Tyre sizes

[irev]

Moreover, whoever gave you that advice should show you their research and development credentials.

It's the kind of pathetic back-of-cornflakes-packet guidance from somebody who should be eating Farleys Rusks... take it, and die.

Clear?

First off take it easy buddy it was only a question following a thread I was reading where an owner fitted a pair off michelin pilot sports to his aprilia scoot with a different profile and in his opinion it improved the ride. I was curious to read if anyone else had tried it and what they thought. At no time did I say anywhere in my post that I was going to do this although re reading my post I guess it came across that way.It certainly wasnt my intention to pee people off.

Not setting me off, simply telling you exactly how it is.

As an ex R&D person whose job was to test precisely these things I could tell you how dangerous it is for small-wheeled vehicles to change tyre sizes on the existing rims (disproportionate difference in rolling radii and contact footprint compared even to larger-wheeled bikes) but there's really no need when you can summarise the issues as easily as `Do it and Die`.

BTW car analogy doesn't apply as the geometry of steering and suspension do not significantly alter by changing rolling radius, nor does the steering moment arm significantly alter when wider tyres are used. It's this that give ideas to fuckwits in the PTW community that it ought to be a good idea for bikes).

Your eggspurt is more than welcome to come here and justify his arguments to save embarrassment.

Yours, not his as there's more than enough expertise here to rip `im a new one, if he even turns up. And if he doesn't, then clearly he's not prepared to back up kitchen-table advice that risks someone elses life. And that makes him a lying arsehole on top of incompetent cretin. I suggest he runs for office as he's fuck all use for anything else.


One additional point that does have relevance to the discussion and does muddy the waters - stated tyre sizes are nominal only and are not supported by regulatory requirement for validation. You can put a range of nominally same-sized tyres alongside each other and be utterly amazed at the range of size and shape differences.

Diameter, rolling radius, shoulder shape and width, proportion of rim width to shoulder, in fact every single measurement can drastically differ between same-sized tyres. It's the principle reason recommendations are always based on matched pairs front-and-rear.

In that situation there MAY be some advantage to mixing'n'matching - hence the notion that varyng a 190 and 200-rear can result in easier turn-in - but it may not be because of the nominal width decrease it can simply be that the profile is more favourable for the front. I have even seen 180 tyres that are actually across the shoulder wider than 200's...
Although again, it could just as easily kill you.

And lest anyone thinks I overstate the case, I've given expert witness testimony at Coroners Inquests over this. Hence no mincing of words.

[macp]

Moreover, whoever gave you that advice should show you their research and development credentials.

It's the kind of pathetic back-of-cornflakes-packet guidance from somebody who should be eating Farleys Rusks... take it, and die.

Clear?

First off take it easy buddy it was only a question following a thread I was reading where an owner fitted a pair off michelin pilot sports to his aprilia scoot with a different profile and in his opinion it improved the ride. I was curious to read if anyone else had tried it and what they thought. At no time did I say anywhere in my post that I was going to do this although re reading my post I guess it came across that way.It certainly wasnt my intention to pee people off.

Not setting me off, simply telling you exactly how it is.

As an ex R&D person whose job was to test precisely these things I could tell you how dangerous it is for small-wheeled vehicles to change tyre sizes on the existing rims (disproportionate difference in rolling radii and contact footprint compared even to larger-wheeled bikes) but there's really no need when you can summarise the issues as easily as `Do it and Die`.

BTW car analogy doesn't apply as the geometry of steering and suspension do not significantly alter by changing rolling radius, nor does the steering moment arm significantly alter when wider tyres are used. It's this that give ideas to fuckwits in the PTW community that it ought to be a good idea for bikes).

Your eggspurt is more than welcome to come here and justify his arguments to save embarrassment.

Yours, not his as there's more than enough expertise here to rip `im a new one, if he even turns up. And if he doesn't, then clearly he's not prepared to back up kitchen-table advice that risks someone elses life. And that makes him a lying arsehole on top of incompetent cretin. I suggest he runs for office as he's fuck all use for anything else.


