[trikes] Greenspeed GT3 gearing choices.

[Ian Sims]

Hi Fran,
        The standard gearing on the GT3 is 52/42/30 on the front, and 9/26 on the rear.

This gives a range of 20 to 98 inches with the 16 x 1 1/2" rear wheel which has a diameter of 17".

Or 19 to 95 with the early 16" x 1 3/8" rear tyre which had a diameter of 16.5"

The 9/26 cassette is a Shimano Capreo cassette, which is made esp. for bikes with small wheels, and will only
fit a special Capreo hub, or a special hub made to fit the Capreo cassette.

The Capreo cassette has a number of advantages over the standard hub, as fitted say to the GT1, and many other
bikes and trikes, on which the smallest cog that can be fitted is a 11t.

The main one is that it gives a wider gear range, for the number of teeth difference between the largest and
smallest cog.

That is it has a 26/9 x 100 = 289% for a 17 tooth difference. Whereas a common 11/28 cassette will only give a
28/11 x 100 = 256% for a 17 tooth difference. This is important with a small wheel trike, as to use the full
range of gears from one extreme to the other, i.e. small to small and large to large one can use a mid cage
derailleur instead of long cage, if you want to have the chain well clear of the road.

The 9/26 cassette is the only one currently available for the Capreo hub, thus the easiest way of providing
lower gears, is to switch the "road" 52/42/30 triple cranks for a "MTB" 44/32/22 crank set, as we do with our
small frame GT3s.

This will give you 14 to 83 inches, with a wider overall range of 593%, V 490% for the standard gearing.

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.

It is also possible to change some of the cogs on the Capreo cassette for larger ones to give you lower gears,
but this has the same disadvantages as the swapping the rear hub, and using a 11/30, 11/32, or 11/34.

If you were to use a 32 t rear cog with the 52/42/32 crank set, then you lowest gear would only be 
17 inches, so in my opinion the easiest way of getting lower gears is the 44/32/22 crankset.

Yet another way is to change the rear wheel for one with a SRAM DualDrive hub. With an 11/28 cassette, and the
standard 52/42/30 crankset this would give you much wider gear range of 14 to 107, but no lower than the
44/32/22 crankset option.

Some people have also fitted the German Rohloff 14 speed rear hub and the Schulmpf mountain drive.
This gives a very wide range of say 9 to 115 inches with our standard 13/60 gearing. However you will suffer a
small power loss, in the lower gears, of about 10%. For some people this does not matter, whereas others find
it unacceptable. Thus IMO each rider should carefully consider the options before changing....


Regards, Ian
Ian Sims, Director
Unit5/31 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


Message: 1
Date: Fri, 15 Oct 2010 15:11:11 -0400
From: mgta4 at aol.com
Subject: [trikes] Greenspeed GT3
To: trikes at bikelist.org
Message-ID: <8CD3AB3DD897DDA-1C74-21D2 at webmail-m100.sysops.aol.com>
Content-Type: text/plain; charset="us-ascii"

I would like lower gears on my GT3 and was wondering if the largest cog in the rear could be replaced by a
larger one without any problems??? Thanks Fran