changing gear ratios

[el_oso]

was thinking about changing the gear ratios on my XJ600 diversion slightly. want to increase the ratios slightly as under normal riding conditions the rev range is slightly out. for example at 30 in 2nd gear does over 5k nearly 6k rpm. change up a gear and the bike sits at the annoying maximum vibration. change up another gear and if i pull the throttle nothing much happens. also when sitting on the motorway at 70mph which is what i mainly use the bike for, it is sitting at 5.5k rpm. what would be better gaining one tooth on the front or losing a tooth on the back. increasing the front would have a more noticeable effect but wondering if it would be too much and put me back into the annoying vibrating band of the bike at 70mph. back wheel is 18" if anyone cares enough to know how to work out this gear ratio stuff exactly.

thanks in advance
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Duke 390
Previous: '05 XR125L | '96 XJ600S Diversion |'05 Suzuki GSXR1000 | '05 Honda CBR125-R | '97 YZF 600R Thundercat | '11 Honda CBR250
Car: Jeep Wrangler 4.0L

[G]

One tooth at the front is the same as about three at the back. (This is based on a 15:45 ratio, but won't be too out for most others)

So if you want an easy reasonable difference, just the front, or go up/down the same number front and back to keep the same length chain.

Up front/down back = up geared, so higher ratios and top speed, less acceleration.
Down front/up back = down geared, so lower ratios and top speed, more acceleration.

If you search for it, there's plenty of pre-made ratio workerouters. Though I tend to just stick the figures into a spread sheet myself.

[serlant]

https://www.gearingcommander.com/
look up you're bike, I expect its the same as the 92 seca, then just change around the final drive ratio column to +/-1 tooth front and rear and compare