The Kahibah rider says he has been charged too much multiple times while using a couple of Sydney motorways, as he transported his bike on the roof of his utility.

"I thought there was a mistake," he said, after looking at his account.

When he recently drove to Canberra and back with three bikes mounted on the roof, Mr Haasnoot used the new NorthConnex toll road and a section of the M2.

Having just driven the new road, he checked his account and was surprised to see he had been charged around $24 each way on NorthConnex, when he believed it should have been about eight dollars (the fees had increased by the time he made the return journey). On the M2, he said, the toll was about $12 each way, when it should have been about four dollars.

"That's when I looked at the rules and thought, 'It's got to be the bikes on the roof'," Ms Haasnoot said.

He looked back through his records and noted on previous journeys along the M2, when he had his bikes on the roof, he had paid the higher toll.

Tim Haasnoot learnt that because his ute exceeded a 2.8-metre height limit when a bike was on the roof, the vehicle fell into a different class that had been set with the toll road operators and the NSW Government. And that different class meant paying a higher toll.

In effect, Mr Haasnoot said, his ute was being recorded by the network's cameras as a heavy vehicle, when he used those toll roads.

"I understand why, but I thought it's a bit crazy as a rule," he said. "My car is not a heavy vehicle, so why would I be charged as a heavy vehicle? I'm not doing any additional damage to the road.

"Just because you're carrying something on the roof, that doesn't justify the extra cost."

The first journey along NorthConnex with bikes on his ute roof in December also prompted Elermore Vale rider Paul Campbell to check his account, only to discover he had been charged in the heavy vehicle class.

Mr Campbell reviewed his previous accounts and said he found he had been charged for the higher tolled class on the M2 up to nine times. He estimated he was close to $200 out of pocket.

"It has me pretty annoyed, to be honest," he said.

He had contacted his tag provider, E-toll, seeking answers and a reimbursement. That email trail continues.

"Having an extra 30 or 40 kilos on the roof I would not consider reasonable to class as a heavy vehicle," Mr Campbell said, adding that the height of his ute with the bikes on top was about 2.95 metres, so he believed it was "a low profile".

Both men have also driven on the M7, with their bikes on the roof, yet Mr Haasnoot had incurred the higher toll only once, while Mr Campbell had not at all. So they were wondering about the inconsistency, when the same classification for vehicles was meant to apply across the toll road network.

Tim Haasnoot has been reimbursed the difference between the two different toll levels for five trips he made on those roads. The amount refunded was $79.19. However, Mr Haasnoot said he received an email from the toll operator, Linkt, telling him that in future if he had items on the roof that were above the height specifications for the passenger car class, the heavy commercial vehicle toll would apply.

"What I'll be doing is going on the normal roads to avoid the toll, and the whole point of these roads is so you don't go the back roads," said Mr Haasnoot.

A spokesperson for Transurban, the operator of those Sydney toll roads, said what Mr Haasnoot was told in the email was not correct.

"Motorists carrying roof-mounted bikes on top of their car or 4WD are not required to pay the higher toll price," the spokesperson said in a statement. "If a customer believes they have been incorrectly charged they are encouraged to contact their toll provider."

The Newcastle Herald asked the spokesperson how a car with a bike on the roof could be recorded as a heavy vehicle. The Transurban statement didn't answer that except to say that generally a bike mounted on a car roof wouldn't trigger the dimensions of the larger vehicle classification.

Tim Haasnoot said he would have to check his account each time after using the network.

"It's an automated system," he said. "So how many people aren't checking?"

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