What tires do you have left ?

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elmt1
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Re: What tires do you have left ?

Post by elmt1 »

Hi John,

Thank you for the explanation. When the tires on my kart hit that limit and start degrading, I usually feel like I am having trouble getting grip in the rear. Instead of lifting the inside tire and turning, the cart will oversteer mostly in the middle to end of a turn. I find that I have to brake earlier coming into a turn and just can't maintain the speed that I could when the tires were newer. I have never had a problem with understeer unless it is raining or the track is really cold. I think that may be because I only have 54% rear weight even with the seat back and 26 pounds bolted onto the left rear side of the seat.

I have tried many things but they don't seem to help much at that point. Usually I will go narrower in the rear but that stops helping if I go more than about 10mm/side narrower. I have also tried narrowing the front to remove grip there in hopes that it will help balance the kart. Other things I have tried were going with negative camber or more caster or turning the front torsion bar vertical. Caster and narrowing the rear seem to have the most positive impact but once the tires are past a certain point, there really isn't a lot I have found that works. Things that I haven't tried, but I am would like to try to gain more experience are changing ride height and axle stiffness.

Thanks!

--David

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John Kwong
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Re: What tires do you have left ?

Post by John Kwong »

What chassis brand are you on?

Sounds like you have a good handle on when and why to do certain chassis adjustments. Handling balance is what I always strive for and with tire wear the chassis feel will change, so you want to be able to make the right adjustments to keep it in the zone while the tires are still worth tuning for. Most of the guidelines that I have seen from manufacturers for seat placement have been too far forward and usually measuring out at 61-62.5cm from the front chassis hoop to the leading edge of the seat on each side. Almost every person that I have coached and tuned with, we have moved the seat back 1-1.5cm to get the chassis to stabilize the rear end. If your chassis tends to go toward being loose once the newness of the tires has set in. From what your post says with less braking grip and losing grip mid to exit, I would look at your seat measurements.

Increasing the caster angle will put more jacking into the frame which I have found is needed in higher grip, rubbered up tracks. Too much will raise the inside rear tire quickly and cause too much steering response. Middle or neutral caster is a good place to start.

Increasing the negative camber will create less turn-in response and increase the duration rise of the inside rear wheel.

So, if you have a lot of caster and it seems unstable going into a turn and makes you loose on exit, I would take out caster and increase negative camber which will also require you to turn the wheel more to get around a corner which makes the range of steering easier to modulate or less knife edge response.

John K
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elmt1
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Re: What tires do you have left ?

Post by elmt1 »

Hi John,

I have a 2014 Kosmic chassis. I just measured and I am at 63 cm on the left and 64 on the right from the front hoop. I read the setup guides for the chassis and the Tillot guide and have the seat as far back as they recommended. I even swapped out for the longer steering column to get as far back as possible. Before I did that, the seat was at the middle of the recommended placement so moving the seat back almost 2 cm made a 1% difference in weight so I went from 52 -> 53%. Then I added 26 lbs to the left rear of the seat to race in masters and that brought the rear to 54% and side to side is pretty close with RR only about 7 lbs more than LR now. I'm not sure why it has been so difficult to get the rear weight up when I am 6' tall and 175 lbs

I generally went with neutral or full caster because it was faster to set up than mid caster. I did just buy some zero pils so that should make it easier to try mid caster.

Your comments really help and give me some ideas. I still have a lot to figure out though, because the fastest drivers are still a few tenths faster and they come from out of state and don't have near the number of laps I have on this track. They do have the advantage, but in some ways disadvantage, of a team setting everything up for them. The track here in Ocala is fairly open with two hairpins back to back. I feel like the turn that matters the most is the one they call the showcase turn and it is big and wide and leads to a long straight that can be taken nearly flat out if the track has rubber and the tires are good. That is where I feel that having bad tires hurts me the most because I will have to brake into that corner and it is easy to have the kart step out about 2/3rs of the way through that turn, right where you want to be accelerating for the straight.

Thanks!

--David

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John Kwong
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Re: What tires do you have left ?

Post by John Kwong »

It still sounds to me like you need to take some steering out of the set-up. Many of our Rotax Masters guys here switched to OTK chassis and I noticed that many of them suffer from high speed turn looseness or instability which really scrubs the speed off. 2 things to try besides what we have discussed. 1. Less pressure in the front tires and 2. shorter length front hubs (borrow these to try if you can). If your camber is set at the 2 degrees negative on each side (1 box on Sniper) and your tires are wearing on the inside more, then the pressure is too high.

If you need more steering response in the slow hairpins, then add toe out.

I know this is a lot to digest and chassis tuning remotely is tricky with all the variables of weather temperature, asphalt type and a tire that I have not tested on yet but many of the principles are the same no matter where you go.

John K
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elmt1
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Re: What tires do you have left ?

Post by elmt1 »

Good morning John,

That is really helpful. I will give it a try. I am using the narrow magnesium OTK hubs with two ridges on it (80mm) most of the time except when it rains. I generally use 15 - 10 mm on the front and have two 5mm spacers right now. Based on what you are saying, I will try lowering the pressure in the front and see how it feels to take out a spacer or two. I have been running about 10.5 to start with the Levanto tires and usually set the rear at .2 less and the inside at .2 more given the inside front as the baseline tire. At the end of a session, my pressures will usually be even at about 13.5 with MXJ wheels and about 12.5 degrees with MXQ wheels.

Your right that it is really difficult to do remotely. What I have done quite a few times now is just go to the track and I will start with the baseline setup then I will do something like progressively add more caster to see what happens. Then I will go back to base line and try with the front torsion bar loose, then tight at 45 degrees then 90 degrees, etc. Pretty much every time I have changed camber to be more negative I went slower and going positive one or two holes didn't change much.

This weekend, they have the USPKS race at Ocala and along with expense, they don't really have a class for me, so I am going to sit that one out. The following weekend is another Rok Cup Winter Tour at Ocala so I will enter that one. I also promised my father in law I would help him move this weekend, but depending on how that goes, I may to to Bushnell or Anderson Raceway.

Thanks!

--David

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Fred
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Re: What tires do you have left ?

Post by Fred »

OK Guys / Gals

After talking to the Supplier and the Kart shops and winter testing it seems that the LeVanto is going to be the best bang for the Buck tire with it being priced exactly the same as a set of D2,s around $270/ set. The US supplier of Maxxis is at $258 / set but I believe you are going to like the LeVanto better.

With the use of the LeVanto you will be included in the Prizes (Entry and Tow fund to the Canadian Nationals) and ROK The RIO ... During the NO49 Event you will also be eligible for the 1 Free entry to a round of the Challenge of the Americas sponsored by Full Throttle Karting.

With the longevity of these tires I believe you will probably need 2 sets a year.. I am hoping to have a couple of practice sets sent also for you guys to get used to.

Therefore with consultation with the Kart Shops I would propose we Run the LeVanto this year and we will also run a set of Maxxis for comparison on T and T to decide if we stay with the LeVanto next year.

evannadeau
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Re: What tires do you have left ?

Post by evannadeau »

Works for me, have the shops given ETA on their arrival?
VLR #42

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Fred
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Re: What tires do you have left ?

Post by Fred »

Tires (All makes ) probably are not going to hit here until Mid April (FREEEEEESHHHHH )

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Fred
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Re: What tires do you have left ?

Post by Fred »

IF ANYONE IS INTERESTED
Tire Test Phoenix.xlsx
(12.25 KiB) Downloaded 253 times

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Re: What tires do you have left ?

Post by [email protected] »

Are we supposed to vote..... go levantos
Glenn

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