I would like to ask a basic question - Why is a large front wheel good for a trailie?

[Rabbitson]

I rode a 650 GS yesterday and it was excellent on the dirt compared to my 1100, but on the tarmac the handling was really slow (because of the large front wheel and the gyroscopics I thought), so it got me thinking 'why is a large front wheel good on a dirt bike?'

 

[CoolCarbon]

Gets over obstacles easier.........

CC

 

[Greg Masters]

So it can roll over bumps more easily?

Greg

 

[Repoman]

Exactly that - try riding a potholed road on a scooter (10" wheels) and then on a 17/19" wheeled bike for conclusive proof..

 

[DrAlf]

I could be wrong here but I would have said that the main advantage of a 21” front wheel is that it slows the steering down giving the rider more time to react to potential “offs”. It also seems that having a 21” front wheel equipped bike enables the rider to ride slower on difficult suffices such as deep sand. I’ve compared my GS (19” front wheel) to an Africa Twin (21” front wheel) on a local byway that consists entirely of deep sand and the Africa is much easier to ride slowly than the GS. The GS needs to be ridden much quicker to feel even remotely stable. I can only assume that the Africa’s larger front wheel offers better gyroscopic forces which help to stabile the bike.

 

[Spout]

A larger diameter wheel will have a greater length of tyre tread in touch with the surface than a smaller one. Hence better grip in mud.
Smaller diameter tend to have to be wider to compensate for this, but then on certain ground they don't penetrate into the ground so well. As the large thin tyre is deeper in the muck the steering feels much safer.

I like 21" wheels, even on the road battling with understeer.

It was also upsetting when the GS rear wheel was reduced to a 17".

Will the 1200 Adv have a 21" front?

 

[The Mechanic]

Throw back....

If you are of an age to remember back as far as me then you will know that older bikes had not much more than 4-5 inches of ground clearance, fine for the road but not much else.

As most Trials and Scramble bikes were mostly cobbled up from road biased bikes one sure fire way of obtaining the necessary higher ground claerance was to fit a larger diameter front wheel so 21 inch rims were laced to the front hubs, whilst at the back 18 inch rims were changed for 19 and so a bit more clearance was obtained. If you look at Sammy Millers Aerial GOV 32 you can almost crawl underneath the engine crankcase with the bike held upright, of course this is one very special bike but it illuminates the big wheel reasoning.

As others have stated the larger diameter was also good for going over deep ruts and log type obstacles, rocks etc. Blimey the Honda XL250 even had a 23 inch front rim (slow steering any one)
Riding at trail bike off road speed and slower nadgery stuff al la Trials sections and you need fairly slow and planted steering, speeded up of course by dammed great wide trials handle bars.

Here endeth the lesson as my fingers are tiring

 

[boundless]

And we really should bring back those....

....goggled flat caps (worn reverso of course) for all future contrapposto japes!

.......GOV 32 you can almost crawl underneath the engine crankcase with the bike held upright, of course this is one very special bike but it illuminates the big wheel reasoning.

[/B]

You say Aerial, I say Ariel.....

You say 32, I say 132:-

But as you say, one special bike!

 

[Rev Chuck]

Was it the bike - or was it the rider?
Sorry for thread hijack, but it seems to me that Sammy Miller could ride just about anything and clear a whole bunch of 'sections'. He was probably just ahead of his time in what he did, and maybe the reason people remember the GOV 132 is that it is a simple reg. OK maybe it was him and the bike...

I don't know the mechanics of why bigger wheels at the front work better for trials and off-road, I just know that I would want a bigger front wheel as possible - with as much grip on the back wheel as you could get, and I didnt't ever think it was due to style.