Confidence and stability going down hill fast

[Michael Warner]

On Thu, 1 Sep 2005 16:30:50 +0800, BruceA wrote:

> I wish I could go fast down hill! I used to max out at about 72kph on my
> old steel bike, now on the CF TCR1 I cannot manage much more than about
> 68kph pedalling flat out in top gear. The price I pay for being a skinny
> bugger and being able to go fast up hills?

Yep, 'fraid so. At 78kg, I can easily catch the real climbers on the way
down the other side

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[Michael Warner]

On Thu, 1 Sep 2005 15:50:23 +1000, suzyj wrote:

> You're probably just gripping the bars too tight.

I try not to grip the bars at all, except when I need a bit
of leverage while climbing, and even that's only for short hard pulls. I
cup the bars between my fingersjust enough to prevent them from being
wrenched out of my grasp if I hit a pothole, bump etc.

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[Kathy]

Michael Warner wrote:

> On Thu, 01 Sep 2005 10:59:13 +1000, Kathy wrote:
>
>
>>Perfectly rideable fast down hill just not actually all that stable.
>>Its a confidence thing but then it allways is; its just a little more so.
>>
>>The later ones are a lot better (so I am told) Some one figured that
>>maybe tracklike handling was actually best left to track bikes. I love
>>my TCR but its an aquired taste
>
>
> Mine is a large '04 - is that later, even though the back wheel is tucked
> in very tight? I've never felt unstable descending at high speed, and I
> like being able to drop into a corner or twitch around a pothole
> instantly.
>

Yeah thats later.. tho each year they have got a tad more conservative.

Mines an 02/3 and it actually has a ding in the back tube to allow the
back wheel to fit. Its so tight that it wont take some tires and the
paint in the ding is worn away by dirt on the tire.

But realistically the shorter wheelbase mostly effects the effort
required to change direction .. Its rake and trail that affect the speed
of the steering as someone else pointed out. And nothing is wrong
with the bikes. They just aint all that stable. Yours is more stable
than mine. Stability as you point out is a trade off. sometimes you
dont want all that much.

Dave

 

[BrettM]

Peka <[email protected]> wrote in
news[email protected]:

>
> Kim Wrote:
>> IIRR, in motor bike land they use the words, "tank slapper"Well, in
>> this case it would just be a 'head shake'. You don't recover
> from a real tankslapper, you hit the ground and hope you don't slide
> into something solid
>
> In motorcycle design, the 2 factors that affect head shake are rake
> and trail. Trail has already been described. Rake is the angle of the
> forks from vertical. Steeper rake (ie. smaller angle), and/or less
> trail will make the bike really twitchy - rake affects this more than
> trail apparently. More trail gives the front wheel a self-centring
> effect. A bigger rake angle slows down the steering.
>
> I can't see any reason for things to be different on a bicycle, the
> same laws of physics would apply.
>
> With motorcycles, you would typically get a head shake/tankslapper
> exiting a corner under power with a rough road surface (though there
> are also other conditions under which it can happen). Many bikes will
> never exhibit this behaviour as the geometry (rake & trail) is such
> that it just won't happen. Some bikes will only do it if there isn't
> enough weight over the front wheel, or the suspension hasn't been
> setup correctly for the rider's weight and the road conditions.
>
> The typical advice for motorcycle riders is to loose the death grip on
> the 'bars (ie. relax, as has already been pointed out - the chicken
> dance is one I've heard before too ), and make sure your weight is
> distributed evenly or even a little towards the front.
>
> Also, why aren't you pedalling on the descent? I've always loved
> speed, so a descent is a great place to sprint and spin out top gear
>
>
>

If anyone would like to experience a true "tank slapper" I recommend the
Suzuki GSXR750H with the 16"front wheel. Just be prepared to replace
the seat cover after the real clenching moment.

Cheers

BrettM

 

[Resound]

"Peka" <[email protected]> wrote in message
news[email protected]...
>
> Resound Wrote:
>> ....the
>> rider/bike mass ratio is pretty much inverted which could screw things
>> upSure, but I would think the geometry would affect the bike in the same
> way? ie. Steeper rake and less trail on a bicycle would make it quick
> to turn but twitchy?
>
>
> --
> Peka
>

Oh, I'd agree with you there, absolutely.

 

[Resound]

"Michael Warner" <[email protected]> wrote in message
news:[email protected]...
> On 31 Aug 2005 19:59:27 -0700, Bleve wrote:
>
>> Pedalling will make it more stable.
>
> Does it matter whether you're still freewheeling or not?
>
> --
> Home page: http://members.westnet.com.au/mvw

I think (and I'm prepared to be corrected on this) that the idea is that
you're pedalling and therefore shifting weight at a frequency that isn't the
natural occillating frequency of the bike.

