Ritchey Comp Carbon Road Fork
 

Can the Ritchey Comp Carbon Road Fork fit a 28mm tire? Listed as fitting 25mm but I'm hoping they are being conservative that that.

Probably best to contact Ritchey and get some measurements from them. Different 28 tires and rim combos can get up to 3-4mm? difference in measurements.

I'll also add that many rim brake calipers these days are more the limiting aspect then the frame or fork's clearances. Many dual pivot calipers have their arms and/or backing plate sit "lower" than the brake bridge or steerer ends do.

As with any situation where the dimensional standards are fairly "fluid" one should really only trust actual testing/trial. Andy (and a good reason to shop locally where one could test fit before leaving the place of purchase)

Man, I hope so. I've got two in my basement right now awaiting winter install.

I was too lazy to actually contact Ritchey. This is what I discovered in my travels:

a) I found something online where someone claimed to have contacted Ritchey and Ritchey said that all of their forks could take 28's.

b) The above sounds great but, at the same time, I don't know if it's true or how far back in time this would apply. My forks, although purchased this year, are not the latest editions.

c) I've thrown my forks on top of a loose front wheel with GP5000 25 tires on it to inspect. There's some room there but, if they can take 28's, it won't be by much with respect to the ETRO 3mm standard or whatever. The limiting thing appeared to be the crown clearance.

d) As you probably know, for the same tire width, a narrower rim will increase decrease the tire height a bit relative to a wider rim. So it might be cozier on an 18 mm rim than, say, a 13 mm rim. So there might be more gap on a 13 mm rim than on an 18 mm rim. [EDIT: thanks to shelbyfv and maddog34 for correcting me on this]
I've got my fingers crossed hoping that you're a more tenacious fork researcher than I.

https://cimg9.ibsrv.net/gimg/bikefor...2c80034490.jpg

wheels flex back and forth more than people like to admit when ridden... what "looks ok" in the garage may not be so good looking when a rider puts some force into the bike... and even tiny scratches in surface finish on a carbon fiber fork sends people rushing to their computers for advice.

you've been warned.

Why is it that modern road forks are not designed with more generous tire clearances? Is that for the sake of aerodynamics? Something to do with the use of carbon?

I have six vintage steel road bikes in my stable and every one of them seems to have more generous tire clearance at the fork than my modern bikes.

Are you sure about this? Cozier in width or height? :foo:

Are you not? It's just geometry applied to an incomplete circle with a fixed, partial circumference right? I'll try to find some time to check the algebra.

Height. As I mentioned, the limiting gap appears to be to the crown on my Ritchie forks.

https://cimg3.ibsrv.net/gimg/bikefor...8fa3596e60.png

If the narrow (13mm) rim increases the tire height, wouldn't that be cozier than with the 18mm?

a narrower rim will DECREASE the tire's height.... more sidewall is used to reach the too-narrow rim.... and the decrease in diameter will be almost totally imperceptible.

the overall width of a tire on a too-narrow rim will also be decreased, and that decrease will also be minimal if both rims are narrower than the designed width of the tire.

tread Contact Patch will be reduced by the narrower rim.. but once again, it's nearly imperceptible in use.

tire pressure alterations effect a much larger change.in contact patch and the two other parameters mentioned, depending somewhat on tire casing strength and construction..

and, as i mentioned in an earlier reply.. the WHEEL is the problem, not the tire, or rim width... they FLEX.. a LOT.

tire casing design/construction/compliance, and tire Pressures, are the bigger difference in apparent "comfort"... and inner Tube thickness/material is also a huge factor. thorn resistant tubes won't lose roundness when deflated, they're so stupidly stiff...

By cozier, I meant more palatable to the rider which, in this context, would imply a larger gap between the tire and fork crown. The adjective usage of "cozy" as shown below.

I didn't mean to imply that the the tire was "cozying up" to the fork in the sense that one might relocate themselves in closer proximity to a warm fire on a cold evening.

https://cimg0.ibsrv.net/gimg/bikefor...ce2f55010c.png

So I did the algebra. It turns out that there's no closed form solution and, rather, a numerical solution is required. So I did that too. Or, at the least, I attempted it. It's time to get this weekend started so documentation and fact checking will need to wait until next week.

