticeably affects pressure inside the tire. Basically, as you increase rim width, cross sectional area (and obviously the resulting volume from integrating over the rim) goes up.

virtually every tire manf recommends lower pressure as tire diameter goes up. I don't see where it matters if the diameter increases by using a wider tire or a wider rim.

I really don't see how angled or vertical sidewalls will make a difference but bigger volume is pretty proven. I'm willing to be convinced can you point to any studies wheresidewall verticallity makes a difference in Crr, or traction, etc.

I would say that compression at the contact patch has an effect in the "local air pressure", not the global air pressure because the upper part of the tire is free to deform, so it would affect tire stiffness.

Are you implying that the air pressure in the contact patch area is somehow at an appreciably (or even measurable) higher pressure than in the rest of the tire? I'd love to see the data on that one ;-)

I agree with what you say, but aren't you parsing words a bit when you say this is incorrect

"but I REALLY wish this misunderstanding would stopt about why wider clincher bead spacing "allows" lower tire pressures."

but this is correct

"it follows that using a wider rim would necessitate a drop in pressure to get similar sidewall compliance."

Granted a wider rim doesn't strictly allow lower pressure, it makes lower pressure optimal, but then again a wider rim doesn't necessitate a drop in pressure.

Rappstar,

Not to steel thread, but would the 4000s also be the best tire on an 808 FC?

"Nah its the internet schoolmarm part. ;-0"

Damn! Went to hit the "like" button and found I wasn't on Facebook.

Have we decided how many angels can dance inside a Conti 4000s on a 303 CC yet?

(But seriously, this is good stuff. Aside from the condescention and all, there's some good stuff here.)