Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

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Brucey
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Brucey » 21 Aug 2019, 12:01am

well yes, except that the suggested rule would only have any benefit for large wheeled bikes and the whole argument is predicated on assumptions about positions of CoGs and coefficients of tyre friction.

Motorcyclists can buy machines which can lock the front wheel (even bolt upright in the dry) because of the weight distribution and/or 'life before grip' tyres. These machines are (quite rightly) avoided by folk who wish to ride quickly and are only safe in the hands of less experienced riders if they are combined with an ABS system.

Any machine which only just lifts the rear wheel under hard front braking (in the dry, upright) will push the front if

a) more rear load is added (many bikes have rear carriers and are designed to take a rear load)
b) the tyre has less grip for some reason ( even wet roads might do it)
c) the bike isn't quite upright when the brakes are used

IME losing the front wheel on the brakes is the fastest way of having a bad accident. I'm sure that there is some scope for improving matters but you run the risk of mking a bike which is 10% better 90% of the time and 100% worse 10% of the time...?

cheers
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Bmblbzzz » 21 Aug 2019, 9:42am

@CJ: We don't pay you but we do appreciate you (and always have done).

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CJ
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby CJ » 21 Aug 2019, 9:29pm

Brucey wrote:well yes, except that the suggested rule would only have any benefit for large wheeled bikes and the whole argument is predicated on assumptions about positions of CoGs and coefficients of tyre friction.

Motorcyclists can buy machines which can lock the front wheel (even bolt upright in the dry) because of the weight distribution and/or 'life before grip' tyres. These machines are (quite rightly) avoided by folk who wish to ride quickly and are only safe in the hands of less experienced riders if they are combined with an ABS system.

Any machine which only just lifts the rear wheel under hard front braking (in the dry, upright) will push the front if

a) more rear load is added (many bikes have rear carriers and are designed to take a rear load)
b) the tyre has less grip for some reason ( even wet roads might do it)
c) the bike isn't quite upright when the brakes are used

IME losing the front wheel on the brakes is the fastest way of having a bad accident. I'm sure that there is some scope for improving matters but you run the risk of making a bike which is 10% better 90% of the time and 100% worse 10% of the time...?

I have never ridden a motorcycle, so I won't comment on that, but it seems that Brucey perhaps does not ride a tandem. A tandem is, I think, a better example (than a motorcycle) of a machine very much more like a solo bicycle, but with its front wheel further ahead of its centre of gravity.

For those who do not ride a tandem, let me assure you that 'taking a header' is something one does not worry about, not at all! It may be possible to make a tandem cartwheel end-over-end (I believe there is a picture somewhere of a track-racing tandem flying upside-down halfway through such a manoeuvre after blowing a front tyre, from the time before UCI banned tandem track racing as too expletive-deleted dangerous!), but it requires something more radical than the application of any front brake that I've ever handled! Basically, given a good enough front brake and a dry road, a tandem can easily out-brake a solo. And yes, on a wet road (never mind an icy road), one can skid the front wheel of a tandem. I've done it once, one rainy night in Ely when a car pulled out in front. I lost contact with the pedals, but nevertheless let the brake off quick enough to keep the tandem flying straight and level, rubber-side down, and missed the car too! I learned a lot from that experience. The longer wheelbase of a tandem means you can do a much more with the rear brake before the back end skids and when it does it doesn't bother the pilot very much. You soon learn to use that brake a lot more whenever the road is not clean and dry.

A tandem is an extreme example, but tandems don't have a special problem with front wheel skids - ask any tandemist. For a less extreme example of a bike with it's C-of-G further behind the front wheel, take a touring bike with nice, big, heavy rear panniers. I really like riding downhill on my loaded touring bike, much more than my unladen audax bike. Why? Because with all that ballast holding the back wheel down I know I can stop it quicker without risk of performing a somersault. So paradoxically, I can go faster downhill in comparative safety. And my audax bike already has its front wheel further ahead of the bottom-bracket than most of my clubmates' road bikes, which may be one reason I descend faster than most of them and on a couple of occasions have dramatically out-braked one or two (who've gone sailing by...) when something untoward happened ahead!

