[Closed] Contact patch of 650b tyre

The size of the contact patch has more to do with the pressure in the tyre (and your weight) than the diameter of the wheel. If the contact patch is larger with a 650b or 29er then it's most likely to be either due to the bike being heavier or the tyre pressures being lower.

Now contact patch shape; that's a different matter.

roverpig - Member

The size of the contact patch has more to do with the pressure in the tyre (and your weight) than the diameter of the wheel. If the contact patch is larger with a 650b or 29er then it's most likely to be either due to the bike being heavier or the tyre pressures being lower.

Now contact patch shape; that's a different matter.

My thoughts exactly, which is why the article was a load of crap.

MTB magazine in "utter twaddle" shocker...

Now contact patch shape; that's a different matter.

which between 26 and 650b is barely different because they are so close in size.

I wonder what next seasons must have will be and what stadard will be ditched?

Maybe super-oversized taper headsets, 22mm through axles, and 137mm of front end travel, think of the extra stiffness, that 16% less deflection* riding through a rock garden composed of 9.8" baby heads.

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*compared to a rigid ritchey logic unicrown fork with a qr the rider forgot to do up.

sheck - Member

MTB magazine in "utter twaddle" shocker...

Aye, it was a shocker. I don't read 'em as a general rule so haven't come across this level of hype before.

You want to read the Banshee blog, it spoke some sense on wheel size physics. Not much sense, but some...

[img] [/img]

from:

http://www.pinkbike.com/news/650B-For-All-Giants-Elite-Level-Mountain-Bikes.html

except 650B is rarely 27.5...

There's a MASSIVE difference - look, here they are, overlaid (assumes slick tyre and flat ground)

[img] [/img]

From this series of articles, some interesting points made, whether you agree or not.

http://www.nsmb.com/educating-the-debate-part-i/
http://www.nsmb.com/educating-the-debate-part-ii/
http://www.nsmb.com/educating-the-debate-part-iii/

So if more is better why not just stick with the 29"? 😉

Which mag? Name and shame time 😉

That pic above - 2cm extra contact patch for a 1" increase in diameter - that's utter, utter bullshit.

Normal Man - Member

Which mag? Name and shame time

What Mountain Bike

swavis - MemberSo if more is better why not just stick with the 29?

That pic above - 2cm extra contact patch for a 1" increase in diameter - that's utter, utter bullshit.

Giant in marketing bullsh1t shocker...

More contact patch = more drag, no? So it's "scientifically proven" that bigger wheels are slower.

You can even see from the Giant ad pic that the 29er 'contact patch' below the tyre is overhanging the actual contact considerably...

Is it Made Up Bullshit, or is it just them taking a perceived difference and attaching an unconvincing reason? (ie, is the difference made up, or is it just the explanation for the difference that's made up)

Creaky - Member

More contact patch = more drag, no?

No.

Make them stop mummy

Utter bollox -

Another thread on marketing bollox? Run!

[img] [/img]

Apologies for yet another wheel size related post, please post your 'Oh no, not again, please make it stop' posts below, if you feel the need. But...

I picked up one of the MTB magazines in a supermarket the other day and while not buying it, I read a review on a tyre which wasn't overly favourable. At the end of the review they stated that 'reports on these tyres in 650b and 29" guise are more positive due to the extra grip offered by the larger contact patch'.

I was fairly gobsmacked at the utter twaddle I was reading, I'm no maths expert, but the size of the contact patch on a 650b can't be large enough over a 26" to offer any noticeable difference?

Not twaddle at all , common sense tells you that bigger wheels have a bigger contact patch so more grip , try a 26" wheeled bike and then a 29er , there is a very noticeable difference .

I was fairly gobsmacked at the utter twaddle I was reading, I'm no maths expert, but the size of the contact patch on a 650b can't be large enough over a 26" to offer any noticeable difference?

Note that he's talking about 650b and 26" tyres.

Not twaddle at all , common sense tells you that bigger wheels have a bigger contact patch so more grip , try a 26" wheeled bike and then a 29er , there is a very noticeable difference .

You're comparing 29" and 26" tyres.

Quite. I might have accepted the fact that 29" offered a little more grip than 26", but 27.5???

Having ridden [s]27.5[/s] 650B and 26, I can say that I can't tell the difference.

😛

Seen it all now

Of all the tosh that get bandied about in the endless wheelsize debates the stuff on contact patch must rank as the most pointless. In most practical situations there is a trade off between grip and drag and you can find the sweet spot for any conditions by changing tyres and tyre pressures regardless of what size wheels you have.

Neil Ramsay, please don't rely on your "common sense".

Try some O level physics: the contact patch area depends on pressure alone.

Neil Ramsay, please don't rely on your "common sense".

Try some O level physics: the contact patch area depends on pressure alone.

O level physics was one that I actually got ,a long time ago I will grant you .

You are of course totally wrong . Are you suggesting that a fat bike tyre would have a smaller contact patch than a 12" kids tyre if it was run at a higher pressure ?

Of all the tosh that get bandied about in the endless wheelsize debates the stuff on contact patch must rank as the most pointless. In most practical situations there is a trade off between grip and drag and you can find the sweet spot for any conditions by changing tyres and tyre pressures regardless of what size wheels you have.

What you say is true but on a ride where you will ride through varying terrain , ground conditions and gradients you would be stopping to change tyres or tyre pressure every 5 mins if you wanted the ideal tyre and pressure which obviously isn't practical . It's always going to be a compromise , many feel that bigger wheels and tyres are better all rounders than 26" .

Well, you can easily change your tyre pressure on a ride.
See that valve? You can let air in and out of there quite easily.

