H: Hubs, Wheels and Tyres 21" Front Wheel

[Albervin]

Would I be correct in assuming that the nearer the mass to the centre of rotation, a lesser gyroscopic effect will be incurred, in other words the brake drums will have a lesser gyroscopic effect than the rim, inner tube, tyre, spoke nipples etc.

Peter, physics was never my strong point. I am more into drugs!! BUT. The mass of the cast iron drums plus steel brake plates as opposed to the steel/alloy rims needs to be taken into account. That will take serious computations that a) I can't recall and b) I don't want to. All I can say is the 21" front wheel on my Rapide is a joy and everone who has ridden it are impressed with the light turning/steering on Australian roads.

 

[Peter Holmes]

Alyn, I am in a similar situation to yourself, with limited knowledge on most subjects, even drugs! but I would have thought that as the brake plates are static while the wheels are spinning, along with all the components fitted to the brake plates, brake shoes, levers, cams etc. none of those will create a gyroscopic effect, only components that rotate will do that.

 

[Albervin]

Alyn, I am in a similar situation to yourself, with limited knowledge on most subjects, even drugs! but I would have thought that as the brake plates are static while the wheels are spinning, along with all the components fitted to the brake plates, brake shoes, levers, cams etc. none of those will create a gyroscopic effect, only components that rotate will do that.

True but it also come to unsprumg weight. As I said, my special topic is drugs so I get a bit waylaid with physics. The brake drums are cast iron and therein is most of the weight. That is why the 8" brakes are not great. The pre-war alloy TT brakes with shrunk in cast iron drums and alloy plates are the best. So Mr Speet missed the boat there.

 

[Peter Holmes]

Of course there is unsprung weight in the front wheel, and it is desirable to reduce that weight where possible, I could defend Vincent Speet's brake design, but I am sure he is more than capable of doing that himself, if he chooses to.

 

[Vincent Brake]

Peter, from my head its the inertia, where the mass is to the raduis, in het kwadraat.
To the power of 2.
The rim and tire do that....

I had one at a time, but it resides now in a display...

Oh and for nice looks, use a new narrower fender.

And in the process get more cooling on the front cylinder head.

Cheers

 

[highbury731]

The thing I can't get my head around is that people who have a 21" front wheel say it handles better, and people with a 19" front wheel say it handles better. So.... can someone explain that?

My tuppence on weight -
rim and tyre weight makes rotational inertia, and affects steering
hub weight makes unsprung mass which affects springing and damping.

 

[bmetcalf]

The 21" fills the fender better! And it makes the speedo very accurate.

 

[erik]

To my mind the difference in the gyroscopic effect between 19 and 21 inch is neglectible because the tyre on the 19 inch is much bigger than the 21 inch tire. There is no real difference in the circumference of a 3,25 -19 and a 3,00-20 and a 3,00-21 tyre. But the heaviest tyre is the 3,25-19. I use the 19 inch rims ,too .In this size there are the most different tires availible.Erik

 

[Bill Thomas]

I watch a lot of youtube,
Off road, Adventure Bikes prefer 21",
But say they are not as good as 19" on the road ?.
Not my thing , Would never go off road, Only by accident .

 

[BigEd]

The 21" fills the fender better! And it makes the speedo very accurate.

My Rapide has a 19" front wheel fitted with an Avon Road Rider. The speedometer gives speed and miles travelled very accurately compared with my Garmin GPS. I guess it is down to the circumference of the fitted tyre being correct for the speedometer and drive gearbox.