Minibuses were in vogue for several years after deregulation, and then they faded away. Recent developments demonstrate that they may be on the way back for a small number of applications, and that’s where Mellor hopes that its Strata will come in. Tim Deakin looks at the vehicle in detail
There is a modest yet consistent market for buses at the smallest end of the size scale, yet the routes that they serve are often susceptible to funding challenges.
That’s where Mellor hopes that its Strata will find favour. In a nutshell, the Strata takes a minibus’ low purchase price and running costs and operational convenience, and combines them with a full-size bus’ passenger appeal.
Mellor, the UK’s fourth largest bus builder, has an established reputation in the accessible sector. But the 7.8m Strata is far from being a reworked mobility bus.
It’s based on a Mercedes-Benz Sprinter chassis with a drop-frame centre section, on which Mellor mounts the coachbuilt body. The Strata is the first of its type to be aimed squarely at bus work, says Mellor, and it has already received European Whole Vehicle Type Approval.
“It is a bus that is cost-effective to buy and cost-effective to run, which makes it attractive for routes that local authorities may be pressuring operators to take on commercially,” says General Manager John Randerson.
A number of low-floor Sprinter van conversions are on the market, but he explains that the Strata has a number of advantages over them.
“It has been developed in co-operation with Mercedes-Benz and the drop-frame section in the middle has given the opportunity to extend the wheelbase, which is 5m. Width is 2.3m, and that means that we can fit two wheelchair bays should the customer require.”
A maximum of 22 passengers can be carried; 2+2 seating is fitted, meaning that up to 21 of those are seated depending on layout. The Strata is PSVAR-compliant, and when the saloon is viewed from the front it is little different to other buses in this segment of the market.
“The low-floor section is installed in Germany by a Mercedes-Benz partner, and as a result it has no effect on the warranty. The prop shaft it lowered by a transfer box and it is contained within the chassis cross members beneath the low-floor section, protecting it from speed humps,” says John.
After installation of the drop-frame section, the chassis cab is moved to Mellor’s Scarborough plant. There, body framing is added, and as John points out, there is no shortage of coachbuilding expertise in the North Yorkshire town. After that, the part-completed vehicle moves to Rochdale for finishing.
The Strata weighs in at 3,550kg unladen and has a GVW of 5,500kg. Thanks to it passing a brake test, the latter is achieved without the need to install a retarder, although one can be added should the buyer want.
Weight has been a priority throughout the Strata’s design process, extending to Mellor pressuring suppliers of GRP panels to ensure that they are produced with no excess material at the edges.
“From day one, the challenge was to design a body that is strong yet lightweight. From the subframe upwards, the focus was on keeping weight down and we have incorporated a lot of composite material into the structure,” says John.
But he is adamant that this weight consciousness does not compromise the Strata’s longevity.
The Sprinter chassis is established as the most trusted in its class, and the first of the new model was dispatched to Millbrook Proving Ground after being shown to the press. There, it will undergo accelerated durability testing to simulate eight years’ urban bus work.
“The Strata is a huge investment for Mellor,” John continues. “The project began two years ago as a conversation about the concept, and we are prepared to stand by and back the finished vehicle. It complements our existing range because it is a completely different model.”
Hitting the ground running
A second Strata demonstrator is already in build. Mellor has taken orders from three customers, and John explains that interest has been received from a number of other potential buyers, including some of the big groups.
Two of the three operators who have signed up already are from Scotland – McGill’s Buses and Prentice Coaches of Haddington – and Mellor is confident that the Strata will return in excess of 20mpg on urban work.
That looks to be an achievable target; the Sprinter can deliver 25mpg or more when used as a minicoach with the added power draw of air-conditioning, and the Strata’s frugality will be aided by the standard driveline choice.
Mellor has opted for the four-cylinder, 2.2-litre OM 651 engine rated at 163bhp coupled to a seven-speed 7G-Tronic automatic gearbox, and this combination has already proven itself the most popular in Sprinter minicoach applications.
It is established as a driveline that gives good fuel returns and a long service life.
The Strata is available with either Kiel Legero or Rescroft CT Lite seats. All forward-facing positions are in the 2+2 layout, while the rear row has four positions to allow space for an offside emergency door.
