[trikes] testing suspension trike on rough trail

[Julian Edgar]

Actually, to answer in more detail  the question about using elastomers as
springing media, I don't like them for these reasons:
 
If the wheel travel is to be sufficient, elastomers require high motion
ratios in the suspension (that is, a large wheel travel for a small spring
deflection). This in turn creates problems in terms of gaining spring
linearity over a decent range of wheel travel, and means frame and
suspension arm loads are high (sometimes unbelievably high). It also means
that any change in the spring rate (eg by the elastomer changing its loaded
length) results in a big change in ride height. 
 
Elastomers are also not easily adjusted for change in loads. 
 
On the other hand, elastomers have two major advantages over other
approaches - low cost and light weight. Some elastomers also have internal
damping - but (and it's another story), I'd suggest that this is not very
effective. 
 
I like rolling lip airbags because they are relatively light (lighter than
steel springs, for example); are very easily altered in pressure to maintain
ride height, irrespective of load; have no stiction; are easily used with
low motion ratios; and have a linear rate that becomes non-linear only near
max deflection (a characteristic that works really well). They also don't
need rose-joints either end - ie the spring ends don't need to stay in line
and parallel. 
 
Their disadvantages are high cost (but that depends where you source them!),
the need to hold their length captive, and a higher weight than some other
springing media (eg elastomers). 
 
 
Regards,
 
Julian Edgar
 
 
From: Philip Donahue [mailto:granpita at gmail.com] 
Sent: Monday, 14 December 2009 12:29 AM
To: editor at autospeed.com
Subject: Re: [trikes] testing suspension trike on rough trail
 
You do some remarkable work. What is the empty weight of the trike at this
point?
 
Also, did you consider using an elastomer suspension instead of the oil
shocks? I ask because I have the last ICE Explorer made. I had it done with
the rear suspension which was a Cane Creek shock but all of Trice's new
models use elastomers. 
 
Thanks,
Phil Donahue
Kennersley Point Marina
410.490.0810 Cell
 
 
 
On Dec 13, 2009, at 3:13 AM, Julian Edgar wrote:



Hi Folks,

After about a 9 months' hiatus I am again back on my self-built suspension
trike. (Hiatus due to moving interstate, changing jobs, etc.)

Details on my trike at www.autospeed.com - search under 'Chalky' - there's a
7 part series that covers its full development. Since that series I have
added front dampers to go with the Firestone airbags (I've always used a
rear damper). 

Today I went on a very rough dirt trail that follows the railway line out of
Bungendore (New South Wales, Australia). You can see a pic of the trike on
the trail at
http://i638.photobucket.com/albums/uu102/JulianEdgar/Chalkyontrail.jpg
(with other photos of the trike development at
http://s638.photobucket.com/albums/uu102/JulianEdgar/ )

The photo doesn't really do the trail justice - estimated 15 per cent
ascents, washaways (where creeks have crossed the trail and removed much
dirt, leaving behind rocks), steep descents, one very quick black snake,
some beautiful birds, lots of large rocks as big as a man's fist (fallen
from the railway's ballast), etc.

I rode with about 10-12kg of extra load - 3 litres water, RT40 Arkel
panniers with lunch and Arkel Tailrider with tools.

I was mightily pleased with the trike's performance: no failures, no
punctures (I think the suspension massively protects the tyres), excellent
handling on really treacherous surfaces, excellent ride, appropriate
physical effort. 

My front Watts Link scraped perhaps 5 times (need to look at this) and the
rear derailleur scraped perhaps 10 times (not much I can do with 16 inch
wheels and the required gear range - except use an internal gear hub with
more than the current 3 speeds). One front damper also has a glisten of  oil
on its shaft - perhaps a weep past the seal caused by overly high
instantaneous internal pressures on the really big bumps. 

Did about 10km on really rough dirt and then the return 10km on the (nice
and smooth!) bitumen road. Tomorrow I'll inspect the (prototype) frame for
cracks and abrasions.

Regards,

Julian Edgar


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