Why narrower (lighter) tyres are quicker.

[another_dave_b]

I was surfing for some tyre wear info, and came across what I think is a super post on Yahoo Answers:

1000 miles from racing tires, 15,000 miles for road tread beach cruiser tires.

The differences are:
The small, lightweight tire with no tread will also have a more fragile rubber compound, and a lot less of it.

The large tire may employ a modest tread without reducing speed, and this allows to use a harder rubber compound, yet faster without loss of wet weather handling.

Why doesn't everybody run a large street tire, such as Schwinn Typoon Cord that surpasses the speed of a racing tire on flat ground, while covering a wider variety of surfaces and being much more flat resistant?

Flat ground is not where the challenge is to a racing bike.

However, beach cruiser tires at 980 grams are far slower on hills than 200 gram racing tires.

Weight, and that's mostly rubber thickness, needs to be multipled by pi because it is rotating weight.

Difference of 980 and 200 is 780.
780 x 3.14 = 2449 grams
There are two tires and thus two such differences
2449 x 2 = 4898 grams
The tubes are heavier.

Let's just call it at 2 1/2 pounds.

We'll skip the rest of the math, but this is not 2.5 pounds of static weight. This is gyroscopic weight, and as such, resists change.

So, not only is it heavier on a hill climb, it is highly resistant to speeding up. Imagine slinging a 2.5 pound weight around in your house (at 26 to 44 miles per hour).
That's a mighty strong gyroscopic effect, which also prefers to remain in a single direction, thus making for imprecise and very wide steering.
For the math folks who are now alarmed, yes, I did mean to say that the effect is a higher progression than pure geometric.

So, the amount of miles you should get from bike tires is highly application specific.

But, if you need to sprint or race up hills, the figure is very small.

See roadbikereview.com and mtbr.com for specific reviews of application specific tires and their various performances, including the best answer you can get on how many miles you can expect the tires to last.

EDIT: There are some different results from the past, now considered "in antiquity" where harder rubber compound racing tires were installed on cheaper bikes to give them remarkable speeds at the cost of very frequent crashes--but it sold one heck of a lot of bikes, at the additional cost of a sudden rush towards giving up on road cycling. Even farther in the past were 3-speed bikes with a safer, wider, treaded, hard compound tire that did not crash.
This long-lasting technology is not generally available today because it will not stop in wet weather and it can slide on corners.
An exception is Tioga's mountain bike slick, which is fast, last long, and crashes often.
Another exception is Schwinn's Typhoon Cord that is big enough and treaded enough that there are no safey concerns while the hard rubber goes terribly fast.
A similar, but softer, mountain bike design is Kenda Kross Plus Yellow Label, where it is hard down the middle (very thick) and has some side lugs that actually work well on gravel.
In racing, where stopping is not the point, hard-down-the-middle, sticky-on-the-sides tires are available, last longer, and work well.

However, the majority of todays tires are completely covered in sticky rubber that does not last. Here's an interesting example from Panaracer that applies to the majority of today's bike tires, including racing tires, and it includes the reason that mid-size MTB slicks do not work.
The slow Panaracer T-Serv, at 26x1.75 has the same rubber compound as the very fast T-Serv 700c x 25mm. This is totally inappropriate, because the 26" tire is not optimized with a different rubber compound even though the contact is wider--just like the vast majority of today's tires.

That's right, tire manufacturers rarely change the rubber compound to accomodate different tire sizes. For cost cutting, wear, and performance issues, the small tire in a "family of tires" is the only one optimized. The rest go slower, but do not last longer.

Previously, we could buy a larger tire, expecting it to last much longer. This is no longer true--unless the tire comes in only one size.

 

[Tynan]

wide tyres faster than thin ones?

been a thread on this and it was pissed on, a fair bit anyway

 

[another_dave_b]

wide tyres faster than thin ones?

been a thread on this and it was pissed on, a fair bit anyway

Not at all. As I read the quote, he's saying lighter (thinner) tyres are faster than heavier (wider) tyres.

beach cruiser tires at 980 grams are far slower on hills than 200 gram racing tires.

Weight, and that's mostly rubber thickness, needs to be multipled by pi because it is rotating weight.

Difference of 980 and 200 is 780.
780 x 3.14 = 2449 grams
There are two tires and thus two such differences
2449 x 2 = 4898 grams
The tubes are heavier.

Let's just call it at 2 1/2 pounds.

We'll skip the rest of the math, but this is not 2.5 pounds of static weight. This is gyroscopic weight, and as such, resists change.

So, not only is it heavier on a hill climb, it is highly resistant to speeding up. Imagine slinging a 2.5 pound weight around in your house (at 26 to 44 miles per hour).
That's a mighty strong gyroscopic effect, which also prefers to remain in a single direction, thus making for imprecise and very wide steering.

I thought it was interesting, because in the past I've read threads where tyre pressure was cited as the only relevant factor, which seemed counter intuitive when the most obvious visible difference about racing tyres is width. Tyre weight seems to me to fit the facts better.

