24mm vs 22mm

[mustang1]

Well, here you go I'm resurrecting this thread, after you slagged of my findings......have a look here,
http://road.cc/content/feature/153488-trend-spotting-why-you-need-switch-wider-tyres
The whole of the TDF riders are going this way, as I think their research is probably a bit more intense than your average club racing findings......

And.....I've just measured (with a micrometer) my 23mm Conti GP4000sII's and they are in fact 24.85mm wide....

Those tdf racers will ride whatever their sponsors tell them to ride.

 

[Citius]

Well, as an example if I had a 35mm tire at 80psi and compared it to a 25mm tire at 80psi, then perhaps the wider tire would have better rolling resistance. But I would NEVER ride a 25mm tire at just 80psi even if it does make a great theoretical lab experiment.

Out on the road, I'd pump the narrower tire far higher than the wider tire. Doesn't that mean something?

As I've said before, the benefit is not linear, so it does not follow that a 35 would roll better than a 25, as other factors like weight come into the equation. Otherwise, the pros would all be riding fatbikes.

Tyre pressure does depend a lot on rider weight and road surface. I routinely ride 23s and 25s at 80psi. My cross bike has 35mm slicks on it currently, which I'm running at around 60psi.

 

[mustang1]

Please see my responses in italics..

If physics is not your thing, why call BS when you instead ask how it works?
It is not BS.
Because i can't get anyone to explain to me why wider tires and narrow tires are compared at the same psi when in practice the narrower tires are inflated to a higher psi than wider ones.

Your assumption is that rolling resistance comes from the formation of the air cushion in the tyre. That is not where rolling resistance comes from.
No, I think rolling resistance comes from the deformation of the tire when it contacts the road.

A tyre is essentially a tubular cylinder and therefore its cross section is its width.
Understood. Then what's the thing that runs 90 degrees to the cross section called?


How did you determine that you got less flats from one width than the other? You make it sound like it is a fact that the one width is less prone to flats than the other. The assumption of course derived from your statement is that the type of flats you got were due to intrusion punctures not pinch flats, otherwise could simply have upped the air pressure to avoid those.
Some time ago when I was using 23mm conti gatorskins, I got flats. When I switched to 25mm gatoskins, I did not get flats. No assumption can be derived wrt type of puncture: I was unable to increase air pressure in the 23mm tire because I had already reached it's maximum of 120psi.

They are not comparable. Besides, what do electric cars have to do with it?
I understand now (another poster explained it) they are not comparable. The reason I mentioned electric cars is since they have limited range, the manufacturers of such cars have tires designed to minimise rolling resistance, and those tires are narrower than what you would get in a non electric car.


Measuring rolling resistance has nothing to do with surface. It is measured on a smooth steel drum and additional "events" such as rocks or mud or surface texture is simply an overlay on the base measurement. Your statements are equally BS for road or rough.
But still no one has explained to me why narrow and wide tires should be measured with the same air pressure when this is not what one does in practice. For example did you see that quote above: "According to Continental, a 20mm tyre with 160psi, a 23mm tyre at 123psi, a 25mm tyre at 94psi and a 28mm tyre at 80psi all have the same rolling resistance.. "

 

[mustang1]

As I've said before, the benefit is not linear, so it does not follow that a 35 would roll better than a 25, as other factors like weight come into the equation. Otherwise, the pros would all be riding fatbikes.

Tyre pressure does depend a lot on rider weight and road surface. I routinely ride 23s and 25s at 80psi. My cross bike has 35mm slicks on it currently, which I'm running at around 60psi.

I'm not trying to be a pita, its probably that I just don't understand physics like you guys. But....
You're right, the 35mm tire weighs more than a 23mm tire. But, well, I would say the 25mm tire also weighs more than a 23mm tire, no? I think so e time ago, 19mm was rather common. Then the switch to 23mm. And now 25mm. I can't help but think in then not too distant future, 28mm will be the pro noted and fashionable choice, and then 35mm. And who knows, someone's do mention fatbikes?

Like I said, not trying to be a pita, but I just get this feeling that the marketing department is behind a lot of this move it the next big thing. I mean, these tdf guys have been racing for.... years... And now they're telling me again to move to wider tires? Just seems fishy and profitable.

Edit: typo

 

[Citius]

The jump between 23 -> 25 in size is tiny, the weight penalty is tiny, but the rolling benefit is supposedly greater than the small handful of extra grammes. But there will come a point in the equation (ie 35mm) where the weight penalty will begin to outweight the rolling benefit.

If you are happy on 23s, then stay on them.

 

[Mark2802]

I don't wanna get scientific, or get dragged into an arguement, or get accused of BS but I recently changed the conti's on my Sempre pro from 23mm @110 psi to 25mm @ 100psi and have felt no increase in rolling resistance at all. My times are no worse, possibly even better and the ride quality on local crappy roads has improved vastly.
Another plus is that bike feels more stable when cornering at speed.
So, for me, 25mm works better.

 

[Tojo]

Those tdf racers will ride whatever their sponsors tell them to ride.

