I've been making a full sized drawing in preparation for making a frame for my C15 - I am basing it on the "Otter" but experimenting with the bits I have and the bits I think I could make. It will be a "special" but, as it is, it wouldn't meet Scottish regulations so I'm not spoiling anything. I love making things I can use, so that's good enough for me! Good luck with yours. I'd love to see your frame jig.
Sounds like a nice project, I'd love to find a lightweight brit bike to do this to. I have most of a b31 in pieces but the engine alone is super heavy.
The frame jig I will make one day I downloaded plans from chopsource website. In the interim I will roughly cobble something together just to alter steering angle. It will only attract critisism so no pics will be taken
Went round to a mate's today and took some measurements from his ty250 mono and they seemed close enough to specs.
While we were talking I realised what I'd done wrong; the calculator called for fork offset but I'd forgotten to include leading axle offset (duh!) so measured and what happens? It all looks good!
So I input steering stem rake angle to 23deg (from 26.2) and trail comes back to about 75mm (from 101mm) which seems like an ok place to start to me.
For some reason the wheelbase didn't change on calculator but I expect it's quite minimal unfortunately as the total current measurement is 1363mm.
I'm just trying to get my head around all this - for a project I am planning. This thread on another site (I hope I'm allowed to post this - please let me know if not and I'll remove it) https://trials.com.au/forum/viewtopic.php?f=16&t=9348 explains the complex relationship between all the geometry you are playing with. It has helped me to realise that just changing one thing to match another bike won't necessarily make your bike better.
Good luck - let us know what you decide and how it works.
What project are you planning?
I have been to the thread "steer clear" a time or two and found it pretty helpful. Yes I expect there will be lots of tweaking and changing as I progress but anything is likely better than the current setup. My main problem may be that I'm 6'2 and carry most of my 105kg up high.
I will keep you all up to date on progress. I should start a build thread I suppose.
Spec sheets are not a good source of geometry information because they don't specify if the bike is laden or unladen or if there is any static sag or what pressure is in the tyres or what tyres.
You will get real numbers by reassembling the important bits and measuring it yourself.
If you are trying to copy a proper trials bike, measure the proper trials bike yourself so you are comparing apples with apples.
Be aware that modern front and rear trials tyres are a fair bit taller than front and rear trials tyres of the past and the heights of the axles are very much affected by pressure.
I agree about spec sheets, although if they are all created equal then it would give me peace of mind to cut 3degrees out of rake.
Unfortunately I have thrown some parts away so can't reassemble. Was going to set back up from front geometry changes.
I only know one guy with a trials bike so will try to measure his although he'll think I'm mad.
I plan on using modern tyres and yes that further complicates things depending on psi.
I'm going to reduce castor angle on my farm bike project, so...I entered current steering geometry specs into an online calculator (I'm lazy and its quicker) but the trail was a lot more than OEM spec when calculated.
I fiddled around a bit and it seems the manufacturers figures are based on having no tyres on rims. This I understand would take out the tyre height variance of different products but seems its not a real world measurement.
Are all motorcycles measured in this way for spec sheet? My bike is completely disassembled so can't check for sure now. I don't want to alter frame until I know I'm comparing apples to apples.
I'd love to use a modern setup but as I'm on a sole parent benefit there is a very tight budget. If I had any money I'd just buy a whole modern trials bike I think.
The weight loss was easy as the farm bike had so much to strip back; carriers, crash bars, road legal gear, even two side stands.
Probably not much to report until I find a more suitable shock.
How about an old ag/farm bike? Heavy flywheel, low geared, low seat height for easy leg assistance by the vertically challenged, plush suspension, pretty much designed for slow speed but still ok to jump and do drop offs. Cheap as chips.
Thanks Yamagodden, always good to see other setups.
Got my shock unit the other day (supposedly a kdx unit) but is way too big and heavy unfortunately so back to the drawing board.
In the meantime I've been converting from electric start to kick only; removal of battery, starter motor, starter clutch, associated wiring, and cutting/epoxying stator cover. Also lacing up some old alloy rims to replace the rusty old steel ones.
Original dry weight of 125kg has been reduced to less than 90kg thus far. Would be happy if final product is 80kg, pretty close to a modified tlr perhaps?
Yamagodden, do you have any more photos of that setup? The shock looks like its mounted really close to the pivot point if its a direct mount. Going back to twinshock?
Hi all, I'm currently converting an old Honda farm bike to trials form.
The bike is a monoshock but as the linkage assembly was badly seized up and made from steel I had to cut it to disassemble. The shock unit is also quite heavy so will be chucked away.
Some advice wanted please; what would be a good setup to use/modify? I was thinking direct mount so as to avoid clearance issues with linkage. Cheap and commonly available would be ideal.
If I used a shock designed for linkage, would I get enough rear wheel wheel travel? I know there's lots of variables: mounting position relevant to swingarm pivot, swingarm length, angle of shock etc.
I'm thinking a linear rate spring would be best but again I guess it depends largely on other factors? Does monoshock angle (pds setup) have any effect on traction?
Lots of questions and I expect some experimentation will have to take place in order to answer them but any help will be much appreciated
Have you got an external fuel filter and is the one in the tank still intact? Don't know if it would gave any bearing on your problem but are filters or fuel line blocked?
Here in NZ they now have a good power to weight restriction in place called LAMS (learner approved blah blah..). A learner can ride up to a 650? as long as its not a rocketship. Shame that wasn't the case when I was a boy.
Well I machined a couple of aluminium spacers, saving 80g of weight in rear one alone but no comparison on front as I don't have original. One more question, how the heck does the speedo cable drive come out? Is it pressed in at factory never to come out or is there a way I'm missing?
So that thin disc you refer to is called "spacer flange" as per parts diagram? If so I'm glad its not essential because that's missing as well! What do people do that remove speedo drive, just replace with alloy spacer or am I having another dipole moment?
This poor old bike has been extremely neglected by someone. Got my new tyres fitted and ready to install bearings/seals, and find my front wheel spacer between bearings was never there. Have tried the previously mentioned partzilla (couldn't access boats.net) for length of spacer but no joy. I know it's not possible to just measure up as its pressed between your wheel bearings but maybe somebody has info or a spare to measure?
Could anyone help me out with swing arm shim dimensions please? Mine are missing, little wonder there was so much play. The bushes seem fine and well greased luckily. I was hoping the local engineering shop might have shims to suit.
My bike is the roughest looking thing I have seen and a continual work in progress. Currently in a dismantled state, however I will put some photos up when it's back together. Planning to make many alloy parts. Will try to collate mod data and post also when I'm finished.
Thanks for the info. Swingarm weight variances were a surprise. Jogged my memory about clutch too. Got the bike down to about 81kg but aiming for 75kg. I think now that it's achievable.
Turniabilityness
in Classic Trials
Posted
Sounds like a nice project, I'd love to find a lightweight brit bike to do this to. I have most of a b31 in pieces but the engine alone is super heavy.
The frame jig I will make one day I downloaded plans from chopsource website. In the interim I will roughly cobble something together just to alter steering angle. It will only attract critisism so no pics will be taken