The question gets asked alot as to why my road wheels are not wider than 19mm well it quite simple -ETRTO.

ETRTO is a standard organisation that lays down specification for tyres and rims. Standards for bead hook design are mandated and for tyres. My rims conform and all the major tyre manufacturers conform to these standards too.

Wider rims are often hookless as well. Hooked rims are recommended for all road and gravel width tyres. Often the rims used for road and gravel are the same and non of the major tyre manufacturers say its fine to use there road tyres with hookless rims. Some say explicitly you should not. Hookless rim are really an mtb creation for tyres inflated to 30 psi or under. While some claim pressures are fine much higher for road tyres remember to hookless carbon rim (its mostly carbon) exists solely because some rim manufacturers find it too expensive to make there bead hooks properly. Some never made them properly in the first place (ENVE bead hooks don't conform to ETRTO standards). I don't offer hookless rims. If your using one no IRC road tyre should be used with them. The gravel tyres I sell should be fine used tubeless and with pressures under 40 psi. 

There are many rim and wheel manufacturers now touting 23mm, 24mm and 25mm internal width rims and some say tyres from 25mm wide are fine. They do this because wider is better innit and it more aero. 

The problem is tyre manufacturers say different. At the extremes when say mounting narrower 25mm or 28mm tyre to a 23mm internal width rim one risk is tyre blow off. This is risk is higher with hookless rims than hooked rims. However this is the extreme for example the 28mm tyre pictured below mounted to 23mm internal width rim/28mm external width. This may not actually blow off but it shows another problem. Tyre shape.

Tyre manufacturers like IRC want there tyres to have a shape range. The top of the tyre should form a circular arc so when riding your on the centre of the tread and when corning you move progressively over the shoulders the more you lean into the bend. 

With a stretched tyre the shape is flattened at the top and this does affect how the tyre handles. You maybe more aero but slower in the bends. This especially true off road with off camber and undulating terrain. 

The side walls are also more exposed with stretched tyres to damage. Gravel and potholes on the road or all those roots, stones and holes off road are more likely to slice a side wall. Nothing slower that a blowout tyre. Tubeless tyre pinch flats are also more likely with over stretched tyres.

This is why i am not following the wider is better trend. It works to a point.

Suggested tyres rims for rim sections. These stretch the older ETRTO guidance a but new guidance was issued in 2020 which confirms my chart. You can actually go wider than i suggest safely but higher pressures would be needed to avoid tyre squirm in bends. This also affects tyre performance so the max width seem to be practical  maximiums. The minimum width really are minimums and with some tyres there may be pinch flat issues. With the wider rims the min tyre width is barely recommended as these are off road tyres and pinch flats are more likely at the bottom end of the tyre range.

Rim  internal width mm       tyre width mm

15mm                                     23mm to 32mm

17mm                                     23mm to 36mm

19mm                                     25mm to 42mm 

20mm                                     28mm to 45mm

21mm                                     32mm to 50mm 

23mm                                     36mm to 60mm

25mm                                      40mm to 65mm

Most of my wheels have aluminum alloy freehubs bodies. Some people worry about cassette sprocket notchng. This concern is misplaced. Notching occurs for very specific and avoidable reasons. 

First riders are not strong enough to cause notching. Regardless of how strong you think you are you can't notch a freehub that has a properly installed lockring.

The pic is of one of my freehub. Notching should not get any worse than this. Its barely notched.

First notching can only occur if the cassette lockring does not provide enough preload to the cassette. Thay preload stops the sprocket slipping and notching the freehub.

Grease freehub splines lubricates them. Dont do it. It is likely to make notching more of a problem. 

Recommended lockring torque is 40 to 50 Nm.

Not all torque wrenches tell the truth. A good mechanic has feel. The tool and feel tell you if your getting tight enough. 

Due to manufacturing tollerances there  an be a range of preload applied to the cassette hence feel is important. So the correct torque  can be aplllied but the correct preload not. Don't be a torque wrench slave. Lubricating lockring threads does reduce the variation in preload applied but also increases it and could result in stripped threads. There we fit lockrings without greasing them. We ensure the threads are sharp and clean.This way the correct preload is applied to cassette when the lockring is at 40 Nm. 

Most lockring tigheneing effort is used to over come friction so dirty or damaged threads mean notching is more likely.

If you get a freehub that notches, file the burrs and thick about what could have caused it. Its not the freehubs fault you just need to be a better mechanic.

One of my alloy freehubs is pictured after a few thousand km. No notching because i avoid the errors above. 

IRC have new Formula Pro tyres due in August. 

Formula Pro Light TL, Formula Pro RBCC TL, Formula Pro X Guard TL tyres have recieved a overhaul for 2020. Initially available in 25mm and 28mm 700csizes with 30mm width being avilable later in the year.

IRC's proprietary technology that blends RB ceramic particles, a hard porous carbon material made from rice bran, into the tread rubber. The RB ceramic particles, which are extremely small (200-300㎛) and are hard, exert a micro-spike effect, and at the same time, have a high gripping power even on wet roads due to the porosity with an excellent water absorption effect. With this update, the rolling resistance is maintained, while the grip, abrasion resistance, and weather resistance are greatly improved. It has evolved into a compound that maintains a high grip on all road conditions, both dry and wet.

Due to the hard porous structure, it exerts a micro-level spike effect on the tread surface. Due to the abrasion of the tread rubber, new RBC particles appear on the face, and the traces that have fallen off also function as minute edges. In addition to the water absorption effect due to the porous body, the small holes that have fallen off temporarily hold water on the road surface like a foam rubber and cut the water film. Useful for improving grip on wet roads.

So the Formula Pro tyres will retain there reputation for unparalleled grip even on wet greasy winter roads.

IRC Formula pro tyres are cobbletastic. The tread extends to the sidewalls improving puncture and cut resistance. Perfect for rough roads.

The Formula Pro X Guard TL tyre gets the 40x40 TPI beadto bead puncture protection belt. This improves puncture protection by 40% over the RBCC tyre model. The X Guard belt is the difference between the two tyres. The X Guard belt being less flexible increases rolling resistance a bit and decreases comfort and grip a bit.

Technology that reduces rolling resistance of tubeless tires. The NR-TEX IAS, the tire's air retention layer = inner air seal is composed of a supple and highly repulsive natural rubber base (NR) compound to pursue faster and more supple performance. You'll like the comfort of these tyres.

180TPI casing. Well that says it all. Comfy.

Pinch flats are possible with tubeless tyres. Without bead protection a bead puncture can happen. While these can be plugged the repair is temporary. The old IRC Formula Pro RBCC tyre victim of these. The Formula Pro X Guard was not due to the bead to bead protection. So the new Formula Pro series get bead protection so all the tyres are now potholetastic or cobbletastic.