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Myles Raymond
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knuckle head
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I can straddle the front wheel of a Triumph firmly holding the tires between my legs ,grab the handlebars firmly wiggle them back and forth while watching the fork assembly twist...I can put my boot to the wheel ,push hard, and see it deflect.....What happens to all this extremely precise alignments with going on? It doesn't seem to affect handling within the limits of the bike's performance...


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The front steering move's left or right when the front tyre is deflected by uneven road surface. It's the front wheel trail which brings it back in to line with the frame centre line.

To allow this to work you don't want to hold the bars with a vice like grip. The flex you feel is not ideal but won't have as much effect as you might think as long as you allow the trail to correct front wheel deflections, that is hold the bars as lightly as possible.

Because of front wheel trail it's why it's important to get the rear wheel aligned to the frame centre line. Permanent misalignment means the steering will be permanently angled off centre to counteract the steering bias from the rear wheel. This creates a permanent imbalance of forces applied to the front tyre and causes steering problems.

Let's hope Tt gets a dictionary in his Christmas cracker.

Last edited by Simon Ratcliff; 12/10/17 10:39 am.

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Quote
I can straddle the front wheel of a Triumph firmly holding the tires between my legs, grab the handlebars firmly wiggle them back and forth while watching the fork assembly twist


I find it's worth minimising that twistiness to get positive-feeling steering on bumpy corners, with some sort of fork brace. Even a long steel mudguard fixed to the sliders and with stays to the end of the guard made a difference on my roadgoing Wideline. Yes I know featherbed Manx Nortons didn't have that stuff!






Quote
Let's hope Tt gets a dictionary in his Christmas cracker.

I've been bad all year, so I don't hold out much hope.

Originally Posted by Simon Ratcliff
move's


"Moves."





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knuckle head
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Originally Posted by Simon Ratcliff
The front steering move's left or right when the front tyre is deflected by uneven road surface. It's the front wheel trail which brings it back in to line with the frame centre line.

To allow this to work you don't want to hold the bars with a vice like grip. The flex you feel is not ideal but won't have as much effect as you might think as long as you allow the trail to correct front wheel deflections, that is hold the bars as lightly as possible.

Because of front wheel trail it's why it's important to get the rear wheel aligned to the frame centre line. Permanent misalignment means the steering will be permanently angled off centre to counteract the steering bias from the rear wheel. This creates a permanent imbalance of forces applied to the front tyre and causes steering problems.

Let's hope Tt gets a dictionary in his Christmas cracker.

Yes, we are all aware of this.. I meant how does frame and suspension flex affect the very precise alignment you mention ? A newer sport bike feels different than a vintage Brit bike including Norton Commandos because the newer frames and wheels are so rigid.....


79 T140D, 89 Honda 650NT ,61 A10 .On a bike you can out run the demons
"I don't know what the world may need
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I think we've wandered away from the OP's intents but...
Modern bikes;
along with stiffer frames often the wheels are smaller (17") & steering centre to fork offset less, reducing trail. also steering castor / rake may be steeper. All things that make a bike fall into a corner (or not). Re. offset; Olde Brit Bike's fork to steering stem layout is quite triangular looked at from the top yoke (not yolk, runny forks would be a joke). Modern bikes are very flat in comparison, the forks & steering stem are almost in a straight line.
I imagine the current crop of GP teams are trying to answer Hillbilly's last question! Those bikes are so stiff & precisely set up & still they don't always work how the rider wants or likes. Too stiff, too much flex, removable frame sections in order to change stiffness or flex etc.

Olde Brit bikes; You can spend many hours acheiving perfect alignment of parts & some of that effort will pay off. The garden shed mechanic can assist this by fitting say, taper roller steering bearings - things that make the handling feel more exact / controlled but often the bike will have some corner cut design-wise for all sorts of manufacturer's reasons, not the least of which was financial. My old road going Goldie had the silentbloc bushes in the swing arm when I first got it. It handled horribly in corners until I replaced them with new ones which felt only slightly better. My race bike had actual bearings in there & handled much better but then again it was a lot lighter, none of that heavy chrome stuff on it for a start. These days our tyres have way more grip than in '59 & can grip better than the bike can cope with. Certainly they ask questions of the bike's suspension & handling.
Also some frames as a rule just handle better than others. Does anyone favour a Triumph twin over a Norton featherbed frame? Anyone who's ridden a bike with a bent or cracked frame will notice how it tips into a corner easier one way than the other or sets up a weave in certain conditions. I've ridden a few like that & also a few that were very nice to ride - ones which had a lot of care taken in setting them up although I'm pretty certain those responsible had access to nothing more technical or accurate than a vernier caliper & some straight edges.