 

[Zoom]

BrettM wrote:
> Peka <[email protected]> wrote in
> news[email protected]:
>
>
>>Kim Wrote:
>>
>>>IIRR, in motor bike land they use the words, "tank slapper"Well, in
>>>this case it would just be a 'head shake'. You don't recover
>>
>>from a real tankslapper, you hit the ground and hope you don't slide
>>into something solid
>>
>>In motorcycle design, the 2 factors that affect head shake are rake
>>and trail. Trail has already been described. Rake is the angle of the
>>forks from vertical. Steeper rake (ie. smaller angle), and/or less
>>trail will make the bike really twitchy - rake affects this more than
>>trail apparently. More trail gives the front wheel a self-centring
>>effect. A bigger rake angle slows down the steering.
>>
>>I can't see any reason for things to be different on a bicycle, the
>>same laws of physics would apply.
>>
>>With motorcycles, you would typically get a head shake/tankslapper
>>exiting a corner under power with a rough road surface (though there
>>are also other conditions under which it can happen). Many bikes will
>>never exhibit this behaviour as the geometry (rake & trail) is such
>>that it just won't happen. Some bikes will only do it if there isn't
>>enough weight over the front wheel, or the suspension hasn't been
>>setup correctly for the rider's weight and the road conditions.
>>
>>The typical advice for motorcycle riders is to loose the death grip on
>>the 'bars (ie. relax, as has already been pointed out - the chicken
>>dance is one I've heard before too ), and make sure your weight is
>>distributed evenly or even a little towards the front.
>>
>>Also, why aren't you pedalling on the descent? I've always loved
>>speed, so a descent is a great place to sprint and spin out top gear
>>
>>
>>
>
>
> If anyone would like to experience a true "tank slapper" I recommend the
> Suzuki GSXR750H with the 16"front wheel. Just be prepared to replace
> the seat cover after the real clenching moment.
>
> Cheers
>
> BrettM

I thought of that one earlier but I couldn't remember the model. It was
on "60 Minutes" and all those types of shows. I think if the tyre
pressure wasn't right it turned into a real death machine.

Zoom

 

[Michael Warner]

On Thu, 1 Sep 2005 22:58:45 +1000, Resound wrote:

> I think (and I'm prepared to be corrected on this) that the idea is that
> you're pedalling and therefore shifting weight at a frequency that isn't the
> natural occillating frequency of the bike.

Makes sense. So if you were pedalling backwards, that would still
help. OTOH, the frantic pedalling of the fixie freak might not

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[Michael Warner]

On Thu, 01 Sep 2005 22:20:34 +1000, Kathy wrote:

> Mines an 02/3 and it actually has a ding in the back tube to allow the
> back wheel to fit. Its so tight that it wont take some tires and the
> paint in the ding is worn away by dirt on the tire.

Mine has the ding too, but there's about 8mm clearance to the 23mm Pro
Races on it, and no evidence of wear. Perhaps it's designed to take 25mm
tyres, as shipped on the OCR3. What are the largest tyres you've
used on it?

Just for comparison, the distance from the outer edge of the rim (Mavic
Elite) to the side of the ding is about 27mm.

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[Kathy]

BrettM wrote:

> Peka <[email protected]> wrote in
> news[email protected]:
>
>
>>Kim Wrote:
>>
>>>IIRR, in motor bike land they use the words, "tank slapper"Well, in
>>>this case it would just be a 'head shake'. You don't recover
>>
>>from a real tankslapper, you hit the ground and hope you don't slide
>>into something solid
>>
>>In motorcycle design, the 2 factors that affect head shake are rake
>>and trail. Trail has already been described. Rake is the angle of the
>>forks from vertical. Steeper rake (ie. smaller angle), and/or less
>>trail will make the bike really twitchy - rake affects this more than
>>trail apparently. More trail gives the front wheel a self-centring
>>effect. A bigger rake angle slows down the steering.
>>
>>I can't see any reason for things to be different on a bicycle, the
>>same laws of physics would apply.
>>
>>With motorcycles, you would typically get a head shake/tankslapper
>>exiting a corner under power with a rough road surface (though there
>>are also other conditions under which it can happen). Many bikes will
>>never exhibit this behaviour as the geometry (rake & trail) is such
>>that it just won't happen. Some bikes will only do it if there isn't
>>enough weight over the front wheel, or the suspension hasn't been
>>setup correctly for the rider's weight and the road conditions.
>>
>>The typical advice for motorcycle riders is to loose the death grip on
>>the 'bars (ie. relax, as has already been pointed out - the chicken
>>dance is one I've heard before too ), and make sure your weight is
>>distributed evenly or even a little towards the front.
>>
>>Also, why aren't you pedalling on the descent? I've always loved
>>speed, so a descent is a great place to sprint and spin out top gear
>>
>>
>>
>
>
> If anyone would like to experience a true "tank slapper" I recommend the
> Suzuki GSXR750H with the 16"front wheel. Just be prepared to replace
> the seat cover after the real clenching moment.


