OK1 Chassis - Rear end and tire wear

Chassis Setup, Tires & Handling Forum
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Dear community,

It is my first post here, so, first of all, very nice to be around and be able to read and learn with the many topics we have here.

I wanted to create this topic to ask your opinion of something that I have been asking a lot of people, and no one knows how to answer this:

I am a Brazilian living in Mexico and racing Skusa Mexico. I have bought a brand new OK1 Chassis (IPK Factory) and am doing the pre-season with an Extra Hard Axle with the standard hub of 95mm (Already ordered the Medium-Racing one, and it is about to arrive).

Here is a comment: I am using the Extra-Hard Axle as, with the old chassis I had from Praga, I found that with the Medium Stiffness Axle the kart was too loose on its end.

My main problem is the rear of the kart. Every opinion is more than welcome so we can reach a solution:

Rear tire wear

The first problem is, the rear tire wear is extremely high when compared to the front tire wear.

Read somewhere that switching to the aluminium hubs would fix this problem, but before spending USD 200 on this, I would like to ask if has anyone tried this and it really worked?

Would there be any other possible solution to this?

Rear loose/oversteering

Sometimes, even with brand new tires, I feel the rear end is impossible to control and that it wants to “overtake” the front of the kart and not being stable at all.

My opinion/guess

Would the rear of the kart be too grippy and that may be the cause of all of this?

General setup of the kart:

Front width - Standard, two lines out
Front Torsion bar - Flat Steel on the standard position
Camber and Caster are on 0s.
Chassis is brand new - Less than two months of use.

I was also considering switching brands as I heard that IPK generally produces a more soft chassis - Therefore, this may be the cause, so I tried to stiffen the chassis as much as possible.

Is this a general issue on the IPK?

Appreciate your help.

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Welcome to the forum firstly, and first question the track you’re running is a low grip track? I’m guessing so if you’re running ultra hard axle.

I’m no set up wizard, @tjkoyen will be along soon I’m sure but as a rule of thumb low grip track you want a soft chassis and stiff axle. Soft chassis to jack the inside rear more readily and stiff axle to give angulation to the outer rear so it can bite at the edge. You say you’re running a front torsion - this will restrict the karts ability to twist and reduce the jacking effect, try a session without it.

I run in UAE where tracks tend to be dusty and slippy but grip up once the dust is blown away, I always start out with hard axle and never run a front torsion bar, I have 1 seat stay each side to keep the rear stiff, it helps a lot.

Tyre wear is normally just down to track surface, I never heard of different material hubs affecting tyre deg. Strange though low grip track is normally low tyre wear…….

If the track is grippy, I’d say you’re running too hard an axle and want to flatten the outside rear by putting a softer axle.

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What do the worn tires look like compared to the front? Can you post some pics of all four tires after the rears wear out? Sometimes seeing how the tires are wearing can help answer the question of why they are wearing faster than the others.

Also, what engine package are you running? Shifter/KZ and X30 = Evinco Red, where KA100 and Swift = Evinco Blue.

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Hi Greg,

Thanks for the answer!

As for Skusa Mexico, we run on Honda 125 Shifter and use Red Evinco tires. Forgot to take a photo of the tires but can describe it here for you:

Inner of the rear tire wearing faster than the outside of the rear tires - That is why we decided to give it a go to the EH Axle.

Now, when comparing the rear tires to the front tires, just so you have an idea, when the rear tires are completely gone, that you cannot even see the little holes that indicates the wear of the tires, I still have plenty of the front ones.

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Hi mate,

Thanks for the answer!

Actually, I am running in a track where the asphalt is very abrasive but still, apparently, this is not an issue with other chassis here, where we run it also get dusty cause Mexico is very very dry but there are drivers on the track everyday, mostly.

I have tried to use the Nylon bar but felt the kart with a lot of understeer and bit lazy to turn so had to be more aggressive on the wheel which I don`t quite like.

