Took longer than expected, but now I have the tires setup on my board, on my old chassis which I modified to fit these. Figured I want to try the tires first before finalising the design of the new chassis I was working on.
These are the Bridgestone YPB tires, manufactured 5 years ago… They didn’t harden up too much by feel though. I had two sessions on them so far, and some very weird findings.
First I started with a 22T motor pinion, as I didn’t have time to switch the motor pinions too and I really didn’t want to miss the first opportunity to try these. My grip circle was showing longitudinal acceleration about 0.5G. This was expected and completely reasonable - the tires I was swapping over from gave me around 0.9G on the grip circle with an about 80-85 km/h gearing (50-52 mph). And with the 22T pinion on the 10" wheel I had an unreachable top speed on paper close to 140-150 km/h or 90 mph. So far so good. It also confirmed that angular momentum is not significant. I could also get the tires up to reasonable temperatures given the pretty bad conditions on that day and some very apparent setup issues still present. Lateral grip was awesome when I kept going for a bit to build up heat.
Then I swapped over to a 12T motor pinion to compensate my gearing, this gives me a top speed around 5% off from the smaller tire setup. Here’s where things really went sideways - I was still logging about half a G on the grip circle for acceleration throughout the full session, and I was pulling full throttle on the remote many times. I also know how to handle more acceleration given I was doing around 0.9G on my smaller set of wheels. Swapping gearing (and doing no other related change) did not increase my acceleration, or if it did it was very marginal. I also completely ate through the 12T pinions so had to finish the session a little earlier than I wanted, but that’s probably just the material not being the proper grade and not hardened. Plus the small size doesn’t help either of course. Backlash was set correctly. The size is definitely not ideal and both gears should be bigger ideally. But people in the hobby do run mod 1.5 gears at 11-12T quite often… Just on smaller wheels usually within faster spinning motors. I did also get decent temperatures into the tire, couldn’t find my IR temp gun but the contact patch didn’t quite fully look like, but definitely started to look like how a kart tire should look. It needs a little bit more temp still, but I don’t think I was too far off the ideal range now. Oh and I was running 10psi (0.7 bar) cold up until now, although I do need to get a more accurate pump, I don’t really trust the readings of this one too much.
That grip circle thing isn’t the most scientific measurement, but this is the only data I took and at the moment my only working motor pinions are 22T, so taking some more scientific data will have to wait a bit.
Given such a weird phenomenon I decided to give chatgpt a ton of context about the setup, what I am doing exactly, which tire it is, etc. Then gave it this very weird preliminary result and asked it to explain it. This is what it came back with:
It thinks if I reach around that 0.5G point in acceleration, then the extra torque I apply to the wheel, just heats up the tire instead of moving the vehicle forward, and this effect is so extreme that it has already plateaud out, meaning if I were to put even more torque into it, it would still only accelerate 0.5G. I really can’t wrap my head around how I could be heating the tires with over a 1000W loss per tire from the extra torque the 12T pinion creates instead of the 22T pinion. The wheels are not slipping that’s for sure though. Is this really a phenomenon? I am technically using front tires that aren’t designed for longitudinal grip transfer I get that. But 0.5G is pretty mediocre especially for my setup…
I do want to eventually get to doing drag times between the two gearings to dive into this deeper. Plus confirm that I am indeed pulling the full current on the electrical side… I am pretty worried now though. Maybe it’s just a fluke, but since I ate all the 12T I can’t retest up until two days before the race. Lecont LPMs should be stiffer sidewall, but I’d ideally figure out what the heck just happened before my race next week, otherwise I gotta do a bunch of work to swap back to the small wheels. Still might end up doing that for the race itself, that is a proven setup afterall.