Three tip-ups are in the wheelchair bay of the first demonstrator.
A three-point seatbelt option is already available and John explains that other manufacturers’ seats will be added as and when orders justify.
Including tip-ups, a Strata with one wheelchair bay has nine seats within the low-floor section. Two shallow steps ahead of the rear axle take passengers up to the raised rear area, and they are edged in high-visibility yellow and LED lights.
What is most notable for a Sprinter-derived vehicle is the Strata’s headroom. In the rear section it is well over 6ft, but an even more positive aspect of the coachbuilt product is that Mellor can fit glazing that is exceptionally deep.
Coupled with an optional glazed emergency roof hatch, light panel and fabric colours and good lighting, it creates a passenger environment that is at least on a par with anything else in the mini or midi sector.
The demonstrator has a climate control system fitted above the platform area. This is not standard, and a simpler alternative may be to specify heater radiators and rely on the opening windows for ventilation. Mellor can also add saloon air-conditioning, where required.
A one-piece, 950mm-wide Ventura plug door is fitted for a simple reason: Had it been two-piece, it would have led to the loss of a seat pair on the nearside.
A manual bookleaf wheelchair ramp is standard. John states that it’s unlikely that Mellor will offer a powered ramp as an option; being sited immediately behind the front axle means that it would be susceptible to dirt and salt ingress, potentially to the detriment of ramp reliability.
In the cab…
The Strata body considerably overhangs the Sprinter’s conventional track.
That could result in a slightly wallowing ride, but in practice that’s not the case, and the very low centre of gravity means that the extended width is not obvious when driving the minibus.
Where it is more evident is when examining the cab. The dashboard is extended at both sides, which gives rise to slightly more engine noise than may be expected.
However, Mellor uses the extension well, and mounted on the offside is a monitor for the standard reversing camera.
On the demonstrator, a ticket machine mounting bracket is fitted but no cab door or anti-assault screen.
Both of the latter can be added, and Mellor is already working on a screen. To the nearside, a luggage partition is ahead of the door.
All switches that control body functions are on a small panel to the driver’s right, beneath the small signalling window. They are labelled with words, not the more common pictograms.
Visibility from the cab is very good. Mellor has almost incorporated a ‘glass bubble’ to the front and sides of the driver, and the Strata retains the Sprinter’s standard mirrors. That makes replacement easy should it be necessary.
…and on the road
Driving the Strata is the same as any Sprinter, which means that it’s simple. The gearbox is a ‘select and forget’ type and there is no shortage of power; 163bhp would be considered sufficient for a bus with a GVW of more than double the Strata’s.
Rattles are non-existent, although on a lightly-laden journey the rear springs make themselves known. Air suspension is an option, but the ride on springs would settle down once some weight had been applied to the rear axle.
The Sprinter gave an excellent showing on a prolonged 10% climb out of Shaw towards Buckstones, holding 30mph for the duration, and it also performed well on the descent despite not having a retarder.
The gear selector makes it easy to hold a low ratio, and in second the Strata remained at around 25mph with regular dabbing of the brakes when returning to Shaw.
A 62mph speed limiter is fitted, and while it was not possible to test the Strata at this speed, it is well-suited to the urban environment.
Drivers accustomed to larger buses will rapidly take to the Sprinter and it will not be an unpleasant place to spend a shift.
Mellor’s new star?
The Strata is a competent addition to the smallest end of the bus market, and Mellor is confident that sales will reflect that.
Understandably so, because there is renewed interest in this type of vehicle: Stagecoach’s recent order with another supplier for 30 low-floor Sprinter van conversions has seen to that.
John points to Mellor’s decision to undertake accelerated durability testing on the first vehicle as an indication of the manufacturer’s approach to the Strata project.
“We didn’t want to rush the first vehicle into the market and then undertake in-service development with operators,” he says. “We have shown the first vehicle to some potential customers, and will incorporate any findings from the Millbrook testing into production buses.
“Operators should realise that the Strata can make low-demand routes more affordable to run, and early indications from those who have seen it are that it ticks a lot of boxes.
“We are confident in the chassis conversion and the product, which is why we are offering a three-year, bumper-to-bumper warranty. It was about coming up with a clever engineering solution that challenges people’s existing ideas, and that’s what we believe it will do.”