The junior classes all have more powerful senior equivalents. The most popular senior class in the country are Rotax Max, Senior TKM Extreme and Senior X30 and there may be other options worth exploring at your local circuit. The once all-conquering TKM Extreme class is now only popular in certain areas, eg in the Midlands, and if you live in such an area it should be investigated. Once some experience has been gained there are further options for the premier international classes, raced primarily at the major championships. These OK class use a variety of 125cc TAG engines, from different manufacturers. OK is unlikely to be seen at club level. They are restricted in maximum rpm for longer life. Both are raced in the Super One Series with OK Senior being the MSA British Championship. Senior classes top out at 85mph.
TKM Extreme is for year of 16th birthday upwards (although as in all the classes very experienced juniors already racing may move into the senior classes earlier). The engine is a115cc variant of the BT82. It’s a popular and economic class and now has a TAG option.
The senior equivalent of Junior Max, with a very powerful 125cc TAG engine. Although the maximum revs are limited electronically, they are nearly as quick as OK, but much lower maintenance, and sealed to prevent unapproved tuning. Care needs to be taken if starting in this class. Like many classes there is a higher weight variant called Rotax 177 for the heavier driver.
A TAG electric start water cooled 125cc engine which is not sealed so anyone can do rebuilds. There is a ‘Tour’ for X30 in the Little Breen Man series and a National Series in the Super One.
Senior 4-stroke classes
There are other 4-stroke classes for Junior and Seniors which run at certain clubs only e.g. Honda classes and World Formula (senior only). More information on http://www.abkc.org.uk/startkart.htm