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

[John Turvey]

My gear calculations use a wheel diameter of 16.2 inches (which, on 
reflection, is probably for the original tyre the Micro came with, not 
that for the 349 Scorchers) and the CORRECT size for the small 
chainwheel which is 34 teeth, not 40 as I stated (that is the small 
chainwheel on my Trice XXL), which gives a low gear of 17.2 inches - if 
the diameter of the Scorcher is 17 inches, then my low gear is 18.1 
inches and my high gear is 132.6 inches.

There is no way to really re-dish the rear wheel - it is built like a 
rear wheel for an upright, with the drive-side spokes nearer to 90 
degrees from the rim than the off-side spokes. but the clearance 
between the 'seat' stays and the Scorcher tyre is about 3mm on each 
side - any change in dishing would not gain me much.

My clearance problems are with the gear mech when the lower jockey 
wheel is at the 6 o'clock position relative to the wheel - so moving 
the chain idler to the right would not make any difference here as the 
gear mech  and jockey wheel would not be moved to the right.

My gear mech is a Sram X9 medium cage and there is not really enough 
chain wrap as it is - when in the small chainring I have to remember to 
only use the larger rear cogs. - if I forget I am in the small 
chainring and run through the rear gears to the 11 tooth rear cog, the 
rear gear mech folds so far that the chain runs against itself and 
makes lots of noise!

The only thing I have done to increase clearance is to remove part of 
the left hand side of the derailleur cage - the lowest bit when at the 
6 o'clock position, as this is the bit that gets bent and then shreds 
the tyre - - on my original gear mech this bit fell off after several 
bendings, and its absence made no difference to gear changing etc, so 
when I replaced the mech, I removed this bit before using it.

I  do wonder why other trike manufacturers persist with dished wheels - 
the only reason for this is to provide heel clearance on traditional 
upright 2-wheelers - so no reason at all to have dished wheels on 
trikes (or, indeed, on 2-wheel recumbents).

That reminds me - must have another dig at Jason P****** - he got a 2nd 
hand Greenspeed and decided he did not want the hub gears, so had a new 
rear wheel built - only after he installed it did he realise there is 
no need to dish the rear wheel on a Greenspeed!

John Turvey

On Tuesday, October 19, 2010, at 11:49 PM, Ian Sims wrote:

> 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
>
>
>> 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!)
>>
>> John Turvey