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28 Feb

Rim width and tyre width.

Posted by Malcolm Borg

Rims are getting wider. Thats a good thing to a point. There are some aero wheels on the market now that have got too wide in our view. 21mm or wider internal widths are marketed for 25mm or wider tyres. Cannondale fit a 23mm vittoria tyre to 32mm wide Knot64 wheels. Brontrager suggest road tyres can be used on  there 25mm internal width rims and trek fit a 32mm tyre to these wheels for there bikes.

So let pick this apart by starting with the basics. A wheel is nothing without a tyre and a tyre is useless without a wheel. A wheel should be designed to get the most out the tyres they are intended for. That means standards and sticking to them. ETRTO set these standards and they are not just about safety.

Whats the perfect tyre shape? Well circular just like a tubular. Thats why tubs handle so well. Tyre type

Clinchers or tubeless clinchers will deviate from that perfect shape. How much will determine how much the handling is affected. If the rim is to narrow and tyre too wide the tyre can light bulb and give vauge handling in the bends.

If the rim is too wide for the tyre the tyre ends up shorter and wider but the crown is flatter and the sidewalls straighter. In the case of knot64 wheels, the tyres Cannondale supply are stretched so much the sidewall curves inward from the bead. 

A tyre thats stretched will not handle as well as if it wear mounted to a rim of the ideal width. That is the

Now such combinations of a over wide rim and narrower than ideal tyre is often paired to lower aerodynamic drag. This however one aspect of the wheel, tyre system.

The move to wider tyres does make some sense. On perfect road surfaces they should show higher rolling resistance but roads are not perfect are they.

Wider rims mean less sidewall flex which in turn lowers rolling resistance and less sidewall flex can improve tyre handling. There are limits though. Sidewall flex also impacts tyre feel. Reducing flex too much can make tyre tyre feel snappy. Tyre flex is your road feel. Stiffer sidewalls still flex but the snap back harder. The result is sudden loss of grip at the limit with little warning. Just like on some cars which give no feedback to the driver. Too much sidewall flex is a problem also. If the the tyre becomes too stretched rolling resistance can increase. Remember the shape of tubular tyre.

When the crown of the tyre is flattened off by mounting on a rim that too wide, the tyre wears in unfamilar ways. When cornering the tyre still ends up wearing the centre more than it would if the tyre is mounted to a narrower rim. In testing various rims i have had 25mm IRC Formula pro tyres and Continental GP5000 tyres mounted to 20mm internal with Velocity aileron rims and wider rims. The wider the rim the more noticable the excess wear in the centre section of the tyre is. 28mm tyres did not show this problem on 20mm internal width rims. Therefore to keep my road wheels compatible with 25mm tyres the internal width are no wider than 19mm. Essentially a narrow tyre on a too wide rim will square off sooner and have a shorter life.

Rims that are too wide also expose the side walls of the tyre and the rim itself to damage more frequently. There is nowt slower than the tyre with a damaged sidewall or a wrecked rim. Pinch flats on stretched tyres are more likely.

In order for a tyre to be made for a rim that really wide it shape has to be altered. Because a bicycle tyre has no shape without air pressure (this keeps tyre weight down) we will not see tyres shaped like you do on cars or motorcycles any time soon. You can alter tyre thread thickness at various points on a tyre though to optimise the crown shape for ultra wide rims. However such tyres then are not optimised for narrower rims and so far there are no road tyres made that way. 

Tyre manufacturers mostly make tyres (unless they state) that meet ETRTO specifications. While the tyre size chart can be a stretched a bit without consequence for example a 25mm tyre on a 19mm internal width rim many of the the current wheels offered by many manufacturers are more than pushing the envelope. Even for those that make tyres and wheels thoe tyres  will  be made to ETRTO specifications. 

This is why our road wheels are 19mm internal width not 21mm or wider because wider maybe more aero but thats too focused. 19mm is wide enough for 25mm tyre to 40mm while preserving the tyre shape the tyre manufacturer intends. A good wheel has to balance characteristics.

Our gravel wheels there for start at 23mm internal width to stop road tyres being used on them (I hope). Gravel wheels use rim widt that are used for MTB's.

I hope you can see tyre shape is key to how a tyre preforms and wears. Since the tyre is what keeps you upright get the most out them. Pick the right rim.

 

 

 

 

28 Feb

Set up of BORG DX hubs

Posted by Malcolm Borg

BORG DX rear hubs use bearing preload adjustment. This has to be set with the wheels fitted and secured to the bike.

The rotor and any adapter must be removed. Use a 1.5mm allen key to undo the grub screw on the left side of the hub and undo the adjuster.

Fit the wheels and secure them normally to the frame or fork. Advance the adjuster till there is just no side to side play. Secure the grub screw.

Remove the wheel and refit the rotor and the wheels can be refitted. 

To inspect the bearings or remove the freehub use a 12mm hex key on the left side and a 17mm spanner and undo the left end cap. At this point you can replace the axle, freehub or carry out any other maintenence job.

 The front hub has no preload adjustment. The end caps are push fit. There are two bearings in a shell. Therefore to inspect the bearings just remove the end caps.

 

20 Oct

BORG rim brake hub maintanence

Posted by Malcolm Borg

These BORG rim brake hubs are simple to service. Take apart for the following reasons

1) to replace bearing

2) to replace freehub body 

3) to add grease to freehub mechanism.

Bearing require changing when they are not longer smooth. When the bearings spin with noise they are worn. They will spin freely at this point but there will extra drag with rider load on the wheel. Bearing life should be long. 

Insert 2x 5mm allen keys into end caps. Normal right hand thread and undo. One end cap will undo.

Insert a 10mm allen key into the axle and with the other 5mm allen key remove the other end cap.

 

 

The freehub bearings should be removed with a blind or collet style puller and refitted. 

Freehub pawls and springs are a spare part and can be replaced.

To remove axle knock it out with a rubber mallet from the drive side. The nds bearing will push out of the shell.

 

 Use a bearing puller to remove drive side shell bearing and a bearing press to fit new NTN 6902 bearings. 

The freehub bearings are NTN 6802. 

Pictured here are shell bearing with contacting seals and a freehub with non contacting seals.

The hubs are made with the tight tollerances that NTN bearings provide. Therefore use of other brands of bearings while possible may affect bearing life and hub performance. 

 

 

24 Sep

Tyre sizing and rims

Posted by Malcolm Borg

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

   

 

 

 

11 Aug

Aluminium freehubs and notching

Posted by Malcolm Borg

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. 

 


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