masters set up + tire pressure's questions

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d4rk5trok3r
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masters set up + tire pressure's questions

Post by d4rk5trok3r »

This is a techy question, but specific to masters briggs.

Tire Pressure? Frame set up?

So far this is appearing to be straight witchcraft.

I was running 11 cold all four corners, and have great traction second to 6/7'th lap, then it just disappears. I have the required tire, but on a 7" rim, so stretched. My track width on the rear may be wider than others as well. I have a steel rear bumper, so may have some stiffening effect. No stiffener up front. No caster / camber adjustment available on frame. I am pretty much exactly 375lbs.

Anything stick out, as a place to start?

I have some 6" wheels I am going to swap over to, to start.

Thanks for any advice!

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SteveO
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Re: masters set up + tire pressure's questions

Post by SteveO »

Hi Jason,

There is no real correct answer, but the easiest place to start is to find someone on the grid that's using the same model of kart to yours, and see how they have it set up.
I run a Birel, and ran about the same tire pressure as you, and I too was losing rear grip towards the end of the race. But I think I can blame a lot of that on my driving style.
If you were to look at the complete Masters Final grid on Sunday, you'd probably find people running up to 15 psi, and as low as 10. Also the rear width would be between 50" and 55".
With respect to rear width, maybe focus one T&T night on that solely. Put in a couple of base sessions with your current setup, then start narrowing the rear width & see how that affects the kart. You'll probably find a happy medium in there somewhere. Tire pressures are a bit trickier, and the track & temperatures are always changing, so it is a bit of a black-art.

Hope that helps a little bit.
Stephen Orton

phil
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Re: masters set up + tire pressure's questions

Post by phil »

Hi Jason,

What chassis are you running? When you say the traction just disappears, are you referring to entry grip, exit grip, front, rear? If you want, I can probably spend some time with you after TAK on Saturday, and see what you have, and maybe offer a few suggestions. The one thing I would stress, is don't get carried away making changes every time you go out, as the track changes, and you can spend a lot of time chasing, when what appears better on the clock, may have been faster yet if you changed nothing.

Phil

Rob Kozakowski
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Re: masters set up + tire pressure's questions

Post by Rob Kozakowski »

I've got nearly no experience on the Vega Green, so take this for what it's worth... this is more theoretical than anything, and based off of mistakes I've made and learned from and seen others make over the years...

(1) I would generally think that 11 psi cold is a "low" pressure for a hard tire like the Vega Green - but I might be wrong.
(2) Generally, the reason that you might start out on a "low" pressure is to avoid generating "too much" grip where the kart starts binding up later in a run as the tires heat up and traction increases. But this generally applies more to soft tires than to hard tires. It would generally take an extremely high grip track surface / extremely hot day / etc. to get a harder tire like this to really bind the kart up. In other words, it's rare that such a hard tire will ever result in "too much" grip.
(3) There can also come a point where starting with pressures too high, rather than binding the kart up with massive amounts of excess grip, the tires overheat to the point where they lose all traction and the kart just slides everywhere. This generally applies to harder tires, and would be more along the lines of what I'd expect from your comments. Only, I can't see how 11 psi on a hard Vega Green would ever get you to the point where your tires are overheating (especially with the weather we had on the weekend).
(4) Which makes me wonder if there's something else that's causing you to have good "traction" early, with loss of "traction" later...

Before looking at kart setup (I doubt things like seat position, camber, caster, track width, wheel width, axle hardness, etc, etc would cause the loss of "traction" that you describe - these things would more likely affect handling from start to finish, rather than causing a sudden drop in performance)... my gut tells me the loss of "traction" is either a tire or a driving issue...

My first question would be how old are the tires (if they're past their "true" useful life, or they've sat all winter since their last heat cycles, they might have good tread life for practice, but might have no more "long-run" consistency and are garbage for racing on)?

And thinking outside the box, is it possible that with the pressures being (IMO) "low" to start, that the "traction" you're feeling is the result of the low pressures allowing the tire to "flex" and dig more into the track, but when they heat up, they lose some of flex and the side bite?

Regardless of whether or not this is what's happening, I'd suggest trying to go out at higher pressures and see what happens. In other words, I'm wondering if you're just not comfortable driving a kart that is "free" and able to generate "forward traction", and you're more comfortable driving with a sensation of higher "grip" that might ultimately be the slower setup if you're comfortable driving the kart properly.

