SOHC.co.uk Forums > CB500/550
500 K cafe racer conversion - build thread
Ewan 500 K1:
--- Quote from: Bryanj on August 31, 2013, 08:20:21 AM ---I wish you would stop remining me of all the problems i had mate
--- End quote ---
When your only tool is a hammer, every problem looks like a nail. ???
Bryanj:
I do know of a "fitter" in a big print works whose tool kit consisted of 4 different hammers and 6 different chisels
Ewan 500 K1:
So today I played about with taking trail and rake measurements . I tried various combinations of rear shocks and steering stems:
a) standard length rear shocks (315mm between mounting hole centres) + bent steering stem
b) standard length rear shocks + good steering stem
c) new longer shocks (361mm between mounting hole centres) + good steering stem
Diagram of what I was measuring is attached, along with raw results
Some key points:
1. All measured rakes were substantially below the stock rake of 26 degrees that is quoted in the shop manual. I calculated mine with someone sitting on the bike and hanging a plumb from the top of the fork (line Y in the diagram) and then measuring the perpindicular distance from the plumb line to the centre of the axle (line X). Length X divided by length Y then gives the tangent of the rake angle and the rake angle can be derived from that. In looking closer at the frame today it has some slight curvature in the front rails .. bowing in by about 2mm half way down on both sides. This must be another artefact of its front ender, as with the bent steering stem. This bowing of the rails is presumably reducing the rake angle ?.
2. The longest trail was found using the bent steering stem despite this set up having the least rake. Presumably this bent stem has the effect of reducing the triple T offset , such that the trail is lengthened rather than shortened that would be expected from the lower rake figure?
3. All measured trails appear to be within an accepatable range and exceed that of the CB350 (85mm according to Clymer). The lowest figure (with the new shocks on) is comparable to some of the CB750 models (94mm?)... all subject to possible marg ins of errorin my methodolgy of course.
I also had a play with RB racing's rake and trail calculator at:
http://www.rbracing-rsr.com/advchoppercalc.html
I couldn't get the calculator to reproduce Hondas stock rake figure by entering standard dimensions for the 500 four,,.. so maybe it doesn't work for Honda SOHCs ? ... but what did seem consistent is that for a change of one degree in rake a change of about 6mm in trail resulted. This is roughly in line with results for the 400/four at : http://www.denoonsp.com/user/image/v3-issue1.pdf. In this article 0.4 degree of rake change results in 2.2mm of change in trail... so 1 degree rake = 5.5mm trail. This is consistent with what happened when I changed the shocks, I got 1 degree of change in rake and 5mm of change in trail. The 440/four article also notes that a 6.25mm increase in rear shocks procuded 0.4 degree reduction in rake. I've increased my rear fork length by 46mm, so if the 400 four figures can be extrapolated this would result in a change of 3 degrees in rake and 15.5mm of trail. I didn't get this level of change in rake or trail when changing from standard to longer shocks , mine are more like 1 degree of rake and 5mm in trail.
If 1 degree of rake change = 5.5 mm of trail change , then my measured rake of 23 degrees with the new shocks should have procuded a trail reduction of 15.5mm against the stock figure of 102.5mm .. but I only get about half that.
So what does all that tell me ? .... that the tolerance in my measurements were too wide such that my figures are unrelaible , or just that that I should follow the advice in mathewmosse's post .. get the bloody thing on the road with the longer shocks and see how it feels ...: ;D
Ewan 500 K1:
Heres how I went about measuring the trail with ref to attached photos
1. Got a broom handle and cut slots in it to accodate various bits of the bike...so that it would sit parallel to the headstock / forks . First photo shows the broom handle with cut outs
2. Second photo shows broom handle sitting on bike .. orientated to extend the line of the headstock down to the ground. The broom handle is lined up with the centre line of the headstock and parallel with the stanchions
3. Third photo shows the plumb line hanging from the centre of the axle and the bottom of the broom handle when orientated as described at point 2. Trail is then the distance between the bottom of the plumb line and the bottom of the broom handle.
The large washer hanging on a string in the third photo is used to measure the rake angle as shown in the diagram in the previous post.
Johnwebley:
you are working hard Ewan,
I suggest you get it on the road,run it for a while,get used to the feel.bed the tyres and brakes in ,
then explore the handling,
I guess you have some great bike roads around you,
go and have some fun
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