I also think that the axle is too hard, but would that affect the tire wear that much? Visually, when my front tires are at the 50% of their lives, my rear tires are totally gone. Do you think that the magnesium hubs by handling the heat better, would help on that?

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All this really depends on the chassis. The axle black magic especially, as OTK uses soft axles in low-grip, whereas maybe CRG uses a stiff. It comes down to how the chassis and axle work together, and what the manufacturer’s axle stiffness range actually is.

Rodolpho,

I don’t have particular experience with the IPK karts but I do know they are quite soft chassis compared to most.

So basically it sounds like you are struggling with big oversteer and poor traction in the rear of the kart. That would not come from the rear being too “grippy”, the opposite actually. The rest of the setup seems pretty standard, so let’s look at the rear of the kart.

Looking at Praga’s tuning guide, they indeed recommend a stiffer axle in the dry when looking to eliminate oversteer. However, they also recommend a softer axle in the wet, which is a bit odd. When tuning an OTK kart, we always go softer on the axle to eliminate oversteer. It helps the rear squat better for traction as well.

I would try going softer in the rear to try and get it to dig better for traction. Especially important in a shifter. I would be less concerned about tire wear and more concerned about overall balance. If you fix the balance, the tire wear will correct itself. Right now the rears are burning off because you have no traction or rear grip.

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Have you checked seat position? How many struts are you running per side?

Are you lacking pace, or is it just the visual of the tire wear you’re unhappy with? With the shifter, driving style and throttle application can have a big effect on rear tire wear. You’re always going to wear the rears out faster than the fronts, so I wouldn’t worry about it too much unless it’s also an issue with the kart’s handling costing you time.

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Hi Evan,

Not actually lacking pace, after buying the new chassis/engine and with a set of tires 60 laps old, my lap times were just 0.4s off the pole position in the same trace and track conditions.

I am just not happy with the wear of the tires being that high on the rears and how the handling feels.

We will be moving seat position this weekend, and I will come back to let you know the results.

We are currently running two seat struts per side. We tried to use one this weekend but again felt the kart was too loose with only 1.

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Hi TJ,

Thanks for your time and replying such a good explanation.

Yes, the rear of the kart is the problem, I am actually quite happy with how the front end works.

Using IPK sometimes is quite difficult as they go on the opposite of what most of the brands say, so that is why wanted to discuss it with you.

Makes sense that I got no grip/traction on the rear and it causes excessive tire wear cause the rear tires need to spin more times to get the correct traction. So, going softer on axle could solve the problem? What is your opinion about going with magnesium hubs in order to dissipate the heat better? Myth?

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I think as Evan said (who knows shifter driving better than I do), the rears will inevitably wear and heat up quicker in a shifter, as there is so much traction demand. I don’t think different hubs will help at all. If you are overheating the rear tires, you need to determine the root of why you are doing that, rather than trying to put a band-aid on the issue. Magnesium will stay cooler than aluminum, but the hubs are not the reason the tires are overheating.

What tire pressures?

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Great answer! So, ok, def not buying the magnesium hubs.

Using DWT LV Magnesium Yellow Box wheels, pressures before leaving to track generally from 8.5 to 9.5 and most of the times coming out around 12 PSI depending on weather conditions - That is what we try to focus on.

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I think you’re in the correct range as far as tire pressures go. Do you have pics of the front and rear tires that you can share?

Keep in mind that depending on the track and surface conditions the Evinco will degrade fairly rapidly, so 60 lap old tires are probably due to be replaced if you’re looking for maximum performance in a shifter.

I’m with TJ on the hubs; aluminum vs. magnesium is going to be a pretty small difference all else equal. You’ll see more impact by changing the length of the hub (at least 10mm increments), so think of the hub material change as a “half step” in terms of tuning for grip.

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Yes, those were the tires that we used in the race weekend before and still managed to be 0.4s off the pole position time with brand new tires.

Great then that hubs wont make a huge difference, managed to save some bucks and not buying something that would be useless for tunning.