 

[fossyant]

23/25mm are about the fastest road tyres, given the state of the roads. 20 mm give too harsh a ride.

23mm Mich Pro Race, Schwalbe Ultremo and Cont GP4000 are probably the fastest tyres for general road use - far faster than cheaper tyres of similar size or larger.

Light tyres make a big difference too.

 

[02GF74]

hmmmm, gyroscopic effect .....

in a straight line, I am not convince tyre weight matters that much as once it is up to speed - a heavier tyre will take longer to get up t o pseed than a lighter one, there is not that much energy required to keep it rolling, ignoring any air resistance that a heavier = perhaps wider tyre may have.

Don't a time trialler use heavier wheels to keep the momentum going?

 

[Steve Austin]

TTers use aerodynamic wheels, which are heavier, as the aerodynamics have a greater effect than the weight.
Heavier wheels (including tyres, tubes etc) are slower.
In an ideal world, you want the lightest most aerodynamic wheelset that you can get

 

[jimboalee]

Everyday folk want the lowest Coefficient of Rolling Resistance, and the lowest Moment of Inertia.
"Aerodynamic" wheels, as you call them are One-piece Carbon wheels because the three and four blade carbon wheels were outlawed due to safety ( they were like a Moulinex masterchef ).

One-piece carbon wheels are not lighter than a S/S spoked wheels, they create less turbulance; Hence Steve Austin's truthful comment.

 

[Tynan]

Not at all. As I read the quote, he's saying lighter (thinner) tyres are faster than heavier (wider) tyres.

'a large street tire, such as Schwinn Typoon Cord that surpasses the speed of a racing tire on flat ground'

 

[swee'pea99]

Weight, and that's mostly rubber thickness, needs to be multipled by pi because it is rotating weight.

Difference of 980 and 200 is 780.
780 x 3.14 = 2449 grams
There are two tires and thus two such differences
2449 x 2 = 4898 grams
The tubes are heavier.

Eh? (Apart from the last sentence, which I understand fully.)

I once heard that 'an ounce off the wheel is the same as a pound off the bike', and I guess the tyre contributes to that equation. But I have to say that having fitted gp4000s partly on account of rumours like these, I'm not overwhelmed. I'm not saying they're bad...just don't get any kind of 'wow!' (as compared with the 'nothing special' 700x23s I always rode before).

 

[another_dave_b]

'a large street tire, such as Schwinn Typoon Cord that surpasses the speed of a racing tire on flat ground'

Fair enough

While he describes the Schwinn as a 'large tyre', I'm not sure if it's the width, or the 'harder' rubber compound, that he's claiming would make it faster than a 'racing tyre' on the flat.

The differences are:
The small, lightweight tire with no tread will also have a more fragile rubber compound, and a lot less of it.

The large tire may employ a modest tread without reducing speed, and this allows to use a harder rubber compound, yet faster without loss of wet weather handling.

There are some different results from the past, now considered "in antiquity" where harder rubber compound racing tires were installed on cheaper bikes to give them remarkable speeds at the cost of very frequent crashes

Rephrasing my point then, as I read it, he's saying that *overall* tyre weight (width) is the most important factor, but in some circumstances other factors (rolling resistance?) are more important. OK?

 

[byegad]

It's a lot more complicated than thin tyre good, wide tyre bad.

If weight were the only factor then thin 16" diameter tyres would be a lot faster than thin 27" tyres. After all they must weigh less as they are so much smaller! The 1960s Moulton bikes proved that small wheels can be fast (the UCI promptly banned them from competition) but he combined small wheels with suspension on his fast bikes!

I have 406 (20") wheels on both my recumbent trikes and a lightly treaded 2" wide tyre (Schwalbe Big Apple) has proved a faster, and more comfortable ride, than 1.35" wide Kojak slicks were on one of them.

I guess the whole truth will only come out when someone has the time to do some hard research on rolling resistance.

 

[xpc316e]

I am no scientist, but I reckon that there's some rather dodgy maths/reasoning going on in the OP.

 

[skwerl]

I think this nutter is referring to MOI. That's basically the square of the radius x mass (assuming intertial constant =1, which it should when looking at a rim/tyre). His maths is crap but it still highlights the the issue: as mass increases the MOI increases as well.

 

[another_dave_b]

Came across the following on the Schwalbe website:

Why do Pros ride narrow tires if wide
tires roll better?

Wide tires only roll better at the same inflation pressure,
but narrow tires can be inflated to higher pressures than
wide tires. However, they then obviously give a less
comfortable ride.

In addition to this, narrow tires have an advantage over
wide ones at higher speeds, as they provide less air
resistance.

Above all, a bicycle with narrow tires is much easier to
accelerate because the rotating mass of the wheels is
lower and the bicycle is much more agile.

At constant speeds of around 20 km/h, the ride is better
with wider tires. In practice, the energy saving is even
greater than in theory as the elasticity of the tires
absorbs road shocks, which would otherwise be trans-
ferred to the rider and so saves energy.