Some nagging questions !!

[tha-mask]

For those of you in the know I thought I would ask some questions about the Mana that have been bugging me !

1. The Manual states that the rear tyre can either be 180/55 ZR17 or 190/50 ZR17. Anybody have any thoughts on this. I know Pete is not a lover of big tyres for the sake of it. My view would be that the more rubber on the road the better, but does that tyre size come at the detriment of anything else other than cost ??

2. What do people do for oil level checking. Without a center stand its very difficult to balance the bike whilst kneeling down to see what's in the sight glass, any slight movement in the bike shows a big difference. Would using a padock stand throw off the levels as it slightly raises the bike at the rear, I'm guessing so. Also what level do you read, the min or the Max. Surely if it has the right level in the Max sight glass the min is going to be fine. On the Yamaha T-Max which is also a dry sump system you only ever read the level from the dip stick, so confused with the Aprilia system.

Any comments greatly appreciated.

[SilverFoxUno]

1. The wheel width is sufficient to use either a 180 or 190 - My books says 180/55ZR17. From what I have read, a 180/55 and a 190/50 have the same mounted diameter (the diameter is dependent on the tire manufacturer - they are all a little different). I have used a 170/60 on a six inch wide rim without any issues. So what doe this mean? Why, just like oil, it's personal preference...

2. Oil level is a bit odd as the sight gage is intended to be a minimum level in the "sump"...not the "tank". This is a dry sump system - which is why you have two measurements. The tank supplies the engine through the primary pump while the scavenge pump puts oil into the tank from the sump after the oil has been through the engine. As long as the sight gage is full, you're good...provided the dip stick in the tank is also correct. It is difficult to make sure the bike is vertical but close is sufficient. See http://www.apriliaforum.com/techtips/other/drysump.htm

[groovymaster]

My view would be that the more rubber on the road the better



Why? And don't respond with "traction" because if you do then you don't understand what traction is.

[tha-mask]

Why? And don't respond with "traction" because if you do then you don't understand what traction is.

I'm more than happy to be educated :)

[PAPASMURF]

For those of you in the know I thought I would ask some questions about the Mana that have been bugging me !

1. The Manual states that the rear tyre can either be 180/55 ZR17 or 190/50 ZR17. Anybody have any thoughts on this. I know Pete is not a lover of big tyres for the sake of it. My view would be that the more rubber on the road the better, but does that tyre size come at the detriment of anything else other than cost ??

2. What do people do for oil level checking. Without a center stand its very difficult to balance the bike whilst kneeling down to see what's in the sight glass, any slight movement in the bike shows a big difference. Would using a padock stand throw off the levels as it slightly raises the bike at the rear, I'm guessing so. Also what level do you read, the min or the Max. Surely if it has the right level in the Max sight glass the min is going to be fine. On the Yamaha T-Max which is also a dry sump system you only ever read the level from the dip stick, so confused with the Aprilia system.

Any comments greatly appreciated. I carry a small mechanics mirror that has a telescopic handle,
I sit on my bike and hold the mirror to check the oil

[tha-mask]

I carry a small mechanics mirror that has a telescopic handle,
I sit on my bike and hold the mirror to check the oil

Great Idea, might have to invest in something similar, or just stick a mirror onto a stick !!

[groovymaster]

I'm more than happy to be educated

The coefficient of friction does not depend on the size of the surface area of contact. That is to say, the force of friction is the same whether the tire is wide or thin because friction is proportional to the force (in this case, weight) distributed to each tire. Think of it this way, a 1000-pound piano wouldn't be any easier or harder to push across the room if the contact patch of each leg were 1-inch or 1/2-inch. In fact, it is equally hard to push a 1000-pound piano whether it has three or four legs. I previously had this discussion with a 3-wheeler MP3 enthusiast who claimed he had additional traction when the reality is that three contact points, rather than two on a standard motorcycle, doesn't translate to additional traction. Simply put, a wider tire doesn't mean more traction. What does impact friction is tire composition, softer tires have a larger coefficient of friction, therefore better traction.

[tha-mask]

Thanks groovymaster for that. I actually understood it.

Therefore is a larger tyre pure eye candy ? I'm sure it has some influence on the handling...does it not ?

I have to say I have always been a sucker for a nice larger looking rear tyre. My Brother in law in Canada has a Suzuki M109 and that looks amazing !

[thunderclap]

As for the oil check--should both the sight glass and dip stick be checked after a ride ?
Sorry if this info is in the manual---the Mana is my wife's bike

[JodyH]

The coefficient of friction does not depend on the size of the surface area of contact. That is to say, the force of friction is the same whether the tire is wide or thin because friction is proportional to the force (in this case, weight) distributed to each tire.

Simply put, a wider tire doesn't mean more traction. What does impact friction is tire composition, softer tires have a larger coefficient of friction, therefore better traction.

Thanks groovymaster for that. I actually understood it.

Therefore is a larger tyre pure eye candy ? I'm sure it has some influence on the handling...does it not ?
You are both "right" and you're both "wrong".

o The classic F = N x mu friction applies to smooth hard surfaces and is only a part of a tire's grip.
o Mechanical interlocking ("hysteresis gearing") of the soft rubber with the road surface is a major factor.
o Molecular bonding of the tire to the track (think Post It Notes) is also significant, particularly on dry roads.
o The last two are temperature sensitive and a wider tire has more area to accept and dissipate heat, thus can be made softer without overheating.
o All else being equal, a wider tire will almost invariably corner faster, but may lap slower due to more inertia, higher rolling friction and or air drag.

http://www.physlink.com/Education/askexperts/ae200.cfm

In the "real world" wider tires translate into more traction, simple physics be damned.

:cheers:

[tha-mask]

thanks for that, I wonder if anyone has fitted the wider tyre on theirs yet, mine has quite a few miles left on it still so will speak to the tyre place when it comes up for replacement.

[williamr]

I always find wider tyres are slower into turns, so I'd query cornering faster.

Wider tyres tend to offer less wet grip as its easier for water to build up between the rubber and the road. Heat dissipation isn't much different as you're heating the air inside the tyre. Anyone who's really keen can calculate the internal volumes and external surface area to see what the real difference is. I'd guess that there's little difference in weight. You could argue that the lower profile of the wider tyre slightly reduces the turning moment about the axle, and therefore the inertia, but I don't think it's enough to matter. Again, you could calculate the effect if you really wanted to. Rolling resistance is negligeable on a bike or car - compared to the air drag it's so small that it's usually ignored in the power/speed equations, and the tyre is included inside the frontal csa, so air drag on the tyre isn't an issue.

Coefficient of friction (static friction until the tyre loses grip), is a function of the interaction between the two materials (tyre and road), but the total frictional force (grip, if you like) is proportionate to the size of the contact patch, the loading (weight) on the tyre, and the coefficient of friction. The same load spread over a bigger contact patch means less friction at any point on that patch. The end result is not a lot of difference overall.

These arguments are only true where the aspect ratio chages with the width to maintain a roughly similar rolling radius.

The main benefit of wider tyres comes from improved traction for straight line acceleration when the tyre is hot and sticky and running soft - basically for drag racing. Otherwise it's down to personal choice. I prefer the sharper turn in from the narrower tyre.

Rob