Will also try to move the seat and see if it corrects a little bit the tire wear…

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I ran shifters for 3 years and mediocre at best, so fact that in when using my input.

How long have you been driving shifters?

What is the track and ambient temp of the track, in Fahrenheit (would make it easy for everyone to understand)? If the track temps are higher (+105F) and the track is grippy, the LV Douglas wheels might be the wrong choice. Do your rear tires start sliding or get greasy.

It is weird that a new kart would come with a HD axle, usually they come with an medium axle. HD axles are at the end of the “stiffness” spectrum and I wouldn’t expect the kart to need it under normal conditions.

Since the inside rear wear is seemingly excessive, have you tried wider hubs? That should keep the axle from flexing as much and might help the wear.

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Hi Larry,

Thanks for your input. Have been driving shifters for the last year.

I haven`t taken notes of track temp, but ambient temp here in Mexico varies a lot, we can go from 50F by the morning to 80F by the afternoon, but not outside of these ranges.

The kart didnt come with the EH Axle, I was using with my previous Praga, but I broke the frame of it, so just bought the OK1 frame and mounted all IPK parts that I had on it. (All latest version).

I also tried the Extra Large hubs by some point, but the tire was wearing the same. Plus, wouldnt it be too much to use EH Axle + EL Hubs?

Starting to think that this might be excessive weight placed on the rear of the kart? Maybe moving the seat a little bit towards the front? I weight 177 LBS myself (80kg).

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Moving weight forward will increase oversteer and rear tire wear and instability.

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Guess I will have to do the opposite then… Thanks for helping me understand this better @tjkoyen

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What are your current seat measurements relative to factory baseline? Based on the diagram below, what are dimensions C, D, and G? What seat do you have in the kart, and do you have to use any ballast?

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Hi, hubs won’t make a difference, although magnesium is the norm nowadays.
Douglas, OTK, Freeline rims won’t make any difference as long as the are magnesium, no aluminum that’s for sure, unless it’s raining.
It is unusual having a brand-new chassis with a hard axle, they always come with medium.
Make sure your rear track is as wide as possible 140cm.
Having said that, shifters always kill the rear tyres, you should see my storage room, I have lots of front tyres in great condition, but zero rear tyres, your driving style also makes a difference, just drive smoothly out of the corners, this is Karting, not drag racing.

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Dear sirs,

First of all, sorry for the lack of feedback - We were preparing for the race.

We moved the seat before we had a weight distribution of 35% to the front and 65% to the rear, so we corrected that and the maximum we managed to reach was 41% front - 61% rear. That was what the OK1 chassis allowed us to do.

The rear track was always set to 140mm.

Still, rear tires wear was very very very high when compared to the front tires, what we found out with another driver that was in the team with us and also driving an IPK is that this is normal for this chassis. We compared our tires wear with other chassis and ours was significantly higher.

We also tried the Magnesium rear hubs on both karts, but we couldn’t evaluate the tire wear as using them (90mm) made the kart be very loose in the back, so, here goes a tip for anyone thinking to expend around 200 Euros in those magnesium hubs of IPK, save your money, they don’t worth it.

We had to use medium tires for Saturday and soft tires for Sunday, surprisingly, we were faster with the medium compound than with the soft ones.

Another thing is that we both had the 30mm frame, which was very good for qualy, for example, I was 0.081 from the pole with medium compound (Saturday) and 0.125 off the pole with the soft compound (Sunday). But for the races, we lost a lot of pace, still, we managed to be constant but not as fast as the qualy while the other chassis’ did manage to be fast in the qualy as in the race and keep their pace.

The tire brand was MG White for Saturday and MG Yellow for Sunday - Pressures were almost the same for most of the drivers.

Finally, we both drivers that drove the IPKs in this SKUSA weekend here in Mexico decided to move to CRG and leave IPK.

IPK was great to start and learn a lot about setups as it is very hard to find the right setup for the track, while we heard that CRGs are way easier to set up.

Thank you all for all the support and opinions are welcome.

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