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Road Surface

Posted: 7 Nov 2016, 10:15pm
by rmurphy195
I've recently been puzzled by a feeling of instability on some downhill road sections near my home - tried different tyres, different pressures etc. but still have to reduce speed in some cases rather than just let the bike roll (Condor Heritage tourer)

Now I'm wondering about the road surface - I'd be interested in people's opinions from viewing this clip https://www.youtube.com/watch?v=F_L0eku_mIk (but lease ignore the mispelling!)

Re: Road Surface

Posted: 7 Nov 2016, 10:48pm
by eileithyia
Sorry can't spot anything wrong.....

Re: Road Surface

Posted: 7 Nov 2016, 10:57pm
by pete75
So longitudinal ridges on the road , your tyre gets into them and the ridges steer you? Not brilliant if that's the case.

Re: Road Surface

Posted: 8 Nov 2016, 12:07am
by Brucey
it could be the road surface but I also think that perhaps your headset might be binding.

cheers

Re: Road Surface

Posted: 8 Nov 2016, 8:46am
by 531colin
Can you describe how it rides no hands?
As a touring bike it should have relatively stable steering, so that it isn't upset by things like poor road surface, sidewinds, accidental "steering" inputs from luggage, rider looking round, and so on. Riding no hands, touring bikes should be relatively resistant to changing course, more so as speed increases. (On the other hand "sportier" bikes tend to have quicker steering so they change course directly in response to rider input....they also change course much more readily no hands, and are more disturbed by poor surface, sidewinds, etc......apparently, people like this.)
According to the geometry table on Condor's website, the Heritage has 71.5 degree head angle when fitted with the original fork, which is unlikely to give quick steering, although its always nice when they also quote the fork offset.

Re: Road Surface

Posted: 8 Nov 2016, 10:00am
by reohn2
I don't think we have enough information to draw any conclusions as to whether it's bike,rider or road surface.
The bike needs to be checked over for faults,steering,wheels,spokes slack,bad tyre seating on the rim(s),etc, and in extremis frame alignment or fractures that only show up at higher speeds,etc,etc.
Is the rider a confident descender?tension in the rider isn't helpful on bad road surfaces.
Does the road have any bad defects,such as ridges,troughing,chip n seal overlaps,diesel spills,etc.

As has been posted above the video doesn't show anything noticeable.

EDITED for typos.

Re: Road Surface

Posted: 8 Nov 2016, 10:14am
by Brucey
FWIW what I thought I saw in the video was that towards the end, the speed seemed a fair bit less and the bike seemed to wander on the road a fair bit more.

The road surface looked pretty rubbish for sure, with longitudinal ridges perhaps, but when a bike wanders like that at lower speeds (if this indeed is the case..?) this can signify a binding headset. At higher speeds the trail force is greater and sticky head bearings are often less evident.

As Colin suggests, riding no-hands (on a good surface) can show if all is well or not, even if it doesn't show exactly what the problem is.

cheers

Re: Road Surface

Posted: 9 Nov 2016, 5:21pm
by rmurphy195
Thanks for the info all -

Speed was between 25 - 30mph, no crosswind in this case. It's the same "tram-lining" feel that I get sometimes with the car on very pronounced raised lines when the alignment needs adjusting (or when using summer tyres in the winter!) - slowed down to about 20mph to regain stability.

On the video - it doesn't show the bike wandering as such, I put it up simply to try and show the road surface - changes of direction are mainly to keep clear of the worst of the road ridges!

Riding no hands - not confident enough for that , thanks! (I'm very much of the "look dad no hands/look dad no teeth" school, comes of seeing other kids coming a cropper in my yoof, later showing off their broken jaws!)

I've rechecked the headset and while it turns smoothly it isn't quite as free as, for example a wheel bearing, so will try adjusting the pre-load a tiny bit and see what happens. (Excellent advice on road.cc for this!)

Cheers all - Richard

Re: Road Surface

Posted: 9 Nov 2016, 5:59pm
by 531colin
You might do better by stripping and greasing the headset......the bearing pre-load can't spontaneously increase itself.
The reluctance to ride no hands is widespread, but I don't understand it. Working in the bike trade, you have to asses customer's bikes, and a 5 minute spin round the block with a burst of hands off riding tells you more about the bike's alignment than a long session with straight edges, plumb-lines and stuff.

Re: Road Surface

Posted: 9 Nov 2016, 6:52pm
by mercalia
what about on road surfaces NOT like the example? The ridges only seemed bad for the first few seconds, towards the end the road didnt seem that bad.

u dont say what wheels and tyres, if they are narrow then understandable

I hate ridged surfaces on my motor bike also.

also 25-30mph is rather fast for a bike?

Re: Road Surface

Posted: 9 Nov 2016, 9:34pm
by Giles Pargiter
[quote="...also 25-30mph is rather fast for a bike?[/quote]

Only if going up a hill :D

Re: Road Surface

Posted: 10 Nov 2016, 5:21am
by tim-b
Hi
mercalia said
also 25-30mph is rather fast for a bike?


My thoughts too. Your weight distribution on the bike might be starting to cause instability on a poor surface at those speeds, and the natural tendency is to sit up and back to enjoy the view...

Regards
tim-b

Re: Road Surface

Posted: 10 Nov 2016, 6:52am
by 531colin
In the normal course of events, stability increases with speed. (as Brucey hints, physics is at work to centre the steering.....the force is tyre drag, which increases with speed, the lever is "trail" or "caster" https://en.wikipedia.org/wiki/Bicycle_and_motorcycle_geometry
There are exceptions; shimmy or speed wobble can occur when the resonant flexing frequency of the frame is the same as the revolutions of an unbalanced wheel, or flapping of loose luggage. We should bear in mind that a mechanical/structural problem which doesn't manifest at low speed could show itself at high speed, but I can't think of an example just now.

Re: Road Surface

Posted: 18 Nov 2016, 8:32pm
by NATURAL ANKLING
Hi,
Been discussed to death before about steering, I read the other day that it might have been a Raleigh also, that the steering was made lively so that when laden it did not feel like a tank.

My Raleigh Randoneur 708 even when loaded still feels nippy.
531colin did remark that the steering was bit quick for a tourer, my bike.

Re: Road Surface

Posted: 18 Nov 2016, 11:08pm
by CREPELLO
If the phenomenon occurs only on the stretch of road referred to, then yes, it may be some combination of road and bike. If it occurs on other stretches of road, then it cannot really be that the highlighted road surface at fault.

Is the bike twitchy in general, or predictable and steady?

My Hewitt Cheviot was a problem for a while. Although general handling loaded or unloaded was just fine, annoyingly whenever I hit a stretch of smooth, newly laid tarmac when riding fully loaded, The bike would shimmy somewhat. No problem unloaded.

Finally, I tightened up the front spokes a bit more (this was after a previous wheelset that exhibited the same problems on two different rims!). The shimmy is now gone. YES!