cinelli13

Hi all, first time poster here - I recently put a pair of 25mm Conti 4000s II on my Cinelli Saetta. The rear tire has plenty of clearance on its sides, but minimal (1mm) on the top towards the brake bridge. After a 20 mile ride i noticed scratches and rub marks on the brake bridge.

So I then put the my old 23mm Conti 4000s back on and noticed that the clearance with the brake bridge is only slightly greater, maybe 2mm. Also, I noticed new scratches and rubbing after another 20 mile ride. Leads me to believe that my tires have been rubbing and scratching all along and i didn't look at it until trying out the 25mms.

Question - is this wear something to be concerned about or is it general wear and tear? I imagine this part of the frame is all carbon with a metal bolt inserted for the brakes, could the bridge also be aluminum or non carbon? Could it be my stock Shimano 501s wheels are not stiff enough, hence the rubbing?

Have contacted Cinelli with no response over last 3 days.

Thanks for any thoughts.

yankeefan

Definitely not normal. Its possible that the wheels haven't been properly placed in the dropouts. You have vertical dropouts so it may be the case that you've put them too far up. Try sliding them down a bit. You should post this in the bike mechanics forum for more responses.

fietsbob

there you go you learned your race bike frame's tire size capacity , and 25 exceeds it .. stick with 23's, or 22mm Sewups .

some designs are not capable of fitting larger tires .. You noted the the space before you rode on the tires with scant 1mm clearance but rode anyhow ?


Note: I've seen Track bike forks made with very tiny clearance .. but the Velodrome, Track, is swept clean .. so the tires dont pick up road grit..

the scratches are likely from road grit on the tires ..

cinelli13

Thanks for feedback....agree it may be maxed at 23mm. I reposted in Mechanics as recommended. Thanks again

chaadster

It's not possible that your wheel is flexing upward and rubbing; as Fietsbob said, it's likely abrasion from grit sticking to your tire. Stick to pavement and you should be fine.

It's most likely your bridge is carbon, but occasional and superficial abrasion like that is not a concern.

Aside from sticking to 23c tires and staying out of the wet and off dirt roads, there is also the possibility to look at your rim width. If you have a wide rim, you could go to a standard width, like a 19mm outside width, which would reduce the tire height a pinch and give you a bit more clearance. 25s on a narrow rim should be no taller than the 23s, by the way.

I would not advocate not fully seating the wheel in the dropout. That's just asking for troubles.

achoo

Are narrower rims guaranteed to lower tire profile?

I can see how they could raise the profile of the tire given the proper - or in this case "improper" - initial and final geometries.

And since tires are rubber, lowering the pressure will reduce the profile a bit, too. I know I can run 28s on one of my bikes but if the pressure gets too high the rear will start rubbing on the brake body. It's a steel bike so the bridge is small enough that the brake body is closer to the tire than the bridge.

chaadster

Good question, and the answer is probably No, they're not.

I'm guessing that factors like how much narrower and bead seat width, would be important factors, as well as casing width.

Of course, I do not know which rims the OP has, either.

I was speaking specifically to the GP4k tires the OP has, based on this HED chart: