I’m constantly overheating my rear tyres and can’t find a setup change to cure it. I run a Birel RY30 in easykart on Vega Reds. I’m 6 foot and weigh 87kg kitted up, with no lead on the kart I’m around the weight limit for the class. The seat (Tillett T11) is set to the default easykart position (59cm/60cm from front rail, 21cm from axle to lip) which gives me a weight distribution of F41.5/R58.5.
The recommended tyre pressure range by easykart is between 8-12 PSI and anywhere in that range usually produces an increase of 3-4 PSI when they come in hot. This happens on new and used rubber. On new rubber the kart handles ok even if the hot pressures are high. When the tyres are a day or two old it feels like the rear is sliding but since the front left grains quite often I’m wondering whether I’m actually understeering and then snap oversteering?
I usually run 1390mm on the rear and between 20-25mm spacing on the fronts but I have played around with widths, front ride heights and 3rd bearing (easykarts have no caster or camber adjustments or rear ride height adjustments). I find loosed seat stays can help when temperature and grip levels increase.
I’m thinking about moving the seat forward to obtain a 43/57 weight distribution to put less stress on the rears? I have many days where I will change front/rear widths, front ride height and 3rd bearing and it doesn’t really effect lap times or see a big change in chassis feel. Could this be due to an incorrect seat position?
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I think if you’ve got a consistent pattern of smoking the rears like that’s it’s worth moving the seat to see if it helps.
You could even take a lazy approach and throw a cushion/sheet of styrofoam behind your back for a few laps.
FWIW, We run the Vega Reds and 8-12 PSI is on the lower side of what we do. We tend to be 12+ most every where we have been. Only time we have been lower than 12 was last year and it was 110F. Only then did we run 10
I would start by getting weight forward since that is really your best option with no caster and camber adjustment and then look at the air. You mentioned the fronts graining. Quick thought is you have a push - kick going on.
To a certain extent, one thing people often overlook is the pressure gain versus absolute pressure. For most racing tires in karting, 3-4 psi pressure gain is concerningly high. Lowering tire pressures beyond 8 would likely make the kart undrivably loose in moderate or ‘green’ conditions.
As people say, perhaps moving the seat forward is the single most impactful thing you can try that you haven’t already.
If the kart works ok for the first few laps and then the rears start getting greasy (hot), the chassis is too stiff for you. There might be cost effective ways to make the chassis work other than buy another one. Softer seat, axle different axle but for me the solution was a softer chassis.
Another chassis or softer seat is not an option with Easykart. The only ways to soften the kart would be loose/no seat stays, no front torsion bar (probably not a option with how often the chassis will get bent) loosened front/rear bumpers/floor tray and 3rd bearing out.
The kart has excellent pace for the start of the race but falls off more than other at the middle/end especially when the day gets hot. I have tried to experiment with low pressures but it can be hard to find the right balance as hopping can occur which then only adds to the overheating problem.
In that case, given what you’ve tried already, I think your next option is what you said at the outset, try a different seat position. You could go forward, or up/raise.
Forward to work the fronts more and place less less horizontal load on the rear… Or move the seat up horizontally. This should help with lateral load transfer which is possibly what you are lacking here… It’s unloading the inside rear early and progressively enough, and rather is sitting flat, then suddenly picking up and dropping back down and is potentially the source of the hopping.
It’s hard to diagnose over the internet though
I think i’d go with up on the seat so that your braking traction stays similar to what you have.
You could also try nitrogen or “dry air” in your tires to help limit the pressure increase. Generally you want to see about 2PSI gain and not much more.
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