FF: Forks New Coilover for Girdraulics

timetraveller

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Just one comment; with the JE mod set up properly there is no forward movement of the wheel spindle. I did publish a diagram some time ago and if it would help then I can retrieve it from the PC and publish it again here. Also, thank you for all the work you put in.
 

greg brillus

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That's, actually not quite correct, the axle does in fact come forward from the lowest point but only a couple of mm at the most, or until the lower and upper links are parallel with the ground. I did some early pictures of the path itself when I first built the racer. The travel was about 85 mm from memory and moved aft about 15 to 20 mm. The other point with the JE mod is the upper attachment for the upper spring box is further forward given the eccentrics are gone in place of the bearings/concentrics. So this actually makes the effective spring rates work higher than a standard set up. They are only small changes, but they do make a difference. Sorry if it sounds like I'm nit picking, It is worth noting the very small working area if a coilover is to be used. It's a bit like trying to get maximum valve travel in the cylinder head when you cant see whats going on once the rocker bearing is in place..............:).
 

timetraveller

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VOC Member
Greg above is correct but according to my measurements one should never get into that part of the movement regime. I will try and copy the curve I have shown before below. Note that this was made by having a pencil fastened into the front wheel spindle hole and moving the wheel up and down. The pencil itself was held up against a piece of imperial graph paper where the larger squares are one inch, and the smaller ones, one tenth of an inch (2.5 mm). The relevant part of the curve is at the lower end of the right hand curve. The line with a zero against it is when the lower link is horizontal and in this case the wheel was allowed to drop below the zero position by about one inch. If one starts off in that position then is it true that the wheel will move forwards by about 3 to 4 mm before is gets to what is intended to be its original starting position. It can be seen that if the spindle starts off about 5 mm below the zero point, the circle on the line, then there will be about zero to one mm of forwards movement before the lower link is horizontal. I have always assumed that this could be ignored and therefor I advise people to try to get the lower link horizontal with them sitting on the bike but always state that up to half an inch below that position will still be acceptable. If you have the option then it is worth while enlarging this graph and studying the details. I found it quite difficult to obtain these curves and it would be interesting to see Greg's measurements and compare his curves with mine.
1543418042801.png
 

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