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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 35061 times)

Offline Brodie

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #240 on: Mar 08, 2019, 16:48:27 »
That is awesome. Totally sort out the cornering clearance issue the stock pegs create.
I'm not sure, but don't ask Brodie.

Way to many build and half done projects to list here.
Sr250, Gs750, Z50A, XV1100, A10, Z160A.

Offline jpmobius

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #241 on: Mar 08, 2019, 18:22:37 »
Not too sure where you are on the foot control levers, but going to pass a couple of things along early just in case.  First, and this may be obvious, the lever arm that pulls the brake rod needs to be at 90o or greater to the rod.  This looks to not be possible with the lever in your pics as you will want the pedal to be angled down considerably with the brake not being applied.  The actuating arm would need to be rotated anti-clockwise considerably to be in an appropriate range.  The second less obvious but potentially more important issue is the location in space of the pivot between the pull rod and the actuating lever.  Ideally, this would be directly coincident with the swing arm pivot.  In this location, movement of the suspension will not affect the action of the brake.  Moving away from this location in any direction will cause motion in the brake mechanism when the suspension moves.  Generally it is extremely inconvenient to locate the pivot in this ideal spot, but moving it rearward along a line between the SA pivot and the rear axle has only very minor impact.  You can not move the pivot up or down from this line very far at all without very noticeable "pumping" of the pedal as the suspension follows bumps in the road.  Move the pivot far enough and the brake can actually become applied with enough suspension movement - very bad!  One common solution is to use a cable like that used on the front which eliminates this problem completely, but is a lot more complex than the simple rod and lever scheme. 
Personally, I spend a LOT of time sorting out the riding position.  The person who will be riding the bike needs to spend at least 15 - 20 -30 minutes sitting on the bike, with the seat at the correct height, hands on the bars selected and adjusted, and feet on mock ups in the expected position.  That would be a pretty short ride, but will indicate if changes are wanted.  It does not factor in wind resistance, but in my experience, that is less important a factor on setting the ergonomics than is popularly thought.
Of course, getting the seat, bars and pegs just right with no concern for the associated machinery invariably makes for a lot of fabrication work to get all the controls to work equally well.  I think it is worth the effort to have a bike that is really comfortable and fits your purpose perfectly.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline zap2504

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #242 on: Mar 08, 2019, 19:09:27 »
Foot position you are exploring is way to tight for me, but I really like the upswept exhaust adapter idea! Gives the ability to clamp the exhaust way after the stock foot peg, improves the look a whole lot, and improves ground clearance.

Offline doc_rot

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #243 on: Mar 12, 2019, 04:55:05 »
If these are parts you plan on selling you might consider making the position adjustable somehow. I personally I never ride with the middle of my foot on the peg, only on the balls of my feet, so that position would be way too far back. Rizoma has some nice eccentric adjusters that look pretty good too. just my .02

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #244 on: Mar 14, 2019, 17:55:05 »
Thanks for the feedback!  This body and footpeg position would not be my choice for a daily rider or even a weekend thrasher,  but this build has pretty much one purpose, so I figured things could be pretty extreme.  Good point about making adjustable ones Doc.  I am not sure I would offer these to customers though - my products are already niche enough, let alone racer position footpegs haha.  I did try placing my toes/balls of my feet on the pegs though because I do that sometimes like you too.  These printed brackets and the plywood template were not quite strong enough to test that properly though.  Jp I'll respond to you below...

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #245 on: Mar 14, 2019, 18:00:12 »
Jp I spent a long while pondering the brake linkage.  The gear linkage is pretty straight forward but yes, the brake is more challenging.  I looked into all sorts of solutions, even converting to cable linkage instead.  But then I remembered I have a spare stock brake pedal that I can modify.  I think the following solution (see attached sketch) will work.  What do you think?  Hope it's clear enough, the proportions are not quite right but I think you get the gist...

And in your response to comfortable body/riding position.  I already assume this won't be comfortable  ;D  I'm going to make my daily rider much more back and wrist friendly though haha

Offline irk miller

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #246 on: Mar 15, 2019, 07:57:32 »
Why have a setup with two levers doing the same work?   Can you not make it so that your rearset lever is pulling the brake linkage without the second lever?

Offline jpmobius

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #247 on: Mar 15, 2019, 10:15:17 »
That is a good solution.  The factory places the pull rod connection point at pretty much the only good spot, so incorporating the original portion can't go too far wrong.  It would be a good idea to consider the leverage of the oem setup as you will likely want to have similar effort required in the new setup.
Mobius


On a long enough timeline, the survival rate for everyone drops to zero.

1973 RD350 Yamaha build  http://www.dotheton.com/forum/index.php?topic=66498.0

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #248 on: Mar 17, 2019, 06:53:29 »
That is a good solution.  The factory places the pull rod connection point at pretty much the only good spot, so incorporating the original portion can't go too far wrong.  It would be a good idea to consider the leverage of the oem setup as you will likely want to have similar effort required in the new setup.

Great, thanks.  I'll post a mock up as soon as I have one.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #249 on: Mar 17, 2019, 06:59:47 »
Why have a setup with two levers doing the same work?   Can you not make it so that your rearset lever is pulling the brake linkage without the second lever?

These were my exact thoughts in the beginning as well - why add mechanical complexity through an extra linkage?

Then it struck me in the middle of mocking up such a solution, then I confirmed my assumptions with google.  The answer is simple, you do not want a control lever attached to a moving part - the moving part being the swingarm.  The reason is twofold:  The action of the lever and its throw is no longer linear to the brake arm - because the angles and position of it change in relation to the brake lever through the rear suspension travel, plus, the required force also changes.  You would even run the risk of weird feeback through the brake lever as the suspension goes through its motion.

Just google any OEM rear set linkage solution (nowadays its mostly hydraulic disk brakes, but look at drum brakes) and you will find an interim linkage that disconnects swingarm to brake lever  ;)