gregf83 

Bunny hop.

slowandsteady

I do that for train tracks and pot holes. I am not willing to try that at 40 mph.

Homebrew01

So, I get off my bike, place a thumb tack on the ground, and walk my bike over the thumb tack (0 lb rider weight) and do not flat. Then I get on the bike, with the same tire pressure, and ride over the thumb tack, I will not flat, because I have not changed the tire pressure ?

slowandsteady

Only in a vacuum at room temperature.

rkwaki

Well I used the exact same tires for training and loved them BUT:
Didn't get great mileage (maybe 1800) and they are a ***** to get off without tire irons. But they are an amazing tire nonetheless, as close to a tubular as you can get.

therhodeo

Duder is an idiot. Vittorias roll like you're floating on a cloud with that 320 tpi but aren't durable bombproof tires.

nhluhr

Here we go

gregf83 

I didn't say that. The pressure the tack exerts on the tire will be the same regardless of rider weight. In the case of no rider the bike alone is not heavy enough to compress the tire around the tack and the bike will lift up over the tack. This won't happen with a rider on the bike.

gregf83 

It's actually easier at higher speed. You don't need to jump as high. At the very least you should try and un-weight your bike over the bump.

bikepro

Yes, Vittoria Open Corsa Evo-CX 320 are excellent tires, but not for your needs. The 320 TPI make them supple but not puncture resistant. They are very good for competition, and when paired with good latex tubes, are "almost" as good as tubulars. However, they are far from puncture resistant. I used them for a year or so. When I tired of repairing flats, I switched to Contintential GP 4000's. I find these have a good balance between performance and puncture resistance.

By the way, the guy at your bike shop is "ill informed", to put it politely.

slowandsteady

I do unweight it. But sometimes it is hard to get my timing just right. I am still too chicken to try a bunny hop at that speed.

slowandsteady

The tack isn't applying any pressure. The pressure is from the weight of the bike or bike plus rider. The pounds per square inch is increased with increased weight.

canam73

Well I don't think you should be rolling over tacks at any PSI. That just sounds dumb.

gregf83 

The pressure the tack applies is equal to the force / area of tack head. The sharper the tack the smaller the area at the tip and the higher the pressure. If the tack is very sharp it will puncture the tire without a rider.

The amount of pressure a tire can push back against the tack with is strictly a function of the tire pressure not rider weight. Heavier riders result in a larger contact patch which is why, in general, fatties get more flats. For example a 200 lb rider might be putting 120lbs of force on the rear wheel. If the tire is pumped to 120psi the contact patch will be 1 sq in. Conversely, a 125 lb rider will only be putting 75lbs of force on the rear wheel and with a 120psi tire the contact patch will only be .6 sq in and will roll through less crap than the tire under the heavier rider.

An alternative 'thought experiment' is to imagine a stationary rider sitting on a bike with a tire over top of a small hole the diameter of a pin. The force required to push the pin through the hole and tire is independent of rider weight and depends only on the shape of the pin head, the tire construction and the pneumatic tire pressure.

Brian Ratliff

Yea... this is wrong. The force exerted on a sharp object is exactly equal to the rider's weight supported by that wheel. The pressure exerted on said object is equal to the rider's weight divided by the contact area with the sharp object. Physics at work... specifically, Newton's third law.

Tire pressure plays a role in determining how much the tire deflects to carry that load. Lower tire pressure results in fewer punctures because the tire deflects more at the ground contact patch, meaning a small, sharp object has less force applied to it because the force of the rider's weight is distributed over a larger contact area. Lower tire pressure also means higher risk of pinch flat because the tire deflects more at the contact point, which, going over point object, might deflect the tire past the point where the bead can constrain the tube.

EDIT: okay, I see where this is going. Greg is talking about running over puncture objects; I thought he was talking about running over point contacts. We are saying the same thing.

gregf83 

That's only true if the sharp object is fully supporting the bike. That's not what happens when you ride over a tack. Most of the weight of the bike is carried by the tire on the road.

Debusama

My Open Corsa tires were plenty flat resistant when they aren't worn out (they even made it through my Spring rubaix races without flatting), but mine wore out quickly, and once the tread got thin, they flatted every time my ass hit the saddle. High thread count means the casing is made of many thin threads as opposed to fewer thick threads, which means the contact patch of the tire conforms to the road more, which helps traction and ride quality, but not flat resistance. Anyway, I thought they were a great race tire, and would buy them again for race day only, but I wouldn't use them as everyday tires, unless you ride very few miles or don't mind replacing them every other month.

As a bigger rider, 25mm tires might be better. I find often the tires that claim to be "endurance" tires work best. as they often have similar ride qualities to race tires (smooth ride, good traction in corners), but weigh 20 or 30 grams more due the the extra rubber that helps them last longer. The Krylion Carbon tires were a good example, but they were discontinued and replaced with the Pro4 endurance, which I would bet work about the same. No matter how far from home you ride, you should always have tire leaver, tube and something to replace it with. Most good tires fit fairly tight and installing them with your hands so you don't ruin your new tube takes practice.

tagaproject6

LOL! Bring out the :

It's not the tack, it's the hole from which the air escapes that causes a flat.

Brian Ratliff

Yup, I agree. See the edit at the end of my post.

nastystang

I ride these tires exclusively but I am willing to pay the price tag and as of now have only had two flats on was a tire killer anyway and would have cut through any tire and tube the other a pinch flat. I have been using these tires for about a year and a half. I prefer the ride quality but would not recommend them for the same reasons the bike shop did. I only weigh 145lbs and maybe that has something to do with the limited number of flats but they are thin tires. They do mount easily for me, that may depend on the wheel being used IDK.

Nick Bain

tldr. but i remember reading that high tpi is more supple and low tpi is more resistant to puncture.

Brian Ratliff

Reading is good. You should read more. Puncture resistance is a function of tire pressure and puncture linings; not related to tpi in any way.

EdIsMe

Tires with more flat protection seem to also have lower tpi... not sure how much of a steadfast rule that is.

I wouldn't buy anything from that LBS guy... it's like he didn't even listen to your needs... let alone other things.

I did manage to find a local shop near me that actually talked me out of purchasing one item in favor of a slightly cheaper one based on my usage and needs. They've been getting a lot of my business since then.

stevebiker

How do Bontrager Hardcase tires compare with those mentioned, for flat resistance?

roadwarrior

Whats even more amusing is how clueless customers can be...especially the ones loaded wth testosterone...difference is that the employee has to listen to it and not break out laughing.