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BiKenG

Forks And Steering Geometry

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Lots of people playing with fork changes etc, but without any real data to judge what effect the changes may or may not make. So I set up a spreadsheet and entered some typical examples to illustrate what happens. But first...

This is done for the 5th gen 800 and it relies on original spec in order to be able to calculate what it does. If anyone needs data for a different model, providing the original spec is available, just let me know.

I have based everything on the suspension being fully extended as that's the only reliable and repeatable state. Hard to measure in practice of course, but that doesn't matter as what we're concerned with really is changes away from standard, which is the line in red.

The fork length is from the upper surface of a flat top yoke/triple clamp to the centre of the front axle. Gull wing yokes and/or forks not being flush with the top of the yoke will have to allowed for as it's impossible to build-in all possible variations. E.g. the standard forks I believe are 780mm overall. But they should extend above the upper surface of the (flat) top yoke by 41mm, plus the top cap which is about 2mm so the length to use is 737mm (780 - 2 - 41).

geom800.jpg

In case that disappears

geom800.tiff

It can be seen that reducing the OFFSET has a significant effect on the TRAIL which suggests that it's not a good idea to replace with forks with a very small OFFSET. It can be counteracted by dropping the front and/or raising the rear to steepen the RAKE, but there's a limit to how far you can go with this.

Anyway, hope this is of interest to others.

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From now on, playing around with forks like this will be known as "Fork Swappage" (thanks JZH) :biggrin:

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