Front wheel traction on a Varna Hand Cycle

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Stradageek
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Front wheel traction on a Varna Hand Cycle

Post by Stradageek »

Hi to all technogeeks

I have a friend with a Varna Handcycle that I maintain for him (see link to picture)

http://www.varnahandcycles.com/hc04.htm

He has a problem with front wheel traction on steep hills.

Does anyone have any clever ideas to help him, note extra weight over the front wheel is difficult to arrange because the wheel flops as it steers (should be clear from the photo).

All suggestions welcome

Cheers

Stradageek
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[XAP]Bob
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Re: Front wheel traction on a Varna Hand Cycle

Post by [XAP]Bob »

Lead lined boots ;)
Can the rear wheels be pushed further back?
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
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notme2
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Re: Front wheel traction on a Varna Hand Cycle

Post by notme2 »

it could be a question of gear ratio

there may be too much torque being given to driving the front wheel causing it to break free

a lower ratio gear will mean more cranking to get the wheel rolling and crawling uphill

it used to be a regular problem with the first generation of front wheel drive cars especially in winter on snow covered hills
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[XAP]Bob
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Re: Front wheel traction on a Varna Hand Cycle

Post by [XAP]Bob »

Spinning in a lower gear is a good policy, and making sure that the cranking action is smooth - I imagine that's bit harder on a hand-cycle, since they tend to be (approximately) a one cylinder engine.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
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squeaker
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Re: Front wheel traction on a Varna Hand Cycle

Post by squeaker »

Try a more grippy front tyre ie soft compound with very compliant carcase? Maybe something suitable from the BMX racing area (if 406 wheel)?
"42"
dakari-mane
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Re: Front wheel traction on a Varna Hand Cycle

Post by dakari-mane »

Not enough weight over the front tyre. Apparently an issue on the Cruzbike recumbents too. I was also going to suggest a tyre with more traction. The longer wheel base ought to work too but I've no idea how you'd go about doing that without making the whole thing too heavy.
Stradageek
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Re: Front wheel traction on a Varna Hand Cycle

Post by Stradageek »

Thanks guys, the tyre issue is difficult as there is very little fork clearance. I've fitted the chunkiest 451 tyre I could find that doesn't foul the fork bridge but maybe lower tyre pressure would help?

The lead lined boots are already in there, my friend has spina bifida so he's already got chunky boots and calipers!

Is there any way to fit electric assist to the rear? It looks tricky especially as the stub axles/wheels have to come off to get the trike in his car. Maybe a motor that runs on the top of the front tyre could add weight and drive together?

Some truly lateral thinking may be needed, maybe I could build some 26" rims onto the rear hubs to tilt the machine forward a bit?
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[XAP]Bob
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Re: Front wheel traction on a Varna Hand Cycle

Post by [XAP]Bob »

Whereabouts are you?

Trying to add anything up front risks badly affecting steering unless there is somewhere on the frame to add it, but then you're just making it harder to go uphill!
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
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squeaker
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Re: Front wheel traction on a Varna Hand Cycle

Post by squeaker »

Stradageek wrote:Some truly lateral thinking may be needed, maybe I could build some 26" rims onto the rear hubs to tilt the machine forward a bit?
Unlikely to have any significant effect - it's where the CoG ends up along the wheelbase that's important, hence Bob's lengthen the wheelbase by moving the rear wheels further away, which puts more weight on the front wheel.

How 'trick' is the front hub? If a standard 135OLN rear then perhaps you could experiment with a wider 406 rim / softer tyre combination?

FWIW I used to find bumpy climbs in the wet on my Raptobike (weight distribution roughly 60/40 F/R) a bit unnerving due to occasional momentary wheel spin :( What weight distribution is there on the Varna (with your mate on it, of course)?
"42"
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[XAP]Bob
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Re: Front wheel traction on a Varna Hand Cycle

Post by [XAP]Bob »

squeaker wrote:
Stradageek wrote:Some truly lateral thinking may be needed, maybe I could build some 26" rims onto the rear hubs to tilt the machine forward a bit?
Unlikely to have any significant effect - it's where the CoG ends up along the wheelbase that's important, hence Bob's lengthen the wheelbase by moving the rear wheels further away, which puts more weight on the front wheel.

How 'trick' is the front hub? If a standard 135OLN rear then perhaps you could experiment with a wider 406 rim / softer tyre combination?

FWIW I used to find bumpy climbs in the wet on my Raptobike (weight distribution roughly 60/40 F/R) a bit unnerving due to occasional momentary wheel spin :( What weight distribution is there on the Varna (with your mate on it, of course)?

It *looks* a bit further back (or rather the rear wheels look further forward)
And the "one cylinder" effect of the hand cranks being in sync rather than out of phase isn't going to help.

Trying to get a belt/chain drive onto a rear wheel might be an interesting challenge (Don't know if the frame could take a reaction arm, so a "standard" front wheel motor could be fitted to one side???)
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
Vorpal
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Re: Front wheel traction on a Varna Hand Cycle

Post by Vorpal »

Stradageek wrote:Is there any way to fit electric assist to the rear? It looks tricky especially as the stub axles/wheels have to come off to get the trike in his car. Maybe a motor that runs on the top of the front tyre could add weight and drive together?


According to http://www.varnahandcycles.com/handcycles.htm they can be fitted with http://ridebionx.com/products/intelligent-mobility/

I might suggest contacting Varna with the problem? They also build custom bikes, so they may already have a solution.
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Stradageek
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Re: Front wheel traction on a Varna Hand Cycle

Post by Stradageek »

Thanks again Guys, Squeaker may be onto something, if I fit a 406 rim I could get a much bigger front tyre and the bike would be geared down a bit too. There's a big hub brake on the front so the spokes are going to be quite short but it may work. GTBM
bobc
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Re: Front wheel traction on a Varna Hand Cycle

Post by bobc »

I doubt that a wider tyre will increase grip at all.
There are electric "friction drives" that might go on the back, there was one in the news recently called "rubbee" or some such, might be worth a google
Stradageek
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Re: Front wheel traction on a Varna Hand Cycle

Post by Stradageek »

Hmm, contradictory advice, should have seen that coming, good thing it adds to the fun!

Can anyone provide hard evidence that a move to a 406 (from 451) rim (giving me more fork head clearance and reducing the gearing a little) then using a wider softer tyre would help, or fail miserably?

And does anyone know if the other suggestion of an electric motor is available in stub a axle version?

Cheers Guys
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[XAP]Bob
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Re: Front wheel traction on a Varna Hand Cycle

Post by [XAP]Bob »

Going 406 and you'll get wider choice of tyres...

A "rear" hub motor could fit, up front as well. There are some stub axle motors sold (I recall researching them for the trike) but I can't cimment on price ot quality.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.
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