In response to previous comments, it's usually worn or misaligned chains that break although sometimes extreme circumstances cause breakages - Ballaugh Bridge IOM being a case in point. That is a rear chain breaker, not what this thread is supposedly about!
Getting good belt alignment has got to be worthwhile, I was probably just lucky with my first b-drive setup on that front. Whilst I agree that the surface table is a wonderful thing, probably 99.999% of old bike fettlers don't have one or access to one or the money to pay someone who has one, to set up their bike / frame. Maybe we might once in a lifetime actually splash out good money for an expert to fettle a bike or frame for us but I bet it's not common. Some of the big money classic racers may go down that path more often.
We can at least use the other accessible methods that have been suggested. That said, I bet many of us have just bolted a bike together, trued the wheels with a straight edge or some string & then happily thrashed the bike around for a few years, adjusting our riding to suit whatever quirks the bike has. Probably an attitude that contributed to the Brit Bike's reputation for sloppy engineering... ;-) Most "Classic" road riders are not pushing the limits of handling on their Sunday ride.

Vice like grip is not how I ride. There was an issue with Ducati Hypermotards (& probably other quick, sit up & beg bikes with wide bars) with riders complaining of weaving at speed. Almost certainly due to rider accelerating hard & hanging on like grim death.. The wide bars exaggerate any rider inputs - as soon as the rider imperceptably pulls the bar one way when "hanging on" they "correct" the movement the other way but overdo it, leading to repeating the mistake the opposite way & before they know it there is a lovely if slighly lairy 100mph weave going on... Holding on lightly tends to prevent it & is a more relaxing way to ride.


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Originally Posted by flowboy
I think we've wandered away from the OP's intents but...
Modern bikes;
along with stiffer frames often the wheels are smaller (17") & steering centre to fork offset less, reducing trail. also steering castor / rake may be steeper.
I imagine the current crop of GP teams are trying to answer Hillbilly's last question! Those bikes are so stiff & precisely set up & still they don't always work how the rider wants or likes. Too stiff, too much flex, removable frame sections in order to change stiffness or flex etc.


Steering castor and trail are the same thing and is designed-in to suit the bikes use. Less for trials bikes more for cruisers. Sports bikes and tourers are somewhere in between with sports bikes having less than tourers.

Number one priority of the frame is to maintain precise wheel alignment. Therefore building in flex is nonsense. Ducati WSB team a few years ago apparently did this. The reason was because the front telescopic forks were seizing at maximum lean due to the forks bending, so they made a flexible frame to absorb the bumps instead of designing front suspension that does not have to steer the bike as well e.g double wishbone as designed by Norman Hossack and fitted to BMW K1200R and the legendary Britten.

Last edited by Simon Ratcliff; 12/26/17 4:38 pm.

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Originally Posted by Simon Ratcliff
Originally Posted by flowboy
I think we've wandered away from the OP's intents but...
Modern bikes;
along with stiffer frames often the wheels are smaller (17") & steering centre to fork offset less, reducing trail. also steering castor / rake may be steeper.
I imagine the current crop of GP teams are trying to answer Hillbilly's last question! Those bikes are so stiff & precisely set up & still they don't always work how the rider wants or likes. Too stiff, too much flex, removable frame sections in order to change stiffness or flex etc.


Steering castor and trail are the same thing and is designed-in to suit the bikes use. Less for trials bikes more for cruisers. Sports bikes and tourers are somewhere in between with sports bikes having less than tourers.

