Mismatched tyres

[McDuck]

Well it clearly has a 17" front. That is the reason behind this whole thread. I don't know offhand whether the rear is 17" as well. If it turned out that the Pirelli Phantom repilcas fitted then they would be the absolute dog's bollocks!

Shit it is late, i think they are both 17''s.

Could be cool to have a set me thinks

[Mikkel]

Were too.

Look, I already told you once... was not!

You assume the tyre is a simple, completely non-rigid pressure barrier.

They're not.

Please sexpand...

On the inside you have air at some pressure - on the outside you have air at @mosFEARic pressure and a road surface. Combined you need to provide some sort of physical equilibrium...

I agree that the tyre construction has an effect upon how the tyre, dynamically, adapts to fulfill this requirement. However, tyre profile, tyre pressure and vehicle weight and weight distributions are still what will dictate the contact patch area of each tyre.

[MarkH]

Pirelli Sport Demon ordered to match Sport Demon on rear. (And told if Pirelli wasn't available than a BT45 would do).

Metzeler M3 (radial) fitted to front because they forgot to get the Pirelli in.

Their story was that the wholesaler was out of stock of the Pirelli. I can vouch for the fact that that was not the case.

So he ordered a tyre, they didn't supply the tyre ordered, they lied about its availability and fitted something else? That is pretty fuckin' shitty IMO! He should tell them that he has been advised that the wholesaler was NOT out of stock and they should have supplied what he ordered and demand they replace the tyre!

Can anyone definitively state that there are handling issues with the tyre combination now on that motorcycle? I don't really know how the front radial combined with the rear cross-ply affects the handling. Regardless - he should have been supplied what he had asked for!

[Jantar]

How so?

OK, an extreme example. Take a trianglar block and and place it such that a corner is touching the ground. the contact area is very small, just the thickness of a line. Now lay it over onto an edge, and the contact area is very large. If this is the profile of a tyre then the same thing happens. A small contact area when upright and large when leant over. A radial tyre with a round profile will not change its contact area much at all.

The air inside the crossply tyre tyre is there to maintain the tyre shape and that is why crossply tyres are less susceptible to changes in tyre pressure than radials.

Even with radials the air pressure only has a small effect on contact area. Here's an experiment you can try for yourself, spread some flour or similar visible dust onto a smooth surface, take an old tyre and place it on the surface then remove it and measure the contact area. Remember relative air pressure is zero. Now repeat the experiment but place a weight equal to the tyre's weight on top of the tyre and remeasure the contact area. Has it doubled? I assure you it hasn't.

[McDuck]

So he ordered a tyre, they didn't supply the tyre ordered, they lied about its availability and fitted something else? That is pretty fuckin' shitty IMO! He should tell them that he has been advised that the wholesaler was NOT out of stock and they should have supplied what he ordered and demand they replace the tyre!

I belive the term used was a 'mix up (IE fuck up) and the M3 was suggested over the phone when (I) rang to conferm they had the tyre i wanted, they didnt have and the M3 was one the shelf.

[Ocean1]

Look, I already told you once... was not!

Was so.

I agree that the tyre construction has an effect upon how the tyre, dynamically, adapts to fulfill this requirement. However, tyre profile, tyre pressure and vehicle weight and weight distributions are still what will dictate the contact patch area of each tyre.

Oh, and tyre profile, now.

Add compound hardness and carcase structural characteristics and you'll have a reasonable picture.

And there's a substantial difference in those carcases, I believe that defines most of what we feel as difference between tyres.

[Mikkel]

OK, an extreme example. Take a trianglar block and and place it such that a corner is touching the ground. the contact area is very small, just the thickness of a line. Now lay it over onto an edge, and the contact area is very large. If this is the profile of a tyre then the same thing happens. A small contact area when upright and large when leant over. A radial tyre with a round profile will not change its contact area much at all.

You are correct, insofar that the tyre can be considered to be rigid... I have no experience with crossply tyres, but for radial tyres such a consideration is invalid...

Even with radials the air pressure only has a small effect on contact area. Here's an experiment you can try for yourself, spread some flour or similar visible dust onto a smooth surface, take an old tyre and place it on the surface then remove it and measure the contact area. Remember relative air pressure is zero. Now repeat the experiment but place a weight equal to the tyre's weight on top of the tyre and remeasure the contact area. Has it doubled? I assure you it hasn't.

So you suggest that the difference between 30 PSI and 15 PSI in a set of radial tyres is unimportant?

