Rennie said the demand for bikes had never been so high and he encouraged locals to snap them up as soon as possible as they might not be there the next time they visit.
"I had a lady came in and look at a bike and she said she would think about it over a coffee. She came back and the bike was gone."
If stock and supplies weren't an issue, Rennie thinks it would have been a record year for bike sales because of the demand.
"The month after the lockdown, it was like Christmas. It was that busy."
Rennie said the "buy local" ethos Covid-19 had created had been awesome.
"There has been loads of support and that's a good thing for businesses. The next couple of months will be a bit tougher on some of the industries relying on stock from overseas."
Velo Ronny's Bicycle Store owner Dayle Cheatley said they were sufficiently stocked at the moment, but that was likely to change quickly in the lead-up to Christmas.
"Stock and supply is becoming an issue. I can see it running out, or being very short-supplied, come December and January for sure.
"A lot of people are purchasing their Christmas bikes now because they know there will be nothing come December, particularly in the kids' bike area and entry-level mountain bikes."
Cheatley said this was a worldwide issue across all sorts of retailers.
"Those people that usually would come in November/December and look are now coming in September and October just to make sure they secure a Christmas present."
Velo Ronny's has bikes delivered weekly, but the quantity they want might not be available.
"We are still going to have bikes, but it's not going to be in the quantity or potentially the model you really want.
"It will be on a first-come, first-served basis."
E-bikes have become increasing popular as the technology continues to get better.
"It's a big market," Cheatley said.
"The demand is very high but the supply is very low. To be fair, a lot of the e-bikes we've got on back order are already pre-sold.
"Not to say that we won't have stock, just a lot of it has been pre-sold."
Cheatley said the Whanganui District Council deserved credit for dedicating resources to shared pathways.
"I can't wait for the Upokongaro Bridge to come up, it's only going to open up it up more for Whanganui people. Hopefully the council keep on building these shared pathways. They are doing a good job.
"It's great that people are recognising a push bike is giving them a fair bit of freedom at the moment, which is great."
"It's great for general wellbeing and you see a lot of families riding on our paths."