I'm afraid they're right, Kiwibacon... :think:

More of it here:

http://www.carbonbla...right-tyre.aspx

Edited 23 July, 201213 yr by Hirundo

Stop ganging up, boys.

It's un-Yeti-like behaviour!

+1

I suggest we should all carry on reading our antipodean visitor's posts just in case he contributes anything interesting/informative. In a monkey/Shakespeare spirit of optimistic anticipation. :wonder:

... and, strangely, length.

But if a 16 or 17 wheel and tyre has the same diameter, length should be relatively representative of pressure. You can choose the starting width of the tyre footprint by fitting different tyre to aYeti, but the length would say the same and only vary by a noticable amount with the pressure.

So by your logic one of those little skinny space saver spare wheels and tyres will have the same contact patch with the road if it's inflated to the same pressure as a tyre that's double the width?

I don't think so. Your calculations are missing a vairiable for tyre width.

If you were to inflate your space-save to the same pressure as your normal tyres, then yes it would bag out until it reached the same contact area.

But they don't, space-savers run much higher pressure.

I'm afraid they're right, Kiwibacon... :think:

More of it here:

http://www.carbonbla...right-tyre.aspx

You do know the difference between size, shape and area, right?

You'll see on that article, attached to that exact graphic is a pressure of 190kPa used. If you decrease the pressure from 190kPa, they'll all get bigger, increase the pressure and they'll all get smaller.

Compare the area of each footprint, they should all be roughly consistent. The rigidity and construction of the tyre plays a big part too.

But if a 16 or 17 wheel and tyre has the same diameter, length should be relatively representative of pressure. You can choose the starting width of the tyre footprint by fitting different tyre to aYeti, but the length would say the same and only vary by a noticable amount with the pressure.

Yes to the first part, but I'd expect the length to be a bit different between a 16 and 17, shorter on the 17 due mainly to the extra width.

Here's a nice graphic for truck tyres showing contact patch with pressure:

We all know how a soft tyre looks compared to one pumped up properly, the increased contact patch (and lower contact pressure) is quite useful in some situations.

Are you for real Mr.Bacon?

What you are suggesting is that a space saver spare at the correct pressure would balloon out like the tyres in the picture above of a 4x4. Cleary that is impossible as even flat they could not balloon out that far.

This is because width IS a factor. Which is why those of us who have done fairly extreme offroading know pressure, tread pattern and tyre width ARE important.

Are you for real Mr.Bacon?

What you are suggesting is that a space saver spare at the correct pressure would balloon out like the tyres in the picture above of a 4x4. Cleary that is impossible as even flat they could not balloon out that far.

This is because width IS a factor. Which is why those of us who have done fairly extreme offroading know pressure, tread pattern and tyre width ARE important.

No I didn't suggest that, you've read past what I have written.

Any tyre can only balloon out until it essentially sits on the sidewalls and rim. A space-saver is about 1/4 of the width of Nadim's DiscoDino tyres and can never bag out that much. I didn't claim it could and I doubt anyone else would have read it that way.

I said a space-saver could bag out to similar contact area as a standard tyre. To do so it would gain most of the increase in footprint length, not the width as the width is limited (obviously) to not much greater than the width of the tyre and rim.

Don't confuse area with shape. Similar area is not similar shape. A skinnier tyre of similar footprint area will always have a longer foot-print. I run my off-road tyres skinnier than most.

Doesn't matter what size your tyres are, the contact patch is determined by the air pressure within.

Err...

Err...

And?

Richard,

It isn't worth it.

never seen so many posts from anyone so full of c---

never seen so many posts from anyone so full of c---

There's no need to be rude ... I haven't made that many posts in this thread!

lol

Who gives a ****, I pumped mine up tp 300psi and got a footprint like Wiggo's bike in the Tour, then they went BANG and now they've got a footprint like DUMBO !!!