Re: Northampton, buying etc

in message <[email hidden]>, PJ

(') said:

In article <[email hidden]>, David Martin

URL: said:

You *don't* need really knobbly tyres. A standard hybrid style tyre
would be fine.

Right. And the knobbly-ness is what makes them unsuitable as road
tyres? Just from a comfort point of view, or are we talking about
significant performance issues too?

About 5% or more on performance, plus noise, plus greatly accelerated
wear, plus considerably reduced grip. There are some reasonable
compromise tyres which have a continuous central ridge with knobbly
shoulders; these run OK on tarmac while still offering reasonable grip
on mud, but they're dodgy on cornering so take that easy.

Basically the better a tyre is on mud the worse it is on tarmac (and, of
course, vice-versa).

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

For office use only. Please do not write or type below this line.

PJ said:

In article <[email hidden]>, David Martin

URL: said:

You *don't* need really knobbly tyres. A standard hybrid style tyre would
be fine.

Right. And the knobbly-ness is what makes them unsuitable as road tyres? Just
from a comfort point of view, or are we talking about significant performance
issues too?

Both. The knobbles don't ride as smoothly (assuming a really aggressive
tyre tread) and take energy to deform to the road shape. They also don't
grip as well. (Grip is determined by the amount of rubber contacting the
road) So they are noisier, grip less well and take more energy to move
*on road*. On hardish paths the same is true though as the mud gets
deeper the treads come into their own.

Quoted message said:

Quoted message said:

The advantage of MTB is that they are cheap and widely available. As
regarding lights, why not use a head torch? It will also be very useful off
the bike.

Aha! Another good idea! I do need something that will illuminate my path, not
just show other people where I am.

The cheap LIDL one is good enough (just) to ride by, but I don't trust
the clip. I have also used the Petzl one. The main problem I found on
towpaths is the security lights of adjacent buildings can dazzle and put
the path into deep shadow.

Quoted message said:

Quoted message said:

A muddy, rigid MTB

Quoted message said:

I was planning to avoid suspension like the plague.

Good idea.

Quoted message said:

Quoted message said:

that looks well worn with obviously home made bodged mudguards will only
require a light lock. A bit of chain and a padlock will be cheaper than a
'proper' bike lock and work just as well.

Okay. This sort of thing had crossed my mind, in a, "who would be desperate
enough to try and nick the sort of bike I can afford?!" sort of way...

Noting that one of my 'talents' is an ability to pick most cheap 'n' cheerful
barrel locks. I read the (not) MIT Lock Picking Guide a long time ago... (:

Quoted message said:

A rack is very useful, great for carrying stuff.

Indeed. I was thinking of fabricating something out of offcut sheel ally
(which is free to me, usually), that I can get a Tescos visit worth of
supplies in. Would be useful. Stability may well become an issue, though. (:

What ever you get, make sure you can demount the bags/baskets easily for
getting through gaps in fences.

Racks are very useful and should be easy enough to scrounge from the
local tip (which may be a good source of bikes.) If you have the right
tools, (and you seem to have the aptitude), trawling police auctions or
the dump would be a good place to get a bike. The rest of the budget can
be spent on Things That Matter, new brakes, new BB, load carrying,
headtorch. If you can find one with a front hub dynamo, so much the better.

Quoted message said:

Thanks again everyone. Responding to each post is a waste of bandwidth, but
your advice is much appreciated - I'm much better off than I was a couple of
days ago... (:

I'm reasonably aware of the bikes on boats scene. My inlaws had a
narrowboat until recently and live next to the K&A near Trowbridge.

...d

"PJ" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Right. And the knobbly-ness is what makes them unsuitable as road tyres?

Just

Quoted message said:

from a comfort point of view, or are we talking about significant

performance

Quoted message said:

issues too?

Knobbles wail like the banshee so are a pain in the ear. They are
inefficient over hard, relatively smooth surfaces so you will need to pedal
harder but most important, they put less rubber onto a hard surface so may
provide less grip. My experience is that they can be particular 'fun' on
wet ironwork (but then any tyre can be).

I would suggest that it is not a question of life and death and that you can
ride with knobblies with care (but again, you need care riding any bike).
If you cannot afford an upgrade yet then wait a bit but make it an early
upgrade. >

Quoted message said:

Quoted message said:

The advantage of MTB is that they are cheap and widely available. As
regarding lights, why not use a head torch? It will also be very useful

off

Quoted message said:

Quoted message said:

the bike.

Aha! Another good idea! I do need something that will illuminate my path,

not

Quoted message said:

just show other people where I am.

Try Lidl and/or Aldi for cheap cycling bits. A light fixed to the bike is a
legal requirement after dark and s also less confusing for a motorist that
an impression of the X-files with a beam sweaping back and forth.
Personally, I would go for the fixed light first.

T

PJ <[email hidden]> wrote in
news:[email hidden]:

Quoted message said:

Err, well - to a point. <snip some interesting stuff>

Part of the reason for knobblies not having as good a grip isn't because of
contact area size. It's because that contact area is on the end of a fairly
flexible piece of rubber connected to the body of the tyre, rather than
being part of the tyre itself. This really only comes into play when
cornering quickly on roads etc. when the knobbles will allow the tyre to
"walk" sideways across the road.