So no Brucey, I'm not convinced there are ANY downsides to having the front wheel a bit further in front of the C-of-G. To convince yourself of that, think about what you do when you fear you might have to stop quick down a steep hill. This is what I do: I get low and slide my bum as far back off the saddle as I dare before fear of snagging my marriage tackle says this far and no further! I do that and I'm sure you do it too, in an attempt to get your CofG as far behind the front wheel as you can. At this moment, would you not like to be able to get a little bit further back? That's what you get if your front wheel is a bit further forward in the first place. Honestly now: what's not to like?
Chris Juden
One lady owner, never raced or jumped.

pete75
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby pete75 » 21 Aug 2019, 11:42pm

Brucey wrote:Motorcyclists can buy machines which can lock the front wheel (even bolt upright in the dry) because of the weight distribution and/or 'life before grip' tyres. These machines are (quite rightly) avoided by folk who wish to ride quickly and are only safe in the hands of less experienced riders if they are combined with an ABS system.

cheers

I used to have a Kawasaki GPZ900 back in it's heyday. It would easily lock the front wheel if the brakes were misused. Most people who bought the GPZ900 wanted to ride quickly including the riders who finished in the first three places in the 1984 production TT.

Brucey
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Brucey » 22 Aug 2019, 12:03am

I've owned and ridden tandems for 30-odd years. If you are very quick you will get away with a small front slide where you might not with a solo; tandems just don't change direction that quickly, and this (thankfully) includes falling over. They are something of a special case because you (in the captain's seat) are right over the front wheel but the CoG is somewhere behind you; this is a highly usual state of affairs on a two wheeler. So is the polar moment. I don't think there is that much that translates directly to riding solos TBH.

Years ago I got interested in the handling of two-wheelers with suspension (mainly motorcycles and mountain bikes) and dug into things like anti-dive technologies. On the face of it there is something to be gained by using an anti-dive approach; many attempts have been made at coming up with a steering system that dives less on the brakes, and/or has less friction than exists in sliding fork stanchion bushings. Turns out all the alternatives have problems too, and some of the changes that accompany dive in tele forks (stiffening of the front suspension spring rate once the suspension compresses, the changes in the CoG position due to 'squat', the changes in the trail geometry of the steering etc) were not just things that folk got used to, they were actually beneficial too. All the theories in the world and all the (many) attempts to make something 'better' than a tele fork count for nought in the world of racing; its either faster or it isn't. Teles still rule the racetrack and the reason is that they are the least bad compromise. So it is with weight distribution; racing motorcycles are always set up so that they will do stoppies in the dry, well before the front wheel locks up. Nonetheless as soon as it starts to rain, the same bikes need fairly major changes if they are not to lock the front wheel very easily on the brakes.

I've lost the front on the road (in the wet on a MTB with a fairly long wheelbase) and I don't ever want to do it again. It was the fastest accident I've ever had; I basically landed on my head and it all happened so fast I still had my hands on the handlebars. when I hit the deck. In other prangs, time seems to slow down enough that you often have a chance to notice things on the way down; but this doesn't happen if you lose the front.

I mentioned before I agree there is some scope for improvement along the lines you propose but I don't think there is that much room for improvement. Suppose you increased the maximum brake power by 10% before the rear wheel lifted; great! Except that now you are not over the front wheel any more and you can't feel so well what is going on, and anyway most people don't fully utilise the brake power they have available at present. Its worth asking 'why not' and 'what will make the biggest difference to stopping distance anyway?' The second one is easiest to answer; it is getting the brakes on to something like full power as soon as possible; any delay just results in you carrying on at full speed that bit longer. The first thing is mostly about confidence. The closer you are to locking the front when you take a handful, the less confident you will (or should) be. Both things are affected by 'cold bite' in the brakes; brakes that don't work consistently degrade confidence and brakes that don't have good cold bite seriously affect stopping distance; after one or two hard stops you will realise that you don't have time to back off the brake and save yourself from a brake that 'comes on' by itself and the result is that you have another reason not to brake as hard as you could do initially.

