I don’t believe that there has been much racing at Carolina Motorsports Park lately, but it looks like they are having an open practice day this weekend and I was considering heading over to try the track (I’ve never driven there).
Does anyone have some recommendations as to where I should start regarding gearing with an X30?
Hey brother. I see no one has responded to this. I recently made a similar thread about KA gearing for 103rd Street, and I didn’t get any responses either. It seems like the forums aren’t able to answer these questions. I’m thinking maybe we should start a megathread or some kind of pinned resource where people share their gear ratios for all tracks they know in one thread. I’m not really sure how to do this because I’m pretty new to the forums, but what do you think?
The reality is very few people have driven at CMP lately. They haven’t hosted a race in a long time. Hence the lack of response regarding gearing.
And I’m fairly sure there are basically no KAs at 103rd, which is why no one knows the gearing there.
If someone has gearing info for any track, post it up and we can make a sticky thread for it. Good idea.
Thank you. A guy I know at 103rd Street suggested I try 11:72, but I don’t have the right sprockets for that. I’m gonna try 10:68 on Sunday and I’ll report back on how it goes.
Try 10:76. I ran a 125cc Leopard (predecessor to the x30) there in 2018 and I had a 10:78 to 10:80 on and was in the low 16000 range.
Oh really? In that case, 10/68 might be too small a rear sprocket for my KA. I imagine a Leopard makes a lot more power than a KA. I might need more teeth.
That is for Kershaw aka Carolina MP
Kershaw x30 gearing was 11:83 last time I was there.
KA gearing at 103rd street (kart + driver = 363 lbs):
I was hoping to fix the RaceStudio glitch I described in this thread (RaceStudio 3 tries to install on invalid drive) so I could get solid data, but I can’t, so I’ll just go with top speeds, laptimes, and seat of pants feel.
I tried 10:68 and 10:66. Not a huge difference between them. Both resulted in 67.9 to 68.9 mph top speed at the end of the straight on the “clockwise with chicane” track configuration and laptimes from high 38s to low 40s depending on new vs. cooked tires. Max rpm was mid 14ks. This held true in both hot day and cool night sessions. I cant say for sure which rear sprocket is faster without RaceStudio analysis of that sector to see which gains/loses time.
I think these ratios are close to ideal for this track configuration. The key is that it didn’t bog coming out of the slow hairpin before the front straight past the pits. I wouldn’t want to go too much lower on the gear ratio unless I was running without the chicane. With chicane, the extra top speed might not be worth it. That hairpin (slowest corner on track) is really slow. Important to keep revs up there.
1 mph of top speed and lap time variations of up to 2 seconds are pretty huge discrepancies. Even with 103rd’s long straight, I can’t imagine 14k is the ideal max RPM for that track. We ran more than that there on Yamahas back in the day. These days, even on long tracks, KAs are spinning far more than that. At SuperNats we had an enormous straight and we were still hitting 18k.
Shame your RaceStudio still isn’t working, would be interesting data to look at.
Highest I’ve spun my KA is 16.4k or so. It can go to 18K safely? Most of that laptime was tires.
Your max RPM range should be 16,000-17,500 in most cases. More RPM for tighter twistier tracks and less RPM for more flowing tracks. But yes, you can run it up to 18,000. Obviously the higher the RPM the shorter the time between rebuilds.
Thanks. Why did you do it, though? Surely it makes less power at 18k than at 16.5k, right?
On tracks where there are very tight corners, you gain far more time over-gearing to accelerate off the tight corners than you lose by spinning a bunch of RPM on the end of the straight. Specifically at SuperNats they had a tight infield and a massive straight, hence the high RPM. On a track like New Castle or Trackhouse you would run less max RPM because it’s a more flowing track so you don’t need the massive acceleration as much and you make your time up by rolling through the fast stuff in the peak torque of the engine.
Peak torque is somewhere around 11k, so technically anything over that is “over-rev”. But the goal is to keep the engine in that peak torque range as much as possible through a lap to be producing max power as much as possible. Gear too low and you don’t get into the peak torque often enough. Gear too high and you blow through peak power too quick throughout the lap.