There's HEAPS of possible reasons for wanting to run different sized tires to the stock sizes!! For example, PeteOz mentioned one - availability; & besides, here in Oz we've got lots of .... errr, let's say 'less than perfect' road surfaces. The OE tire size doesn't give the rim much protection if you hit a rock or pot-hole, & the relatively low profile of the tire means rim damage &/or blow-outs can be a regular occurrence. Sure, you could ryde everywhere at 20mph to avoid that ever happening, or you could ryde only on the good roads; but seriously, we've got a pretty big country here, with many places over 100miles apart - and lots of sometimes marginal roads in between them with not much else around except phenomenal scenery & thousands of square miles of space!! So by ryding at 20mph you could end up taking 5 hours or more to get from one property to the next; or by fitting the next higher profile tire you could safely ryde at 50mph & only take 2 hours to get there..... and maybe make it between 2 towns in a day!! :shocked:
Then there's the heat of those surfaces we ryde on too - it gets hot here in Oz, sometimes VERY HOT!! High 40's is not all that uncommon, especially out in the wide open spaces we have plenty of, & that means the road surfaces can get hot (can even start melting!!) & your tires will get even hotter as you ryde. So, you need a reasonable air volume inside them to allow all that heat to be managed appropriately without blowing the tire to pieces or melting the tread off rapidly as the tire turns (compound is only half of the wear equation, tire size is just one of the other halves!
) - smaller, low profile tires might work OK in the city & on smooth roads when you only hafta travel for an hour or two, but not so great when you are on a roughish road for hours at a time!! Besides, would you feel happy if your OE tires ONLY lasted a max of saay 5000 miles while EVERY OTHER vehicle using the same road (motorbikes included) could run slightly larger tires that lasted over 5 times longer AND also provided better ride, traction, & handling AND they reduced the previously mentioned risk of road damage at the same time??! Where do YOU draw that line? I wouldn't stand for 5000km, nor even 10,000km, so I've changed my tires and am achieving MUCH better tire life AND ride, handling, traction, noise, & more!! Then there's also the potential for gearing advantages, load carrying advantages, handling improvements in certain circumstances, traction improvements in a wide range of circumstances, and the list probably goes on (& on, & on!)
In fact, MOST OE tire sizes are basically a compromise size arrived at between the designers, the engineers, the tire specialists, and the $$ mob (& probably a few more too) all aimed at achieving the manufacturers best guess as to what MOST users will want/need from them - and very few riders actually want a compromise..... they want whatever works BEST FOR THEM!! And in tires, that often means a slightly different size to the manufacturers best guess, which can give them things like a different tread pattern; or maybe they want a wider tire for better traction in the dry (& possibly better traction at lower pressures in the wet too!); possibly they want a narrower tire for greater 'penetration' thru surface mud & goop (orright, not many of us are likely to want that); or a little taller for longer legs & higher top speeds; or potentially a slightly shorter tire for better acceleration outta the hole - the point is, MOST ryders want their Spyder to suit THEIR wants & needs a little better than just the manufacturers best guess at what will make most of the potential buyers out there think they'll buy one of them....
But if you want to ride on the manufacturers best guess at what will suit you & every other potential rider out there, that's fine - but like most people, I want MY ryde to suit ME! And that means there's now a couple of different gauges in the holes on the dash; a different seat to the stock seat the Spyder left the factory with; better shocks & different spring rates; even a firmer stabiliser than the OE gear; and not so surprisingly to me, it means running different tires to the POS excuses that my Spyder left the factory with, & for a variety of reasons, the tires I chose are not exactly the same size as the OE spec tires - but they work very well at doing what I want/need from them! :thumbup:
Then there's the heat of those surfaces we ryde on too - it gets hot here in Oz, sometimes VERY HOT!! High 40's is not all that uncommon, especially out in the wide open spaces we have plenty of, & that means the road surfaces can get hot (can even start melting!!) & your tires will get even hotter as you ryde. So, you need a reasonable air volume inside them to allow all that heat to be managed appropriately without blowing the tire to pieces or melting the tread off rapidly as the tire turns (compound is only half of the wear equation, tire size is just one of the other halves!

In fact, MOST OE tire sizes are basically a compromise size arrived at between the designers, the engineers, the tire specialists, and the $$ mob (& probably a few more too) all aimed at achieving the manufacturers best guess as to what MOST users will want/need from them - and very few riders actually want a compromise..... they want whatever works BEST FOR THEM!! And in tires, that often means a slightly different size to the manufacturers best guess, which can give them things like a different tread pattern; or maybe they want a wider tire for better traction in the dry (& possibly better traction at lower pressures in the wet too!); possibly they want a narrower tire for greater 'penetration' thru surface mud & goop (orright, not many of us are likely to want that); or a little taller for longer legs & higher top speeds; or potentially a slightly shorter tire for better acceleration outta the hole - the point is, MOST ryders want their Spyder to suit THEIR wants & needs a little better than just the manufacturers best guess at what will make most of the potential buyers out there think they'll buy one of them....
But if you want to ride on the manufacturers best guess at what will suit you & every other potential rider out there, that's fine - but like most people, I want MY ryde to suit ME! And that means there's now a couple of different gauges in the holes on the dash; a different seat to the stock seat the Spyder left the factory with; better shocks & different spring rates; even a firmer stabiliser than the OE gear; and not so surprisingly to me, it means running different tires to the POS excuses that my Spyder left the factory with, & for a variety of reasons, the tires I chose are not exactly the same size as the OE spec tires - but they work very well at doing what I want/need from them! :thumbup:
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