The numbers don't necessarily work out as you might expect them to. For sake of argument lets suppose that you are doing 10m/s and the bike will do a 1G stop (but it is limited by weight distribution, and the tyre has enough grip to allow a harder stop if required). Lets suppose that the target is a linear stop of 1G. The whole stop takes 1s and the distance travelled is 5m. In the first 0.5s the distance travelled is 3.75m and in the second 0.5s the distance travelled is 1.25m. If it takes 0.5s for the brake to 'come on' because the cold friction coeff isn't as good as the hot friction coeff, too bad; you might start at 0.6G and after half a second be (suddenly, say) up to 1G but you are already in trouble; instead of travelling 3.75m in that first half a second you have travelled about 0.5m further than that, and it will still take 0.7s more to come to a full stop during which time you will travel about another 2.6m or so. Thus the whole stop takes just 0.2s longer but you travel almost 2m further. If it takes (say) 0.5s to realise that you are not braking as hard as you could do and you can increase the brake power that's too bad; its too late again, in much the same way.
However if you look at the maximum benefit you might get from (say) a 1.1G stop then you might shorten your stopping distance by ~0.5m i.e. to ~4.5m. In other words if the change to the bike might mean less confidence and/or less powerful initial braking, it takes relatively little of this to outweigh any potential gains there might be.

The things that really help you to stop quickly are the things that let you get the brake on fully as quickly as possible; good cold bite and plenty of confidence.

So put it this way, if you have the choice of brakes that you can apply fully, with confidence, and that immediately slow you down with as much deceleration as they will manage, they might be preferable to brake that are nominally a bit more powerful but that you can't (initially) so confidently apply fully.

So yes, there is something to be gained for sure, but there is plenty that might be lost as well. If you are more remote from the front wheel and you know that it can more easily lock up if you run over a wet leaf or a bird poop or something, you just won't want to apply the brakes hard to start with; this can make far more difference than an increase in the maximum brake power will, unless you can definitely use it all the time.

If you manage to move the front wheel out or the CoG back far enough to make your bike prone to locking up the front when it is slightly damp and/or when you have a slightly greater rear load than normal, this would be a complete disaster.

Another thing to ponder is the type of accident you are going to have when it all goes horribly wrong. Given the choice between flipping over the handlebars/car bonnet and losing the front during braking, I'll take my chances with the former.

cheers
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Tigerbiten
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Tigerbiten » 22 Aug 2019, 3:12am

The main reason I ride a recumbent trike is because with only one hand there's no easy way to set the brakes up on a bike.
I'd either have to use one lever to work both brake. Which is fine in the dry but a very iffy in the wet due to the risk of the front wheel skidding.
Or try and fit twin levers on a single bar, which is possible but not simple and/or cheap, so that I can balance the brakes front/back as needed.

On the bent trike, I can slam the front brakes on and not worry about going over the top.
On good dry tarmac and with new brake pads it's just possible to bunny hop the back wheel a few inches off the ground.
But it's more normal to just skid both front wheels.
In all my time on the trike, I've never had a skid/spin because one front wheel has locked up and is skidding and the other isn't while the back wheel also skidded.
Unless I've gone out in icy weather and tried to do just that ........ :D
The back wheel on a tadpole trike has so little weight on it that trying to only use it to stop quickly tends to just skid the wheel.
So I've set mine up with a friction lever so I can mainly use it as a parking/drag brake, not as a stopping brake.
The only time I've seriously used it to stop me was when the front brakes froze in icy weather.

Luck ......... :D

Brucey
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Brucey » 22 Aug 2019, 12:35pm

FWIW I recently met a chap with a fairly new ICE trike. He'd had one before with 70mm SA drum brakes but with this new machine he went for 90mm SA brakes.

These brakes were not yet bedded in but the tyres were grippy and the brakes were so powerful that he could very easily lift the rear wheel, whereas it had been a struggle with the 70mm brakes, he'd said. I'd imagine that the 90mm brakes would be deemed 'too powerful' by most folk with normal hand strength.

cheers
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The utility cyclist
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby The utility cyclist » 23 Aug 2019, 12:32am

CJ wrote:And in reply to the suggestion that the Audax and/or Touring bike is dead (sorry, but I don't visit here often nowadays), I would say that it's more like the roadies have come around to our way of thinking! For now they are adopting bicycles they call road bikes or gravel bikes that have tyres of similar breadth to that which we always held to be optimum for audax or touring respectively! And since UCI were dragged kicking and screaming into acceptance of disc brakes, these road and gravel bikes do not have any reason to skimp on tyre/frame clearance. Yes, there is often room to fit a proper mudguard!