I didn't think this effect was noticeable until I started riding road bikes
again after years of having only a mountain bike. There is a difference,
but then again that feeling may be down to the fatter tyres (even when
pumped up rock hard). I have torn off several knobbles on a rather scary on
road downhill once (scary as in "who put that hairpin bend there -
agghhhh!!!!!"😉

Graeme

PJ said:

Err, well - to a point. Tyre grip is a complex, sometimes counter-intuitive
business, arguably not properly understood by anyone, but only well
understood by very few and I'm not one of them. Writing in Racecar
Engineering, Paul Van Valkenburgh suggested that, "It's possible that all the
increased contact area contributes is better control over the absorption and
dissipation of heat energy. In other words, is it possible that a skinny tyre
would provide the same traction as a wide tyre (of the same compound) for
that brief period when its surface temperature was the same?" He then goes on
to present supporting evidence and to suggest ways in which mechanical tyre
grip may be increased without changing the compound or increasing the size of
the contact patch.

That's for race tyres for car which run very hot - you ever noticed the
tyre heaters while they're waiting to be fitted and the commentator
comments about tyres coming up to temperature after a pit stop.

Quoted message said:

What relevence this has to bikes,

None unless they are motorbikes

Quoted message said:

I don't know, but the primary reason why
knobbly tyres do not grip as well in this context may not be due only, or
even mainly, to the size of the contact patch. I wonder what sort of readings
a pyrometer would give on a bicycle tyre?

Unreadably low unless you have just locked and slid your wheel at speed
to generate friction heating

Tony

PJ said:

Indeed - this issue had occured to me. But I wonder how good fixed lights are
at illuminating the road, or pitch-black path, ahead?

Especially at the legal limit of 2.4W

Tony

"PJ" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Indeed - this issue had occured to me. But I wonder how good fixed lights

are

Quoted message said:

at illuminating the road, or pitch-black path, ahead?

There are lighting systems that can put enough light on the road to turn
night into day -- cheap systems can be had at about 30 quid but the good
ones tend to be above my pay grade :~(

Typically they use a combination of a wide angle 'flood' and a tighter angle
'spot' (flood & spot being very loosely defined here).

An alternative (and more tradition) approach is to mount the lights low --
down on the forks. This puts more light on the road -- but the pool is
relatively small so you do tend to need to go slow enough to react inside
that.

Most of the problem of night cycling is not the dark. If it is dark
relatively little light in the right place is sufficient to light your way.
The problem is that cars and security lights can put so much light into your
eyes that any night vision is destroyed -- suddenly you can see SFA. You
can cycle a country lane with a single glow worm powered Never Ready --
until plonker in a BMW comes at you with mega-joules of lighting energy
without dipping. Suddenly you have no idea where the road, road edge etc
are -- all you can do is aim to the left hand side of the lights and pray.

T

in message <[email hidden]>, PJ

(') said:

As a side question, looking as suspension bikes with motorsport eyes
(and noting that I know next to bugger all about competition
motorbikes, with which bicycle suspension no doubt has more in
common), how much setup and adjustment do serious competition riders
do? You have adjustable damping (seperately for both bump and
rebound?), but what about spring rates and preload? Do the springs get
changed depending on the course conditions?

Most serious cross country racers use air suspension units; this is at
least partly for weight reasons (air is lighter than steel) but also
because air units are much easier to tune. Good units these days have a
very wide range of adjustment. In addition to the things you mention
there is also the issue of pedal bob - the shock needs to react
instantly and smoothly to lumps and bumps in the track without reacting
to the rider's pedalling. Current generation suspension units
increasingly have 'stable platform valves' or equivalent technology
which is intended to tune out the lower frequency pedal bob while still
responding rapidly to higher-frequency movement. In addition suspension
lockout is a common feature (because suspension is not needed and not
beneficial when on smooth hard surfaces) and on-the-fly adjustable
front travel is increasingly common to cope with the different needs of
climbing and descending.

Remember that while the weight of the rider is under 50% of the total
vehicle weight of most sporting motorcycles and under 20% of the total
vehicle weight of most sports cars, it's 85%-90% of the total vehicle
weight of a cross-country mountain bike. Consequently effective
suspension tuning is even more important on mountain bikes than on
motor vehicles.

This is a large part of why good mountain bikes are getting so
expensive.

<URL:http://www.dtswiss.com/index.asp?fuseaction=rshocks.bikedetail&id=3>
<URL:http://www.magura.com/english/frameset/default.htm?http://www.magura.com/english/gabeln/04_federbeine_odinplus.htm~Hauptframe>
<URL:http://www.foxracingshox.com/website/.
\BackOffice\UploadedFiles\OwnersManual\shox_en05.pdf>

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Friends don't send friends HTML formatted emails.

PJ said:

Oh, and as a cycling boater, one thing I *will* be fitting to my bike is an
audible warning device - the number of times I've had to jump out of the way
of cyclists zooming up quietly behind me, devoid of a bell, or even a
shout...

I have been tempted to fit a 3" ships bell ;-) Now that *would* be
different.

