Tire sizes - school me on what to use

[Ductard]

If there's already a thread on this, or a good resource, feel free to point me in that direction....

So I have a general idea for what the numbers mean on the side of a tire mean, tread width, aspect ratio, rim size....

But I used to think that 160 = lightweight/motard, 180 = midweight, 200 = heavyweight...

That was fine, esp. when I was running whatever the tire dealer said I should on different bikes, but I've started to buy take-offs and have started to get a bit confused.

My 1199 came with a 200/55 in the rear, but apparently Dunlop doesn't even make that size?

Oh, and the Pirelli website doesn't list a 200/55 Supercorsa (SP or SC), which is weird, b/c as mentioned that's what came on the bike.

To add to the confusion, I've heard that the measurements aren't *really* comparable between different brands.

I've also heard that a different tire size can affect the performance of electronics like traction control. Doesn't sound right b/c if my math is right, a 200/55 has a 3.40m circumference, a 190/60 is 3.43m, and a 190/55 is 3.37m...in other words they're all +/- 1% of reach other.


So, given that my understanding is that rear tire size is a balance of contact patch size (exit drive) and handling (with larger = harder to flick from side to side)

1. Is there a "right" size for a specific class of bike, or at least one that most people agree is best?

and

2. If the answer to #1 is "yes" would it also depend on the track being ridden? For instance would you sometimes choose a smaller tire on a tight technical track like NHMS where you might want a larger tire for a faster track like NJMP (or vise versa?)

[PhilB]

Some modern bikes, and yours may be one of them, have tires designed specifically for that bike, and those tires will mainly be available only from the dealer. So, for example, Pirelli might make a 200/55 Supercorsa, but they make it for Ducati, for that model bike, and pretty much only sell it to Ducati dealers.

Your understanding is pretty much on. Rather than a "balance", I'd say a "compromise". The best tire for a bike is the smallest one that has enough contact patch to handle the bike's drive. Many bikes are over-tired -- that is, they have larger tires than they need -- because people think it looks cool and makes their bike look faster. My own bike is one of them; it came with a 180/55, but works better with a 160/60. If I ever need to replace my rear rim, I will go 1" narrower so I can fit the smaller tire.

In general, changing tire size a bit shouldn't cause any problems. Modern electronics and TC may make it pickier, but even there, there ought to be some tolerance, because even tires of the same nominal size do differ. You might talk to your dealer and ask what their experience is with different tires on that bike.

PhilB

[Ductard]

The best tire for a bike is the smallest one that has enough contact patch to handle the bike's drive.

Thanks, this is helpful...but how do you determine the "smallest one that has enough contact patch?"

I mean, if I wanted to, I could probably throw a 200 on my 600 and spin up the rear if I treated the throttle like a light-switch.

Alternatively, I could probably throw a 160 on the 1199 and be ginger enough with the throttle to keep from spinning up the rear.

Those are extreme examples but is it just a matter of "feel" / user preference / YMMV?

[Schramm]

Thanks, this is helpful...but how do you determine the "smallest one that has enough contact patch?"

I mean, if I wanted to, I could probably throw a 200 on my 600 and spin up the rear if I treated the throttle like a light-switch.

Alternatively, I could probably throw a 160 on the 1199 and be ginger enough with the throttle to keep from spinning up the rear.

Those are extreme examples but is it just a matter of "feel" / user preference / YMMV?

I spun up my 200 in the race last weekend, if that helps haha. The technicality of the track isn't what judges tire size I don't think. I learned to race on a tight 1.1 mile go kart track, and we were running 200s there and those helped a ton, but that's because we were constantly on the gas to get out of slow corners. On faster (but still technical) tracks were momentum, power and nimbleness come into play, I think it may be a different story. The 180 will be quicker, offer less drag on horsepower, and handle more spritely. The 200 stuffed on a 5.5 rim is also taller, and has a different profile (making it harder to lean back and forth). But damn can you get on the gas early

[nhbubba]

Also remember that tire section width will effect handling. A 200 will slow handling down compared to a 180, and vice-versa. So it is a tradeoff.
Other issues are the rim width and clearance in the swingarm. My DRZ cannot fit much more than a 150 in the swingarm and the wheels aren't meant for a wider tire anyway. Seems most that build SM wheels for this bike build off wider than OE hoops to handle a 160. And so on and so forth.

I ask what everyone else runs and follow their lead. Very easy with an SV.