Exploring wider rims

It is the latest “trend” but there is some science behind the move towards wider rims. How wide is too wide? Is it a bit like the hash tag #doyouevenenduro? Well it depends on what sort of tyres you run and whether or not you run tubeless (who doesn’t these days?). These wider rims are designed to benefit tyres that are 2.4″ or larger.

As part of my exploration, to have the most reliable equipment for my Trans-Provence race (Project544), I have been looking at NOBL wheels. They have helped develop a new lighter version of the Onyx-Racing infinite engagement rear hub. There is a slight weight penalty over something like a DT240S however the upside is that the hub is completely silent and the engagement really is instantaneous. I test rode a set of the TR33 wheels a couple of weeks ago and was extremely impressed.

Anyway faced with a choice between the TR33 and the TR38 I wanted to look at how my favourite tyre mounted up on the TR38. So grabbed a spare (but used) Continental Trail King 2.4″ Protection and mounted it on a rear TR38 wheel.

TK2.4 on NOBL TR38

What I really wanted to check was that it fit in the rear triangle of my Nomad CC 27.5. It appears that it most certainly does.

It is easier to list the respective dimensions of the comparative rims:

NOBL TR38: Width: 38 mm; Inner width: 31 mm; Profile depth: 30 mm; Weight: 480 grams.

ENVE M70-30: Width: 30 mm; Inner width: 25 mm; Profile depth: 34 mm; Weight: 463 grams.

I have also listed the new(er) ENVE M70-30 HV as it is closer to the TR38 in size.

ENVE M70-30 HV: Width: 36 mm; Inner width: 30 mm; Profile depth: 30 mm; Weight: 469 grams.

It appears that as rims get wider the profile does not need to be as deep in order to maintain the strength and rigidity. The NOBL rim also benefits from asymmetric and angled spoke hole drilling which allows a more even spoke tension and less stress on the spokes. It also uses ‘normal’ spoke nipples so that one can perform a minor truing with a standard spoke key without having to remove the tyre and rim tape to access the spoke nipples. This is a big plus in my book having had to replace spokes on my ENVE rims in the past.

As a curious sort of chap I noticed that the sidewalls appeared to be wider than the tread which just did not seem correct so I reached for the verniers. I was surprised to find that my eyes were not deceiving me and that this is actually the case for the Continental Trail King on the TR38 and the ENVE M70.

I was also somewhat surprised that given the large difference in inner width between the rim that the change in tyre width was only 2 mm.

TK2.4 on NOBL TR38 sidewalls     TK2.4 on ENVE M70 sidewalls

I was more surprised that the tread width ended up being slightly narrower on the wider rim than the narrower rim;

TK2.4 on NOBL TR38 tread      TK2.4 on ENVE M70 tread

The difference is slightly less than 1 mm.

So why the trend towards wider rims? Well there is the volume. I am not going to do the maths for you but 2 mm wider over the entire tyre must add up to a few cubic centimetres of volume. I certainly noticed that I ran the compressor longer to get the tyre to 22 psi than I do with my ENVE wheels (same tyres). There are several articles about how a wider rim maximise the advantage of a wider tyre’s contact patch so I won’t repeat the points here.

It is now generally accepted that the wider rim allows the rider to run a lower tyre pressure for more traction with lower risk of burping the tyre when pushing hard. How wide is too wide? I am not sure but I am certainly going to give the TR38 wheels a good testing this summer with my Trans-Provence training and I anticipate that they will be more than up for the job.