I doubt it as they have personal choices with saddles, shoes, pedals, bars, and no doubt a choice on what width tyre they run from the manufacturer that supply's the team...

 

[mustang1]

@Tojo posted this (hope you don't mind me pinching this off you):
According to Continental, a 20mm tyre with 160psi, a 23mm tyre at 123psi, a 25mm tyre at 94psi and a 28mm tyre at 80psi all have the same rolling resistance.....

Just taking the 23 and 25mm tires as an example.

Which tire has lower rolling resistance out of 23mm and 25mm at 94psi? 25mm (but why not pump the 23 to 123?)
Which tire has lower rolling resistance out of 23mm and 25mm at 123psi?

I don't wanna get scientific, or get dragged into an arguement, or get accused of BS but I recently changed the conti's on my Sempre pro from 23mm @110 psi to 25mm @ 100psi and have felt no increase in rolling resistance at all. My times are no worse, possibly even better and the ride quality on local crappy roads has improved vastly.
Another plus is that bike feels more stable when cornering at speed.
So, for me, 25mm works better.

Ditto. 25mm on all my race bikes. They came with 23mm OEM stock.

 

[Citius]

Which tire has lower rolling resistance out of 23mm and 25mm at 94psi? 25mm (but why not pump the 23 to 123?)
Which tire has lower rolling resistance out of 23mm and 25mm at 123psi?

Not quite sure what you are trying to establish here. In all but the most extreme cases, and assuming the same construction, a tyre with a higher volume will roll better at a given pressure than one with a lower volume.

 

[derrick]

Most people would not tell the differance.

 

[mustang1]

Not quite sure what you are trying to establish here. In all but the most extreme cases, and assuming the same construction, a tyre with a higher volume will roll better at a given pressure than one with a lower volume.

So if there is a tire of a certain width, let's just say 25mm, would it roll better with 80psi or 120psi, or does it not make a difference?

 

[Citius]

So if there is a tire of a certain width, let's just say 25mm, would it roll better with 80psi or 120psi, or does it not make a difference?

On a completely smooth surface, any tyre will roll better at a high pressure. In the real world, an individual tyre will roll best at a pressure which is appropriate to your own weight, and the road conditions.

 

[Yellow Saddle]

@Tojo posted this (hope you don't mind me pinching this off you):
According to Continental, a 20mm tyre with 160psi, a 23mm tyre at 123psi, a 25mm tyre at 94psi and a 28mm tyre at 80psi all have the same rolling resistance.....

Just taking the 23 and 25mm tires as an example.

Which tire has lower rolling resistance out of 23mm and 25mm at 94psi? 25mm (but why not pump the 23 to 123?)
Which tire has lower rolling resistance out of 23mm and 25mm at 123psi?


Ditto. 25mm on all my race bikes. They came with 23mm OEM stock.

No finer work on rolling resistance in bicycle tyres has been done than that of the late Jobst Brandt. He was a brilliant engineer with a passion for cycling and designed a range of tyres for Avocet in the 1980s.

Have a look at this link and the data in the graph. The data requires some working through but you seem genuinely interested and may thus invest the time in understanding what's what.

http://www.analyticcycling.com/ForcesTire_TireRollingResistance.html

I'll summarise it as follows (but please take time to look at the graph and explanation): Rolling resistance comes from hysteresis, which is energy losses. This energy loss in a bicycle tyre (car tyres have other issues in addition) comes from the rubber compressing but not "shooting back" with the same energy. Think rubber ball that bounces lower and lower until coming to a rest. If you drop it from one meter, it only bounces back to 800mm. The 200mm lost is hysteresis. Tyres compress (forget about the air column compressing) at the contact patch where the road squeezes the rubber between it and the air column. The more rubber in there, the more the losses. In other words, thin tyres have less loss than thick tyres of the same material. That's why 35mm tyres have higher RR than 28mm tyres because generally the rubber is thicker. The cords inside also have an effect and again, bigger tyres have thicker cords which have more hysteresis.

Incidencally, there are two types of tyre rubber in use; namely carbon black and silica. The latter can be coloured but the former is always black. Silica tyres used on bicycles have less RR but less grip than carbon tyres used on cars.

Study the page in the link and we'll chat again.

 

[mustang1]

On a completely smooth surface, any tyre will roll better at a high pressure. In the real world, an individual tyre will roll best at a pressure which is appropriate to your own weight, and the road conditions.

So in the real world, one would pump a narrower tire to a higher pressure than a wider tire. And if that's the case, then when promoting "wider tires have lower rolling resistance at a given pressure", why are equal pressures used in both wide and narrow tires?

 

[Citius]

So in the real world, one would pump a narrower tire to a higher pressure than a wider tire.

No - I don't think you're getting this at all. That isn't what I said. If you inflate 23s to 100psi, you can also inflate 25s to 100psi and potentially roll better and with more comfort. Come on mate, seriously..

And if that's the case, then when promoting "wider tires have lower rolling resistance at a given pressure", why are equal pressures used in both wide and narrow tires?

You asked this question before, and I answered it before.