carbon fork for short reach brakes and large tires

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carhillclimb
Posts: 37
Joined: Fri Jul 04, 2008 1:45 am
Location: MA, USA

by carhillclimb

I have been trying to search for this and not been successful.

Any hints on carbon road forks 1 1/8 inch steerer that take short reach brakes for 700c rims, and as large a tire as possible? For example, ENVE 1.0, the Scapula, Kinesis RC03 and the Ritchey I have all accept a Vittoria EVO CXIII 700x25 at 1136mm circumference, but not a Continental GP4000S2 700x28 at 1157mm circumference. The Kinesis RC03 appeared to claim to take a 35, and it would accept the GP4000S2 if the tire were perfect. Note that specified tire size is not consistent even within a brand; the Continental GP4Season 700x28 is 1139 circumference, almost identical to the Vittoria 700x25. I have a steel fork that will accept a 700x32 and uses a short reach brake.

I do have a thin blade Blackwell Research aero fork from 8 years ago that will accept the GP4000S2 700x28 but it is 460 gram and I am looking for lighter.

Does a carbon fork need more material below the brake hole to be strong enough?

Michael Wilson
Michael Wilson

RyanH
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by RyanH

The Cervelo R2 fork, if you can somehow source it is on the longer end of what short reach brakes can handle since it's supposed to be the same as the Mud forks.

I was able to clear Vittoria Pave 27mm with gobs of clearance on my enve fork though.

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by Weenie


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Marin
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by Marin

My Ritchey Logic fork will take a true 28mm tire. I'm currently on Open Pave 27mm with some room to spare.

Note that Gp4000s II 25 are almost 28mm wide/tall, and my 28s measured 31mm.

carhillclimb
Posts: 37
Joined: Fri Jul 04, 2008 1:45 am
Location: MA, USA

by carhillclimb

The Vittoria Pave 700x27 measured about the same as the Vittoria EVO CXIII 700x25 which is 2136mm circumference. I did not keep the Pave long enough to actually measure the circumference; I measured it when I was attempting to measure height above rim.
I know the GP4000S2 700x28 is large, but I assumed it was the one that was true to size, not the one that was oversize.
My 2014 GP4000S2 700x25 at 2129mm circumference is a bit smaller than my EVO CXIII 700x25

Tires grow in the first week or two, and that is not accounted for in my measurements.

I am liking the GP4000S2 700x28 on the Kona Zone but may go back to Compass Stamped Pass 700x32. I am also liking the Vittoria EVO CXIII 700x25 on the BMC TMR01. I have 3 mm clearance on the BMC but that is not enough for the Continental.
Michael Wilson

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Isn't circumference a slightly inconvenient metric for whether a tire fits your fork?

Btw, my Open Paves are a true 27mm, measured with calipers, after months of use.

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carhillclimb
Posts: 37
Joined: Fri Jul 04, 2008 1:45 am
Location: MA, USA

by carhillclimb

I have more trouble with the outside diameter of the tire hitting the top of the fork crown than I do with the section diameter being too large and the tire rubbing the side of the fork. Overall diameter is harder to measure accurately than circumference because the hub gets in the way of the diameter but the circumference is easily measured with a $2.50 clothing measuring tape off of ebay. So circumference is what I measure, and while my spreadsheet computes diameter from the circumference, circumference is what I remember because that is what I enter into the sheet. (And it was 2 or 3 days before I bothered to add the diameter column ...)

Height of the rim sidwall from the bead seat is not consistent from rim to rim and the height from the top of the rim to the top of the tire hard for me to measure repeatably, so I stopped doing that. Width of the inflated tire varies with internal rim width, and somewhat with rim sidewall height, and is less relevant to my typical clearance issues. I include it in my table along with the rim used for measuring but it is not a number I mention often. Circumference changes a small amount with rim width but not much.

That said, circumference and the resulting diameter computation assumes a round tire and they are not actually round, so a better method would be to make a guage on a fork. Anyone have such a guage, or seen one available? Then we could also at least estimate the out-of-round on different tires and have that part of the tire comparison table. Round tires are really much nicer to ride.

Also it appears from memory that the out-of-round varies with age of an individual tire.

As sometimes happens, the question I ask results in useful answers to somewhat different questions.

Michael Wilson
Michael Wilson

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