Lose grip as the day goes on

[Dan Pingston]

I am hoping for some help. I just got a new kart, FA V2 (32mm) running Mojo D2 in Rotax Masters (405lbs). We are really fast in morning warm-ups on old, hard tires. We did testing throughout the winter when no one else was out there, so very little rubber on a cool track and I was very fast. Last weekend for the first race I had times in practice that would have put me on pole, but after I put my brand new tires on I slowed down almost .3, and then slowed down another .2 in the pre-final, and another .2 in the final. It seems like the more rubber that got laid down, and the higher the track temps the less grip I had. It was like I was driving on ice. We are running completely neutral, out of the box OTK setup with MXP wheels and N axle.

Thanks,
Dan

[TJ Koyen]

What's your weight distribution look like?

And what is your tire pressure looking like compared to other guys (I'm not really familiar with the Mojos these days)?

First thought is that you're overheating the tires somehow.

But if you put new tires on and go .3 slower, it's almost always a case of having too much grip, which sounds like the opposite of what you're feeling.
_________________
T.J. Koyen
OKTANE VISUAL - Custom Helmet Paint & Graphic Design
www.oktanevisual.com
www.facebook.com/oktanevisual
--------------------------
DB Motorsports
Exprit/Leopard

[Dan Pingston]

I know, that is why it is so frustrating to me. We are very balanced as far as weight dirtribution goes. We are at 43% front, 57% rear, and 50/50 left and right. About 175lbs front and 212 rear (with me in the kart). Air pressure was around 10psi all the way around running CCW (5 left turns and 3 right). Based on my videos it looks like I could gain on the leaders in the slow, twisty sections, but they would pull me on a high speed left and a high speed right. Theoretically, you are right and that's why I am here, asking for help. You would think that if you are fast when the track is slick and you slow down when it rubbers up you are too bound up, but it felt like I was on ice when I put the new tires on and at about the half way point of the final I got so loose I thought I had a flat right rear tire. Maybe it is over heating the tires, because I drove the next two laps a little cautiously and then my times picked back up. Do you think it could be one of those instances where you need to slow down to go faster?

[TJ Koyen]

Well your weights sound pretty good. I wouldn't be afraid to move the seat back slightly though to even go to around 41% front, but 43% should be fine. You could probably go to 41 though if you wanted.

I know with the B'stone YLBs it can feel like ice driving on the first heat cycle on new tires sometimes. Feels like you're on top of the rubber rather than digging in and getting grip. We try to go down on air pressure a bit to get the tire to flex and dig sometimes. But you're already at 10psi.

It seems counter-intuitive, but I'd be curious to see if MXC wheels helped. Might keep the tire more consistent and stop them from being overworked. They typically free the kart up, so it doesn't really make sense in theory, but it might be worth a try if you've got them.

Could be driving too, though I'd think if you were overdriving, your problems would go away on new rubber with the extra grip.
_________________
T.J. Koyen
OKTANE VISUAL - Custom Helmet Paint & Graphic Design
www.oktanevisual.com
www.facebook.com/oktanevisual
--------------------------
DB Motorsports
Exprit/Leopard

[Justin Martin]

Now I am new as well, and also run Mojo's. As tire pressure go, they are all over the place.

What is the ambient temp outside when this occurs?

I never run down in the 10's with Mojo's. Try on your next testing day to bump it up .5 psi every few laps, and stop when you stop getting faster.

It sounds counterintuitive, however after a few Gatorz guys recomended the same thing, that is now what I do. I am commonly in the 17-18 range on a normal 60-70* day.

It is just a suggestion however, ask around and you will find everyone is all over the place when it comes to Mojo pressures.