DaveLeeNC

I have a relatively new Conti GP 4000 ii clincher with a very clean 1/4 inch gash in the side wall. Can I fix this with just piece of duct tape on the inside of the tire or do I need to do something more permanent to keep the split from growing?

Thx.

dave

Andrew R Stewart 

While it's doubtful that the slit would grow much longer what can happen is that any boot/patch you use will it's self fail. Generally booting a slash is considered a get back to the house/car/finish and then replace the tire. But hay, it's your tire so do what you wish and report back. Just be smart and use the damaged tire on your rear wheel. Andy

epnnf

replace the tire

DrIsotope

A big needle (like one for denim.) some dental floss, and rubber cement.



If it doesn't hold, you're out a couple bucks.

CliffordK

I assume this is a full thickness cut. What tire size and pressure?

MTB riders apparently frequently sew their tires closed with a sewing awl, but perhaps primarily to get themselves out of the woods, and at low pressures.

Hmm... that is an idea. What if you put your sewing machine on wide zig-zag and just sewed it up, possibly with some non-stretch reinforcing material on the inside.

DaveLeeNC

I think that I will just follow the advice of my LBS. BTW, I don't see how the sewing solution would work long term. Dental floss (with or without rubber cement) seems to me to be no match for asphalt.

dave

CliffordK

You said it was sidewall damage, so it shouldn't be grinding on the pavement.

If you do sew, you can put a patch over the top if you wish, also on the underside.

I think the issues with sewing are multi-fold. First there is a risk of it pulling through where the threads were cut.

Also, tires are a very dynamic process of repeated pressure, compression, bending, and torque.

Nonetheless, it might be interesting to try. I did run one Continental tire with a Radial Tire patch on the inside, and an ordinary REMA patch on the outside. I put on quite a few miles like that before the tread wore too thin, and I lost a chunk of very thin tread rubber elsewhere on the tire.

DaveLeeNC

For clarification it is sidewall but (depending on pressures and wear) real close to pavement. I am running 23's right now (typically 90 pounds). I wouldn't be comfortable counting on it never encountering pavement.

dave

SBinNYC

You probably got the cut because you are running a 23 mm wide tire at too low a pressure. Depending on your weight it should be: 100 psi for a 130 lb weight; 115 psi for a 185 lb weight; and 130 psi for a 240 lb weight. If you want to run 90 psi, you should use 25mm for 130 lb weight; 28 mm for 185 lb weight; and 32 mm for a 240 lb weight.

DaveLeeNC

I am not familiar with the concept of 'risk of sidewall gashes' and marginally lower tire pressures. I certainly am familiar with snake bite punctures but this is clearly different. Could you elaborate here.

FWIW, this website ( Bicycle tire pressure calculator ) would put me at 83 pounds front and 103 rear at 23mm. I do pump up before every ride and stop when my (checked against a regular tire gauge) pump passes 90 on the front and the rear might get another push. My pressure don't seem unreasonable at my 150'ish pounds and nothing worse than occasional chipseal. I don't encounter many potholes. I'd be interested in other opinions here.

Until recently I was running 25mm Gatorskin tires. Suddenly (manufacturing tolerances I assume) I was struggling to keep 25mm Gatorskins from rubbing my front fork where before I didn't have that problem. Never did really understand what happened here. This is my first go at the Conti 4000's (which are more comfortable than the Gatorskins).

FWIW, the 'gash' is so clean it is hard to spot and ends about 1/8" from where the tire wear starts on the tire (5-700 miles roughly on the tire).

Thx.

dave

Andrew R Stewart 

Dave- Sounds like you have a bike that was made when the mantra was "Skinner is better". These days the industry has finally understood that having more traction, greater load capacity, longer tread life and a smoother ride are marketable features Andy

DaveLeeNC

Well, OK. But your tires can weigh as much as 20 grams more EACH

1996 Bianchi EL/OS frame. Actually a pretty nice frame, but ....

dave

SBinNYC

It's basically the same mechanism for pinched flats. The tire sidewall rubs against either the ground or the wheel flange. There's no guarantee that the tube will find a void between tire and wheel before the sidewall will find a spot where it should not be. To a large extent it depends on the flexibility of the tube and sidewall at a given pressure and weight load.
Tire pressure and wheel load determine the road/tire contact area. If the wheel load is 75 lbs (1/2 of your 150 lbs) and tire pressure is 75 psi then the contact area is 2 sq in; if the tire pressure is 100 psi then the contact area is 0.75 sq in. How that contact area is distributed across the length and width of the tire depends on tire construction and rim width. A under-inflated narrow tire, with flexible sidewalls mounted wide rim should favor more width in contact with the ground than one with less flexible sidewalls mounted on a narrow rim. The second tire will favor more contact area along the tire's circumference.

The different front/rear pressures means you used the Heine calculation. Tire manufacturers usually have some idea about how their tires should be used. The trend away from narrow tires means one must go to archival info on the web for 23 mm inflation recommendations.

Here's what Schwalbe recommended: https://keyassets.timeincuk.net/insp...rt-630x207.jpg, This is what I used for my recommendations. Here's what Michelin recommended: https://c2.staticflickr.com/4/3734/92...0110889a_z.jpg.

As you can see, these tire manufacturers recommend higher pressures for your combination of tire width and weight.

DaveLeeNC

I just got back from my LBS and here is the verdict. As the mechanic said "what you have here is a really good trainer tire". The point being that when it failed it could easily fail in a way that would not be easily fixable on the road.

So I now have a brand new GP4000 II.

dave

raria

Whilst @DrIsotope may churn out more watts, miles and elavation than I do I'll top him and anyone in this group when it comes to cheapness. It runs through my veins.

But even I wouldn't repair a gash in a tire that big. If it fails and your in a middle of a ride, what happes?

Well maybe I would fix it if its a errand bike that is going to be no more than a few miles from my home (see I can't help myself).

Dan Burkhart 

What amazes me is how many decades it took to come back to this realization.

Andrew R Stewart 

I attribute this, the trend to skinny tires during the 1980s on, to the strength of marketing and it's mistaken idea that racing is the pinnacle of cycling. Remember the build up to the 1984 Olympics and Alexi Grewal's gold in the road race? I see that as the pivot from the touring centric media view of cycling (here in the US during the 1970s) to the racing view. Then 9 years later along came an kid called Lance, the icing on the "racing is what counts cake". And in between there was Greg LeMond and the tour win. Andy

dabac

DrIsotope

I dunno. I glue the cuts in my tires with R/C tire glue all the time. My tire-related pre-ride checklist goes: are the tires aired to the correct pressures and holding those pressures? Then good to go.

I ride 'em until they pop. When it fails, jam a dollar bill and a tube in there and head to the nearest bike shop. Because I am also cheap-- and when that is help up against my annual mileage, I have to buy at least one tire every 10 weeks.

I can't let a small cut end a tire's working life. It basically has to not be able to hold air anymore.