Cycling UK Forum

Hi - Newbie here,

I'm after a good all round bike that can handle a little bit of off-road if need be.

Research has led me to the Marin Four Corners which seems a good all rounder.

But I also like the look of the Marin Nicasio (plus it's cheaper).

The Nicasio is a road bike but I'm reading that you can change the wheel size from 700c to 650b to potentially accommodate thicker 'off-road' tyres.

Is this a costly/complex change? I presume I'd also have to tweak the gears and all sorts. Or maybe buy other parts besides the new wheels?!

Any advice would be most appreciated - thank you!

If you are switching purely to 650b then you would need new wheels and tyres. The hubs are still in the middle, whatever the wheel size, so the gears wouldn't need touching. You may need to re centre the brakes if the disc isn't in exactly the same place.

If you are keeping a 700c set as well, then you would need an extra cassette and new discs that are the same size as the current ones. It wouldn't be a massive or expensive change.

However, how big do you want to go? Google says that it can take a 40mm tyre on 700c, and you might find that a 38/40mm tyre on the 700c rims will be enough. I'm quite happy playing on Lake District farm tracks and forestry roads on 38mm Gravelking SKs.

Hi McShroom,

This is really helpful info - thanks so much.

Best,

Ben

Just a very general comment in case other posters act on information here.

A brief check shows that your bike has disk brakes but for those using rim breaks the change in rim size moves the breaking surface and that might give problems.

I don’t know what the relative rolling diameters of both sets of tyres are but I’d be surprised if the bottom bracket didn’t sit a little lower with the new tyres - it’s probably not significant and circa 15 mm.

I find that the gap between the chain-stays is limiting factor as to what of size of tyre will fit on a bike - varies a bit between makes and models. Unless you’re at the limit of available 700c sizes I’d be surprised if changing the wheel size allowed you to fit significantly wider tyres (within the chain-stay gap).

This article - and data - might be of interest to some readers: https://en.m.wikipedia.org/wiki/Bicycle_wheel
700c tyres appear to be available is wide widths, but they might not be compatible with the width of your existing rim : https://www.cyclinguk.org/cyclists-libr ... tyre-sizes

Carlton green wrote:I don’t know what the relative rolling diameters of both sets of tyres are but I’d be surprised if the bottom bracket didn’t sit a little lower with the new tyres - it’s probably not significant and circa 15 mm.

Depends what tyres you use of course, but the design is underpinned by the principle of using a larger tyre on a smaller wheel. So, for instance, a 700x32 comes up the same size as a 27.5x2.0. The clearances of the frame and fork will be designed to accommodate a single outer diameter, with enough lateral clearance to permit the choice of whichever 700c or 650b tyre ends up at that diameter.

To an extent, yes. My Genesis Vapour is sized for 38mm tyres on a 700c wheel. The diameter of a 650b wheel would allow a wider tyre, but the other area of constraint would be the bulge between the seat stays as Carlton green says. Looking at my current bike when it has 38s fitted, I doubt I would be able to go much wider on the rear, even with the smaller wheel.

In the OP's case, the frame can take 700x40c, or 650x47b, so they do have a chance to make a go wider.

mcshroom wrote:To an extent, yes. My Genesis Vapour is sized for 38mm tyres on a 700c wheel. The diameter of a 650b wheel would allow a wider tyre, but the other area of constraint would be the bulge between the seat stays as Carlton green says. Looking at my current bike when it has 38s fitted, I doubt I would be able to go much wider on the rear, even with the smaller wheel.

Well, yes, that's what I was saying. A frameset designed for both wheel sizes would have the clearance for the wider 650b tyre. But the Genesis Vapour is not such a frameset: it's a 700c bike. So you shouldn't expect it to take a wider 650b tyre, because it hasn't been designed to do so.

Any 700c disc-braked frameset, such as the Vapour, will take a 650b wheel, and some (eg my Trek Crossrip) will take a larger 650b tyre than they will a 700c tyre. But they'll rarely if ever take a sufficiently wide 650b tyre to reach the same outer diameter as the largest 700c tyre they're designed for (and outer diameter determines BB height and trail, and hence pedal clearance and steering geometry). That's the point of a specifically-designed 700c/650b frameset: it's intended to be compatible with usable tyres in both sizes without altering the handling.

Carlton green wrote:Just a very general comment in case other posters act on information here.

A brief check shows that your bike has disk brakes but for those using rim breaks the change in rim size moves the breaking surface and that might give problems.

I don’t know what the relative rolling diameters of both sets of tyres are but I’d be surprised if the bottom bracket didn’t sit a little lower with the new tyres - it’s probably not significant and circa 15 mm.

I find that the gap between the chain-stays is limiting factor as to what of size of tyre will fit on a bike - varies a bit between makes and models. Unless you’re at the limit of available 700c sizes I’d be surprised if changing the wheel size allowed you to fit significantly wider tyres (within the chain-stay gap).

This article - and data - might be of interest to some readers: https://en.m.wikipedia.org/wiki/Bicycle_wheel
700c tyres appear to be available is wide widths, but they might not be compatible with the width of your existing rim : https://www.cyclinguk.org/cyclists-libr ... tyre-sizes

Edit. I believe that the next standard 700c width increment above 40mm is 47mm, perhaps you have to go to 650’s to get the required clearance but I don’t believe that 650 tyres are a common size whilst 700c’s are widely available.
https://bike.michelin.com/en/tires-and-tubes
https://www.marinbikes.com/gb/bikes/20-nicasio-1

Carlton green wrote:I believe that the next standard 700c width increment above 40mm is 47mm, perhaps you have to go to 650’s to get the required clearance but I don’t believe that 650 tyres are a common size whilst 700c’s are widely available.

Plenty of 42 and 45mm tyres in 700c, along with a few stragglers in between. And 650s are very common now thanks to the rise of the 27.5" MTB standard, which led to "road plus". Once that was around, it was only natural that 650b gravel bikes bridged the gap between road tyres and full-on knobbies. In essence, you can find pretty much the same range of styles of tyre in 650b/27.5" and you can in 700c/29", from 23mm up to 3" and everything in between.

IME most bike shops have about 1/10th the stock (or less) of 584 tyres vs 622 ones. Most of the ones they do have will probably be knobblies. 'Very common' in this case means you might be lucky and be able to buy something locally/off the shelf/in an emergency, but if you want a really good choice it is mail order.

To a first approximation if you fit 584 wheels with tyres that are 19mm fatter (than on the original 622 wheels), you will have the same overall wheel diameter.

cheers