rear tire question

kenwood guy · 07-02-2007, 09:46 PM

hey guys the bike I was looking at getting is the sv650s as a starter bike however I was talking to a guy about bikes and he said that bikes with wide rear tires are better and more stable I notice that the sv650s has a standered rear tire that looks like the front , is a wider rear tire safer??? and more stable then others such as the ninja or other bikes with wide rear tires

richtazz · 07-03-2007, 05:49 AM

"stability" is a tricky word. A wider rear tire can help make a "twitchy" bike less so, but will also slow the turn in on an already stable bike. I think it's less the tires and more the bike and it's frame/suspension geometry. If you put a wider than stock tire on an already stable bike, it will make it turn slower due to the higher initial inertia of the larger tire. I own a Harley Fatboy with a standard rear tire, and I've ridden one with a "300" rear tire. I don't like the feel of the big tire bike, it's like it wants to only go straight.

speediva · 07-03-2007, 02:45 PM

Quote:

Originally Posted by richtazz

"stability" is a tricky word. A wider rear tire can help make a "twitchy" bike less so, but will also slow the turn in on an already stable bike. I think it's less the tires and more the bike and it's frame/suspension geometry. If you put a wider than stock tire on an already stable bike, it will make it turn slower due to the higher initial inertia of the larger tire. I own a Harley Fatboy with a standard rear tire, and I've ridden one with a "300" rear tire. I don't like the feel of the big tire bike, it's like it wants to only go straight.

+1

Honestly, the point of a motorcycle is to LEAN... anyone can ride fast in a straight line, which is about the only benefit I can see of a wider rear tire. Besides, once you get moving, centripetal force and inertia will keep you moving without any real problems.

kenwood guy · 07-03-2007, 04:40 PM

so its not needed depending on the bike that is...... and if i get a sv I can lean the sameway a let's say r6 or ninja does???

jeffcoslacker · 07-03-2007, 07:53 PM

The wider tires on a sport bike are specially radiused to put a large contact patch to the road surface through the whole lean, increasing GRIP, while the shape of the radius and not the contact patch is where you get your stability...it's a tricky trade-off. This is for track use...which doesn't always translate to street use...

Same as with a car, a wider tire will give you more bite on a dry, smooth surface. It will also make you LOOSE traction on a wet, loose, or rough surface. The reason is simple...

Contact patch for a given vehicle puts the same weight down regardless of patch size...but the weight per square inch of contact is different. So a tire with 6 square inches of contact patch with, say, 350 lbs (roughly half the bike and rider) bearing on it is gripping the road with 58 lbs per sq. in...where the tire with, say, 3.5 square inches of contact patch is gripping with 100 lbs per square inch, nearly twice the "dig" of the wider tire...the narrower tire will "bite" much better on a less than perfect surface. The wider one will hydroplane easier, and won't cut through loose stuff you might encounter on the road, preferring to "float" on top of it.

There is a cut-off point where larger contact patch wins out over patch area bite, that's where the engineers try to keep tire designs for cycles. There are some other considerations, like a larger tire carcass is better at dissapating heat, beneficial on the track, along with reduction in belt squirm and loading on the tire bead...

Anyhow, the steamrollers you see on sportbikes aren't going to make it handle better or more stable, it will actually make it harder for a novice rider. Sportbikes are designed to maintain maximum grip at insane bank angles at high speed, not stability.

Ask a military pilot if a fighter jet is stable...it's not, it wants input from you contantly, instability and manuverability go hand in hand...the same things that make it able to do what it does so well at high speed are what make it so hard to fly at low speeds....sportbikes are the fighter jets of motorcycles...not really designed for stability or beginners....

Not to say one can't learn to ride on one...many people do...but you gotta have a sharp leaning curve and a lotta self-control, or it'll get ahead of you...

jeffcoslacker · 07-03-2007, 08:04 PM

PS, the SV650 is WAY more bike than you'll need for a long time...I know several people who now have them after riding bikes for decades, all different styles and makes.

Each of them describes it as the "perfect" mix of twisty road capability and straightline stability...you can play with the sportbikes in the turns, but ride comfortably on the superslab for 400 mile days...each of them says they never thought they could be happy with just one bike, but that one fits all the holes..

aussieidiot · 07-04-2007, 03:50 AM

i'm trying to figure out if the guy you were talking to actually knew about bikes or just made a casual observation about bikes that went hard and fast that usually have larger rear tyres and therefore "better" bikes than than slower bikes with smaller rears.

my first bike was a 250 and only had a 140 rear tyre. it would fall into corners and was easy to ride. tyres were cheap too.

now with the litre bikes, they run a 190. about $300AUS and only last 5000K's

at the track, guys run a 180 and it gives them a quicker turning bike but they also change the height from a 50 to a 55. this gives a slightly higher rolling diameter which in turn raises the rear slightly. this in turn changes the steering to be much faster. BUT much faster also means shit scary when you're not used to it. a slight push on the bars will effectively drop the bike into a corner where a standard will be more gradual.

there's no point putting a larger rear on a sports bike. it'll only turn slower. chances are it will also affect the steering geometry. most bikes can't accept wider rear's between the swing arm too. it may fit between stationary but when its loaded up on a corner and it flexes out to the side, it will rub and stuff you up.

harleys may put on larger tyres but i'm not sure whether they do it to look cool or what.

richtazz · 07-06-2007, 03:57 PM

Quote:

harleys may put on larger tyres but i'm not sure whether they do it to look cool or what.

Most custom bikes do it just for looks. that's why I commented as I did. If making my bike look "tougher" makes it handle like a brick, forget it (not that a Fatboy is a canyoun carver to begin with).

jeffcoslacker · 07-06-2007, 04:05 PM

Quote:

Originally Posted by richtazz

Most custom bikes do it just for looks. that's why I commented as I did. If making my bike look "tougher" makes it handle like a brick, forget it (not that a Fatboy is a canyoun carver to begin with).

Rode a Victory Hammer with the 250 rear a month or two ago...was doing figure eights in the parking lot, getting the feel of it before hitting the road...damn tire made me feel like I'd never rode a bike before

Doesn't take long to get used to, though.

But then I rode an Eight Ball with the 170 rear or whatever is on it, and found myself much more confident in the curves...

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