So I've now completed the work on the kinematics for a baseline setup and decided on a final design. This is the 10th iteration of the third design which is not as good as the first, better than the second, but crucially requires no mount modification to either the swingarm or frame. It uses a 2012 - 2014 BMW s1000rr 310mm shock with a 62mm stroke and uses a 9.5n/mm spring. The only compromise is that it does require a custom top mount to make the shock a little more vertical.
Couple of points on the kinematics:
The ratio is pretty close to GSXR 1000 K5 with motion ratio of 2.20 - 2.04 through it's 130mm range and 62mm stroke
The swingarm angle is very close to the original slingshot arm
The swingarm is 20mm longer and should give a wheelbase of 1423mm
The seat/ride height is a little higher at 821.9mm
Here's a rough render of the bike, thought it might be interesting for people to see my vison for it.
Any thoughts are welcome. My thoughts so far are that, I'm not happy with the tail section, little too 'boxy' at the moment. I haven't decided how to do the subframe; potentially thinking folded ally and I am not a fan of the stock switch gear, looks too messy, but it is very functional and in-keeping with the bike. Thinking of just using a race style self-adhesive foam for the seat, no upholstery and certainly no brown leather.
Here's a side view as it might be easier to see the tail lines and end of the frame. Also playing with a small fairing at the front, would definitely be a lot less pointy, closer to the 89 slingshot at the front with twin round lights and a snub nose.
So back to the physical world... Something I've been toying with since I bought my R1M callipers is how to make them fit properly to the ZZR1400 front end. They were the right 108mm spacing, but sat 7mm too far out. Ultimately, I could see five options:
Buy 330mm Brembo Serie Oro discs and add spacers - Which is expensive, and adds a fair bit of unsprung mass (couldn't find any other discs that worked off the shelf)
Buy a different set of callipers, either the standard ZZR tokico numbers or a set of Brembo monoblocks - I didn't really want to go down from the monoblocks of the R1M callipers and the Brembo M4s seem unnecessarily expensive for my needs
Drill out the grub screw and remove fork lug, then either swap out the fork lug (hoping the thread is the same) - Seemed like a right arse and also would have required a new axle as the lugs for the mt10 damaged forks I was looking at only had a 20mm spindle
Machine the fork lug calliper mounting faces - I planned on doing this in a swivel vice clamping around the stanchion with a 43mm billet block clamp then milling it down 7mm. Alternatively, I did also consider using an ER collet chuck in a lathe and mounting the fork lug on the cross slide. Ultimately I did a free body diagram and decided that this was just way more hassle than it was worth.
Just machine the 7mm of the calliper... - This is what I did, 4mm came off the dowel (which unlike the regular R1 is actually part of the casting on the R1M) and then 3mm of the face.
I should add I have also retained the standard amount of thermal expansion gap from the original callipers.
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