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Ftwelder

Steering angle.

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I scored a BSA Victor with a B250 motor and figured I would build a trials bike out of it. I brought the head angle in, brought down the upper shock mounts etc. 

i am up to the point to set steering stops. My forks (old betor) have 70mm offset and my tank is really narrow.  Would 90* be a good point to set stops?  I can make thicker bumpers later. 

thanks. Frank 
 

49713383556_78cf375579_b.jpg

 

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If you want to read about bike geometry, steering head angles,swing arm angles, etc, go to,

"Trials Australia", then; forums; next "Twinshock and classic trials", next, scroll down to, "Steer clear, understanding steering". Its really useful. Great looking project by the way, Good luck

Edited by still trying
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Thanks for a quick reply but I am looking for help setting up the steering stops and would like to know how many degrees to allow the handlebars to rotate. Thanks. 

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3 minutes ago, Ftwelder said:

Thanks for a quick reply but I am looking for help setting up the steering stops and would like to know how many degrees to allow the handlebars to rotate. Thanks. 

Just set the stops so the forks don't damage the tank or whatever, you can't have too much lock.

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58 minutes ago, Ftwelder said:

Thanks for a quick reply but I am looking for help setting up the steering stops and would like to know how many degrees to allow the handlebars to rotate. Thanks. 

90 degrees is an awesome design target. If you've got it, flaunt it. I'd love to see a photo.

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On 3/30/2020 at 6:52 AM, feetupfun said:

90 degrees is an awesome design target. If you've got it, flaunt it. I'd love to see a photo.

It looks like I am just short of 90 degrees. It’s my first fuel tank build so I am reluctant to attempt an alteration before welding. 

I’ll set the stops a little short and let nature do it’s thing  haha  

 

A70CE060-5E60-4B72-9178-91F6A1C4711F.jpeg

Edited by Ftwelder
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Excellent. Thank you. That is fairly serious steer angle

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For comparison, this is a standard Kawasaki KT250 front end. I chose this photo because this bike has the most steering angle of any of my bikes.

20200401_130847.jpg

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90 deg of lock won’t do you any good as none of the tractive effort of your back wheel will be rolling the front. It will all be trying to skid the tyre sideways. Feetupfun’s photo could be a good guide, or measure any modern trials bike. Maybe you could weld on two threaded bosses and then insert a bolt in each as a lock stop. That way you could do a bit of testing before finalising.

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90 deg wont work in practice for the reason Trapezeartist mentioned. Two threaded bosses are the way to go. In the real world you very rarely use full lock as you run the risk of the front end tucking under. I would not exceed 80 deg but would also fit threaded bosses. M6 is fine angled so that the head of the bolt, I use allen bolts but choice is free, contacts the yoke at 90 deg.

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14 hours ago, feetupfun said:

For comparison, this is a standard Kawasaki KT250 front end. I chose this photo because this bike has the most steering angle of any of my bikes.

20200401_130847.jpg

Mine 

20200401_135136 (4).jpg

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Agreed, something between the BSA and the KT looks right. I appreciate the advice, thanks! 
 

Frank

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10 hours ago, Ftwelder said:

Agreed, something between the BSA and the KT looks right. I appreciate the advice, thanks! 
 

Frank

Just leave yourself enough adjustment for when you eventually discover your wrong.

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13 hours ago, b40rt said:

Just leave yourself enough adjustment for when you eventually discover your wrong.

 

13 hours ago, b40rt said:

Just leave yourself enough adjustment for when you eventually discover your wrong.

Thankfully I picked up on the fact that flexibility in design is pretty important. A good example is foot peg location. Originally I used Michael Wallers Youtube advice regarding positioning and was going to weld on tubular brackets but went back and designed new peg mounts that attach at swing arm pivot.  My fork offset is 70mm and all at the crown/yoke/triple clamp so bolts are a great idea. When I changed the head angle I made an extra large diameter head tube and could potentially make adapter cups that alter head angle. 

Since I have your attention, should I make the swing arm as short as possible? The adjustment will be at rear axle. 

Thanks for the advice. 

Frank

 

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Generally a trials swingarm should be as long as possible yet still achieve the wheelbase that you want.

For a bike with something like your B250 engine (an engine that is long from front to back) you will probably end up with as short a swingarm as will fit an 18" trials tyre and the wheelbase will still be on the long side of ideal.

Edited by feetupfun
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