...d

PJ said:

In article <[email hidden]>, Tony W

URL: said:

A light fixed to the bike is a legal requirement after dark and s also less
confusing for a motorist that an impression of the X-files with a beam
sweaping back and forth. Personally, I would go for the fixed light first.

Indeed - this issue had occured to me. But I wonder how good fixed lights are
at illuminating the road, or pitch-black path, ahead?

That depends on the lights and the speed at which you are travelling.
I was out last night riding in the dark and wet, and a standard 2.4W
light (OK, the low power side of my SMART) was fine for up to 15mph. You
won't get close to that on a towpath, especially loaded, unless you are
seriously hammering along.

Generally fixed lights work well because they cast a more visible
shadow, making the bumps visible. With a head torch you get very flat
light, so seeing the bumps can be a bit harder. Then again, you could
always ride slower ;-) On a bright moonlit night you could probably get
away with not using lights on the towpath. Obviously that would be
illegal on road.

...d

PJ said:

I haven't done the sums, but my only idea was to ditch the coil
spring in favour of a torsion bar at the point where the rear control
arm (or whatever you call the bit that attaches the rear wheel to the
frame - 'scuse my total lack of appropriate terminology), pivots off
the rear of the frame. This should be lighter than a coil spring,
with the advantage that it could be changed simply by sliding it
sideways out of the pivot assembly, without having to strip the
suspension unit down.

Couple of problems here : first is that the actual spring isn't much weight
at all. All the other gubbins for doing the actual shock absorbtion/damping
would still need to be there.

And don't forget a coil spring is merely a wound up torsion bar.

However, having a flexible bit of metal instead of a bearing at that
location is quite a good idea in some ways - see eg cannondale scalpel IIRC.

BTW Changing the springs in our forks is a completely trivial matter should
we wish to do it. They're held on with two bolts - the forces involved are
much smaller than with cars, and there's no preload to speak of (this
happens with 'sag'.

cheers,
clive

This all starts to get rather technical..

I used to have front suspension on my MTB/commuter (RST231 forks).
They are still on there but have rusted solid (again) and I can't be
faffed to strip them down and fix them. The elastomers got quite a
battering running at -15C.

Any recommendations for cheap, reasonable front sus forks (ideally with
both disk and canti mountings) that have a 1" threaded steerer?

Hmm.. thought not.. Might be better to get a new MTB set up for off road
and swap the front forks on the MTB/commuter for lightweight road ones..

...d

...d

David Martin said:

This all starts to get rather technical..

I used to have front suspension on my MTB/commuter (RST231 forks).
They are still on there but have rusted solid (again) and I can't be
faffed to strip them down and fix them. The elastomers got quite a
battering running at -15C.

Any recommendations for cheap, reasonable front sus forks (ideally with
both disk and canti mountings) that have a 1" threaded steerer?

Hmm.. thought not.. Might be better to get a new MTB set up for off road
and swap the front forks on the MTB/commuter for lightweight road ones..

If you can find some that have a 1" threadless steerer, and beg / borrow
/ steal a threadcutter, you can soon have a set. Keep an eye on eBay.

Jon

David Martin said:

This all starts to get rather technical..

I used to have front suspension on my MTB/commuter (RST231 forks).
They are still on there but have rusted solid (again) and I can't be
faffed to strip them down and fix them. The elastomers got quite a
battering running at -15C.

Any recommendations for cheap, reasonable front sus forks (ideally with
both disk and canti mountings) that have a 1" threaded steerer?

Hmm.. thought not.. Might be better to get a new MTB set up for off road
and swap the front forks on the MTB/commuter for lightweight road ones..

...d

...d

ISTR that Marzocchi will still do a 1" steerer if you contact the
importer. They are also the standard suspension fork and even the cheap
ones are pretty good.

Tony

David Martin said:

This all starts to get rather technical..

I used to have front suspension on my MTB/commuter (RST231 forks).
They are still on there but have rusted solid (again) and I can't be
faffed to strip them down and fix them. The elastomers got quite a
battering running at -15C.

Any recommendations for cheap, reasonable front sus forks (ideally with
both disk and canti mountings) that have a 1" threaded steerer?

Hmm.. thought not.. Might be better to get a new MTB set up for off road
and swap the front forks on the MTB/commuter for lightweight road ones..

...d

...d

ISTR that Marzocchi will still do a 1" steerer if you contact the
importer. They are also the standard suspension fork and even the cheap
ones are pretty good.

Tony

In news:[email hidden],
David Martin <[email hidden]> typed:

Quoted message said:

This all starts to get rather technical..

I used to have front suspension on my MTB/commuter (RST231 forks).
They are still on there but have rusted solid (again) and I can't be
faffed to strip them down and fix them. The elastomers got quite a
battering running at -15C.

Any recommendations for cheap, reasonable front sus forks (ideally
with both disk and canti mountings) that have a 1" threaded steerer?

Hmm.. thought not.. Might be better to get a new MTB set up for off
road and swap the front forks on the MTB/commuter for lightweight
road ones..

Pace ones were availabe with 1" steerer last time I looked, but I guess
they're not cheap.

A