The one area (apart from gears, still stupidly high on all off-the-shelf bikes) where the roadie still has to learn some common sense is front centres. There is no good reason for this dimension to be so short as it remains on a modern road bike, to the detriment of basic road safety. A bicycle already has a worse braking performance than almost every other vehicle on the road, not because its brakes are bad (nowadays they aren't) but because its centre of gravity is high in relation to its wheelbase, so it tips over forward before it slides. The roadie's obsession with a short wheelbase thereby runs counter to basic road safety. A modest lengthening of the front would do no harm and some good to the all-round performance of the bicycle. It would still tip over before sliding, but at a quicker rate of deceleration. If the UCI are really interested in safety they should legislate on that. A simple rule that the tyre miss the rider's toe by at least 1cm would make bikes that can be raced faster in safety and that Joe Public can fit a mudguard onto without kicking it to bits - or worse!


You should get out the shed watch some modern cyclists who are braking very hard and locking up, they certainly aren't tipping forward before sliding, I've ridden some decent quality short wheelbase racing frames and I've never launched forward before the wheel locked up and induced a skid (which you can easily do on rim and disc). Maybe you think that that ridiculously rare occasion of being thrown over the bars is worth a much worse handling bike, I certainly don't and neither do those who race for a living or for sport.

But out of interest how many roadies have been launched over their bars in pro racing for instance, say in the last 30 years? How many would have been launched off a sheer drop because the geometry you think is a big safety feature meant not being able to get arund tight bends at speed, and why the hell would you want mudguards on an out and out racing frame? :?
Or are you talking about absolute noobs who grab a massive handful of front brake with no finesse whatsoever locking the front wheel up and given their inexperience would crash a wheelbarrow in the back garden?

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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby PH » 23 Aug 2019, 1:55am

CJ wrote:And in reply to the suggestion that the Audax and/or Touring bike is dead (sorry, but I don't visit here often nowadays), I would say that it's more like the roadies have come around to our way of thinking! For now they are adopting bicycles they call road bikes or gravel bikes that have tyres of similar breadth to that which we always held to be optimum for audax or touring respectively! And since UCI were dragged kicking and screaming into acceptance of disc brakes, these road and gravel bikes do not have any reason to skimp on tyre/frame clearance. Yes, there is often room to fit a proper mudguard!

In reply to what? Has someone said touring bikes were dead? What I said was
IMO the traditional Audax bike is dead, you can get bikes that do everything they do without the tyre size restriction.

Which is pretty much what you've repeated, except I did it without the tribalism.
And who's this "we" who've always know the optimum width tyre for Audax and what is that? I've long considered 32mm tyres to be the right balance for the Audax I've ridden. Yet none of the Audax bikes I've seen reviewed in Cycle over the years can take that.

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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Carlton green » 23 Aug 2019, 10:00am

I haven’t read the whole thread but rather the last few posts.

I would comment that whilst the height of the combined centre of gravity is important to braking so is its horizontal distance behind the front wheel. There is a turning moment about (centred on) the front tyre’s contact point with the road, a low centre of gravity assists in the bike not turning over and so does one way behind the front wheel contact point.

Weight is shared between the wheels in proportion to their distance from the centre of gravity and the direction of deceleration forces. Weight ‘shifts’ to the front wheel during deceleration. Due to the height of the c go g weight also shifts towards the front wheel when going down hill. To avoid the front tyre skidding you need both weight on it and a suitably heigh coefficient of friction, different tyres will make an important difference to friction as will road conditions. I used to know the physics well but no longer work with it. Here we have a compromise, to keep weight on the front wheel (to stop it skidding) you need it near the centre of gravity but to stop the bike tipping over part of what you need is a c of g well back from the front wheel’s contact point with the road.

I can’t recall ever having had a front wheel skid but whilst I ride with care (generally slow and mindful of surface grip) I do seem to recall the back lifting at very slow speeds. When coming down hills I too push my weight both back and low; in part that’s to put weight onto the back brake whose wheel doesn’t have enough weight on it to stop the brakes locking it (that is if you have decent brakes rather than the basic side pulls on my utility bike) and in part that’s to lower the turning or tipping moment about the front wheel’s contact point with the road.

