How-To/Mechanics: fork crown tire clearance

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- CommentAuthoratanz
- CommentTimeJul 2nd 2009
so I just bought some new tubulars for my merckx - I installed conti gatorskins because of their reliability. they're 22mm and they rub the inside of the fork crown at full pressure (10 bar). to get around this I've pulled the front wheel down about a 1mm for better clearance at the crown and tightened the bolts in that location - so the axle is not exactly tight against the underside of the front drop outs. so my question is it safe to run the front wheel like that? I'm pretty sure the axles rely on the clamping force of the bolt (also known as a slip critical connection) rather than bearing on the axle - I'm assuming this is how the rear axles work as well. can anyone confirm? thanks.
- CommentAuthorgiosSR215
- CommentTimeJul 2nd 2009
i mean it's not normal practice to have your wheel semi out of the front drop out. maybe you could have them slightly less inflated. or maybe trade them back in for 20's that would clear for sure.

In other words i don't think it's smart to run it like that. but to each their own.
- CommentAuthoreaglerock
- CommentTimeJul 2nd 2009 edited
Posted By: giosSR215i mean it's not normal practice to have your wheel semi out of the front drop out. maybe you could have them slightly less inflated. or maybe trade them back in for 20's that would clear for sure.

In other words i don't think it's smart to run it like that. but to each their own.

Or swap the tires for a different brand, which runs truer to size. The general consensus is that Contis run at measured size or slightly over. Other brands, such as Panaracer, have a deserved rep of running small for the measured size. It may be that if you pump the Gatorskins up to pressure and slap a caliper on it, you may find that the marked 22mm is really 24-25mm.

Basically, you need either a different tub, a different wheel (something with a lower E.R.D., perhaps?) or a different fork. But running the wheel halfway down the dropout sounds like a really bad idea. What happens if the clamping force isn't quite up to snuff, you hit something and the axle slides in the dropout? Scary stuff.
- CommentAuthoratanz
- CommentTimeJul 3rd 2009
No one worries about their real hub slipping out of the drop outs, do they? The clamping force is sufficient to keep the wheel in place and resist the pulling force of the chain.

What rims are known for having smaller ERD?

I might just try lower pressure - but even at 8 bar the clearance is less than 1mm. Is this still too tight?

Thanks for the input
- CommentAuthortyler215
- CommentTimeJul 3rd 2009
as long as its not rubbing its fine why dont you just get smaller tires like 20's or 22's ? you definetly dont need a new fork and you should be running the full psi.
- CommentAuthorupthemaiden
- CommentTimeJul 3rd 2009
I've done it, you'll be fine. If you're riding on the street and hit a bump there's a chance the wheel could push up and start to rub, so you'll have to make sure the axle nuts are tight enough.

The only real difference is that the only real force the back wheel has is you pedaling, and it still slowly moves forward. The front wheel will have to deal with the vertical force of every single bump and crack you hit on the road, and will probably move faster. The back wheel is still supported vertically by the top of the track end.
- CommentAuthorAaron C
- CommentTimeJul 3rd 2009
also, if the shit really hits the fan, if your back wheel falls out or jams against the frame you damage your components look and look like an ass. if some how your front falls out you end up with a rev-x style, fork ends into pavement, fuck yourself up wreck.

i'd say you are most likely fine but why take the chance of destroying yourself, or worse yet the merckx
- CommentAuthoratanz
- CommentTimeJul 3rd 2009
well I just rode 40 miles on it and no movement what-so-ever. but even if the wheel did move up where its supposed to be the rubbing isn't all that bad - it still rolls, just catches at one spot where there is the slightest hop in the wheel. once I true it, it should clear fine - even at 9 bar

and no, i'm not getting a new fork or wheel. if it causes any problems in the future I'll definitely get a smaller tire - but damn I love those gatorskins for the street/park.
- CommentAuthoreaglerock
- CommentTimeJul 3rd 2009
Posted By: atanzWhat rims are known for having smaller ERD?

Spocalc is not comprehensive, but it does have E.R.D. (Effective Rim Diameter, the diameter of the rim measured from the seated position of the nipples) for a lot of common rims. It's a number that's used in calculating spoke lengths.

What rims do you have now? In clinchers, I've found that Ambrosios often run big; I don't know if their tubs do the same. I'm trying to rassle a Conti UltraRace off an Ambrosio Super Elite right now, and I'm not sure I'll be able to get it off unless I can find some steel levers. Did you have a lot of trouble getting the Gatorskins on the rims?
- CommentAuthoreaglerock
- CommentTimeJul 3rd 2009
Posted By: atanzit still rolls, just catches at one spot where there is the slightest hop in the wheel. once I true it, it should clear fine - even at 9 bar

Well, that's a key thing. Once you true it, it may be fine. I had the same problem with a set of Michelin Jets, which brushed against the brake adapter at one spot in the rotation. Once I'd trued it up, no problem.

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