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Discussion Starter · #1 ·
I have a Gunnar HyperX with a Wound Up Road Disc-X fork. I'm currently running Sector 28 tires on Velocity Fusion rims with plenty of clearance all around on the fork.

I just placed an order for November's featured build Pacenti SL25 rims with Clement PDX 33mm tires.

I'm concerned with the clearance on the fork's crows after looking at my current setup. There seems to be plenty side to side. Eyeballing with a metric measuring tape I get about 60mm side to side near the top and if I lay the measuring tape's zero end up against the inside of the fork crown I estimate the center of the fork's dropout to be about 655mm.

I've looked at the Wound Up fork specs and Clement PDX specs but no mention of the "height" of the tire or fork.

Any idea on how to determine if my new wheels/tires will fit my current fork. Being a disc fork I'd suspect more clearance that typical road fork, but since it is not CX or Gravel at bit worried. Do I need to know the circumference of the outside of the tire? How do I measure the fork correctly?

Wound UP Fork Specs Road X Disc Specs - Wound Up Composites

PDX Tire Specs PDX Clincher | Clement Cycling, Cyclocross Tires, Adventure Tires, Mountain Bike Tires, Road Bike Tires
 

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Banned Sock Puppet
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The chain stays may actually be more of a clearance concern than the fork.

As Jay implied, the deed is done. You already ordered the wheels and tires. So the easiest way to find out if they fit is the mount them on the bike. Worst case scenario is you will end up paying return shipping if they don't fit - besides the disappointment.
 

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Discussion Starter · #5 ·
Wheels/tires not in hand till end of the moth at best.

I've got a message out to Wound Up.

November won't process the order for the new wheels for 10-14 days. I can cancel the order if I know they won't fit. Thus avoiding hassle for both me and November. They are great guys, I'd like to do the least damage.

I'd also not like to deal with purchase/return of cassette and rotors.

While I appreciate the input on other thoughts, how about actually offering up answers to my original questions? Proper dropout to crown measurements and circumference/radius/diameter of that specific tire. ie center of hub to most distant point on the tire (probably the end of tread lug).

While there are all sorts of calculators online for gearing, I was kind of expecting that for forks/tires. I'm not having much luck searching.
 

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Wheels/tires not in hand till end of the moth at best.

I've got a message out to Wound Up.

November won't process the order for the new wheels for 10-14 days. I can cancel the order if I know they won't fit. Thus avoiding hassle for both me and November. They are great guys, I'd like to do the least damage.

I'd also not like to deal with purchase/return of cassette and rotors.

While I appreciate the input on other thoughts, how about actually offering up answers to my original questions? Proper dropout to crown measurements and circumference/radius/diameter of that specific tire. ie center of hub to most distant point on the tire (probably the end of tread lug).

While there are all sorts of calculators online for gearing, I was kind of expecting that for forks/tires. I'm not having much luck searching.

I'm not really familiar with your frame. Specs aside, how much clearance do you have with your present wheels and tires? This should give you some clue. Sorry, but I don't have a better answer. As I said, I think you have more concern on stay clearance.
 

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A rough approximation to see if you will clear the fork crown is to measure the distance from the edge of your current rims to the underside of the crown. If you end up with a distance equal to the width of your new tire plus 5 mm good chances are you should be ok. For the 33mm tires you listed that would equate to 38 mm at a minimum.
Different width rims than what you have now will change the profile of any tire by up to +/- 2mm as will different make tires. A good quality tire with standard casing would have roughly the same height as width.
Again, these are rough approximations to see if you are at the right path.
 
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Discussion Starter · #8 ·
Gunnar says 35mm frame clearance. I've heard of people successfully running 40s on the Hyper-x. It is a cross frame. The real issue has been that it is a model from 2011 when Gunnar built them with a 1-1/8 head tube top and bottom so there were not many disc fork options. Most CX or road Disc forks are tapered as is the newer Hyper-X frames. I started with Cro-mo Salsa fork. Switched to this fairly pricy carbon Wound Up Disc X Fork. I was using the bike for light gravel, commuting and rough asphalt and Sector 28mm tires.

Work situation has changed, no longer using the bike for 40 mile round trip commutes. I'm hoping to repurpose the bike for more dirt roads and a bit more gravel.

Wanted the new wheels so I could swap the total setup form smooth to knobby by only flipping QR levers, not spend my time swapping tires and sealant.

Current tires have plenty of clearance side to side on both frame and fork. It never dawned on me about the "height" of the new tires until after I placed the order. I'd say 6-8mm of clearance between the sector 28s and the inside of the fork crown.
 

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Switching wheels is not going to make a significant difference in tire height. The larger tire will. Expect a 5mm wider tire to be 4-5mm taller.

As DC Griz says, slap your old tire and wheel in the fork and check the clearance. You are probably good upsizing tires 50-75% of the space between your current tire and fork. For example, if you have 8mm between your tire and crown you can probably upsize the tire by 4-6mm.

Only you can judge how much clearance is enough to account for mud and crap that might stick to tires.
 

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Most tires have a circular cross-section, so with 33mm tires on a 622 rim, 688mm diameter, and 344mm radius (axle to top). If your fork TRULY has 655mm axle to the top, then your fork is made for some sort of freaky 36" size wheels.....
 

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Discussion Starter · #12 ·
..., then your fork is made for some sort of freaky 36" size wheels.....
Thanks No Time T. Poor typing on my part 355! But that is with the tape touching the very top of the crown where the steerer tube intersects. Sounds close but hopeful. I was worried this was more like a true road fork. I think I might have a chance here.

Still nothing back from Wound Up.
 

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Also, my calculations don't consider tread depth. Some tires have extra rubber on the tread (like my Tufo S33 pro's), and that is hard to calculate. If you have a theoretical 11mm clearance, count on 2-3mm just for normal tread depth, but if these are dirt/gravel tires, a good 7-8mm might be required. That may leave you with only 3mm clearance, and 3mm wide gravel bits are pretty common...
 

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Discussion Starter · #14 ·
I'm moving in a different direction. Going with the same wheel set, but Schwalbe S-One 30mm tires. 99% sure they will fit. If I need more traction I'll figure that out down the road. Hoping the wider rims and wider tires make for a stable ride all winter.
 
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