One additional point that does have relevance to the discussion and does muddy the waters - stated tyre sizes are nominal only and are not supported by regulatory requirement for validation. You can put a range of nominally same-sized tyres alongside each other and be utterly amazed at the range of size and shape differences.

Diameter, rolling radius, shoulder shape and width, proportion of rim width to shoulder, in fact every single measurement can drastically differ between same-sized tyres. It's the principle reason recommendations are always based on matched pairs front-and-rear.

In that situation there MAY be some advantage to mixing'n'matching - hence the notion that varyng a 190 and 200-rear can result in easier turn-in - but it may not be because of the nominal width decrease it can simply be that the profile is more favourable for the front. I have even seen 180 tyres that are actually across the shoulder wider than 200's...
Although again, it could just as easily kill you.

And lest anyone thinks I overstate the case, I've given expert witness testimony at Coroners Inquests over this. Hence no mincing of words.

Thankyou well stated and very well put and for what its worth I for one will be sticking with standard size tyres

[gn2]

If you are considering a width/aspect ratio change from the bike manufacturer's recommended size, you need to find out the rim width and then find out from the tyre manufacturer which tyres they recommend for that rim width.
Far easier to just stick with the correct size.

[macp]

If you are considering a width/aspect ratio change from the bike manufacturer's recommended size, you need to find out the rim width and then find out from the tyre manufacturer which tyres they recommend for that rim width.
Far easier to just stick with the correct size.

As I say I had been reading a thread on I think an american scooter forum where a guy fitted an oversize front and I was just interested to know if anyone here had done the same. Mind you would you admit it on here if you had

[gn2]

Americans are fond of fitting car tyres to motorbikes.
Fecking nutters, best to ignore them.
I once had a 10mm undersized rear fitted to my GS850 by mistake, it seemed to be OK because I did over four thousand miles on it round Europe two up with full camping luggage in three weeks.

[irev]

Americans are fond of fitting car tyres to motorbikes.
Fecking nutters, best to ignore them.
I once had a 10mm undersized rear fitted to my GS850 by mistake, it seemed to be OK because I did over four thousand miles on it round Europe two up with full camping luggage in three weeks.

Absolutely right. I ended association with the Americo-centric Burgman USA forum over their resolute desire to kill themselves by using car `tires`,

They have much to learn and little to teach. Ironic, when they actually invented the maxi-scooter.

[Bluebottle]

I'll tinker with most things but not tyres.

[Liam]

When I had Lambrettas in the 70's, it was common place to replace 3.50 x 10 tyres with 4.00 x 10

[Data]

Liam, you can 'get away' with replacing both tyres with a 'slightly larger' section if you know what you are doing. But often, it's just not worth doing as it usually doesn't result in any real benefit. It adds to unsprung weight, increases drag and rolling resistance. And your insurance company will disown you unless you can prove it's a recognised modification that's been tested to be safe.

On what irev says, I couldn't agree more with his sentiment about everything he says. The American site is a good one with lots of good people on it. But I find Americans generally can be so aggressive if anyone dares to disagree with them. Also it's important to understand that the USA is largely a third world country when it comes to bike regulation. They do not for example need to have any sort of bike insurance in many states. Something we find completely unbelievable and unacceptable. All they do is have to declare they can cover any resonable damage to a third party if they have an accident when they register the bike for licence! Yeah...right! Helmet law does not exist in many states either. They can fit car tyres (tires!) with impunity and dam anyone who tells them it's dangerous... But hey ho, that's the world...or more precisely the States. Just that in the States they are so far behind the rest of the world with bike stuff. By the way, I'm not anti-American. I have family over there too.

[gn2]

in the States they are so far behind the rest of the world with bike stuff

So much so that many of them think Harley Davidson make very good modern motorcycles.