You can also change your tyres for different rides far more easily (and more cheaply) than you can change wheel size.

Sorry , I like to ride my bike when I go out for a ride not stop every 5 minutes to adjust my tyre pressure . When I get home from that ride I like to clean the bike and put it away until the next time . I certainly don't want to be thinking where is my next ride going to be and what tyres should I put on for it ?

You are of course totally wrong . Are you suggesting that a fat bike tyre would have a smaller contact patch than a 12" kids tyre if it was run at a higher pressure ?

In a static situation if the situation isn't being skewed by sidewall behaviour or the rise in pressure under load, then yes.

Anyone claiming that one size is conclusively better than another doesn't know what they're talking about. There are pros and cons to everything!

Anyone claiming that one size is conclusively better than another doesn't know what they're talking about. There are pros and cons to everything!

I don't think anybody at any time in this thread has claimed that .

I certainly don't want to be thinking where is my next ride going to be and what tyres should I put on for it ?

This whole thread is about "tyres", so stop wasting your time here if you don't want to think about them.

Changing tyres is easier than changing wheelsize, and it's effective, but it doesn't sell new bikes.

Ramsey Neil - Member

You are of course totally wrong . Are you suggesting that a fat bike tyre would have a smaller contact patch than a 12" kids tyre if it was run at a higher pressure ?

Of course it would be, as I said above, basic physics.

http://www.schwalbetires.com/tech_info/rolling_resistance

cynic-al - Member

Of course it would be, as I said above, basic physics.

Think your physics are being a bit too basic here. If you were dealing with perfect, circular wheels that didn't deform in contact with the ground and had identical curved profiles, then yeah. But realistically a fatbike tyre will have a much squarer profile, and a wider contact patch, even if pressure/deformation etc are all equal.

kelvin - Member

I certainly don't want to be thinking where is my next ride going to be and what tyres should I put on for it ?

This whole thread is about "tyres", so stop wasting your time here if you don't want to think about them.

Changing tyres is easier than changing wheelsize, and it's effective, but it doesn't sell new bikes.

This thread is about a magazine saying 650 and 29er tyres grip better than 26" tyres . I don't really think I've strayed off topic . You seem to be trying to turn it into a wheelsize debate .

honourablegeorge - Member

Think your physics are being a bit too basic here. If you were dealing with perfect, circular wheels that didn't deform in contact with the ground and had identical curved profiles, then yeah. But realistically a fatbike tyre will have a much squarer profile, and a wider contact patch, even if pressure/deformation etc are all equal.

You re getting confused - it really is that simple - there is no factor other than pressure.

I was fairly gobsmacked at the utter twaddle I was reading, I'm no maths expert, but the size of the contact patch on a 650b can't be large enough over a 26" to offer any noticeable difference?

So, back to this... same tyre, same width, same tread, same compound ,same rim profile... any "noticeable" difference in contact patch between 26 and 650b versions? Anything more than messing around with pressures would achieve?

cynic-al - Member

You re getting confused - it really is that simple - there is no factor other than pressure.

I'm not remotely confused - a cylinder and a sphere won't have identical contact patches - length yes, but not width.

I didn't say identical, I said identical area.

You'd still be wrong, then.

prove it.

This is the internet. I don't have to prove anything.

Cynic-al is right

Its as simple as this:

Say you and the bike weigh 200lbs

Each tyre* is supporting 100lbs If each tire has 25 psi of pressure it must have a contact patch area of 4 square inches

Shape of the contact patch differs for different wheel and tyre sizes but the area doesn't as long as the weight the air in the tyres has to support remains fixed.

*the back tyre will have more weight on it on the front but the example still stands

Precisely.

I win.

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explained...[/url]

So given the simple physics lesson Giant's claims have a very distinct whiff of shite about them.

Contact patch area for 26" and 27.5" has to be the same for the same rider with the same pressure in their tyres.

Contact patch length?

I'm not clever enough to work that out but if the tyres were the same width I can't see how the contact length would differ by 2 cm (a 33% increase!) when the difference in circumference of the wheels is less than 5%

I'm not clever enough to work that out but if the tyres were the same width I can't see how the contact length would differ by 2 cm (a 33% increase!) when the difference in circumference of the wheels is less than 5%

there will be a difference, theoretically, in "feel" a short wide contact patch will be different to turn compared to a long thin contact patch. Once you throw in rocks, roots, wheel diameter i doubt you would feel it in the real world.

I'm not clever enough to work that out but if the tyres were the same width I can't see how the contact length would differ by 2 cm (a 33% increase!) when the difference in circumference of the wheels is less than 5%

Nope, I can't make the maths work for that either. I can see that the length would increase, but can't make it jump by that amount no matter what assumptions are made.

When you increase from say a 2.1 to a 2.3 tyre on a 26" wheel you generally run it at a lower pressure, because of the increased volume?

I might be missing something here, but assuming you're running the same width tyre on a 26" and a 29" wheel wouldn't you run the tyre on the 29" wheel at a lower pressure because of the higher volume of the tyre, which in turn would give a larger contact patch?*

* this could be completely wrong.

Nope, I can't make the maths work for that either. I can see that the length would increase, but can't make it jump by that amount no matter what assumptions are made.

Fit a really narrow tyre and let all the air out 🙂 I doubt that Giant have made it up, but I bet they've made some very unrealistic assumptions.

For the record I have a 26" bike and a 29er and I've never felt this supposed increase in grip. The bike that grips best is the one with the grippier tyres. If they both have the same make/model of tyre fitted then it's the one with the lower pressure. Beyond that I really can't feel a difference in grip, but then again I'm not a particularly sensitive soul.