Number one priority of the frame is to maintain precise wheel alignment. Therefore building in flex is nonsense. Ducati WSB team a few years ago apparently did this. The reason was because the front telescopic forks were seizing at maximum lean due to the forks bending, so they made a flexible frame to absorb the bumps instead of designing front suspension that does not have to steer the bike as well e.g double wishbone as designed by Norman Hossack and fitted to BMW K1200R and the legendary Britten.

Telescopic front forks look good, but that's about it. Newell and his cronies designed and manufactured some magnificent "Feet-Forward (FF)" machines in the 1970s and 1980s, including a Z1300 Quasar (or was it a Phaser?) with a top speed of approx 165mph (measured at MIRA). Michael Dunlop sitting in a fully-faired FF 220bhp bike would probably reach 240mph on the Isle of Man. He might take off at that speed.

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It was the Quasar. I remember a feature in 'Bike' magazine of one of the first which had a Robin Reliant (plastic pig!) engine and hub centre steering front end, so the power to weight ratio was poor but due to its low centre of gravity, full fairing and rigid chassis it could leave a contemporary Ducati sports bike for dead around the TT course according to Royce Crease. The front end was so strong that a collision with a car left the Quasar undamaged but wrote the car off - that's retribution for you!

If telescopics were any good they'd be fitted on cars but they're too flimsy. A long term plan of mine is to fit a BMW double wishbone front-end (bought off eBay) to a Commando frame that got crash damaged on the Island during this year's Manx when a BSA rider did a U-turn in front of me!



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As I recall, Royce Creasey was once warned by the police for frightening other road users in traffic due to general appearance and extreme angles of lean whilst filtering in an FF bike. I want one.

Forty years on and they still look futuristic. Reliant engine was about 40bhp, current BMW engine with 200 or so bhp would probably slot right in.

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Great design and still a good looking bike. There was one available in the classifieds not too long ago and the price was about £10,000 I think, which, for such a rare, but totally useable classic was a bargain.

P.S There's a website www.quasarworld.co.uk
Used ones ready for the road go for about £15,000, still a bargain.

Last edited by Simon Ratcliff; 12/27/17 7:42 pm.

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Originally Posted by Simon Ratcliff
It was the Quasar. I remember a feature in 'Bike' magazine of one of the first which had a Robin Reliant (plastic pig!) engine and hub centre steering front end, so the power to weight ratio was poor but due to its low centre of gravity, full fairing and rigid chassis it could leave a contemporary Ducati sports bike for dead around the TT course according to Royce Crease.


You probably mean Royce Creasey.


Have Quasars won more TT races than Ducatis?


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I doubt if a Quasar would meet UK regs for racing (fairing).

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Originally Posted by Dibnah
I doubt if a Quasar would meet UK regs for racing (fairing).


I doubt that the guy's head is very comfortable like that, either.

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Luxury!


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A well upholstered seat!

Originally Posted by Simon Ratcliff
Number one priority of the frame is to maintain precise wheel alignment. Therefore building in flex is nonsense. Ducati WSB team a few years ago apparently did this. The reason was because the front telescopic forks were seizing at maximum lean due to the forks bending, so they made a flexible frame to absorb the bumps instead of designing front suspension that does not have to steer the bike as well e.g double wishbone as designed by Norman Hossack and fitted to BMW K1200R and the legendary Britten.

You've obviously been following the tech more closely than me. I couldn't recall exactly where I'd read that frame flex thing but I beleive the Ducati GP bikes also went to part aluminium frame after they had problems with the carbon fibre front section they had - around the time of Casey Stoner's many crashes - something to do with frame flex or lack of? Certainly there has been press comment over the years about sports bike frame design allowing more or less flex. Perhaps the word "flex" paints a picture of something being elastic in a rubbery way rather than a material being fractionally more or less stiff...
The Hossack forks look pretty cool to me, there used to be a guy who brought one of those race bikes to race meetings a few years ago. It may have benefits over the tele fork but I assume is more expensive to make. The telefork is judged to be "good enough" by manufacturers & riders are also accustomed to their behaviour - hence the rather elegant telelever not really catching on - with riders saying they lack/ed feel although experienced BMW riders may well think they're great. However, I've never ridden one. .




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