The Return....................Fingertight Sidecar MkII

[Moooools]

I think Mools is correct. On a go kart where you have a wheel on both front corners it is OK. With yours it will lift turning one way and drop going the other. I have not looked at side car setups but as yours is now will want to turn left all the time. The center of the Tyre contact should the line where the steering pivot meets the contact patch of the Tyre to the road. Good looking effort though. Do they work any good with a motorbike fork set up with very little caster or rake?

Bang on. A kart is neutral at the beginning of braking, but if any trail-braking is used the force will come on slowly and will be predictable as the kart turns in and load transfers to the outside wheel (this is if the kart has front brakes - most don't and will not suffer the side-effects of scrub radius). On the sidecar the steering torques will be at a maximum right from when the brakes are applied. Not great for providing a predictable response to steering and brake inputs.

[mr bucketracer]

if you look at this, the pivet is as close to the wheel to cut down on leverage factor , still a promblem , but not as bad, this runs kart wheels

[Drew]

if you look at this, the pivet is as close to the wheel to cut down on leverage factor , still a promblem , but not as bad, this runs kart wheels

The origonal was a full sized F1 long chair...the rules got changed very shortly after it showed up at a track.

[Grumph]

The origonal was a full sized F1 long chair...the rules got changed very shortly after it showed up at a track.

Have a look at the bucket sidecar rules. Different to full size. I'd be looking hard at building a feet forward setup as it's not currently illegal.
Tony Foale has a front suspension of a curved bottom wishbone and a strut which could work well on a chair.

[Pumba]

Nice going.

First off: congrats on the use of RHS. Perfect material for the job here - nice and simple.
The overall layout looks really good as well.

I am very worried about that front end though. Having the steering axis so far from the centre of the contact patch will make it pull hard right under brakes - like really hard.
I have done some quick math on this for you, and I estimate that under brakes you will have to apply 70kg of extra force on your right hand than on your left to stop it turning. I would look at getting that steering axis as close as you can to centred in the tyre, but that is pretty difficult with kart wheels unless you go to a more conventional setup. The numbers I used for this are attached as an image.

If it were me I would also move that front wheel back towards the engine to shorten the whole lot up - but that is pretty unfounded, really just my musings about what makes a sidecar fast around a short track.

I think Mools is correct. On a go kart where you have a wheel on both front corners it is OK. With yours it will lift turning one way and drop going the other. I have not looked at side car setups but as yours is now will want to turn left all the time. The center of the Tyre contact should the line where the steering pivot meets the contact patch of the Tyre to the road. Good looking effort though. Do they work any good with a motorbike fork set up with very little caster or rake?

Thanks guys (and the others after this). I knew there was a bit of an issue, but to be honest those calcs you have rolled out Moooools are a bit of a worry.

I have been thinking about this particular design for a while and given how far through I am I am going to push ahead and get it running for some real world tests (probably away from the track so when it it is a dismal failure there is as little evidence as possible). Almost everything I have done so far will not be wasted even if I have to cut the front end off and redesign it (I like to think of myself as an environmentalist they way recycle things).

[Grumph]

Everything's QD if you own a disc grinder.....

[Drew]

I don't like agreeing with anyone, hence my signature. But that steering pivot is a looooong way from the wheel.

This would normally be a concern, but there's an easy fix that means all the steel and hardware stays right where it is.

You barely need brakes on a bucket chair. Run a brake set up like a full size chair. One master cylinder for the rear and chair wheels, and one for the front wheel. Oversize the front master to all fuck, and I mean 3/4in. feeding a single piston push bike caliper. Size the one for the rear on the almost too small side.

Now you've got ten times the braking g power at the back that you do at the front. Problem solved.

[Pumba]

Everything's QD if you own a disc grinder.....

Was meant to ask the other day. "QD"?

[pete376403]

Was meant to ask the other day. "QD"?

Quickly detachable?

[Pumba]

Quickly detachable?

Even if it that is not what it stands for, I like that.

[Pumba]

.

Hey Moooools, what did you use for your deck? Pictures look like you made a ply and poly panel laminate sheet.

[racer40]

looks pretty good to me, if possible put more braking to rear, as the front kart wheels tend to lock up, espacially in the wet. with this bike i am hopeful of 12 or 13 sidecars for the GP as 2 more old ones have come out of the woodwork and been passed on.

[Moooools]

Hey Moooools, what did you use for your deck? Pictures look like you made a ply and poly panel laminate sheet.

I started with that, but it turned out to be a little weak and annoying to use. It could be done right but it would require vacuum bagging to get good adhesion (Any warpage in the ply leaves high points where it was not stuck to the poly, even with a pretty good bit of weight holding it down). In saying that it could be done better without the ply, and just doing a fiberglass layup with some woven cloth on each side (I should have just done this).

I ended up using non-skid truck deck. It is sold under a few different names, but it is essentially just ply with a hard-wearing resin on both sides. It weighs a lot more than the sandwich panel solution but it is also much, much easier to deal with/drill holes in/predict strength of.

[Henk]

If anyone is after a sidecar talk to Rick or I, we'll be looking to get get rid of ours once we have the axle replaced, which will hopefully be in the next two weeks.

[Pumba]

So finished off the last few bits for the front end and bolted it all together.

Must say I am now "almost willing to accept defeat" on this front end design. On top of the concerns with the location of the pivot, stability under brakes, etc. there is a significant amount of play that in the whole thing that i am not happy with.



Got an FXR frame and steering head here in the shed which I think will form the basis of a more conventional front end design.


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