Karthikeyan put on an impressive drive from 14th to fifth in May’s Sugo round, prompting him to suggest that he could now fight for podium finishes.
However, he couldn’t live up to those expectations - including at Motegi, where he qualified a strong fourth but failed to convert it into a big points haul.
The Indian eventually finished 15th in the final drivers’ classification, with the aforementioned fifth place finish from Sugo the only points result to boot.
Speaking after the end of the season, Karthikeyan said that Nakajima Racing suffered from tyre degradation more than some of the other teams, which meant he was unable to take advantage of his qualifying prowess.
“It’s so tight in Super Formula,” Karthikeyan told Motorsport.com. “The team has improved in general. The set up of the car has improved. But we have a lot of tyre deg in races.
“So sometimes it’s hard to keep qualifying position. I qualified fourth at Motegi but a little bit on strategy, the deg. The deg is quite big for us. The race set up has been a problem.”
He added: “It’s so different. Each circuit is very different in Japan and in Sugo we had a fantastic car. I was able to finish quite easily in fifth position.
“But then when we qualified well we couldn’t capitalise on that. There are so many factors you know keep changing in Japan.”
Karthikeyan gained two places off the line at Suzuka finale to run sixth in the early stages of the race, but a drive through penalty for speeding in the pitlane dropped him down to 17th position.
“I had a drive through,” he revealed. “It was a good start, passed Kamui [Kobayashi] and [Ryo] Hirakawa on turn 1, on the outside and turn 2 also.
“But after that pace was OK on the soft tyre. We’ve been suffering with a lot of deg this year. It held up quite well until lap 18.
“We could have gone on more but I decided to pit and the entry was deemed to be a 2-3 km/hr more so I got a drive through. On the medium I had a lot of understeer and I got stuck behind dillmann so kind of hard.”
Karthikeyan confirmed that he would continue to race in Japan with Honda in 2019, but refused to reveal if he would stick in Super Formula, which is introducing a new-generation car next year.
A potential move to Japan’s other major series, Super GT, could be on the cards after he tested a Nakajima Racing-run Honda NSX-GT during the winter of last year.
“I’ll race in Japan for sure, with Honda,” he said. “I don’t know with the new car coming and everything [where I would go].
“I’ve tested the [new Super Formula] car. You are not getting younger so it might be difficult to keep the position. But no harm trying I suppose.”