Hi all Bantamers.
I am very lucky to be in the motorcycle trade and because of that I get to go to trade shows. Visiting a show in 2012 there was a KTM 125 GP bike on display, and then in 2013 there was a Honda Moto 3 bike on display. On both occasions I had the opportunity to measure the bikes. Obviously I measured them in order to compare them to a Bantam. Both bikes are longer and lower than a Bantam. The C of G of both can only be approximated at slightly higher than a Bantam (in consideration of both bikes being lower). The length is not surprising when you compare the tracks they are raced upon compared to what we race on but the height I found a surprise. I have come to the conclusion that it is because of the very close competition necessitating slipstreaming in order to keep up with the opposition. You can make of these facts what you will but I remain convinced that a Bantam needs to be longer and have a higher C of G than standard (see my posts on handling). If it is taken as read that a Bantam needs to be longer then the mounting of a cantilever/monoshock is no problem at all as the extra length in the swing arm gives you all the room needed to fit it in. If the standard wheelbase is going to be adhered to then it is a little bit more complicated. As Andy has already done it’s possible to fit it alongside the top frame tube. It is also possible to fit it above the top frame tube. Yes in this position space will need to be made in the fuel tank, but as most fuel tanks are at least as twice as big as necessary then all that needs to be removed is air space. Another possibility is to consider the Britton which had its rear shock fitted in front of the engine operated by tie rods and linkages. This was done for very good reasons of mass centralisation and weight distribution. I do not think that it can be fitted to a Bantam in this position because of the clearance needed by the front wheel, but it can be fitted under the lower frame rail like the Yamaha RD500 V4 (quite a few road bikes have their rear shock fitted under the engine for purely packaging reasons). All of these options need access to fabricating and machining facilities, but whichever of these options is chosen the mass centralisation / C of G will be improved to lesser or greater degree depending on what choice is made.
To conclude it is possible to build a cantilever/ monoshock Bantam at any length you like but if you chose to stick to a standard wheelbase then it as more difficult to get everything fitted in with the leverage ratio’s correct.
Mick.
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Sun Jan 19, 2014 8:31 pm