So the first weekend on my factory new DR S97 is finished. The kart was set up pretty well right off the bat, probably just needed a better component behind the wheel.
However, on Saturday I noticed I was getting a slide mid corner through some of the tighter turns. Turn in was great, and it felt good on exit too, but in some turns (cell tower, scoreboard, and I-70 at New Castle, IN for those familiar, the kart would slide on exit and kill my speed coming out. We had the CRG gold wheels on, which are the stiffest wheel they make.
Sunday we switched to the softer black wheels and it got rid of the slide mid corner but the kart felt more skittish and not as well planted on turn in. I think I liked the gold wheels more in general if I could have gotten rid of the mid corner slide.
During the weekend at one point we had widened the rear width and kept it at 54 3/4. Other than that we really only changed tire pressures for the frame, and the kart was quick on the Sunday. I think with a draft I may have been able to lap about the same times as the leaders.
I’m wondering if narrowing the rear track down again would have helped on gold wheels. We also contemplated putting a softer axle in or switching to the Tillet T11 VG from an NEK medium stiffness but chose to change wheels instead.
Would any of those have helped, or what else could have been done to try and change that?
Good on entry but oversteer at apex on tight corners indicates too much initial jacking to me. Kart is picking up too much and overworking the outside tire.
I would’ve tried to go to 55" in the rear to see if you could settle it down slightly on entry. Also could try reducing caster a bit/adding negative camber to get it to calm down.
Good advice from TJ as always. @Aaron_Hachmeister_13 I have a tillett t11 vg in my kart as well. It would definelty help with the slide in my option but it make the kart tighten up as track takes rubber. As I had that issue on Sunday. But Sunday I also felt my front tires losing their edge in the prefinal on Sunday. Doesn’t help that hurlbert abs stammer took me off. For the final, We threw too many changes at the kart and the higher grip didn’t help as I was not as smooth as I could have been. I also noticed that Brombrek had a t11 vg in his kart. Was their issues with that? I was loose in the final. Your thoughts?
Yeah Bromberek ran a T11, according to Danilo there’s no difference between an NEK and a VG except the NEK is more comfortable but I would be testing that before I believe it.
I don’t think Bromberek had any issues with it, but it’s hard to tell what his kart is doing from his feedback sometime. Apparently they got his gearing wrong since Woltjer tunes their motors differently than FMS but Idk. I was faster than him in the Final but I didn’t have a draft after my incident. He just said his kart had no top end but I didn’t notice that when I was behind him.
It was kinda weird, like I said I was struggling for grip Sunday on the black wheels, but I didn’t have a slide through the corners. Looking back on the weekend I would have preferred to stay on the gold wheels and made some of the changes TJ mentioned but hindsight is 20/20.
Could it be something as simple as a bump or surface change in the track?
Did you get a chance to do a track walk?
I have to say, I’m pretty skeptical of “soft vs hard” wheels. I think there’s some effacy behind heat dissipation and volume differences. But stiffness is hard for me to rationalize.
I don’t think it was a bump, I didn’t feel anything like that whenever I drove all weekend.
I did walk the track and there weren’t really any surface changes I could see.
I really don’t understand the soft vs. hard wheels thing either but that’s how the guy tuning for us this weekend was talking about it. Stiffer wheels put more grip into the kart, softer wheels take grip out.
I think wheel material is more important than “stiffness”. The material is going to affect how much heat goes through the tire. Without changing the tire compound, you can’t alter how much grip the actual rubber has. However, you CAN change how quickly and efficiently you reach the tire’s optimal grip level. The OTK MXC wheel seems to keep the tires cooler, helping them stay in their optimal working range for longer. From my experience, an aluminum wheel tends to overheat easier.
TJ is right. We had overheating issues on friday with the mxj rims on friday unlike saturday and sunday with MXC rims.
So the gold wheels were getting the tires to temperature faster which is why it felt like they had more grip on them than the black wheels?
They were probably keeping the tire in the temp window better, not necessarily getting them to temp faster.
To follow up with what TJ is talking about on “maintaining the window”, nitrogen (or “dry” air) helps with this as well if you’re not already using it.
Atmospheric air carries moisture, what worse is that amount can vary. Naturally, inside the tire, moisture plays a role and becomes a variable. It’s a good idea to isolate it if you can.
Typically you will see less pressure increase over a session with nitrogen over air. But it’s important to understand that it’s not the nitrogen gas itself that makes the difference, but the lack of moisture that it contains as supplied.