My personal experience is that an easy way to inadvertently upset a bike’s stability is to fit a handlebar bag.   Without rear panniers it upsets the bike in a X-wind and it’s weight forward of the handlebar stem makes the bike more twitchy as the bag’s weight increases.   Longer mounts that move the bag further forwards must make these effects worse.

I have never tried having a bag on a rack on top of the front wheel but I imagine this might cause the same problems?

You're absolutely right. Most cyclists with their brain in gear try to distribute the weight on a loaded bike equally between the wheels whether they know about the Centre of Gravity and the dynamic couple between the front and rear wheels or not. It's long-established common sense.

But very few know about another movable point, called the Centre of Aerodynamic Pressure, which acts, to simplify matters, through the side profile of the bike, which makes the distribution of surfaces extremely important because it is imperative for the stability of any vehicle that the centre of aerodynamic pressure be behind the centre of gravity.

If you contemplate the side surfaces of the front of the bike and of the rear, you will see that with the rider on board there is just about zero chance of the centre of aerodynamic pressure moving forward. Panniers are put first on the back for a good reason, so is any further loading of the rack. The height of any load with much surface at all also goes on the rear rack first rather than the front, and lowrider pannier are fitted low down because you don't want the dynamic centre of aero pressure to slope downwards towards the back of the bike.

If the cyclist as his only load on the bike except himself fits a rack bag and high up at that, he unsettles the distribution of side surfaces and the stability of the bike in side winds as small as that caused by a hatchback passing him. The bike wants to swap ends because it is quite possible that in addition the front to rear aero couple now runs downwards.

That's what your experienced. Note that in yaw all these forces (vectors) may be ameliorated or enhanced. A good example is a large flat side truck passing close by. With the bike's design side surface and consequently aero handling upset by a possible doubling of the front surface by the rack bag, a point may arrive where you don't know which way the front wheel will break, which adds another layer of uncertainty.

Once, at a crossroad with high hedges on all sides, a gust of wind knocked me off my bike. A trucker stopped and helped me (I hurt a lot -- I'd been travelling at speed) and said, "You're not a blow-in [a recent arrival in the countryside]. You should know better. All the flatsiders [closed truck drivers] know about this corner." I'd been riding there thirty years. I hadn't even thought of the aero CoP because a lot of the aero effects I was used to in motor racing don't matter with a four-wheel vehicle until you're travelling well over the ton and you anyway have large flat surfaces well behind the rear axle. I calculated up the side areas on my bike and instantly discovered that a handlebar bag, while very convenient, is an invitation to road rash in a windy area such as I live in on the River Bandon.

Jobst Brandt, probably the leading theoretician of bikes in the latter half of the 20th century, used to say, "If the front wheel goes, there's nothing you can do. You're gone." It's one reason the centre of pressure and reaction to invisible side forces like crosswinds must remain behind the centre of gravity of the bike under all dynamic conditions, because you can recover from a rear-end upset whereas at the front recovery falls somewhere between extremely difficult and goodbye.

By comparison I can not feel any negative handling effects with the tyre on the front 1/4 inch bigger than on the rear.

That's hardly surprising; it's a modest change, well within the design parameters for any competent touring bike, which has large reserves of dynamic safety built in. But make the front much wider than the rear, and take the bike out on a fast downhill with curves, and you'll frighten yourself. A bike that turns in sweetly at moderate speed in rush hour traffic will suddenly become a health hazard. And worse with a touring load on it.

For a while, because I just couldn't find a wide rim (24mm across the beads, minimum) actually in stock anywhere, I used a motor built into a narrow front rim with the fat tyre on the fat rim with the Rohloff at the rear. On hilly lanes I'd been riding for decades, it was pretty obvious that the bike was nervous enough for me to cut apex speed from 55kph on the sweeping downhill curves to just over 30kph because the 60mm Big Apples just weren't working the same predictable way any more. Until then I'd declared the difference in the rims "not such a big deal", which was true enough when the referring to riding on the level under 20kph. It was one reason that for my next venture into electrifying the bike, I bought a mid-motor, to move the weight and the motor aero area backwards and downwards -- and to return to my fabulous 24mm rim width all round.

https://ridewithgps.com/trips/180810750

Downunda we are in Autumn/Fall but we had a magnificent day yesterday, 4C to 16C , clear sky.

