Branimir

Cheers everyone!

This is NOT "yet another 23mm rim" thread.

I have wheels built with Ambrosio Balance rims and I had Vittoria Rubino 700x25c tires on it, with no problems. The bicyle is an early 90s Columbus EL-OS with a pretty tight geometry - short chainstays.

This week I decided to upgrade tires to Conti GP4000s, as everybody rave about them, so I purchased 700x25c also.
Conti's have a very very nice round profile, grip better, I'm totally happy with the tire, but...

Marketed 25c from both manufacturers varies. I used a caliper measurement tool to see how actually wide are the tires, once mounted.
I had Rubinos pumped a bit higher, probably 116psi's, but they measured below 25mm width, something like 23.5 or 24mm I honestly cannot remember, maybe because it didn't matter much, tire clearance was tight, but I never thought it could be a problem, since the wheels weren't too close to the seat tube or fork.
With Conti's pumped to 108psi I get 25mm in the front and 25.5mm in the back.

Ambrosio Balance rim is 19mm wide and internal width is 14mm.

The tire clearance is now really really tight with Conti's. The fork clearance is actually okay, should be 3mm at least, but the clearance of the rear wheel against seat tube is maybe 1mm!
There is no rub of the tire against the seat tube and I've ridden the bicycle at poor weather normally, did descents on a road bit some debris and generally I like 25c due their cushion and my brain thinks they are better for rough roads that we have here.

Question is:
Would a wider rim profile (outside measure), like 20mm or 21mm help with the overall size of the wheel with these tires? I suspect, with a wider rim, the tire would get even wider, but the overall size of the wheel should diminish, am I right?

Hope somebody can shed some light on this topic, I really like my bicycle and would like to keep using Conti 25c's.

Photos:


Thanks!

rpenmanparker 

With a 23-24 mm outside measurement rim you could run a 23 mm tire and get a ride similar to a 25 mm tire. Or else you could continue to run 25s with the wider rim and have them be a little shorter profile and less likely to interfere with your seat tube. Either way you are not likely to be disappointed in the ride quality.

chaadster

A wider rim with a higher BSW (bead seat width) will make the tire both wider and taller to a point. I'm not sure, but I think that point is within the range of typical road rim widths, though a 24mm BSW as found on the 700c Velocity Blunt, would change things, though I don't know if a 25 c tire would even be stable at that width.

So, I don't think a wider rim will help you gain clearance.

Bike Gremlin

I will never understand, for people not racing, why do they not leave enough room in the frame for at least 28 mm tyres. Not to mention fender and rack mounts. How much more room, weight and cost would that add. Making a bicycle 100 times more versatile and useful.

I'm not sure how a wider rim would affect tire height. Whether it would make it better, or worse.

chaadster

Ah yes, sizing down the tire on a wider rim may work! But, I think the same size tire on wider rim will exacerbate clearance problems.

chaadster

This recent thread may be helpful to consider: https://www.bikeforums.net/road-cycli...re-volume.html

rpenmanparker 

I'm thinking as the tire beads reach further to the sides of the rim to attach, the tire flattens a little. Hence the larger contact patch on a wider rim. But I could be wrong. Perhaps someone else has some definitive information.

chaadster

rpenmanparker 

Yes, a good reference. I stand corrected. Thanks for clearing that up. So it looks like OP can't do better than the 25 mm tire on the 19 mm rim for seat tube clearance at least with these representative rims and tires.

Branimir

Interesting graphics, seems like roundness profile of 25mm GP4000s is more or less the same at any size rim, either 19mm width or 23 or even 25mm wide rim. I fail to understand how can same tire be that larger depending on the wideness of the rim, what, the tire stretches in all directions?

Of course, wider rim yields wider tire profile, but why all of the sudden tire is bigger in width and height? Even pumped to a lower psi?

What is the source of this graphic? Is this tested in the any or just an illustration?
That's what I'm thinking also...

rpenmanparker 

I think that if you add the imaginary arc between the rim edges into the total circumference of the tire (assume more or less perfectly circular cross section) you increase that enough to affect both the height and width (horizontal and vertical diameters which should be similar anyway). Think about increasing the size-diameter of a wedding ring. You open the hoop and insert more gold. Similar here. The space between the rim edges is part of the circle made by the tire cross section. So wider rim, bigger circle. But that is partially offset by how far the imaginary arc that is between the rim edges drops down into the wider opening. The difference would be the tire height. Maybe it is not a monotonic function, and the height will rise and fall as the rim width is opened up.

Igualmente

Might want to keep an eye on the rear tire clearance over time: as I understand it the tires tend to get bigger with time and miles.

The above graphic seems to come from here: Ardennes+ long term review - Slowtwitch.com

Branimir

I see what you mean by comparison with the wedding ring, but bear in mind, that while the imaginary wedding ring is expanded by more material in the rim, the tire size is still the same, and if you look at the photo of a clincher tire, I fail to understand the physics of expanding vertically.

The "wedding ring's" component called rim is irrellevant since the tyre's bead is always hooked at the same point at the rim.


