Holy obesity epidemic, what have we got here?! Mountain bike rims have been trending wider and wider in recent years, but the new 650B Ibis 741 (and their 29er version, the 941) take things to a new level of phatness. Ibis aren’t known for their wheels, but we are super excited about testing these.
The width of these rims is not a gimmick or simple point of difference – there’s a perfectly sound basis for making mountain bike rims far wider than they have traditionally been. Ibis does a good job of explaining the theory in the video below, but in a nutshell, a wider rim should allow you to run a tyre at lower pressure, with greater stability and less tyre roll and, hence, less chance of burping air from a tubeless setup).
Of course, lower pressure equate to more grip and reduced rolling resistance on rough terrain, but dropping the pressures too far has traditionally meant a squirmy ride and a serious risk of a flat tyre or damaged rim – Ibis say their mega wide rims go a long way towards alleviating both of these problems.
So just how wide are they? The 741s have an external with of 41mm and 35mm internal – that’s between 10-15mm wider than your standard cross-country or trail rim in both internal and external measurements. And believe it or not, the weight of these wheels actually puts them head-to-head with some seriously well regarded XC and trail wheelsets – the pair come in at just 1660g including tubeless valves.
Other noteworthy elements? The rims use ‘hookless’ bead construction (similar to the Specialized Control wheels we tested last year) which gives the rim far greater impact strength and the tyre more volume. They’re also spoked in a very conventional manner, with 32 spokes front and rear in a two-cross pattern which will appeal to the mechanics out there.
We’ll be fitting these wheels to a variety of bikes over the coming weeks and months. With the swathe of carbon wheels we’ve been riding lately (ENVE, Specialized and Bontrager amongst them) it will be very interesting to see how these unique offerings compare.