Sidecar on late 60s single frame?

[iansoady]

Yes, I can see that there are so many things affecting it. I have changed the rear units for the ones I took off which are stiffer (I was going to use them for the sidecar body but they wouldn't fit...). Checked again all alignment - the rear wheel was very slightly out (1/4" at the front wheel) so corrected that. This didn't make any difference to the toe in at 3/4". I'm going to try dropping front tyre to 28 and rear to 32 as advised by David Angel. I know I should only do one thing at a time.....

[DAVE BRADY]

Hi,

If you go for an hydraulic steering damper there are adjustable ones available.  This will allow you to set it so that normal steering is smooth and with no resistance. Once the wobble starts the damper will resist it and the more it wobbles the more the damper will resit.
If you take the spring off a rear shock the damper can be moved relatively easily if done slowly but try and do it quickly and it becomes very difficult so the same will apply to a steering damper.

Dave.

[iansoady]

OK, have fitted the stiffer rear units (Falcons) and reduced the tyre pressures to 28 front and 32 rear (left the chair one at 25) and checked aligment carefully. The back wheel was about 5mm out of alignment with the front so have corrected this but toe in is still between 1/2" and 3/4".

so full of trepidation I tried it out. The shake has definitely reduced significantly but is still there. It's worse under power: coasting seems relatively OK although still only tried at 10mph and under. I feel there may still be some play in the steering head bearing so will jack the front up and adjust it.

Classic Bike Spares, my local shop, has a pre-unit BSA steering damper complete which may be worth adapting. I'll give it some thought. https://www.classicbikeshop.co.uk/triumph-bsa-norton-steering-damper-complete-kit.html

So slowly getting there I think. I may try reducing tyre pressure by a couple of pounds or so more.

On the positive side, I was flagged down by a bloke who besides being very complimentary about the outfit wanted to show me his dismanted TriBSA that had been in the corner of his garage since he built it when he was 17 (now 77). It was a bit sad looking but complete. I did have to tell him that prices had plunged but he was in a position where he couldn't do anything with it and none of his potential will beneficiaries had the slightest interest. While we were chatting another old bloke stopped and was loved the outfit and took pictures. Fortunately he'd gone when I wobbled off!

[limeyrob]

My outfit riding memories are coming back. One thing I did was fit a wide set of braced handlebars. These really helped and gave me a lot more control when it decided to wobble.  I don't remember ever having problems at speed (well 40 - 50 which was flat out on a Golden Flash with a heavy chair) but low speed could be tricky and I would always wind the damper down. Also hard braking (to be avoided) needed a lot of force on the bars to stay straight.
I did many miles on both a Plunger GF / Swallow and a SW GF and Watsonian and I'm trying to compare. The plunger frame had a better rear location and was stiffer.  I do recall the rear wheel on the SA basically fell apart due to the hard work it had to do.  I used to run Speedmaster rears on the front.

[iansoady]

I've got about another 3/4 of a turn on the steering head adjuster which gives smooth movement lock to lock but with slight resistance so probably as tight as I want to go. I can see than any slackness there would be magnified at the tyre/road interface. I'd already tightened the adjustment up but perhaps not enough. Funnily enough the bike handled very well solo!

Maybe try it again this afternoon.

[rhyatt]

"The shake has definitely reduced significantly but is still there. It's worse under power"

I remember my Bonneville with a PALMA attached to it - under power , the rear wheel is trying to pull the bike around to the left , I did cure some of this by having longer /wider trials type handlebars to give me extra leverage which worked well and simple to try out.

I remember pulling up Ross on wye hills with my wife and son in the chair , with my POPEYE arms trying to keep the lot straight up the hill !!

but being fed jelly babies from my wife - via the chair window- on the way down !!

[iansoady]

Now some good(ish) news. I filled in a query form on the Avon (now Goodyear) website and was very surprised to get a phone call in return from a very helpful chap. He stressed that he was calling rather than emailing as nothing he would say could be construed as "advice" for obvious legal reasons. Anyway, he was very helpful regarding tyre pressure / load combinations and it's clear that I've had the front tyre overinflated - and it still is, probably, at 28 psi. The unladen weight on the front wheel is 86kg - let's say that increases to 120 fully laden. According to my chap, this would correspond to a pressure of 21 psi (the lower limit to stop the tyre coming off the rim). I'd be very uncomfortable at that so will try the effect of 25.

I have been trying to work out the effect of front tyre pressures and it has struck me that lower pressure equates to a bigger footprint which would act to increase effort required to rotate around the steering axis - exactly the same as the effect of a steering damper. Like trying to steer a car with flat front tyres and no power steering. So I think I'm eventually on the right track(!). Hopefully I'll have another short test today at 25.

I must say I've never bothered much about tyre pressures on solos, taking a starting point for most as 28 front, 32 back although these are for bikes weighing 180 kg or so. I seem to remember the Tiger liked 42 at the back but it was a big heavy beast.

[limeyrob]

Contact width is critical, this is what an aircraft anti-shimmy tyre looks like.  Not common as I think the found better fixes but it gives you the idea.

[iansoady]

That's fascinating Rob. The roadrider tyre has quite a rounded - almost V - section so if it's over inflated is almost at line contact. I may change it for something like a Mitas - the Avon sidecar tyre is only available in 19" size as far as I can see.

I've just had another very short run and a great improvement. 25 psi in the front: much much better especially on smooth road surfaces. A biggish bump still knocks the bars but at least they don't start oscillating. I got up to about 20mph and felt relatively safe.... I may try even lower pressure but won't go below 23. Another long conversation with a passing couple who used to have bikes in their youth, and the postman who said he could do with something like the outfit to do his round. I did offer to sell it to him but he said he preferred to remain married.......

I have started to wonder about the back and sidecar tyre pressures - currently 30 and 25 respectively.