Stretch the tire left and right, it should compress in height, not expand, and when we consider the lower pressure also, there's no logic in 25c tire being bigger both in width and height, maybe we could see some actual numbers, it would be easier, since the graphic from a few posts above seems like an illustration.

Seems I'm not the only one who thinks like that:
Flo Cycling Blog: FLO Cycling - Component Series Part 4 - FLO WIDE RIDE Rims

rpenmanparker 

Be damned if I know what the truth is, but the Flo illustration is what makes the most sense to me.

Branimir

I think we are all victims of wheel marketing hype that's going on for a couple of years now

chaadster

Yes, the comparison graphic with the GP4kS tires is from HED's blog. Given its specificity about tires and width, and given that it's HED, I tend to believe it. FLO's graphic is not specific in what it's depicting, and they use it only to show the width of the tire compared to outside rim width, and nothing more.

As to how to explain differences, knowing bead seat diameter (BSD) is critical. Lower BSDs will shorten effective casing length, while higher BSDs will lengthen effective casing length, and in combination with the bead seat width, you'll see tires either getting taller or shorter.

I think that, generally speaking, the HED graphic expresses what goes on for most road rim/tire combos. Extreme rim widths, as I mentioned earlier with the Blunts, create a different dynamic which is not expressed in the HED graphic, and American Classic's Road Tubeless and Argent wheels have a particularly high BSD, again changing the dynamic.

Branimir

I tend to disagree:

Both website use graphics and their interpretations of it.
HED says they used plaster mould, no numbers.

FLO has it's own graphics with no numbers.
Flo Cycling Blog: FLO Cycling - Component Series Part 4 - FLO WIDE RIDE Rims

You said their graphic is not specific in what it's depicting, actually it's explained in the text above the graphic on the linked website:
On the right we have a standard 19mm rim and a 23mm tire. You can see the tire is wider than the rim. On the left we have the FLO WIDE RIDE rim and a 23mm tire. The rim width is nearly identical to the tire width.

The kind of information both these website provide are more or less on the same level. Graphics with explanations, no numbers, anywhere, only the results are opposite.

Why two very similar products have such different physics?

Bike Gremlin

For me it would be logical for the tyre to be lower profile on a narrow rim (like half the tyre widh) - talking about the inner diameter of the rim, of course.

As the rim gets wider, the tyre will get "taller". Until a point where the rim is near the tyre widh. Then the tyre "height" will start dropping again, but it would take about 1.5 times the tyre width wide rim to get the height back to the hight lower than a narrower rim. All because the tyre is round - it's carcase (is that the english word) keeps it near a round shape.

Chaadster's drawing points that out. The tyre is lowest with a 13.6 mm rim, then gets higher with a 17 mm one, then gets a bit lower (but not as low) with a 20+ mm one.

Branimir

Hm, let's presume that on 19mm width rim tire is lower profile than on a 23mm width rim.

What happens if we put the tire on a 17mm rim? The profile will get even lower??

How these things operate then? I know I changed a few wheels a couple of years ago, and with the same tyre mounted, one had a bigger profile/height than the other one.

The point is, I want to understand what influences overall tyre height, since I noticed it varies from wheel to wheel, with the same tyre mounted of course. I know I had some pretty old beaten up low profile rims (non aero) laced to 600 hubs and when I switched to CXP33 rims, the tire was noticabley higher in profile and I could not put it inflated to my road bike that had horizontal dropouts.

What's going on with the internal width of the rim?

chaadster

To be clear, when I say "specificity", that means more information. The FLO image has less specifity than the HED image. There's not debating that. FLO do not mention which tire, whether both tires are even the same, nor bead seat widths, nor inflation pressures, all info contained in the HED graphic. They are not on the same level at all.

I'm repeating myself here, but also note while the HED graphic is explicitly comparing tire height on different width rims, FLO only talk about casing width; anything else you ascribe to the FLO graphic is unsubstantiated by FLO. There is comment on accuracy of that image.

So, since you don't know what you're looking at, you can't rightly conclude that "similar products have such different physics." They may not. HED say wider rims make the tire taller. Why don't you ask FLO what they say, because that image makes no comment on that question, other than appearing to show it, but again, the purpose of the image was not that, but rather to show carcass width compared to outside width of the rim.

Lastly, I believe the tire height (assuming same tire, same rim construction, variable BSW) will increase through a range of BSWs as they get wider, but at some point, begin to draw lower. What that point is, I don't know, but if you spread something far enough, eventually it will flatten.

chaadster

Did you miss the part about BSD? You seem not be considering it.

Branimir

Yikes! Seems I missed it!

Now that changes my perspective on this subject

Hm... Manufacturer don't really give this info often...

chaadster

Yes, and it would be good to know in considering this tire height issue because it makes sense that how up the rim wall the tire attaches would have an impact on the overall height. At least it does to me!

Bike Gremlin

It would be good if they didn't make frames with so little clearance. I'll never buy a frame without room for fatter tyres AND bloody mudguards.

LesterOfPuppets

You could remove the dropout adjustment screws if they are in there, to get a few more mm tire-seattube clearance.