msl109

Hrllo folks - I know there's no absolute answer to this, but I wanted to get some opinions - built my wife a bike off a Cannondale 3.0 Crit frame. The "skinny" (23mm) tires I installed made her nervous (she's only ever ridden a mountain bike), so I switched them out for 32mm Gatorskins. Quite a jump, I know. My issue now is deciding whether the clearance between brake / fork and tire is safe - I'm attaching a couple pics. If not, I'll go with 28mm. I read in one Cannondale catalog, for what it's worth, that the CPSC recommends at least 1.6mm (1/16 in) between tire and any part of the bike. That seems like not very much to me, but what do I know. Anyway, it's definitely more than that as is. Posting a pic of the front, my main concern. Rear will have more clearance, I believe. Appreciate any well-informed feedback.

Just focusing on the top. I'll post another of of the side, though I'm not worried about that.

smashndash

1.6mm at the top is cutting it close but it’s not the worst. Some people say you could end up with a pebble or whatever jamming in there, but I’m not convinced this is a real problem. For any given amount of tire clearance, isn’t there some pebble size that can ruin your day?

I think the standard for new bikes sold in america is 4mm on all sides.

If you have less than 2.5mm of clearance on the sides, I would worry about tire rub from wheel/frame flex in corners and while swaying the bike.

If your wife doesn’t weigh much and doesn’t ride super aggressively then perhaps it doesn’t matter too much. I’d stay away from gravel though.

DiabloScott

Probably not dangerous, although it will amplify the danger if other things are off a little bit too - like wheel trueness.

I have tried this with about the same clearance and it worked but it was very annoying because sand and grit from normal riding would scrape and rub off under the brake calipers.

70sSanO

I'd go with the 28mm. You might find some 30mm.

I can't believe that you could get 32mm to fit on the rear of a Cannondale crit.

John

Edit Added: I realize that is a front wheel in the pic. But I wouldn’t think a rear would even fit in the dropouts without touching the seat tube.

sheddle

I have this on one of my bikes from the "zero clearance" era of Miyata frames, and the annoying bit is that running in the wet causes weird sounds as the caliper "scrapes" water on the wheel.

Probably doesn't help that my frame was originally set up for 700Cx20mm

Stormy Archer

I don't think it's so much a safety issue as it is a risk of rubbing on the frame a ton if the wheel is out of true or misaligned.

My 2 cents, 28mm gp 4000 will ride waaay better than 32mm gatorskins anyway.

Andrew R Stewart 

Some bike companies consider about 4mm of tire clearance the minimum. The shown image has far less then this, way too little if it's the front tire. Ever hear of a spoon brake? This bike has a road derbies brake, effectively. Andy

Litespud

I run Rubino Pro 25s which run a little narrow (24mm with a gauge). I switched wheelsets to a wider pair (17mm internal width) and suddenly my nominal 25s are actually 26mm. Not a problem, except they're pushing what can fit in my front fork (Reynolds Ouzo Pro). Eyeballing it, I have maybe 2-3mm each side, and 3-4mm at the top - fine as long as the wheels remain true. They're pretty stiff (Campagnolo Zondas) so I'm not concerned about flexing. However, I found myself on a newly chip-sealed road a while back, and the sticky road surface (and the suddenly sticky tires) whipped a procession of gravel chunks up and forced them through the top gap - fairly scratched up the underside of the fork - horrible to listen to, and not much better to look at. Granted all the scratches are no deeper than the clearcoat, but still.... I cleaned up the fork this evening and applied some clear nail polish just to seal the scratches. Rear tire clearance is better - maybe 6-7mm each side at the chain stays, and plenty of room at the brake bridge. However, looks like the fork is imposing a hard limit of 25mm tires for this bike.

msl109

Ok - all points well - taken. If not outright dangerous, the size is young to interfere with proper braking and collect debris ... I'm going to move to 28 or 30mm. Can't remember what companies make a 30 but I know a couple do.
As to Grand Prixs vs Gatorskins, yes - if I can get them in 28mm, I will. Don't think they come in 32, which is why bI went with the gators.
Appreciate all the help!

msl109

and it looks like you have more clearance than I do. 28 it is ...

msl109

And a road debris brake, aside from having less than ideal stopping power, is pretty rough on the rims!

msl109

Yes, when everyone was riding the thin rail. Still have a bike with 19s on it.

msl109

It doesn't touch the seat tube, but it's not pretty.

msl109

She doesn't weigh much or ride aggressively, and it's a very stiff frame, but I'd like her to be able to get more aggressive if she gets more into riding.

Can't believe CPSC only mandates 1.6mm and Cannondale publishes that in the manual!

msl109

I didn't pay much for the frame, but someone did a nice pro repaint on it, and it would be a shame to start peppering it away around the fork. And yes, I'm sure a wider rim would allow the tire to balloon to the sides more, but I'd think it might slightly reduce the height, no?

Andrew R Stewart 

My reference to a spoon brake is about the bikes before cables were "invented". The brake was a plate of metal, shaped roughly like a spoon, that could be pivoted to apply pressure on the tire's outer surface.



If the OP gets a big enough rock, picked up by the tire, it can jam under the fork crown. It will be like throwing a wall switch with no modulation, just full lock up right away. Andy

msl109

I follow you now - going to reduce the tire size; sudden full-on spoon brake doesn't sound very attractive.

JohnDThompson 

That's what the British would call "***-paper clearance," usually only seen on track bikes, which would be ridden on a clean velodrome surface. I'd be concerned riding with that little clearance on an open road.

It depends on the tire and the mass of the pebble. A large pebble weighs more, and is more likely to fall off before it hits the fork crown. And an aggressive tire tread is more likely to hold large pebbles than a smooth tread. The OP's smooth tire tread decreases the likelihood of a large enough pebble jamming under the crown, but the consequences of a front wheel lock-up can be serious enough for this to remain a concern, in my view.

Litespud

Great - now i have another nightmare scenario to haunt my waking hours.....

zacster

Make sure the QR is very tight so the wheel doesn't shift. I have a very tight clearance in the rear of my bike with a 25 tire in it and a slight shift caused it to rub. And when they rub, they wear, and when they wear they get weak, and then they blow. Don't ask me how I know this.

msl109

think I can guess how you know ...

msl109

That was the kind of issue I imagined that motivated me to start this thread. Pebble, small branch, lockup. I also agree that there's a pebble size for every clearance gap -- but as the debris gets larger and thus heavier, I'd think it less likely that the wheel is going to throw it the way of the gap between my bike and tire, no?

msl109

For the record, the clearance is larger than 1.6 - more like 2.5 at the closest.. The number came from the CPSC as a minimum clearance requirement, according to Cannondale's literature. But my guess is their main concern is adhering to the standard - wild be hard to sue them if they're meeting v established guidelines. Doesn't mean 1.6mm is a good idea...

coffeecherrypie

I also think you are likely to run into a fit issue in the rear.

Kapusta

I’ve run that little. As others have said, the main risk is rubbing the sides of the fork if the wheel goes out of true.