What tyre sizes and brands are people running on track bikes? From what I understand, you can fit a 120/70 front and 140/50 rear on stock wheels. I have a 87 2kr Cheers
Those sizes are for the wider 3LN wheels 2.75x17 and 3.50x17. You need to use narrower tyres to suit the 2.15x17 and 2.50x17 wheels on the 2KR. Bridgestone BT39SS are track tyres with sizes to suit your rims. Don't get BT39 as they are street tyres. BT39SS are Super Sport race tyres. In Australia Whites Racing Products are probably your only source. 90/80 front and 120/80 rear https://www.bridgestone.com/products/motorcycle_tires/products/battlax/bt39ss.html
Didn't have time to post properly before, but going for wider tyres is often not productive on the smaller bikes - slows down handling and direction changes especially from full lean one way to the other. The advantage of these small bikes is that they are very nimble and can run rings around bigger bikes where it matters, with a skilled rider. You also don't have as much power to play with, so you are using what you have nearly all the time, while the bigger bikes are still braking and setting up their 'point and shoot' style, you will be on the power the whole way through. My anecdotes on riding 3LN FZR250's - the 100/80/17 and 130/70/17 setup was noticably more nimble than a 110/70/17 and 140/70/17 configuration. I haven't ridden a 2KR so I can't really comment on what they're like, but I would imagine they are slightly more nimble given the smaller tyre and rims.
The rim sizes for RS125's and Moto 3 bikes are 2.5in front and 3.5in rear. Slicks for those can be fitted to the 3LN rims. Forget nimble - that can be adjusted in. Grip is paramount.
Moto 3 slicks are the best tyres if you fit a 3LN rear wheel (it goes straight in). Note that you cannot use them in Australian Historic Road Racing P6 Production class. The specs for the Bridgestone front slick say it is ok to use with the 2KR 2.15 front wheel. If you really get carried away you can also fit either the TZ125 or SRX400 2.5x17 rim to the front. If so I would recommend the SRX400 rim over the TZ125 rim because it will handle off track excursions much better. When I compared the slicks in 90 and 120 sizes against the 100/80 17 and 130/80 17 tyres the wider tyres made the bike feel very slow steering.
Thanks, this gives me a good starting point and I can just play around with it a bit more. Would it matter much with me being a bigger dude? I'm 105kg and 6'1, obvs I'm not going to be as fast as someone who weighs less but I'm just curious if the tyre size would make a difference due to my weight
Yes definitely, these bikes are designed for small japanese jockeys. You will need suspension tuning, most likely springs in the forks. Not much adjustment available on these other than preload on the rear, and changing springs in the forks. Someone might do some gold valve emulators
There are some suspension guides in the resources section. RaceTech can do gold valves for just about anything if you can give them dimensions. Normally I shy away from recommending larger tyres, but for a big fella like yourself I would say definitely go up from standard.
What an awesome website, I wish all parts sites were like this, it actually helps you find what you need instead of just a bunch of random stuff!
I'll look into the forks as I know they can't be modified to compete in period 6 but can you swap out the rear shock? I had a read through but wasn't sure
You should fit the emulators and springs to improve the underdamped undersprung JDM forks. You can change the shock for P6.