[trikes] Greenspeed GT3 gearing choices. (John Turvey)

[Ian Sims]

Hi John,
        I was wondering how you came to the gearing range you quoted? By my
calculations you would have a bottom gear of 17x40/32 = 21, and even
16x40/32 = 20. In top I would expect 17x52/11x1.65= 133.

We certainly do not have any chain clearance problems with the Scorcher rear
tyres on the GTs. Maybe you could dish your rear wheel to the left, or/and
move the idler pulley out to the right to improve your chain clearance. Many
trike makers just use standard bicycle practice and dish the rear wheel to
the right, so that the tyre is centered about the dropouts or axle locknuts.
This weakens the rear wheel, and can give chain clearance problems, due to
the longer chain run on a recumbent. Whereas on a trike there is no need to
have the rear wheel on the centre line of the machine, as proven by the
Windcheatah, which runs quite a large offset. Thus you can build the rear
wheel symmetrically about the hub flanges, making it stronger and giving
more chain clearance, provided the frame is built to accommodate the tyre
offset. On a new trike I have built, I've discovered I still have chain
clearance in bottom gear, even with a 2.35" tyre :-)

We are using the Shimano Tiagra rear derailleur on some of the GTs, and
there have been no ground clearance problems with this derailleur. It is not
supposed to cope with larger than a 27 t rear cog, but I've found if the
hanger is long enough there is no real problem with a 32, apart from a bit
more noise in bottom gear...


Regards, Ian

Ian Sims, Director
Unit 5/31 Rushdale Street,
Knoxfield VIC 3180
AUSTRALIA
Phone +61 3 9753 3644 Fax +61 3 9753 4434 Email: ian at greenspeed.com.au Web:
www.greenspeed.com.au  Skype: ian.gs


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Today's Topics:

   1. Re: Greenspeed GT3 gearing choices. (John Turvey)


----------------------------------------------------------------------

Message: 1
Date: Mon, 18 Oct 2010 21:54:18 +0100
From: John Turvey <johnturvey at onetel.com>
Subject: Re: [trikes] Greenspeed GT3 gearing choices.
To: trikes at bikelist.org
Message-ID: <E03A6D55-DAF9-11DF-9D4C-00306566DC3C at onetel.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed


On Sunday, October 17, 2010, at 01:30 AM, Ian Sims wrote (IN PART):
>
> It is also possible to swap out the rear wheel for one with a standard 
> hub which will take say a 11/34
> cassette, but this will require a long cage rear derailleur to use all 
> gear combinations, which could give you
> ground clearance problems on unmade roads, or if you retain the 
> standard mid-cage rear derailleur, you will
> need to remember not to use combinations like small to small, which 
> may allow the chain to drag on the ground,
> or large to large, if the chain is adjusted to tight, when you could 
> damage the rear derailleur.
>

I have an early Trice Micro which uses the same 16 inch wheel as the 
GT3 - it has a standard hub with 11 to 32 cassette, 52 and 40 teeth 
chainwheels and a Speed-drive, giving gears from 17 inches to 126 
inches, and uses a Sram medium cage gear mech.  The clearance below the 
rear gear mech in some gears is minimal - a puncture in the rear wheel 
can mean the clearance is negative (I have replaced the rear mech once 
already as the original was wrecked as a result of punctures on high 
speed descents, and previously had replaced the lower jockey wheel in 
the original rear gear mech).  The other problem I have is that the 
clearance between the tyre and the rear mech is also minimal 
(especially as I use Greenspeed Scorcher tyres which are wider than 
most tyres) - after a rear wheel puncture, the cage on the rear gear 
mech can be bent, so using the lowest gear can quickly shred the side 
wall of the rear tyre (I have done this three times now - I keep 
telling myself to check the gear mech is not bent or misaligned, but 
forget occasionally - only when it IS bent or misaligned!)



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