Tuning my Tillotson /Tonykart 401rr, findings, questions, etc

I am an old SKUSA pro shifter racer from the early 2000’s. My (adult) son Riley and I have been racing the spec tillotson 225rs on some Tony 401rr’s for a year or so now at Orlando, mostly in the league nights where we were winning or on the podium often, and went 1-2 in the last league championship. This year we are doing the Orlando Cup series which is much more competitive, with a Tilly Sr class of around 20 karts. We finished 6th (me) and 9th (Riley) at the first round. The podium was around a half second quicker on the full Orlando track.

We ran the recommended OTK setup from the sheet (OTK seats too), with the seats back 15mm and the minimum caster setting as the only difference. We are using Maxxis T4 tires, 7.1 rear width. This produced around 58.5% rear weight. The karts felt balanced, but just seemed slower than the front runners.

I noticed that all the karts on the podium were setup soft with the seats more forward than ours. No front bar, soft seat, min caster, no seat struts. Also they had a lot of front width and less rear, more like a rain setup.

I did my best to copy that soft setup for some testing yesterday (57% rear weight now with the seat moved back to the stock location) and found that the kart seems to accelerate much better from apex to corner exit, felt more composed on braking, and was generally more enjoyable and easy to drive. It had a more floaty and free feeling, vs the planted feeling from the standard setup. Track temps and ambient were comparable to the race day and I had faster min corner speeds on my used race tires on the new setup yesterday, so I think it is an improvement. The track layout was different so I couldn’t compare lap times.

Questions:

  1. It seems the kart is staying flatter, yet it feels more free to accelerate. I always thought “free” meant getting the inner wheel up and keeping it there so the kart could pull without having to scrub that inside tire. It seems like this setup is the opposite of that, yet it seems to work. Can anyone explain what I am missing, and why this setup is less bound up?

  2. We are running MXJ wheels, but I see some MXC’s on fast karts. What is the difference and why would one choose one over the other?

  3. Any other 4 stroke or tony specific tuning tips that might help?

I am sure I will think of more as time goes. Thanks in advance for any input.

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I’m racing with CRG and using an similar engine 4T (Tillotson).
I have the same feeling as you, and I´m around a half second slower them the first placed.
This weekend I should carry out some tests to improve the balance of the kart.
If I have a positive result in this tests, I come back here to share
If you have any news about , please tell me
tks

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OTK definitely has a pinpoint baseline setup. It will vary by driver build. It also offers a wide tuning window from baseline. It sounds like you are headed in the right direction. @tjkoyen is the resident OTK guru. He can help answer your questions.

The difference when tuning with the power of a Tilly or similar is that you do not have the power to drive the tire as hard into the track and not bog. So a typical setup that you’d run in something like KA or X30 sometimes provides too much binding for a low hp 4-stroke, as you’re really pushing the outside tire into the track and that physical twisting of the tire’s carcass and the associated friction can bind the kart up even if it is lifting the inside rear. A kart with more power can power through when you hike the inside wheel and push that outside tire into the track. That level of flex and dig can drag down something with less power. Col from KRacer used to drive this point home and I think it is often overlooked.

  1. I had this conversation just the other day. There are two ways to skin the cat here. The inside rear must be unloaded for the kart to rotate properly. However, if you OVERload the outside tire, you will also run into problems as I noted above. The kart may be flatter without all that jacking in the chassis, but it also isn’t putting as much force through the outside rear either. The inside might be unloading even if it doesn’t appear to be lifting as much.

  2. MXJ isn’t a great wheel for the most part. It generates a lot more heat than the MXC so I find it to overheat in about 4-5 laps in KA. In 206 or Tilly maybe you can get away with it on a green track or on a cooler day. The MXC is a much better wheel all-around. It’s stiffer and it controls heat/pressure much better to keep the kart consistent throughout the run.

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Thanks for the info, it makes good sense. I hadn’t considered the flex of the outside rear as a source of binding.

I am not an OTK expert by any means, but I have tuned quite a bit of low hp stuff. TJ’s number 1 is spot on. Reduce the lift as much as possible. You want just enough to turn the kart, but not waste any energy picking up the inside rear more than you need to. In the local 4 stroke community, we call this “flat slide” tuning. Its about energy conservation and keeping momentum up. It will also require smooth/steady hands more so than the “pitch and catch” style that a lot of higher hp guys use.

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My nemesis right here…

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This is also how we used to tune on hard tires and low hp at the club. There was no real way to get the kart to lift, as the tires were rock hard and the kart had no power to flex the frame, so everyone ended up making the kart a noodle to get it to just flat-slide a tiny bit to reduce scrub on the inside tire. It worked for club racing but then when we would go to higher grip stuff as we transitioned to regional and national racing, we couldn’t understand why our tuning changes were not working. Until we realized, you simply can’t slide the kart like that when there is some grip on the track.

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You just described the exact reason I only race the first 2 and last 2 races of every season. If I tried to race NCMP in July, I could jog around the track faster than my stuck down 206 can pull me…

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Thanks again. I have a pretty ok “smooth” mode, tons of miata and formula Vee on iracing!