The ride was 80% bike paths, the rest quite suburban roads.

If you can open the RidewithGPS link, the spike was to the coffee shop and back.

Mike

For spoke length, there's no substitute for measuring the ERD of the rim yourself, I know that adds a second postage fee, but it's a lot cheaper than getting it wrong.

It's what I usually do nowadays.

It was easier up to about 20 years ago because I could source rims and spokes locally from a bike shop about 2kms from home.

More recently, I would order rims that the local shop couldn't get via Internet, then get the spokes locally, they had a good stock and would order odd lengths if necessary. But that shop closed a few years ago when the owner retiired.

Six weeks of rides from spring into early summer –

After an early end to a mild dry winter with barely 110 cms of snow – half of Ottawa’s longterm average of 220 – we waited for spring, and waited some more.  After the Easter weekend at the end of March, I rode across the river and into the Gatineau Hills.  Below, some notes and a few photos from several rides from early April to mid-May.

In early April the woods were desperately and dangerously dry.  (See Photo 1 below) The big river, the Ottawa, was a metre or more lower than its usual level during the spring run-off – no kayakers riding the big waves midway between the Ontario and Québec shores.  Up in the hills, the usual gurgling streams of spring were silent, reduced to a few semi-stagnant pools barely dripping into one another.

“Normally”, I would not ride up to Pink Lake lookout until late April, when the parkway would be free of snow and ice.  Photo 2 below shows Freddie at Pink Lake under a pale early-April sun.  The ride across the river on the Champlain Bridge, nearly a mile wile, is always a treat.  Photo 3 below shows the Québec side of the bridge from the bikepath downstream.  This photo, taken from a gap in the shrubbery at the water’s edge, gives a rider’s view of the structure.  (The bridge crosses three small islands on the Ontario side.)

In the following 4-5 weeks, we have had some rainfall, easing our collective anxiety about summertime fire hazards.  And, just to remind us of the source of our passports, we had some 24 hours of the worst road conditions I’ve ever encountered in Canada, a mix of wet snow and wind-driven rain.  Fortunately, I made it home safely from my midweek evening shift at our bike-recycling shop 6 kms to the west of our place, exhaled, and thanked the designers of 10-year-old wee 4wd Subaru.

This “extreme weather event” was, the weather guys said, the result of a “Colorado low” – warm moist air from Mexico meeting cold sub-Arctic air from northern Canada over Colorado, and whirling northeast.  My reckoning is that a Colorado Low is the evil and lesser-known twin of the “Rocky Mountain high” of pop-culture fame.  And why, Mr John Denver, did you not tell the whole story?

But one of the real benefits of a bit more precip, combined with warming temps, is that all-of-a-sudden in early May, we lurched into early summer. Photo 4 below shows a roadside apple tree in bloom, a reminder that this part of the Gatineau Park was farmed from the mid-19th-century onwards.  (Hardscrabble it was, too, but that’s another story.)

(cont'd in next post)

Plenty to think about

For now, I've got 26-inch wheels front and back, but with a much wider rim on the front.

Velocity Dually 26”
https://www.velocityusa.com/product/rims/dually-559

This has a 39mm internal diameter compared to the Ryde Andra 30 which I think is 19 mm internal diameter on the rear.

It makes a noticeable difference to the tyre profile with more of the tread in contact at the front.
(it also lets me run tubeless at the front with pepi tire noodle, insert so that when I'm not carrying lots of luggage upfront, I can use a lower tyre pressure).

For interest, I'll probably end up trying the 27.5" Front wheel after seeing how this current set up handles for a few months.


While theoretically this might all make sense; on my E bike which I use for commuting with moderate load. I've got 27.5 inch wheels front and back but a much wider front tire.
2.35" at the back and 2.8 at the front"

Since making this change to a much wider front tire on the E bike the handling has felt much more stable and giving me a lot more confidence on my commute. (about 15 miles each way half of which is off-road on relatively rough tracks)

However, I did make other changes to the E bike at the same time, such as bamboo handlebars and a redshift suspension stem.

Will report back in a few months once I've made a comparison.

Ewan