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Author Topic: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp  (Read 37174 times)

Offline pidjones

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #220 on: Dec 28, 2018, 21:13:46 »
Nice setup.

The brake lever should be set up one notch lower, or you pull it over 90 degrees.
Plus, you'll get a bit more adjustment room on your cable.
"Love 'em all.... Let God sort 'em out!"

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #221 on: Jan 07, 2019, 07:03:39 »
Thanks all!

Nice setup.

The brake lever should be set up one notch lower, or you pull it over 90 degrees.

Great point!  Will do when setting up in the final assembly.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #222 on: Jan 07, 2019, 07:07:46 »
Somewhat but not entirely related...  Have spent a lot of time the last couple of weeks filming my wheel building process and editing it together as an instructional video.  Now that wee project is complete work will continue with the this build!

To build wheels I came up with this taping method.  Perhaps others do this too?  Anyway, I find it makes a headache of a process into a pleasantly therapeutic one. 



I also wrote a blog post about spoked wheels.  They are rad!  https://www.jadusmotorcycleparts.com/single-post/2018/12/30/Spoked-Motorcycle-Wheels---The-Best-Motorcycle-Wheels

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #223 on: Jan 10, 2019, 13:53:54 »
Both sets of fork springs finally arrived this week and both fit! 

Now I can work out the spring rates of both sets and draw up some spacers to make them work.

I am however having second thoughts.  After seeing these, I am actually thinking it might be better to use cut stock SR250 springs, calculate the necessary length for the necessary/desired rate, then make some spacers for that and use the spring end adapter I designed.  Then I can get testing the performance of these and if it's good, it could be something to offer customers - a much cheaper solution to buying springs from other bikes and saves shipping hassle as well. 

Offline pidjones

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #224 on: Jan 10, 2019, 14:29:36 »
Just as long as you don't coil-bind.
"Love 'em all.... Let God sort 'em out!"

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #225 on: Jan 11, 2019, 07:40:10 »
Just as long as you don't coil-bind.

Good call.  I'll be able to check that with my threaded rod set up and a few measurements. 

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #226 on: Feb 11, 2019, 13:06:29 »
Not so much to post for a while but things are ticking along.  I developed a simpler fork preload and cap kit to see if I could bring down the cost of production for customers - more on that later.  Plus I checked a lot more things with cutting the stock springs - worked out lengths, rates, preloads and suggestions for rider weights.  I also checked how the spring would be at full compression at it most extreme cut length - see attached.  The adapter I designed works a treat to spread the load of a cut spring end.

I ordered a magnetic angle finder as well that works off of level - so you can place it on the fork stanchion and work out rake and therefor trail as well.  I need to do this because the current set up I have with an experimental rear shock length of 350mm ends up with 23 degrees rake and only 85mm trail.  I want 100mm of trail minimum for this slightly higher speed SR and certainly more rake than that.  So I will therefor work with rear shock length and front fork lowering to achieve this.  Rake will land between 26 and 28 degrees.

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #227 on: Feb 17, 2019, 09:13:49 »
So the angle finder came and is awesome.  What a great way to measure these things with pretty good accuracy.  Anyway, I worked for some time with rear shock height and lowering the front forks until I got something acceptable.  One problem is that I am still a little driven by the look and proportions of the build - so I wanted to achieve this flat line of the seat and tank still.  This meant a slight compromise for these figures.  But I ended up with a rake angle of 25.5 degrees and trail of 95mm.  Which is a little border line but still within the acceptable realms of sport bike specs.  When I get the bike running I will be careful when coming up to speed at first and if it feels necessary I can install a steering damper as well.

The final rear shock height is 340mm and the front forks are lowered 40mm.  I double checked these physical measurements with a quick CAD sketch and they are almost spot on - meaning they are reliable figures/measurements. 

Now I just need to find a rear shock that is in that length and is soft enough for a 100-110kg bike...  There are plenty of rear shock options for that length with the correct 14mm diameter eyelets, but they are all for much heavier bikes.  This would mean a very stiff spring and almost non-functioning rear suspension.  I have written to a few companies inquiring about custom set up YSS shocks.  Anyone got any other suggestions?  I would consider Hagons if their shocks didn't look so damn vintage!  And I haven't heard very good things about RFY shocks (shame because they look cool).

Offline JadusMotorcycleParts

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #228 on: Feb 17, 2019, 12:13:15 »
And here's how those dims/set up looks.  You can see that the rear frame rails are parallel to the ground - one of the visual goals I couldn't let go of.

Offline pidjones

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Re: Ton up SR250 - a cafe racer by the numbers: 100mph, 100kg, 30hp
« Reply #229 on: Feb 18, 2019, 07:58:16 »
I wouldn't worry as much about coming up to speed as backing off from speed. The front dives, rear lifts, and both decrease trail.
"Love 'em all.... Let God sort 'em out!"