Tire to Fork clearance safety margin?
 

I've been considering springing for a set of wider wheels -- currently I run some old Mavic Ksyrium Elite wheels (ca. 2004) which probably are no wider than ~19mm on the outside rim, but not sure. Mounted on these are 25mm Pro4 SCs V2.

As it stands, back wheel isn't an issue. Front wheel I have about 3mm clearance either side of the tire. With a wider wheel I've read that the tire will tend to inflate wider than it does on a narrower wheel. Without buying a wheel and later finding out it doesn't work, what's your guess? Nominally the tire/wheel should still fit fine, but how much allowance is there to be safe for wheel or fork flexing?

FYI, wheels I'm looking at include the Boyd Altamont and the November Alloy Nimbus Ti's with the Pacenti SL23 v2 wheels.

Having a good relationship with a few local shops I would take the frame down and mount up some similar wheel/tire combos from their stock and see how the clearance is. YMMV

That's a good idea.. and on this related note, what are reasonably priced stock options for mainstream brands of clincher wheels with ~24mm outside width?

That's tight already. Tough situation.

I can only share my limited experience here. I had a biker with similar clearance are her fork. No issue ever with the tire itself contacting the fork. But the thing would collect leaves and other junk and rub for a bit.

Oh crap, you are supposed to have a safety margin? Good thing I sold that frame, huh? I upsized my new tubulars to 25s and could barely see the space between the tire and the fork crown underside. It's a good thing that I could ride them a lot softer than my 23mm clinchers, because at about 110 psi they rubbed. At 90 psi they were okay, but just barely. Laterally they were always okay. I didn't pay any attention to it. No issues. I hope the new frame/fork has more clearance though.

I may try and get to one of the (evidently quite few) shops that are authorized Boyd demo locations. None that are too easy to get to though. I guess that would pretty much nail the question.

offhand, does anyone know if the LBS's that are Boyd dealers, if they sell the wheels at same prices as Boyd's direct website (not talking about the clearance stuff, but regular current stock)?

Dremel tool with a sanding drum...

I don't think my tire has enough rubber to spare to consider grinding it down.

Do frame makers really need to make clearances so tight ?? Jeesh.
Do they not realize stock parts get replaced once in a while.

:roflmao2:

Sure, but you are supposed to use replacements that fit.

I think the better question for wheel + combinations is the inside track width. My carbon rim brake tracks are thicker than ALU, so the tire diameter to wheel set ratios don't work.

For example... my old mavic wheels had a 15mm inside track, and with a 23mm tire, they would measure out at 23mm. My boyd 60s with a 23.5mm outside track specs at 16.3mm inside... but with 25mm tires it measures out at 27.5... so, each combination is likely to be unique.

It is well known that wider rims add width to the tire mounted on them relative to the nominal size. Which brings up a good question. Will nominal tire sizing ever be normalized to the wider rims rather than the narrower ones?

You ok? Having a stroke?

Thanks for asking. Damn phone.

Ok but to keep the question simpler... Is there a consensus as to what minimum margin of distance should remain between tire and fork? If my 25s grow to 27 on a wider rim, resulting in only a 2mm gap each side. Is that enough?

Sy, enough for what?

I agree that a little more clearance would be desirable. Why restrict the bike to 23mm tires (and sometimes to just the subset of 23 mm tires that tend to run narrower than spec.)? A few more mm of clearance would allow the use of 25 - 28 mm tires while not making any noticeable change in the bike's handling. My Cannondale fork will let a 25 mm just clear but when riding on a road that's had some sand blown onto it I keep hearing a little buzzing followed by a 'ping' as a sand grain gets stuck under the fork crown and then ejected.

Robert
Enough to be reasonably assured that tire and fork won't rub when bike is being ridden aggressively. Ie from combined lateral flex of fork and/or wheel.

Sy, there is no hard number here, just things to consider. Like wheels don't always stay true on a ride. Stuff happens. If the wheel goes out of true (breaks a spoke, you crash, ...), are you willing to risk scraping off the faint and ever abrading the carbon fiber a bit to ride home or call a spouse or other for a ride to protect the fork? If you have steel, it's just paint, but not many ride steel forks any more. The risk does go up of having an object jam between the tire and fork. Not likely but still ...

These are all judgement/degree of risk calls.

There is a remedy, but it is a step back in time. Go to a frame maker and have him build you a steel fork with appropriate steerer. Steel is, spacewise, a far more efficient material. For the same distance of fork crown top to hub, you would have a wide choice of fork crowns that were wider and higher over the tire. Brace yourself if you think you want to go this route. The fork will cost you $4-700 and add an easy pound to the bike weight.

An incident of relevance here. Early on in the life of my moniker, that 1979 Peter Mooney, I was in a town line sprint. A rider stuck his quick release into my spokes. I leaned into his wheel to be above to separate from him and not crash. I rode the bike to a standstill with 8 consecutive spokes on that side broken. There was a 1/2" patch of bare steel on the inside of the brand new fork. This on a fork that had a mile of tire clearance. Had the clearance been tight, I highly doubt I could have saved myself from crashing. As it was, had the fork been carbon fiber, it would have been compromised severely. As I said above, stuff happens. Yes this was "competition", but sticks and dogs also get into bike spokes.

Ben

Thanks Ben.. couple notes, I do have plenty of clearance above the tire -- not worried about clearance above the tire, only the sides. Also, I realize there's no hard and fast rules -- dependent very much on actual wheel and actual fork characteristics. I'm really just looking for anecdotal experiences.. ie. if everyone said that no way, 2mm isn't enough.. or the opposite (ie. plenty of room), then I'd at least have a starting point. Also.. I'm not entering a race anytime in the foreseeable future; for me this is all exercise/recreationally driven. Finally, before I spring for the cost of a new fork, I'd just get narrower tires that do work.. but I'm still trying to figure out what generally will work (from this clearance perspective) before I start down this path.

Really don't want to start a poll... "How much clearance from your tire to your fork do you currently have?"

Got it. My situation was all on top, not the sides. I see your problem.