I apologize if this has been covered ad nauseum, but searching has been disabled for a while, and I got tired of waiting.

Does squaring of tire affect performance? Especially safety wise. If so, how? Perhaps less stable contact with the road surface while cornering?

Er... squaring of tire? What?

I would not really think it would, if anything it may just be more prone to punctures, because the tread area is thinner.

Not a big deal if it is only the rear tire and you're not using a super high tire pressure. Your front tire does most of the work when you are cornering. I let my rear tire run down until the cords start popping through the rubber.

When a tire is used for a long time, the contact patch tends to flatten out, giving the tire a squared off look.

I'm sure it increases rolling resistance by a good amount, and it probably affects cornering as well. How much, I don't know though, I've never really noticed it but I'm sure it's because I adapted to the feel of my tires as they wore, as it takes too long for a tire to square to produce a noticable change.

Just replaced a set that had become badly squared. Had no problems from a riding/handling point of view. Biggest problem was the increased contact area made them magnets for road debris. Had a few more flats than normal. Someone told me the rolling resistance would be increased--if it was, it was unnoticeable.

Technically the rolling resistance increases due to the larger contact patch, but not to an appreciable level (as noted earlier). Personally I don't like severely squared off tires, but I know it makes no real difference.

Uh, how much bigger do you think the contact patch really became? 0.5mm in width?

From his response...I'm guess 6-penny nail (6D) bigger...

All the larger contact patch attracted was the huge pile of B.S. as far as I can tell.

It helps me balance better. I'm always falling over when I put new tires on.

- THANKS! I just woke up my sick 4-month old by laughing.

Lower rolling resistance. Less rubber to deform. Honest. Put on fresh tires and see if you go faster. I say you don't. If we could afford tires with 1 mm rubber, nice and flat, that's what we'd use. Just like...race car slicks.

Edit: Not that I think race car tires have 1 mm rubber. And yah, I know they generally don't lean much around turns... Ah, whatever. Why do I second guess myself for appearances sake about things I KNOW. Ok. Here's an idea. For all you logical folks, try testing your theories prior to posting. 'Wider equals more rolling resistance'. Are you SURE? How about 'Thicker rubber equals more rolling resistance'. How about 'Higher pressure hard rubber equals lower rolling resistance.' While you're out there testing, let me know what happens when 'High pressure + hard rubber meets a turn'. I'm sure I haven't quantified that one, even by feel. For all I know, hard rubber doesn't necessarily mean less friction, depending on formulation. Well, to be honest, I do know that for climbing shoes, some hard rubbers are hugely grabby, and others are skate city.

Final thought: Don't crash because your tires are unsafely worn out, and you're trying to squeeze a few more rides out of them.

Yeah but you're forgetting that smaller tires aren't necessarily better, especially if you aren't riding on roads made of smooth glass.

Is this true? Obviously you steer with the front.

Your rear tire just follows the front from a handling perspective, so it's not a big deal if it gets really squared off. You can afford to let your rear wear down a lot more than your front, b/c if you flat on your rear, it's not a huge deal - but if you flat on your front, then you can be in for a world of trouble (hence why you shouldn't rotate your tires).

Both tires handle the lateral forces.

Unless you pump up your rear tire to 180psi and you weigh 90 pounds, the contact patch will be unaffected by any squaring off. i.e., your weight over the tire tends to square it off anyway.

This is really bad advice. I don't know about you but I frequently hit speeds of 30+ mph, I wouldn't want to find out what shredding a tire at that speed is like. I know a guy who had one shred on him at high speed years ago and it isn't a pretty story. I replace my rear tires when they look fairly worn and squared off but I'd never wait until the cord started showing through.

A squared off rear will affect handling slightly, because as you lean over, instead of having a smooth curve from the center of the tire to the side of the tire, you are now going to have a sharp angle, so as the tire transitions from contacting the road at the center of the tire to the side of the tire, it will be more abrupt with a squared off tire.

A squared off tire is very noticeable on a motorcycle, but I have to be looking for it to notice it on a bicycle.

- Your dancing around the one basic set of forces acting...Tires carry load. Pressure in the tire helps prevent the tire from deforming uner the load. Rolling resistance is a function of the load and the contact area (amount to which the tire deforms under load), and the frictional forces involved in cornering that are also a function of the co-efficient of friction and load and contact patch. Handling and wear charachteristics are a balancing act of the forces involved and the tire's mechanical/chemical properties.

I agree with your final thought, but it seems as though tire replacement has become another holy war right up there with chain maintenance and life discussions....Maybe we should move all chain and tire threads to the Politics and Religion forum.....

1. Can you explain how a squared off tire is different than having less air pressure in your tire?

2. doesn't the rear tire have a higher chance of skidding out in a turn (or is that just if there is sand/gravel)?

Rear tire is more likely to skid in a turn. However a skidding rear tire is no big deal, easily corrected without significant consequence. Skidding a front tire, however, particularly on a road bike can be an adventure.

I am not a physicist, nor do I play one on tv... I didn't even stay at a Holiday Inn Express last night...

The answer to your forst question... sort of...

The contact area is not necessarily related to the flatness of the tire's profile. So, a flat tire is not the same as a flat tire...

An old trick... To weigh a car, inflate all tires to the same pressure and measure the contact patches of all four tires. Multiple the total contact patches (in square inches) by the tire pressure (in PSI) the reult is the weight of the car.

I believe that the same is relatively true for any pneumatic tires.

Disregarding the potential impacts of things like sidewall rigidity etc, a 2" tire inflated to 90 PSI has the same contact patch size as a 20 mm tire at 90 PSI... The patches are different shapes, but they will be the same size.

The size of the contact patch on a bicycle tire is primarily a factor of:

1) Tire pressure

2) Weight of rider plus bike plus anything being carried on the rider or the bike.

Any other aspects impacting contact patch are somewhat irrelevant.

Now if someone comes up with a good argument for the fact that an elongated contact patch is preferable to a square one, then we've got a different discussion. There is also an issue between treaded and slick tires... tread, especially aggressive tread robs power... As an example, that sound that knobbies make on pavement is sound generated by the tires, and sound generation takes energy. But, that is also a different discussion.

Barring differences in the compounds, which impact tires of all sizes, smaller tires tend to have lower rolling resistance than wide ones for only one reason... they can handle higher pressure and this is what reduces the size of the contact patch...

I am not a physicist, but I believe that smaller tires of similar construction as larger tires can handle higher pressure because they have a lower volume of air at that pressure exerting stress on the tires bead... THe ability to use highwer pressure is also impacted by bead design on the tire and rim... and of course the composition and construction of the tire and rim...

The answer to your second question... I don't know, nor do I have any logical guesses.

EDIT: In my ramblings I never summarized the answer to your first question.

The answer I was trying to get to is that a tire with a flat surface will generally have a smaller contact patch than a round tire with lower pressure.