Gearing

When I did Cadwell park in September 2003, I couldn't understand why I was losing so much time to a mate on his ZXR400, averaging 6/8 seconds per lap! Now he is a better rider than me as he's got a lot more track experience and has a very nicely sorted bike but I should have been a lot lot closer than that.

When I got an instructor to follow me, he informed me that I was only achieving 100mph along park straight, I should have been reaching 125mph, especially as my exit corner speeds were high out of charlies 2.

Laptime wise I was hitting circa 2 min times on the 400 on the full circuit. My mate was hitting 1:53 to 55's which was disappointing as I was aiming for 1:55 which I was sure I was capable of, especially as that's what I achieve using the zx6R.

When I got back home, I discovered a few things that didn't help my top end speed loss:

• Gearing was too high
• Possible air leak at the carbs leaning off the mixture at the top end hence losing power
• Rear brake caliper was rubbing on the wheel

Gearing

After speaking to a few people, they advised me that the gearing on the FZR400RSP was over geared for most tracks. Neil Smith runs various sprockets ranging from 38-45 for the rear and a 14 tooth for the front to cope.

I stripped the carbs down and gave them a full cleaning out with carb cleaner. I did find that the clamps holding the carbs to the airbox were not sealing correctly so this could attribute to the leaning off of the mixture.

I then by chance looked at the rear end around the brakes & couldn't believe what I was seeing. The previous owner had fitted a caliper from an FZR750 & had filed off the bottom to give it some clearance. Problem was it wasn't enough & it's actually been rubbing on the back wheel, wearing away aluminium in the process! Luckily I had a spare FZ400 rear caliper so swapped it over, rebled the lines & spun the wheel. About 1 mm of clearance, jeez leave it tight don't they!

For Anglesey (report), I decided to fit a 14 tooth front sprocket & see what a difference it made. Acceleration was improved and the bike seemed to respond better to the throttle. Unfortunately Anglesey has no long straights although I was hitting approx 95mph along the main straight (in the wet on sports tyres!). The real test would be back to Cadwell to compare with previous dates, just hope it's dry!

Gearing charts

Speed-vs-RPM charts for stock and modified sprocket combinations, worked out with the gearing calculator below.

Want to work out your own combination? Grab the gearing calculator spreadsheet from the Downloads page.