Are wider rims better: I ask a wheelbuilder

Are wider rims better? I think so, but to get a professional take on this, I asked local wheelbuilder extraordinaire Josh Beck of XLR8 wheels why wider rims are better on the road.

Josh has been building bikes and wheels for 25 years and puts my developing mechanical skills to utter shame.

TM: What is the effect of riding wider tyres on a “standard” (around 19-21mm) rim? What is the widest tyre that can be ridden before we experience tyre squirm.

There is not a simple answer to the second question, as all tyres are designed (to some extent) to squirm under a cornering load, in order to maintain friction with the road in cornering. It's tyre and pressure specific.

But my answer to the first question provides some context ….

The benefit of a wider tyre on a wider rim is that it is supported (at its bead) so that the tyre profile is not “pinched” at the bead. Think of a fat tyre on a skinny rim (let's say a 23c tyre on a 19mm wide rim like a Mavic Ksyrium): the tyre will be the shape of a lightbulb – the tyre beads are only about 15mm apart, yet the widest part of the tyre casing is 25mm apart. On a wider rim (the same 23c tyre on a 23mm rim), the tyre bead are 19mm apart (20% further apart) – the tyre has a rounded “U” shape.

Additionally, the tyre and tube actually holds a greater volume of air.

This second point is really important. More air volume within the casing means that you need less pressure to ensure that the rim does not bottom out on the road when you hit irregularities. XLR8 has found that tyres can be run about 10%-15% less pressure on a wide format rim.

Less pressure means more comfort, and the tyre can absorb small road imperfections (rather than the bike being forced up and over them, or through them). This has been proven to save effort (much like a suspension fork on an MTB means that the bike can roll faster: the suspension ensures less “impediments” to progress). Most experienced riders know that higher tyre pressures don't mean a faster ride (unless you are on a billiard table smooth road, and I don't know anyone who rides those).

As the tyre has a U shape, the transition of contact point across the tread (as the bike leans in cornering – from centre to side of tread) is far less aggressive, and the lower pressure soaking up irregularities means that cornering is a far less stressful affair. There is less of a “commitment” or “transition” point in turn in – that instant where one asks oneself – “am I really going to lean this over, this far?” On a wider rim/tyre combo, getting to bike over on an angle (to corner fast) is a more natural dynamic affair, supported by more rubber on the road, on a tyre that has a very constant U shape.

TM: At what width should we head to a 23mm rim? 25c tyres?

I recommend a 23mm rim for just about all general purpose racing and training road wheels. The benefits far outweigh the only real negatives I can think of. The main negative is a tiny bit of extra weight (very minor), and aerodynamics.

A skinny tyre/skinny rim combo is more aerodynamic: but who wants to ride 19c tyres on 19mm rims? Anyone who has done that before, usually doesn't do it again: it's very harsh, and cornering is simply not fun.

Most riders are riding 23c tyres, as they have been the best comfort and speed compromise (even on skinny rims). On a wider rim, the further comfort and cornering benefits are very easy to feel. A 25c tyre on a wider rim provides most of the benefits, but due to the added tyre volume again, one can drop pressures further. This is especially handy if you ride awful roads or “gravel grind”.

But a 23mm rim with a 23c tyre is a great setup for most riders on reasonable roads: who want speed, comfort and that extra confidence in cornering. If you live near a major city, this is a great setup for you.

TM: So, would you recommend a 23mm or 24mm rim?

I would go to a 24mm or 25mm rim if you ride terrible roads, and would like to run 25mm tyres. It's also worth the effort for Cyclocross applications where one will run a 28c to 34c tyre.

TM: So what about tubeless? Tubeless 23/24 rim or tube-based 23/24 rim?

Tubeless is still lagging in acceptance. When tubeless first arrived on the scene for MTBs (early 00s) the advantages were immediate, and very pronounced for off road riding. You had the ability to run lower pressures without pinch flatting, meaning more grip and traction, and a softer ride. There was an undeniable speed advantage. Uptake was almost immediate.

Road tubeless theoretically has advantages (primarily less rolling resistance, and more supple ride), but these are certainly not as pronounced as it was in MTB. In fact, the migration from a narrow rim to a wider rim tends to offer all the advantages and more, without the mucking around and expense that is tubeless.

Tubeless setup is more time consuming, but in theory means less flats. Tubeless tyres need to be heavier for puncture protection, so this counters tyre suppleness a bit.

So in summary, the jury is out on this one now. I think the market will move in this direction over time. The big tyre and wheel companies love new “technology” to drives the sales of new “faster/lighter/stronger” products so it's in their interests to make you think you need tubeless.

[Ed: As an aside, one of the local blokes where I live has been riding tubeless for 3 years and is yet to have a puncture. And this is on truly shitful Northern NSW roads. I mean, they're truly, horribly, terribly, awful.]

TM: Is there a benefit in descending with a wide tyre/rim combo?

Most definitely.

The suppleness of the lower pressure tyre means you:

• Maintain traction at the limit for longer (and should grab more “gently” again if you slip).
• Are less likely to “lock” a tyre under braking as traction is greater (more tyre contact on the road).
• Get shaken about less by road imperfections at high speed.
• The “rollover” transition as the bike leans is gentler, inspiring high speed cornering confidence.

TM: Weight penalty? We're only talking mere grams between a 23mm rim/25c tyre and 20.8/22mm right?

There is very little additional weight in an equivalent wider rim, maybe +2 to +5% (no more than 20g).

There will be additional weight in moving from 23c to 25c tyres though, as there is more rubber at the meaty tread face of the tyre. It's about 10%-12% generally (say 25g on a Continental GP 4000s). That said, if you ride bad roads, you are likely riding 25c tyres already anyway.

But, on an average racing bike on medium duty tyres, moving to a wide rim (but retaining your 23c tyre width) might add 40g to your bike. Adding around 0.5% extra weight to the bike, for all those benefits? Seems like a good compromise to me.

Are wider rims better?

Bottom line, I think Josh makes a good case for why wider rims are better. To get the best benefit, couple them with wide tyres (why wider tyres are better).

Wider rims are faster, and they save you power (that is, they're more efficient), particularly on rough roads.

Moreover, wider rims are better on descents.

You can find out more about Josh's business building kick-butt wheels at XLR8 Wheels.