Of the two disasters I’d prefer to skid than flip, but I’d have thought it sensible to avoid both. (In day to day riding I’m more concerned with the front end simply breaking away whilst I corner, grippy tyre’s and weight on the front helps providing the road surface is good.) I try to seek out reasonably ‘good’ types and if either tyre has worn tread then I aim to have the best tyre on the front wheel. When I have the pick I prefer to have plenty of toe clearance ....... but bikes are a mix and series of compromises.

I hope that the above helps.
Last edited by Carlton green on 23 Aug 2019, 2:10pm, edited 5 times in total.

pwa
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby pwa » 23 Aug 2019, 10:11am

I love it when you talk physics.

My nightmare braking situation is when on a narrow, very steep descent you find a wash of sand, grit or gravel across the road on a tight bend, under which circumstances I have had both wheels locked up together and the bike drifting across the road at 5mph with no sign of being able to come to a halt. It has never seemed likely that any change of brakes or tinkering with geometry might help. It could be that an extreme form of tyre might help (very soft and wide) but I'm not even sure about that. The best tactic is to see the dodgy road surface soon enough and get off.

I once had such a change of underwear moment on this bend.
https://www.google.com/maps/@51.8286023 ... 6?hl=en-GB
Gravel across the width of the road.
Last edited by pwa on 23 Aug 2019, 10:24am, edited 2 times in total.

Carlton green
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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Carlton green » 23 Aug 2019, 10:22am

pwa wrote:
The best tactic is to see the dodgy road surface soon enough and get off.


Definitely agree with that. :D

If it’s too steep to climb or to too steep to safely descend - or otherwise dodgy - then get off and walk.

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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby hondated » 23 Aug 2019, 2:41pm

Brucey wrote:I've owned and ridden tandems for 30-odd years. If you are very quick you will get away with a small front slide where you might not with a solo; tandems just don't change direction that quickly, and this (thankfully) includes falling over. They are something of a special case because you (in the captain's seat) are right over the front wheel but the CoG is somewhere behind you; this is a highly usual state of affairs on a two wheeler. So is the polar moment. I don't think there is that much that translates directly to riding solos TBH.

Years ago I got interested in the handling of two-wheelers with suspension (mainly motorcycles and mountain bikes) and dug into things like anti-dive technologies. On the face of it there is something to be gained by using an anti-dive approach; many attempts have been made at coming up with a steering system that dives less on the brakes, and/or has less friction than exists in sliding fork stanchion bushings. Turns out all the alternatives have problems too, and some of the changes that accompany dive in tele forks (stiffening of the front suspension spring rate once the suspension compresses, the changes in the CoG position due to 'squat', the changes in the trail geometry of the steering etc) were not just things that folk got used to, they were actually beneficial too. All the theories in the world and all the (many) attempts to make something 'better' than a tele fork count for nought in the world of racing; its either faster or it isn't. Teles still rule the racetrack and the reason is that they are the least bad compromise. So it is with weight distribution; racing motorcycles are always set up so that they will do stoppies in the dry, well before the front wheel locks up. Nonetheless as soon as it starts to rain, the same bikes need fairly major changes if they are not to lock the front wheel very easily on the brakes.

I've lost the front on the road (in the wet on a MTB with a fairly long wheelbase) and I don't ever want to do it again. It was the fastest accident I've ever had; I basically landed on my head and it all happened so fast I still had my hands on the handlebars. when I hit the deck. In other prangs, time seems to slow down enough that you often have a chance to notice things on the way down; but this doesn't happen if you lose the front.

I mentioned before I agree there is some scope for improvement along the lines you propose but I don't think there is that much room for improvement. Suppose you increased the maximum brake power by 10% before the rear wheel lifted; great! Except that now you are not over the front wheel any more and you can't feel so well what is going on, and anyway most people don't fully utilise the brake power they have available at present. Its worth asking 'why not' and 'what will make the biggest difference to stopping distance anyway?' The second one is easiest to answer; it is getting the brakes on to something like full power as soon as possible; any delay just results in you carrying on at full speed that bit longer. The first thing is mostly about confidence. The closer you are to locking the front when you take a handful, the less confident you will (or should) be. Both things are affected by 'cold bite' in the brakes; brakes that don't work consistently degrade confidence and brakes that don't have good cold bite seriously affect stopping distance; after one or two hard stops you will realise that you don't have time to back off the brake and save yourself from a brake that 'comes on' by itself and the result is that you have another reason not to brake as hard as you could do initially.

