Hello everyone, first time posting here.
I’m from Nova Prata, Brazil.
We have a track here in the city that is 700m length and 7m width.
It has about 3 or 4 kart every Saturday with MG red tires (medium/hard). So I assume it’s a low grip track, right?
I run a birel bravar, I think it’s similar to a birel art.
The record lap time is a 32.17s and I’m trying to tune the kart for a 31sec.
The problem I have is always on entry, the front respond very quick (not excessive) and the rear won’t grip in the transition from entry to mid, on exit I can exit well, some corners a little oversteer but not too much.
The top speed for the track is around 107km/h and we have a fast corner right after it around 90km/h, on mid/exit it has a lot of oversteer ( only this corner).
I already tried to fix the entry problem doing this : Harder axle, more Camber, less caster.
With the setup above I got also 32.18.
Then I raised the front and moved the seat back 1cm.
That has made the kart a lot better to drive. The back in the fast turn is very planted to the ground and the entry is not perfect but very good, the front has decresead the agility some amount. And the final lap time is: 32.9s .
I don’t feel the kart boggin down or being slow mid corner.
Anyone can help?
It sounds like you’ve made the kart more comfortable to drive by decreasing the amount of inside rear wheel lift and the amount of dig the outside tire is giving. This will make the kart more stable but runs the risk of binding the kart by not unloading the inside rear wheel on exit, slowing your exit speed, which is why you are slower after those changes.
What engine and tire pressures?
Both days I were with MG yellows, the day of 32.18 I was using 12 front 13 rear
32.9 same tire (exact same, 5 laps older) 11 and 12 pressure.
Engine is 125cc iame MY, same as a a tag but without a clutch, like a x30, without balancing shaft and clutch.
I didn’t feel the engine bogging, but it could be.
It looks like the same exit oversteer than before.
What I felt was that at mid acceleration the engine looked like hopping. This wasn’t happening the day before.
One important detail I forgot, the curves have a very generous angle. Banked corners.
Here the video of the 32.18 lap
This lap was done before the 32.17 lap. With a softer axle and a little bit more caster.
If the track surface is low grip, 12 or 13 psi cold on MG Yellows is probably okay but that does seem a little high. Typically we run between 8.5-11 psi as our range in normal conditions. I wouldn’t be afraid to try a little lower to see what it does.
One thing with banked corners like that is the kart may not feel like it’s bogging down because the banking will help keep the kart rotating and feeling okay, so you may not notice it easily if the kart is sitting flat on the exit of the corner.
The track looks pretty fast for the most part. I would say put the seat back to where you had it when it was faster, and continue to take a little more caster out if you can. On long flowing corners, the caster will scrub the front end more and slow you down. Plus, it will make the kart more twitchy and sensitive through the corner, where you are experiencing it snapping to oversteer. If you can’t take more caster out, I would also consider narrowing the front width, as that will have a similar effect.
Seat changes are quite big and can really upset the balance of the kart. You’re only looking for a tenth or two, so small changes might get you there.
Yesterday I reversed the changes to the seat. I think Saturday I may give another try.
What you suggest me, a birel freeline b axle (blue) ~80, or a ~90 orange birel axle (I think it’s from Brazil birel) I have?
Any suggestion on front and rear height?
Main problem is entry/mid in turn 3-4 after the long left and turn 7, the 2nd longest, before last corner.
I would leave the ride heights alone for now. Focus on making small adjustments to see if you can fix the issue before bigger adjustments like ride height. If you make too many or too big of an adjustment you might end up on the other side of the problem and create new problems.
Birel recommends the blue axle for low grip, so that seems like it would be okay.
The kart is snapping mid-corner at max load, so the kart either is jacking too much weight or not enough weight. Since taking caster out seemed to help, that tells me the kart is jacking too much weight.
Thanks @tjkoyen, will follow your guidelines and try it on track. Will film it again and post here!!
Totally agree with TJ about the tyre pressure and keeping the changes simple before trying an axel or something like this.
Just keep in mind that the Bravar is not a Birelart if you are thinking to copy an Birealrt setup from someone else.
I’ve driven the Birel Sudam R32 (previous model before they came with the Bravar) in Brazil for a while and it wasn’t too similar to the Birelart.
Definitely would go lower on the tyre pressure and try to get it on the 12-13 hot