This is what I get for a 28 mm tire casing that I estimate to be 71 mm wide:

18 mm rim internal = 25.629 tire height.
16 mm rim internal = 25.512 tire height.
13 mm rim internal = 25.245 tire height.

So, for this particular set of conditions, a narrower rim appears to beget a lower tire height as I proposed earlier.

The difference in height is small (0.38 mm). But, then, so is the target gap (3 mm). That's 13%. It is what it is.

https://cimg9.ibsrv.net/gimg/bikefor...9144b493c0.png
https://cimg8.ibsrv.net/gimg/bikefor...eab0856be4.png
https://cimg0.ibsrv.net/gimg/bikefor...cc9b2bb3b9.png

I see the problem now... I said it in reverse the first time. I meant to say that a narrower rim begets a shorter tire. So we all agree.

Oh well, I've long wanted to sort out the math on this anyhow

:thumb: And there you have it, we are in agreement. Canadian vs US usage. Here's this as well.
https://cimg5.ibsrv.net/gimg/bikefor...e9ab266ac9.png

[QUOTE=shelbyfv;22981673] Here's this as well./QUOTE]

Yes, the non-circularity of the real shape introduces rather a lot of complexity. In the source for that, do they mention whether the shapes were got at by way of measurement or analytical modelling? I would guess measurement.

With the right software toys and tire properties, I probably could predict the real shape analytically. It might be easier to just fabricate my own forks however.

I expect measurement as well. Apparently Conti did the graphic and it's been floating around the web for years. If I ever knew the original context, I've forgotten.:rolleyes:

ok so skinny rim is smaller tire 👍 thanks for the advice. I'm ok with very tight clearances. I'm tall but lightweight and to be honest a pretty weak rider so i'm not worried about wheel flex. It hasn't been an issue on my lemond.

I agree. And the seat tube clearance is also often the limiting factor before the fork.

DOH (head smack)! Why didn't the rest of us think of that?!

I wonder if this diagram is based on math or getting a few examples for each and averaging them (i.e. sampling)? Plus, different tires, marked the same (say, 25mm) will behave differently on the same rim.

Good question, why didn't you? Some possibilities:

1) Folks did think of it but did not care enough to bother developing the numerical solution required to solve it.

2) Folks recognized in advance that the effect would trivial, such that the effort was not justified.

3) Folks anticipated that the impact of tire non-circularity might of a similar magnitude such that the effect of rim width would get lost in the "noise".

....

Frankly, when I dove into this, I was surprised that I wasn't able to find some kind of online calculator to do the same thing.

At some point, I might have been able to muddle my way through this sort of math, but I no longer have the ability to put my mind to such stuff. Either degrading capabilities or increasing laziness (I'm almost 70, I'll have you know!). Out of practice in required concentration, for sure.

I was just going to edit one of my posts to echo what you've written - that to me, at least the differences between the rims I have (one has an 18mm ID the others, ~13-15 ) is really trivial to me. At least it doesn't seem to affect what I feel on the road. And the measurements I've taken of mounted tires of the same brand and width are "only" a mm or two and can go either way depending on different manufacturers.

It's just a cross section circumference problem. An 18mm rim adds 5mm of cross sectional circumference than a 13mm rim does (or actually a little more than 5mm since that distance is not an arc).


However, no amount of math is going to take into account tread shape or the variation between manufacturers on what they call "28mm".


(There does come a point where the tire height begins shrinking if the rim is very wide and the tire is not. Aspect ratio.)

Back to giving the OP an answer: I am running a Shamal Ultra C-17 with Vittoria Rubino Pro Graphene 2.0 25s [MENTION=88036]100[/MENTION] psi under a brand new Ritchey Comp Carbon from Performance Bike. It's tight - maybe 3-4 mm of clearance to the top of the tire.

FWIW/YMMV...