So I was having a conversation with a buddy of mine and I told him one of the guys I race with, his kart gets faster as the laps progress, whereas mine gets tight and begins getting slower toward the end of the race. Not all the time, but I’d say about 60% of the time it holds true.
He said its a sign that the chassis is aging out. Not sure if I agree with that but I thought I’d pose a two part question:
What is your tactic to combat the kart geting tight?
Do you think the age/ wear of the chassis has anything to do with that?
A part of me wonders if I should bring in the rear hubs as the track rubbers up and my kart get tight, just to free up the rear end more?
For me I think this has very little to do with a kart wearing out, and more to do with driving and setup not being optimized for longer runs and/or higher grip levels. If you don’t practice on similar track conditions to that of which you race, you’ll never have a truly apples to apples setup comparison. Additionally, many drivers are not sufficiently acclimated to the lower tire pressures that may be required for a longer run and/or high-grip setting. In those conditions a kart may take a few laps to come in, which will make it difficult to drive in the early laps. Naturally this creates a tradeoff between setup optimization for the first half of a race vs. second half.
Probably nothing to do with the chassis age in this case, as Evan said.
If your kart is getting “tight”, you’re overworking the tire in some way and getting it too hot. So you need to drop air pressure to delay that, maybe change wheels to something that helps the tire stay in it’s ideal operating temp longer, or it may be a driving or fundamental chassis setup issue. If you’re really rough with the wheel or using the front tires to scrub speed too much on entry, you’re going to work those tires faster. If you’re sliding the kart too much, you’ll work the rears faster.
And as Evan said, setting the kart up to be good in the latter stages of the race means it will be less good in the beginning. Really, you can optimize it either way, as there will be a trade-off. A kart that is really good in the beginning may fall off by the end of the run. A kart that is set up to be good at the end of the run might take some extra skill and finesse to maintain your position early on when the kart isn’t as good.
Most people are setting up so the kart just starts to fall off at the end, or stays in the whole race. In general, it’s much easier to give the driver a kart that takes a while to come in, so they can hustle and drive flat-out the full race, rather than forcing them to start managing the tires halfway through the race.
And it will take a skill set to start to feel the moment when the kart is falling off, and adjust your driving around that so you don’t drive the kart off the handling cliff by continuing to wring its neck when you’re already over its limit.
The kart chassis has no idea if it’s lap 1 or lap 20. There’s only two things that tighten up over the course of the race.
The tires
The driver
Honestly, with masters and newer drivers, 75% of the time it’s number 2.
Driver starts holding wheel tighter, starts over driving and heating tires up. Starts turning in earlier thinking he’s driving harder, tightening up kart on exit.
Pick a straightaway. Take a deep breath on a mark every time and stay focused. Eliminate driver before adjusting kart.
My 15 years old chassis still get really tight towards end of the races. One of my solution is throwing away my comfortable deep seat, put back standard kart seat back. It frees up the kart a lot, but hurt my ribs a lot too.
Had you tried other tuning adjustments to compensate for the Deep Seat being stiffer? The standard seat may work better, but broken/bruised ribs could mean you’re out of the “seat” entirely. You could try running fewer seat struts, cut a slit in the top of the seat to allow it to flex more, or loosen the crotch bolts where the seat mounts to the chassis. Just a few ideas in case the standard seat continues to beat you up too much.
I did play with some easier way, no struts and etc, none of them works. Swap the seats make a huge differences, saved a lot of weight too. I wear my Bingio no matter what, so standard seat is not that bad, but deep seat is way much more comfortable. I always want to try the Jecko/Imaf seat with leg support, maybe I will give it a shot this season.
As someone who had to tune around the DeepSeat’s specific characteristics (I was injured and had to run it, plus my dad owned DeepSeat at the time), we found that trimming top roll lip off softened the seat significantly, and we even tried running the seat mounted on rubber isolators instead of plastic spacers. The rubber isolators was too much flex for sure, the seat was moving like an inch either way during cornering. But cutting that lip off or making some relief cuts in the waist area on either side both helped the seat react a lot more like a normal seat. We were able to run up front nationally after we did those things.
There are still some inherent disadvantages to the seat, mainly stemming from the fact that you cannot move your body and work the kart as much, which is its intent partially.
That’s also part of reason I went back to standard seat. Once you are "clip"in by the lip, you are kind of stuck here. After I got a Bingo, rib does not bother me that much, so I decide to be lazy by going back to standard seat.
Could it be a pressure thing? I’m guessing tires that start optimal pressure would get less grippy as opposed to tight as they go up past optimal. Any difference in weather/temp when you notice this going on?
May have missed it but what chassis, track, temps etc.
Of note, 15 PSI is rather high for vega reds. We’ve ran them for years with Cup. We tend to be 10-12 most places. Cooler temps or lower grip we do go higher.
15 psi is the baseline and I usually air down as the temps warm up. I used to run 10 psi religiously, but after talking to some faster guys, they were all around 15psi. So I was just mimicing what the fast guys were doing.
In most circumstances in Florida, track temps start in the 40’s in the a.m. and warm to around 70-80 by the afternoon.
I’m speaking to current winter time conditions. In the summer is starts in the 70-80’s in the a.m. and can raise to the high 90’s by noon.
Track is Monticello, FL. (1.1 mile)
Chassis is 2017 TB Kart S55
Every kart and driver is going to be a touch different. I say the next time you’re out on a practice day, do nothing but air. Record your data and see what the kart and you like.
When we were searching for what we wanted for hot PSI with a new chassis, we set it high and would run 10 laps. Record hot PSI, then knock off .25-.5 and go immediately back out. For a quick 3-5 lap stint. This gives you more instant feedback on hot tire PSI. If was better we’d come back in and let tires cool and record PSI.
We’d then go back out at cold temps for another 10 laps and repeat recording and lowering of PSI.
Did this until getting back on track immediately had no improvement in handling and/or lap time.
This isn’t a sure fire way to find everything you need but it’s a quick way to record results and have data in your set up book for later. Can get through a lot of laps and PSI in a handful of sessions.
TJ, I am struggling with the stiffness of the DeepSeat, I understand trimming the top roll lip but what do you mean by “relief cuts in the waist area on either side.” I think I am struggling with getting the inside rear to lift on hairpins.
