Wheel sizes vs Handling

[Mick F]

Just been fettling our daughter's bike. Dawes Mixte 501 with 27" (630) wheels. 5sp freewheel and a double chainset.
Took it for a test ride.

First thing I noticed, was how the bike handled. I have two regular bikes - as many of you no doubt know - a Mercian with 700c (622) wheels, and a Moulton with 20" (406) wheels. They both handle and feel very different to each other of course.

I would have expected that the Dawes would have felt the same as the Mercian.
The wheel diameters aren't very different numerically, but the size to look at and to steer, felt very different indeed.

Is it just my imagination, or is this actually true?
Is 700c very different to 27"?

[charliepolecat]

Dawes Mixte 501 with 27"

Did you ride this bike before the wheel change and if so how does the bike differ from that ride? Comparing bikes to bikes rather than wheel to wheel is more applicable.

[Mick F]

The Dawes Mixte 501 came with the 27" wheels. They are the originals.
Centre-pull brakes too.

[reohn2]

Geometry,mostly steering IMO..

[Mick F]

No, I don't think that's it, though there must be some element in it as well.

Moulton is the extreme. Small wheels are twitchy to steer as the wheelsize vs handbars is small.
700c are bigger of course, and 27" bigger again.
The bigger the wheel, the more the effort to swing it side-to-side.

[charliepolecat]

Is 700c very different to 27"?

You asked the question and you seem to be answering it as well:

The bigger the wheel, the more the effort to swing it side-to-side

[reohn2]

No, I don't think that's it, though there must be some element in it as well.

Moulton is the extreme. Small wheels are twitchy to steer as the wheelsize vs handbars is small.
700c are bigger of course, and 27" bigger again.
The bigger the wheel, the more the effort to swing it side-to-side.

It's the same with slow steering,so could be a combination of the two,though a 630 isn't that much bigger,whereas a 20in wheel is tiny compared to a 622.
Have you tried riding no hands with 20 in wheels?

[Mick F]

Yes.
Twitchy but just about ok.

[JakobW]

What was different about the Dawes' feel? 27" wheels are only 1.3% bigger than 700C, so I'd be very surprised if you could reliably tell them apart if used on otherwise identical bikes.

Off the top of my head I can think of any number of differences that would affect the feel, including
- different front-end geometry
- different contact points (and thus weight distribution - does the Dawes also have drop bars?)
- different width tyres and thus BB drop & pneumatic trail
- frame flex - the mixte will be significantly floppier.

[Brucey]

most bikes with 27" wheels do have a different steering feel (vs when fitted with 700C wheels) but IMHO this is often because the 27" wheels are heavier than 700C ones rather than the difference in diameter per se.

Having said that things change very quickly in terms of MOI when you make wheels bigger. Assuming that you keep the design of the rim and tyre the same between wheel sizes, the mass is simply proportional to diameter. The MOI is proportional to mr^2, so in effect it is proportional to r^3 when the tyre and rim are kept to the same design.

Thus x1.013 in diameter (between 700C and 27") is actually worth about a 4% change in MOI; more than this if the 27" wheels have heavier rims and/or tyres. There is also a small trail value change too.

FWIW I have yet to ride a bike with small wheels that I am really happy to ride no-hands and normally I find it virtually impossible to do at all. By contrast I can ride for miles no-handed on a well-set large wheeled machine.

cheers

[andrew_s]

Why do you blame the wheel size for the difference in handling between the Mercian and the Dawes?
I'd have thought that there would be differences in head angle, fork rake etc that would swamp the minor difference in wheel size.

[pjclinch]

Why do you blame the wheel size for the difference in handling between the Mercian and the Dawes?
I'd have thought that there would be differences in head angle, fork rake etc that would swamp the minor difference in wheel size.

Indeed. I also have a Moulton TSR and also a Burrows 8 Freight, both have 20"/406 wheels. The handling is, unsurprisingly, quite dramatically different!

One of the odder handling differences I've come across is changing the bars on an overseat steering 'bent from aero to tiller style. In either case the bike's geometry is fundamentally the same, and with no weight on the bars and seating position pretty much the same (arms excepted) there shouldn't be any difference in handling. But I can't get really comfy with tillers on any bike I've tried them on, and have always got straight on with aeros (other people find the precise opposite, or don't do underseat steering). It's purely psychology and familiarity.

Pete.

[foxyrider]

Back in my youth, when I couldn't afford n+1 i, and many of my peers used 27" all winter then put the 700c sprints in for racing across the summer. Couple of minutes adjusting the brakes and off you go. Can't recall it feeling any different other than weight, the bike was hardly lightweight to start with!

As regards smaller wheels, I have an Airnimal with '24"' wheels alongside my big wheelers. It generally rides very much like the big wheelers as I have it set up but it can feel a bit 'light' at speed - especially if it's not loaded. On the plus side, its very stable when loaded for touring and you can do a 180 degree turn in barely more than the wheelbase? I have managed no hands on it but it's never a great idea on a loaded tourer!

[Mick F]

.......Thus x1.013 in diameter (between 700C and 27") is actually worth about a 4% change in MOI; more than this if the 27" wheels have heavier rims and/or tyres. There is also a small trail value change too.

Correct, I reckon.
The issue is probably a combination of it all.

Maybe, the difference in order:
Tyres
Rims
Diameter
Geometry
However, with a Moulton, the order would be different with diameter being far the larges effect.

I'm trying to get my head round a theory of mine. I can see what I mean, but it may be difficult to put this across well enough.

For any steering done by the 'bars, for every degree turned left or right a small wheel moves further left or right than a big wheel for every foot distance travelled forwards.
Hence a small wheel bike will be twitchier than a big wheel bike because it moves more left and right.

[Samuel D]

For any steering done by the 'bars, for every degree turned left or right a small wheel moves further left or right than a big wheel for every foot distance travelled forwards.

By what mechanism? I don’t see it.