Yup, I want to try and do this now. KTM 250/300 SX converted to a supersingle. I'd love to talk to GPTech for advice as he's got the most positive content posted on the subject but I think I'm a bit too late, sounds like he's stepped back based on older forum posts? To start I'm going to try and find a modernish linkage rear bike and... feel it out from there.
I had an opportunity to ride a Kramer last summer for a session at Mid Ohio. Simply put, the bike was fucking awesome. Pulled hard all the way down the back straight which surprised me. I hope to own one some day.
I'm now on the hunt for a 2012 250/300 XC as I think I want the 6 speed gearbox to start, linkage suspension.
Kind of related. The thunderbike/supertwins rules in the UK just added weight and dropped displacement on single cylinder bikes for 2019. The Kramer has been dominating over there.
What about a 250 TPI motor in a RC390 frame that is on a diet? I have been wanting to do a 2 stroke super single for a while. I was going to start that build this winter and then I ended up with a good deal on a RZ350. So that pushed my project back.
I don't think the 250/300 TPI can be competitive as is vs the Kramer. 50hp vs 80 to 90 last I recall? It would be a fun machine, but I'm hoping for a lot more go.
I would say 60hp maybe a little more would be possible. The tuner side of me really wants to play with a EFI 2 stroke. I wonder if BRC will make their 500 kit capable of using the TPI setup. I have not read through the whole thread, but have you looked at the BRC 500 kit for the KTM motors.
The BRC 500 is what I'm planning around, figure that with a linkage based chassis for maximum tuning options is the way to roll. XC transmission, 2012 to 2017 250/300 XC should be the hot ticket?
Yeah that is probably a good setup. I would say for road racing you can probably get a lot more aggressive with the porting, and a much bigger carb than the typical BRC kit. That should make an awesome bike. I would like to do one as a 250 so I can run it in SOS3 with AHRMA. It would be competing with 125gp bikes so it is possible it could do well.
So, I think I found the flaw in my plan: Starting with a 17" rear wheel setup, using a 300's taller primary gear, XC trans for tallest final gear, and the biggest front / smallest rear sprockets I know of, the bike tops out at 103mph, about 30mph short of where it needs to be at Loudon and no chance at any longer tracks. I don't think the big 500 can make power much past 7250RPM, so spinning faster isn't an option and I'm not aware of any other KTMs to steal a taller primary setup out of. The XC-W gearbox ends with the same final ratio as the XC so that's no help. Bah.
I would never (again) put a large single anything into a TZ chassis. Waste of time and $$ due to unreal vibration issues. It's not clear to me what you're trying to do : might help if you explained the rules for the class you're trying to enter into against the Kray-mahzzzz. If they're the same dudes from Bah-ston that showed up at the AHRMA vintage mess, there's nothing wrong with their throttle hands, but mid corner they're ...um....vulnerable.
I'm currently contesting ULGP (LRRS specific, think old CCS ULSB prior to SVs being allowed plus some vintage exceptions) along with CCS ULSB and GTL. For single cylinder machines there are no rules in those classes. The guys running Kramers in LRRS did not show any notable weaknesses in corner speed that I observed. By going from an FZR based machine to a single, I gain access to Supersingles, LW Sportsman, LWSS, LWSB as well, where the Kramers did very well. On the vibration front, this machine will be counterbalanced. I also got confirmation that the primary ratio is different for the motor, putting it where I want it to be, ish. Still won't have much legs for longer tracks but it's at least Loudon viable.
Yep, had same issue, also when geared super tall, the things can struggle to pull top gear. Are you dead set on a single cyl bike? If you're a tall dude, NSF250R might be too tight a squeeze. But they're a hella nice ride, very peaky power like a smoker. I do have a TZR SP roller if you're interested in a project.
Are you going to be using the KTM hub and spoked to a 17" wheel? I would say you could likely get smaller rear sprockets buy running a TZR or TZ rear wheel. Maybe even a SV rear wheel would do the trick. Just need something with a smaller sprocket bolt pattern. Also, Idk if the room is there. but alot of the 250cc single karts would run an offset sproket to allow them to run a bigger sprocket. The offset would help the chain clear the clutch mechanism.
