Carlisle United in 2016/17 were like a van tearing down the outside lane of a motorway with one of its rear doors flapping open. It got to its destination more often than not, but you couldn't take your eyes off it, partly out of excitement, partly fear.

Often vibrant going forward but with a brake pedal in need of attention, the Blues got into the promotion picture because of some of the best attacking play in the club's recent memory.

They stayed there, just, in spite of a defensive record that did not improve in line with the work upfield. They fell, ultimately, because there were only so many aspects of their play they could rely on.

Fighting spirit, certainly. A never-say-die attitude, beyond doubt. Nicky Adams' ability to produce quality at any given moment, no question. These and other features were imported by Keith Curle, and they should not be lost in the rush to ask what went wrong.

Carlisle, in the final analysis, finished sixth, with their best points total since 2007/8. Take the volatile journey out of the equation and that is still another significant improvement. Had the campaign been flipped around, we would have marvelled at their end-of-season form.

That is how well they started things: unbeaten and unbeatable until mid-November. Through October in particular they were a force of nature. Yet even then, they were rarely capable of locking the back door for long. When that autumn form then dipped, they couldn't bank on a few clean sheets to keep their promotion hopes honest.

After 46 games United's defensive record was the worst of League Two's top 15 clubs. While this in part may be a consequence of their attacking style, that cannot be the explanation entirely, and it cannot absolve the need for fundamental work in that area.

Exeter, who reached the play-off final, had attacking fluidity too. They built much of their bid on lively young players. They did not strike you as the tightest of units (they certainly weren't in four games against Carlisle), but even they conceded 12 goals fewer than the Blues, and scored six more.

Curle's reply might be that they finished level on points, and needed a 95th minute winner to edge the play-off semi-final. Perfectly true. Margins, in the end, were tiny. But still - turning United into a side that respects the goal-difference column a little better must be top of summer's list.

Carlisle's defence has boasted several combative players, particularly the now-departed Michael Raynes, but has lacked pace and consistency. Gary Liddle has at times been a calming presence but had a poor play-off experience. Shaun Brisley's signing did not deliver the results the manager must have expected. Macaulay Gillesphey's early partnership with Raynes seemed promising but a young loanee is always subject to the vagaries of form and fitness.

Curle also went cold on Mark Ellis, eventually loaning him out to free up funds. At full-back, a return for Alex McQueen was a failed gamble. Danny Grainger started the season emphatically but a mid-campaign injury was a blow. Tom Miller and Mark Gillespie, who started more games than anyone else, completed the rearguard set.

There are some fans who believe none of those individuals should be safe from an overhaul. Wholesale reform at the back is unlikely, given all but Gillespie remain under contract. But a significant addition or two is surely required, even if the return to fitness of Mike Jones will improve United's defending considerably.

The insistence that because Curle was himself an elite centre-half he should be able to make a team defend better isn't always that straightforward. A coach's strengths may differ dramatically from his playing assets. One of non-league's best defensive records in 2016/17 was assembled by one of the most carefree attackers in Carlisle's history (Matt Jansen at Chorley).

When the Blues last won the fourth tier, a team prepared by a former attacking midfielder with a wicked left foot (Paul Simpson) reeled off 20 clean sheets.

Equally, who would have anticipated a former Premier League centre-half would unlock some of Carlisle's attacking potential as Curle has? Yet this only excuses so much. It was always a risk to imagine United could be like Peterborough in 2010/11; conceding in bulk but scoring at an insane rate. Being able to coach a little security into a team can go a long way.

This, though, dwells on the flaws in a team that were still promotion contenders until the final seconds at St James' Park. Let us not forget, too, how the season brought some of the best players in United's recent history to Brunton Park.

The finest, with daylight behind him, was Adams. If consistency is the best mark of a player, it was significant that the winger set up three of United's five goals in the play-offs, when the stakes were highest.

Even when Exeter doubled up on him, Adams still went to the end, setting up John O'Sullivan's 90th-minute equaliser with the sort of cross that opponents feared all campaign.

At his best when released on the left, with enough room to go either way against a full-back, Adams has quality that should not be in League Two. Fortunately, he seems very happy at United, a tribute both to his own positive character and the environment Curle has built.

O'Sullivan, a more recent arrival, also fronted up in the play-offs. The former Blackburn winger seems the sort of player who won't go down unless there are flames around him. Carlisle need more of his type, and it will be interesting to see him unleashed after a full pre-season in 2017/18.

While last summer's emphasis in quality over quantity caught them short in the end, some of that quality was still striking, while others rose to the challenge. As well as the excellent Jones, Jason Kennedy, until injury, was Adams' rival for United's most influential player.

His goal from two inches at Exeter was a bittersweet reminder of what they had missed since late January. Kennedy has been a catalyst for improvement, a model pro and an example of how someone can enhance themselves at his stage of career by trusting in his work ethic and being open-minded to new demands. Luke Joyce, in the first half of the season particularly, also shone in these ways.

Injuries to Jones and Grainger at Luton in December were arguably the most damaging moments of the season. They disrupted the collective and unsettled partnerships. Other additions like Jamie Devitt and Shaun Miller flickered and flashed but consistency wasn't often on the table - yet there is enough in both for Curle to nurture. It wouldn't be the first time that attacking players produced more in their second season.

Reggie Lambe started well and finished brightly, too, but dipped in the middle. There is no doubt, meanwhile, that the winter upheaval cost Carlisle their best chance. By the time Charlie Wyke had been sold, and new faces like Jamie Proctor, James Bailey and O'Sullivan had bedded in, it was a shade too late.

Bailey's most promising glimpses came only late in the campaign. Proctor played valiantly through an injury, and his winner at Exeter was for the ages, but four goals didn't fill the Wyke void quite enough. Other additions, like George Waring and then a glut of short-term signings, filled squad spaces and were perhaps useful training-ground personnel, but they brought little to the team. Of these, only Samir Nabi has been deemed worthy of a more substantial chance.

Some of the mainstays since 2015 are also on their way. Jabo Ibehre's personality has been an asset to United; his goals, in bursts, also inspirational. Replacing all that he brought will be a challenge this summer.

So will dealing fully with the loss of Wyke. His 18 goals, before Bradford swooped, were the scaffolding for United's challenge. As Grimsby also showed, minus Omar Bogle, few sides can trade that sort of return and not expect their flow to be disrupted.

Wyke had embedded himself into the club and team over two years and knew where it clicked. Carlisle got a deal worth £250,000 for the striker, restricted by a release clause, but Grimsby collected £1m from Wigan for Bogle.

It is suggested that United might not have landed Wyke at all had they not made certain concessions. But one wonders if there is a grey area of negotiation where the Blues must be tougher in future. Curle, openly frustrated by Wyke's cut-price departure, certainly seems to think so.

Towards the end of the season, similar to the previous one, Carlisle seemed too direct in style. Curle's love of a long throw and a set-piece need not be dismissed on aesthetic grounds, but many felt a little more trust in United's carpet-footballers might have inched them further forward.

Exeter, in those play-offs, seemed in greater harmony with their best qualities, even as Paul Tisdale chopped and changed. Carlisle had to fight back twice because they lost the initiative twice.

Again - no team was better at counter-punching than the Blues in 2016/17. But having to do so in the first place pinpoints where a decent side can get better from here.

For too many seasons now conceding goals has been part of United's DNA. It is to Curle's credit that he has removed the defeatism that this also used to bring. Now it's up to the manager, and his staff, to show they can build walls as well as knock them down.