I’m new to karting, just picked a Rotax sr and only have a few weekends under my belt and am trying to get a better handle on chassis response and handling. The last time I went to the track, I noticed that the first 5 or so laps have been fairly consistent, within maybe a tenth or 2. After those first several laps, my lap times gradually slowed down till they were consistently about .5 seconds slower. I have a feeling it is probably attributed to tire pressure/temps but I wanted to see what the general thoughts are.
In general, Im running near the end of life on my tires, which maybe has a larger factor than I am giving it credit for. I also have a bit of uneven wear towards the inside of my front tires, which I think I need to address with camber adjustments.
Now before I get new tires, I will probably squeeze another weekend or two more out of my existing ones. If my late session slow laps are likely a pressure problem, thats easy enough to play with. If its more likely chassis adjustment, is it worth chasing now or wait till I start with fresh tires? Any common adjustments that could help? I just need to make sure I continue to dominate over my friend who is also new to Rotax
Back when I used to run, the first two laps were always the fastest, typically the 2nd on Bridgestone YHCs. Just like any racecar, lap times will drop off as the tires heat up etc. Half a second is a bit large, but if you are using older tires that is going to happen. If you are feathering the inside of the tires that means the front is pushing or the kart is bound up overall. Try changing some of the chassis bars or rear width, dont remember what way to go on caster etc on a kart to help that problem anymore.
As Eric noted, with old tires, they will overheat quicker and drop off more over a run.
If the kart is handling well but just getting slower, you’re probably best off playing with tire pressures and dropping them down a bit to get the kart to stay in longer.
Never tune a kart on old worn out tires. It’ll react differently to changes than it will on new tires. Often you can chase and chase and chase setup on old tires and you’ll only end up so far out of the tuning window that when you throw new tires on, you don’t pick up any time and you’ve given yourself a handful of new handling issues.
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Every time you heat cycle a set of tires you take some life out of them. Take a look at the karts on the grid for qualifying. Most will have a new set of tires. Mid compound tires seem to be the worst. Take a Bridgestone YHC for instance. They are done after one day in my opinion. If you kart is consistent in the first several laps, then goes off, sounds like too much initial air pressure over heating them.
Agree with all, old tires are tough to work with, especially as old as these sound like they are.
Try checking the air pressure as soon as you get off the track, with the tires hot, bleed the pressure down to what you go out on and and see what that does.
Example, if you go out on 10 pounds and come in and the pressure is 13, take them down to 10 hot.
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