The numbers don't necessarily work out as you might expect them to. For sake of argument lets suppose that you are doing 10m/s and the bike will do a 1G stop (but it is limited by weight distribution, and the tyre has enough grip to allow a harder stop if required). Lets suppose that the target is a linear stop of 1G. The whole stop takes 1s and the distance travelled is 5m. In the first 0.5s the distance travelled is 3.75m and in the second 0.5s the distance travelled is 1.25m. If it takes 0.5s for the brake to 'come on' because the cold friction coeff isn't as good as the hot friction coeff, too bad; you might start at 0.6G and after half a second be (suddenly, say) up to 1G but you are already in trouble; instead of travelling 3.75m in that first half a second you have travelled about 0.5m further than that, and it will still take 0.7s more to come to a full stop during which time you will travel about another 2.6m or so. Thus the whole stop takes just 0.2s longer but you travel almost 2m further. If it takes (say) 0.5s to realise that you are not braking as hard as you could do and you can increase the brake power that's too bad; its too late again, in much the same way.
However if you look at the maximum benefit you might get from (say) a 1.1G stop then you might shorten your stopping distance by ~0.5m i.e. to ~4.5m. In other words if the change to the bike might mean less confidence and/or less powerful initial braking, it takes relatively little of this to outweigh any potential gains there might be.

The things that really help you to stop quickly are the things that let you get the brake on fully as quickly as possible; good cold bite and plenty of confidence.

So put it this way, if you have the choice of brakes that you can apply fully, with confidence, and that immediately slow you down with as much deceleration as they will manage, they might be preferable to brake that are nominally a bit more powerful but that you can't (initially) so confidently apply fully.

So yes, there is something to be gained for sure, but there is plenty that might be lost as well. If you are more remote from the front wheel and you know that it can more easily lock up if you run over a wet leaf or a bird poop or something, you just won't want to apply the brakes hard to start with; this can make far more difference than an increase in the maximum brake power will, unless you can definitely use it all the time.

If you manage to move the front wheel out or the CoG back far enough to make your bike prone to locking up the front when it is slightly damp and/or when you have a slightly greater rear load than normal, this would be a complete disaster.

Another thing to ponder is the type of accident you are going to have when it all goes horribly wrong. Given the choice between flipping over the handlebars/car bonnet and losing the front during braking, I'll take my chances with the former.

cheers

Just a quick point Brucey. BMW motorcycles seem to have solved this problem as my GS1200 does not dive when braking and in fact after selling one GS and buying another I brought a Honda and I couldn't sell it quickly enough because of the way it cornered.

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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby pete75 » 23 Aug 2019, 3:04pm

hondated wrote:Just a quick point Brucey. BMW motorcycles seem to have solved this problem as my GS1200 does not dive when braking and in fact after selling one GS and buying another I brought a Honda and I couldn't sell it quickly enough because of the way it cornered.


The BMW telelever front suspension gives superb handling and road holding, little dive on braking and remains very stable in cross winds. I'd choose it over telescopic forks anyday. What works best on the racetrack isn't always what works best on the road.

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Re: Audax Bike (Spa?) with Tourer Gearing & Double vs. Triple

Postby Bmblbzzz » 23 Aug 2019, 3:36pm

pwa wrote:I love it when you talk physics.

My nightmare braking situation is when on a narrow, very steep descent you find a wash of sand, grit or gravel across the road on a tight bend, under which circumstances I have had both wheels locked up together and the bike drifting across the road at 5mph with no sign of being able to come to a halt. It has never seemed likely that any change of brakes or tinkering with geometry might help. It could be that an extreme form of tyre might help (very soft and wide) but I'm not even sure about that. The best tactic is to see the dodgy road surface soon enough and get off.

I once had such a change of underwear moment on this bend.
https://www.google.com/maps/@51.8286023 ... 6?hl=en-GB
Gravel across the width of the road.

I know that place! As for the gravel on a bend situation, I tend to assume that on twisty narrow downhills – the kind of road in the link – there is bound to be gravel, potholes or an oncoming vehicle on the bend.