A lot of drivers complain of lack of grip... and they make lots of adjustments to generate more and more "grip"... constantly trying to make the kart work in a way it's not really meant to work... and while they feel more comfortable behind the wheel with more "grip", they never really get much faster - and sometimes get slower. It's not until they learn (and accept) that the problem isn't a lack of grip, it's a lack of kart driving skills, that they actually get faster. It's like my golf game... rather than going back to the basics and learning how to properly swing a club, I use a million little quick-fix band-aid solutions that make me feel more comfortable, but result in a really awkward looking swing that will never allow me to actually be any good at that stupid sport.

d4rk5trok3r
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Re: masters set up + tire pressure's questions

Post by d4rk5trok3r »

This is all great feedback.

So what I have gleamed so far;

-try higher pressures

-the vega is a hard tire that doesn't need low pressures

-try narrowing rear track


Last, what is ‘forward traction’?

d4rk5trok3r
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Re: masters set up + tire pressure's questions

Post by d4rk5trok3r »

SteveO wrote: Mon May 27, 2019 9:24 am Hi Jason,

There is no real correct answer, but the easiest place to start is to find someone on the grid that's using the same model of kart to yours, and see how they have it set up.
I run a Birel, and ran about the same tire pressure as you, and I too was losing rear grip towards the end of the race. But I think I can blame a lot of that on my driving style.
If you were to look at the complete Masters Final grid on Sunday, you'd probably find people running up to 15 psi, and as low as 10. Also the rear width would be between 50" and 55".
With respect to rear width, maybe focus one T&T night on that solely. Put in a couple of base sessions with your current setup, then start narrowing the rear width & see how that affects the kart. You'll probably find a happy medium in there somewhere. Tire pressures are a bit trickier, and the track & temperatures are always changing, so it is a bit of a black-art.

Hope that helps a little bit.
I have an old Haase frame, that Fred tells me is for a shifter, and is relatively stiff. Not ideal by any stretch, but trying make it as usefull as possible.

Rob Kozakowski
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Re: masters set up + tire pressure's questions

Post by Rob Kozakowski »

d4rk5trok3r wrote: Tue May 28, 2019 10:24 am Last, what is ‘forward traction’?
Back to basics... a tire has only so much available "grip" or traction. That traction must be used to (a) slow the kart down, (b) turn, and (c) drive the kart forward. If it is being used to do any one of those things too much, it won't be able to do the others as effectively... technically, if it is being used to do any one thing at all, it won't be able to do the others as effectively.

So, what's "forward traction"? It's the ability to apply the tire's grip to drive you out of the corner... remembering that the higher the exit speed from the corner, the faster you should be travelling at the end of the straight.

Based on my experience, less experienced drivers (I was one and every time I get out of the seat for a while, it takes some adjustment) almost always complain (especially on harder tires) that the kart doesn't have enough "grip". The reality is, more often than not, they struggle to explain what they mean when they say that, but generally it has to do with the kart sliding at some point of the corner. The problem is, that more often than not, that sliding has far more to do with driving than with the tires or the kart setup.

What many people end up doing is rather than fixing their driving, they adjust the kart to add more "grip" - and normally it's more "mid-corner" grip. What this normally does, is it makes the kart more "comfortable" to drive by giving a better sense of control over the kart. The problem with this is that if you get too much mid-corner grip, you slow the kart too much mid-corner and lose out on the transition to corner exit, sacrificing the forward traction and killing the straight-line speed.

Now, an old shifter frame is not ideal for a 4-cycle either. However, I don't know that this would have much impact on you "losing traction" as the race continues. Again, the chassis itself should create an issue from the start, rather than one that develops with changing tire pressures, or in how you're driving.

Remember, I've never watched your driving, so anything I've said is only a guess. One guess is that the lower tire pressures are giving you more sidewall flex in the tires and hence, a feeling of digging into or rebounding from the track a little more early on (the feeling of more mid-corner grip) before they heat up. Another guess is that maybe as the laps go on, your confidence goes up or fatigue sets in and you start over-driving into the corners, and you just don't have enough tire to carry that entry speed around the corner. There's so many possibilities, that it's hard to say what it actually is. But I'd start with higher pressures and see what impact (if any) that has. Make no mistake, the kart will "change" as laps go on, but it should be more progressive rather than a sudden loss of "traction" like you're explaining which has me a bit puzzled. I wouldn't start by chasing chassis setup too much. Maybe a tire pressure change works, maybe it doesn't.

If all else fails, maybe get an experienced driver to do a few laps in your kart and let you know what they think the problem might be.

d4rk5trok3r
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Re: masters set up + tire pressure's questions

Post by d4rk5trok3r »

This is fantastic. Thank you all for the thoughtful, and very descriptive responses. I am definitely looking forward to my next t/t day. Heck, my first year I had a flat cam lobe, and also had a season of wtf. So, this is much better being able to make actual adjustments, instead of being at a total loss. I would 1000% agree on overdriving the corners...I do spend the most time in the weeds hands down!

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