Your argument is flawed insofar that you assume that the rigid strength of a steel-belt reinforced rubber torus is zero...

The more valid experiment would consist of taking a tyre on a wheel and applying first 500 kg and then 1000 kgs to the axle and see what difference in contact patch area is observed. You will see an increase very close to 100% between measurement 1 and 2.

[Mikkel]

Was so.

Look, if you are just going to be difficult I'll have to send you off to bed early young man...

Oh, and tyre profile, now.

Add compound hardness and carcase structural characteristics and you'll have a reasonable picture.

And there's a substantial difference in those carcases, I believe that defines most of what we feel as difference between tyres.

I might be mistaken, but I actually thought that the compound characteristics changed throughout the tyre... If that is not the case, I would have to grant you that I might not have answered your query adequately in the post which I posted as a response to Jantar.

[Jantar]

You are correct, insofar that the tyre can be considered to be rigid... I have no experience with crossply tyres, but for radial tyres such a consideration is invalid...

No, I am not assuming that the tyre is rigid nor radial. I am saying that it is not perfectly elastic either. A crossply tyre is far more rigid when inflated than a radial tyre.

So you suggest that the difference between 30 PSI and 15 PSI in a set of radial tyres is unimportant?

Your argument is flawed insofar that you assume that the rigid strength of a steel-belt reinforced rubber torus is zero...

The more valid experiment would consist of taking a tyre on a wheel and applying first 500 kg and then 1000 kgs to the axle and see what difference in contact patch area is observed. You will see an increase very close to 100% between measurement 1 and 2.

If the weights you have suggested are within the tytre's rating then go ahead and try it. I would suggest that if you are going to use an inflated tyre, then measure its contact area with normal inflation and within its weight limits, then double the air pressure and remeasure. I thinkl you'll find that the decrease in contact area is around 50% for a radial tyre and around 10% for a crossply tyre.

[Mikkel]

If the weights you have suggested are within the tytre's rating then go ahead and try it. I would suggest that if you are going to use an inflated tyre, then measure its contact area with normal inflation and within its weight limits, then double the air pressure and remeasure. I thinkl you'll find that the decrease in contact area is around 50% for a radial tyre and around 10% for a crossply tyre.

Very interesting. I'll have to put it on my to-do-list, the chance of me owning a non-radial tyre within the foreseeable future is pretty close to nil.

So what is it, between radial and crossply construction, that causes this very considerable difference in mechanical rigidity?

[Jantar]

The name "crossply" may give a clue. The plys cross each other at an angle effectively giving a triangulation of the plys. It makes for a very rigid construction.

[Kickaha]

Also remember that most crossplys were desinged for spoked rims which means they must be fitted with a tube.

cross ply tyres have been available as tubless for years (if not decades)

I am gutted that Pirelli are only putting out those Phantom replica tyres in 17".

So am I

So what is it, between radial and crossply construction, that causes this very considerable difference in mechanical rigidity?

Belt angle, belt material blah blah blah

Car stuff but it should give you an idea
http://www.tyresite.com/tyrearticle.asp?page=11

Motorcyle related
http://books.google.co.nz/books?id=8...esult&resnum=3

http://books.google.co.nz/books?id=l...esult&resnum=7

[DEATH_INC.]

I belive the term used was a 'mix up (IE fuck up) and the M3 was suggested over the phone when (I) rang to conferm they had the tyre i wanted, they didnt have and the M3 was one the shelf.

There's two questions here, Did the custy 'ok' it before it was done (or ok it when the bike was collected), or not?
And of course, is it safe?
On a bike I don't think there'd be any massive safety issues (I've run them mixed, the turbo had a radial rear when I bought it) but I suggest that a quick e-mail to the tyre importer to get their view may be in order.
If it is legal and the customer said ok, then there is no issue.
If either is not the case then there's a big problem.
If the tyre manufacturer says it's ok, then the shop has done no real wrong, but should perhaps look a little at their service in the future...and perhaps the customer should consider a different tyre supplier....

[boman]

Here is a very basic diagram displaying the differences in the Two tyre types.

[ynot slow]

Pretty simple really,you ask(politely)can you grab me a tyre xyz size,if not can you suggest an alternative before you even place a replacement on the rim.The client should have the option of saying no sorry,that's not what I want.Not picking up the bike and finding something else is used.

Much like you go in and order a new Falcon XR8 GTP (after you've won lotto),upon arriving to pick up they hand you keys to a 1989 Mazda 626,they say well it is a Ford replica vehicle.