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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.

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. Next job...build frame jig.

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?

If I have to I'll make some alloy linkages but would prefer to go direct mount. Picking up an alloy body kdx200 shock unit tomorrow so that'll be at least a lightweight starting point. Will be reinforcing swingarm at mount point so time for some experimenting coming up. That TLR is really cool setup, keeps the weight low too. I will post some pics in next day or two.

Air shock...hadn't thought of that. Maybe I could fill it with hydrogen and make those rear wheel hops with much less effort

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

What is the reason for filling between front frame tubes?

I really dont know much but have you tried again when engine cold?

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?

I'm very interested to learn more about increasing axle diameter. Presumably to run hollow alloy axle? Ah yes I was having a bit of a brain hiccup regarding the speedo drive! I have an old myford lathe here so looking at turning all spacers/axles/steering shaft etc from alloy.

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?

Thanks so much.

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.