I was wondering if anyone has looked at having a custom 6th gear made to drop rpm in top gear for cruising?

I’m running a CBR engine in my BEC with a cassette type transmission which can be swapped out without too much drama so my thoughts are that I could run a spare transmission to use for cruising events rather than racing and swap them out depending on the occasion, the car is mainly road use and 7100rpm on the highway gets annoying on a 4 hour round trip on some of our runs.

What size of wheels are you running? always cheaper to start there than overdrives etc. I used to have two sets for my Landy, tall skinny's to raise the gearing for the road and small wides for the mud plugging.

Although if your using a chain drive the answers obvious.

[Edited on 4/4/24 by Mr Whippy]

No-one wants their locost to look like a 4x4 though

Changing to a bigger tyre would be an issue, I only have about 5mm clearance between the tyres and cycle guards on the front, even to the point that different tyre manufacturers sometimes won’t fit even though they are the same size (175/60R13).
I don’t want to lose the acceleration it currently has by changing the diff ratio, etc (currently 3.54) so would prefer to leave everything the way it is outside of using 6th as basically an overdrive.
I thought that maybe someone had already gone down this path before so was hoping for some feedback on how it went but I may have to be the guinea pig on this one.