H2.. Nothing else will ever come close


>
> Cheers
>
> BrettM

 

[BrettM]

Zoom <[email protected]> wrote in news:[email protected]:

> BrettM wrote:
>> Peka <[email protected]> wrote in
>> news[email protected]:
>>
>>
>>>Kim Wrote:
>>>
>>>>IIRR, in motor bike land they use the words, "tank slapper"Well, in
>>>>this case it would just be a 'head shake'. You don't recover
>>>
>>>from a real tankslapper, you hit the ground and hope you don't slide
>>>into something solid
>>>
>>>In motorcycle design, the 2 factors that affect head shake are rake
>>>and trail. Trail has already been described. Rake is the angle of the
>>>forks from vertical. Steeper rake (ie. smaller angle), and/or less
>>>trail will make the bike really twitchy - rake affects this more than
>>>trail apparently. More trail gives the front wheel a self-centring
>>>effect. A bigger rake angle slows down the steering.
>>>
>>>I can't see any reason for things to be different on a bicycle, the
>>>same laws of physics would apply.
>>>
>>>With motorcycles, you would typically get a head shake/tankslapper
>>>exiting a corner under power with a rough road surface (though there
>>>are also other conditions under which it can happen). Many bikes will
>>>never exhibit this behaviour as the geometry (rake & trail) is such
>>>that it just won't happen. Some bikes will only do it if there isn't
>>>enough weight over the front wheel, or the suspension hasn't been
>>>setup correctly for the rider's weight and the road conditions.
>>>
>>>The typical advice for motorcycle riders is to loose the death grip
>>>on the 'bars (ie. relax, as has already been pointed out - the
>>>chicken dance is one I've heard before too ), and make sure your
>>>weight is distributed evenly or even a little towards the front.
>>>
>>>Also, why aren't you pedalling on the descent? I've always loved
>>>speed, so a descent is a great place to sprint and spin out top gear
>>>
>>>
>>>
>>
>>
>> If anyone would like to experience a true "tank slapper" I recommend
>> the Suzuki GSXR750H with the 16"front wheel. Just be prepared to
>> replace the seat cover after the real clenching moment.
>>
>> Cheers
>>
>> BrettM
>
> I thought of that one earlier but I couldn't remember the model. It
> was on "60 Minutes" and all those types of shows. I think if the tyre
> pressure wasn't right it turned into a real death machine.
>
> Zoom

I don't know about 60 minutes but I have a wonky (easily dislocated)
shoulder after an altercation with a guardrail due to one of these (and
my lack of ability).

But d*mn that bike was fun....

Cheers

BrettM

 

[Zoom]

BrettM wrote:
> Zoom <[email protected]> wrote in news:[email protected]:
>
>
>>BrettM wrote:
>>
>>>Peka <[email protected]> wrote in
>>>news[email protected]:
>>>
>>>
>>>
>>>>Kim Wrote:
>>>>
>>>>
>>>>>IIRR, in motor bike land they use the words, "tank slapper"Well, in
>>>>>this case it would just be a 'head shake'. You don't recover
>>>>
>>>>from a real tankslapper, you hit the ground and hope you don't slide
>>>
>>>>into something solid
>>>>
>>>>In motorcycle design, the 2 factors that affect head shake are rake
>>>>and trail. Trail has already been described. Rake is the angle of the
>>>>forks from vertical. Steeper rake (ie. smaller angle), and/or less
>>>>trail will make the bike really twitchy - rake affects this more than
>>>>trail apparently. More trail gives the front wheel a self-centring
>>>>effect. A bigger rake angle slows down the steering.
>>>>
>>>>I can't see any reason for things to be different on a bicycle, the
>>>>same laws of physics would apply.
>>>>
>>>>With motorcycles, you would typically get a head shake/tankslapper
>>>>exiting a corner under power with a rough road surface (though there
>>>>are also other conditions under which it can happen). Many bikes will
>>>>never exhibit this behaviour as the geometry (rake & trail) is such
>>>>that it just won't happen. Some bikes will only do it if there isn't
>>>>enough weight over the front wheel, or the suspension hasn't been
>>>>setup correctly for the rider's weight and the road conditions.
>>>>
>>>>The typical advice for motorcycle riders is to loose the death grip
>>>>on the 'bars (ie. relax, as has already been pointed out - the
>>>>chicken dance is one I've heard before too ), and make sure your
>>>>weight is distributed evenly or even a little towards the front.
>>>>
>>>>Also, why aren't you pedalling on the descent? I've always loved
>>>>speed, so a descent is a great place to sprint and spin out top gear
>>>>
>>>>
>>>>
>>>
>>>
>>>If anyone would like to experience a true "tank slapper" I recommend
>>>the Suzuki GSXR750H with the 16"front wheel. Just be prepared to
>>>replace the seat cover after the real clenching moment.
>>>
>>>Cheers
>>>
>>>BrettM
>>
>>I thought of that one earlier but I couldn't remember the model. It
>>was on "60 Minutes" and all those types of shows. I think if the tyre
>>pressure wasn't right it turned into a real death machine.
>>
>>Zoom
>
>
> I don't know about 60 minutes but I have a wonky (easily dislocated)
> shoulder after an altercation with a guardrail due to one of these (and
> my lack of ability).
>
> But d*mn that bike was fun....
>
> Cheers
>
> BrettM

