Baby Bobber and public participation

**Big Dog** · 12th July 2016, 17:49

Originally Posted by Goosifer

There is quite a bit of cautioning against going monoshock, what would the main pitfalls be other than cost?

Just hazarding a guess but getting a good enough mount / welds on a swing arm and frame (not designed for that paricular setup )to get past the lvv inspector.

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**Big Dog** · 12th July 2016, 17:59

In theory at least, a monoshock swing arm needs to be more rigid as it needs to soak up the lateral force normally managed with the independence of dual shocks. This means the swing arms mount to the frame is normally chunkier on a monoshock too.
Both ends of the monoshock now need to be up to 2x the job of either of the dual shocks.

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**OddDuck** · 12th July 2016, 18:17

Originally Posted by Goosifer

There is quite a bit of cautioning against going monoshock, what would the main pitfalls be other than cost?

It's a pretty major mod, I'd see issues with WOF, possible LVVT cert needed. Pinch of salt with that, that's just a guess, I haven't been there myself yet.

You'd need to have a reasonable understanding of vector diagrams and forces so that you could select the right monoshock and pivot positions. If you're going to try, get Tony Foale's book on Motorcycle Handling and Chassis Design, he covers this in some detail. Haven't done it yet myself, I've just read the book.

Also possible to bog down in a hopeless morass of delays, cost blowouts, running around to various places trying to buy things, racing the clock to get there before closing, etc etc... I've been there way too many times. If you take on too much then the project's doomed. Physical energy and drive is limited, it's easy to dream big but sometimes you've got to draw clear lines about how much you take on.

**OddDuck** · 12th July 2016, 18:24

Originally Posted by Big Dog

In theory at least, a monoshock swing arm needs to be more rigid as it needs to soak up the lateral force normally managed with the independence of dual shocks. This means the swing arms mount to the frame is normally chunkier on a monoshock too.
Both ends of the monoshock now need to be up to 2x the job of either of the dual shocks.

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Sorry Big Dog but I disagree, every shock absorber (single or dual) I've ever seen has used rubber or spherical bushings precisely to avoid lateral loadings through the shock. Swingarms flex in use, that's bad, but shocks jamming up and not sliding would be really bad news.

The only way to stop a swingarm flexing is to make it as torsionally rigid between wheel axle and swingarm axle (and axle mounts) as possible.

**Big Dog** · 12th July 2016, 21:04

I'm not a mechanic so I won't argue the lateral loaf aspect but the same total load still needs to pass through half as many mount points.

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**Mike.Gayner** · 12th July 2016, 21:54

I like #1 a lot - it's also by far the easiest build.

**Goosifer** · 13th July 2016, 09:11

Thanks, excellent points.

Motorcycle Handling and Chassis Design has just been ordered

Biting off more than you can chew is a sure way to doom a project before its even started, should this build go well, I'll take another look at swingarm setups.

**caspernz** · 13th July 2016, 19:18

For my taste, #1 is clean and simple, but #4 also appeals to me in a weird elegant sort of way.

Personally not into spending loads of dosh on what could easily become a bottomless pit, but hey it's not my money.

Learning new stuff is always fun though, so good luck with your project

**Drew** · 13th July 2016, 20:32

Originally Posted by flashg

I like no 1, it'll need rear brakes though, you appear to have removed them in all your design's

Double the sprocket as the brake disc.

**Mike.Gayner** · 13th July 2016, 20:34

Originally Posted by Drew

Double the sprocket as the brake disc.

Grease and brakes are best friends.

**Drew** · 13th July 2016, 20:44

Originally Posted by Mike.Gayner

Grease and brakes are best friends.

Don't lube the chain in place. Have the pads grip further in than where the chain runs. There is precedent on dirt bikes. It's a fucken VL250, it's not gonna eat chain.

**Goosifer** · 14th July 2016, 09:02

Originally Posted by Drew

Double the sprocket as the brake disc.

And there I was thinking you were joking.

http://www.tolle-engineering.se/stor...8-teeth-418906

**Drew** · 14th July 2016, 09:10

Originally Posted by Goosifer

And there I was thinking you were joking.

http://www.tolle-engineering.se/stor...8-teeth-418906

Nope, it was my plan for the sidecar. Ya need a fairly big sprocket though and we wouldn't have been able to go big enough at the front to get the right final drive ratio.