Minimum Tire Clearance

[SleepyCyclist]

Looks like these Conti GP4 25s are just too tight on this Alpha Q fork.

What is the minimum tire clearance you're ok with? Especially for the front where it would seem to be more critical.

thanks, M

[JasonF]

For me, 3-4mm of tire clearance, either at the fork or the caliper (whichever is lower) is ideal. Your pic is a little too close for comfort. My Seven Axiom has a "stock" 5E fork (i.e., not long reach) and it can comfortably fit every 28c I've tried, many 30c (if they measure out to no wider than that). It's available in multiple rakes so I bet you could find one that works with your frame. How's the brake bridge & chainstay clearance on the Serotta? Looks like a nice bike.

[Cicli]

More than that. Maybe 3-5mm.

[TimD]

I'm reliably informed that there is an NHSTA spec for minimum tire clearance, though I've never looked it up. The existence of such a spec goes a long way toward explaining why manufacturers will not 'approve for use' tires of more than a certain size but which obviously 'fit'.

[EDS]

Interesting in that the Alpha Q on my Serotta (I believe it is a GS-10) clears 28s.

[thwart]

Interesting in that the Alpha Q on my Serotta (I believe it is a GS-10) clears 28s.

Alpha-Q was in business for many years... starting way back in the day when a 23 mm tire was considered 'fat'... this must be an older model fork.

[marknreimer]

I've got a Cervelo R3 and my clearance is pretty close to that with 28s. I haven't had any rocks jam in there and catapult me over the bars, but I do notice a lot more wear on the paint/surface from bits of sand and debris getting sucked through. It's doable, but in my opinion not advisable. Also, better be riding in bone dry conditions.

[ColonelJLloyd]

That's not enough for me.

[SleepyCyclist]

rear clearance looks fine.

I'll probably just run 23s as it's tighter on the front than my teeth care for!

The Alpha Q fork bugs me for another reason - the front dropout on one side is very tight. The opening measures a little over 8.5mm diameter, whereas the other is a little over 9mm. Makes mounting the wheel a real chore. Anyone experience a similar problem? Just sand the tight dropout a bit?

it's a 1" threadless, so replacements choices are limited.

m

[ColonelJLloyd]

I think a Ritchey Comp Carbon fork should allow you at least a healthy 26mm tire; probably a 28mm.

[Cicli]

Yeah. You can sand the dropout to get some better clearance for the axle. Better than any other fix for that.

[scharny]

I have a 2002 Allez steel frame that has clearance for 28mm tires, but when riding sand and mud the rear brake catches a lot of buildup. Stays still have clearance. Anyone know of a rear caliper road brake with more clearance than a recent Shimano 105?

[Cicli]

I have a 2002 Allez steel frame that has clearance for 28mm tires, but when riding sand and mud the rear brake catches a lot of buildup. Stays still have clearance. Anyone know of a rear caliper road brake with more clearance than a recent Shimano 105?

Planet X CNC have alot of clearance.

[Mark McM]

Looks like these Conti GP4 25s are just too tight on this Alpha Q fork.

What is the minimum tire clearance you're ok with? Especially for the front where it would seem to be more critical.

thanks, M

The width of an inflated tire will be determined by both casing width and rim width. It looks like the tire in your photos is mounted on a wide rim, which will make the tires wider than if they were installed on a narrower rim. If you measure the actual width of those tires, I'll bet you'll find that they are wider than 25 mm (and will also ride like they are wider than 25 mm).

Additionally, tire height will also vary with tread thicknesses. Those Conti GP4 tires have a very thick tread. A different model of tire of the same width may more clearance than those tires.

Personally, I like to see at least 3 - 5 mm clearance under the fork crown.

[Vinci]

Yeah. You can sand the dropout to get some better clearance for the axle. Better than any other fix for that.
Just make sure you don't sand the upper part of the dropout. It doesn't look like you can spare any vertical clearance...

[dsillito]

Disclaimer: I've never tried this.

This makes me think of the Sheldon Brown post where he cut a rear axle flush with the surface of the locknuts before installing it in the frame, so he could shift the wheel back a bit (to take up chain slack). Here is the quote:

"This bike has truly vertical dropouts, but I wanted to set it up with a flip-flop hub: fixed gear on one side, two-speed freewheel on the other. The vertical dropouts don't allow chain tension adjustment because the axle is a snug fit in the slot. I solved this by cutting the axle off short, so that it does not extend past the cone locknuts. Only the quick-release skewer goes through the dropouts. Since the skewer is thinner than the axle, this allows some front-to-back adjustment. So far, I've had no problems with this unorthodox rig, but I carry a spare skewer, just in case."

From the page:

http://sheldonbrown.com/org/hercules.html


I was looking at this in relation to a 96mm OLN hub I want to build up. If I put spacing washers on either side, so the fork legs don't have to flex inward much (for a carbon fork that is already a bit wide, I think, I wouldn't worry about it in a steel one), then there is barely any axle that it sitting on the seating surface on the fork dropouts. I was looking around to see how much overlap was recommended when I found the Sheldon Brown post, where he has zero axle sitting in the dropouts. On a rear wheel no less!!

So...with that in mind...could you not just drop the front wheel a tiny bit in the dropouts? Put in two spacers of equal thickness between the upper axle surface and the fork ends? Put the QR a tiny bit tighter than you would otherwise? The worst that could possibly happen (in my mind anyway) is that it gradually works its way the last couple of mm into the dropout, such that it becomes fully seated. How much road force on the front wheel is supported by the axle seated against the fork ends, and how much by the clamped QR, is the question? Anyone...Anyone? ....Bueller....Bueller?

Probably another one of those things that nobody knows, but everyone has an expert opinion about, ha ha. Maybe I'll try it on my commuter just for a fun "experiment". Hit some potholes and see what happens.

[SleepyCyclist]

A little filing did the trick. Slides in/out much more easily.

23s give plenty of clearance.

Thanks, M

[Peter P.]

Had I known the dropouts were aluminum, I would have readily suggested filing the slot.

As to the tire fit, I see after switching to 23mm tires you gained adequate tire clearance vertically, but still too close for comfort laterally. After looking at a ruler, I too have to say 3mm minimum, 5mm optimum for clearance.

Unfortunately, due to the nature of carbon forks, the crown area has to be constructed with a greater volume to have adequate strength. Consequently, that volume swallows up tire clearance.

You could easily build a steel fork with the same axle to crown measurement and gain gobs of vertical and lateral clearance, laughing at those that have such concerns.

[SleepyCyclist]

wonder how old this alpha q fork is? we did race on 20s back in the day.

m