I have a few scary motorbike stories, in hindsight I'm lucky to still be
alive. I've banned myself from looking at motorbike magazines in the
newsagents, lest I be tempted.... But I will always love Fred Gassit!
http://www.alphalink.com.au/~mkprasad/mainindex.html

Zoom

 

[BruceA]

"Peka" wrote

What gearing does it have? I hit 65kmh on my MTB the other day
> and I'm sure when my fitness gets better I'll be able to beat that. My
> top gear is 42-11.

Top ratio is 53 - 11 or 12, not absolutely sure.
I guess when I say flat out, it's not as hard as I could absolutely go.
It's still hard work to get to this speed, and I don't think I would go much
faster at max effort. I notice how much harder I have to work on the CF
bike compared to the heavier steel bike to achieve similar speeds (about
4.5kg difference). I do admit that although I love descending as fast as I
can, I also work by the philosophy of saving my energy going down hill so
that I am more refreshed for the next uphill. I think this is a bit of a
survival instinct I developed from growing up in Tasmania! Having said
this, the speeds I referred to are when I decide to see just how fast I can
go down hill.
I don't know just how much difference each extra kilo makes to downhill max
speed, but at 73 kg and on a mountain bike that probably puts you at
something like 13 kg heavier than my combined weight. As I mentioned, I
noticed the difference with only 4.5kg difference!

Mind you, none of this is helping AC with his original post

BruceA

 

[Michael Warner]

On Fri, 2 Sep 2005 09:36:37 +0800, BruceA wrote:

> I don't know just how much difference each extra kilo makes to downhill max
> speed

I imagine terminal speed is determined by your wind drag versus your
weight. Heavier people have a relatively small increase in drag for the
extra weight, esp when get into a tuck.

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[Paulie-AU]

On Fri, 2 Sep 2005 09:36:37 +0800, BruceA wrote:

> I don't know just how much difference each extra kilo makes to downhill max
> speed

I imagine terminal speed is determined by your wind drag versus your
weight. Heavier people have a relatively small increase in drag for the
extra weight, esp when get into a tuck.

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What about wheel profile

LotteBum manages to get a higher speed than myself on the same hill where I actually maintain a higher corner speed than her (we are very similar in overall on the bike weight). All we can put it down to is that she has deep dish shimano wheels whereas I have normal profile rims. Oh and her shimano hubs do roll better than my ritchey ones.

Also, while some bikes may be twitchy, alot of fast decending is about confidence. I once had a friend comment that grip is a figment of your imagination. The majority of times you will make it through a corner at much higher speeds than you would expect. That said I think if you believe you will make the corner you are more likely to be relaxed on the bike and as a result corner faster.

I do find a am a little tentative (as opposed to reckless) in some corners on the road because I am not real keen on finding the absolute limit of my tyres on bitumen. I like my skin connected to me and not the road.

 

[Michael Warner]

On Fri, 2 Sep 2005 15:02:42 +1000, Paulie-AU wrote:

> Also, while some bikes may be twitchy, alot of fast decending is about
> confidence. I once had a friend comment that grip is a figment of your
> imagination. The majority of times you will make it through a corner at
> much higher speeds than you would expect.

Yes, most riders are much too conservative about how tightly they can
corner at a given speed. Me included


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