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07 Sep

Tubeless tyre inserts - how they work

Posted by Malcolm Borg

There is alot of misunderstanding of tyre inserts. Many think they primary function is rim defence well that part of what they do. In fact the charactetisics of the insert (size, responce to air pressure and the material itself) detemine how they work and what type of riding they are best suited too. 

So here is a detailed guide with some Physics. I used to be a physics teacher so I cant help my self. 

A tyre , insert and air system is essesially a spring with an overal spring constant.So the Insert really acts as a way of giving more control of the air pressure required to give the spring constant needed to stop your tyres botming out and squirming.  

Springs in series add in the following way. k(t) is the total spring constant of the system, K(a) is the spring contant of the air, k(r) spring contant of the rubber tyre and k(i) the spring contant of the insert. The spring contant of the air and tyre  are non linear which complicates matters

1/k(t) = 1/k(a) + 1/k(r) + 1/k(i)

or k(t) = [k(r)k(i) + k(a)k(i) + k(a)k(r)]/[k(a)k(r)k(i)]

Now it should be clear the tyre used has a big influence on the pressure that can be run.

The spring contant of the air (low pressure) is the lowest term so 1/k(a) is relatively high compared to the tyre and insert term which are lower. So for tyres with flexible casing the air term does not dominate as much as trail tyres with stiffer casings. i.e you can run lower pressures in tyres with stiffer sdiewalls then with tyres with more flexible sidewalls. That does not mean however that inserts only work best with tyres with stiff sidewalls. Thats not the case at all.

The insert is important. The firmer the insert the more dominatant the air term becomes. If you have a 1kg trail tyre you will need a firmer insert to run the lowest pressures. In the PTN range the Rokkline work well but the Revolution insert is best. 


Run flat works best with stiffer tyres but the stiffer inserts (Rokkline and Revoluition) do all run flat with light XC tyres. Most occasions where you will be running flat there will be some residual air pressure even if its 5 psi. With a stiffer tyre and  an insert the air term dominates again in other words your able to ride on air and a stiff sidewall will limit the squirm.

The lower pressures can be be used allow lower rolling resistance. However the insert needs to reduce in size with air pressure and not be in contact with the tyre with the riders weight on it. Some insert are so big and stiff when the rider sits on them the tyre is in contact or the air volume so small (vittoria airliner) that there is very little tyre displacement before your tyre is in contact with the insert. That contact increases rolling resistance. 

If the tyre is not in contact with the insert then the insert is the last line of defense when you and or strike an obsticle preventing the tyre bottoming out on the rim and the consequential damage that can result. 

The lower tyre pressure improve grip and traction and as the tyre can conform to the gorund better you suffer lower vertical accelerations (bounced about less) and that is how rolling resistance is lowered. 

Essentially these insert work. Come insert like Crush Core or the vittoria and geared more to gravity riding as they are dense and very impact resistant. Crush Core is also heavy compared to PTN. PTN actually have a new heavier (slightly) and firmer insert called rockline which is aimed at enduro riders and E bikes. . Schwalbe pro core is quite good as you can alter the spring rate of the inner chamber to tune the system. However I have punctured pro core with a long thorn. The firmer inserts are better suited to trail tyres and the lighter inserts are better suited to lighter tyres. Many of the other inserts are heavy or heavy and dont offer good inpact resistance. The is a good article on this here.

So this is a suspension system in the tyre and should be viewed as such. Sorry it got all technical.


What inserts do a summary. 

  • allow lower tyre pressures improving comfort
  • reduce rolling resistance ( see above for explaniation and caveats)
  • rim and tyre defense is a consequence of being able to run the lower pressure
  • more traction and cornering grip for the same reason as you get lower rolling reistance. 
  • Run flat potential.
  • Anti burping

 

22 Jul

Miche hub maintenance -how to guide

Posted by Bold Apps

Miche hubs are simple to service. 

Play in Axle:this can be adjusted out. First make sure the end caps a tight. Use two 5mm allen keys and note the direction arrows on the left end cap. reverse thread alert. 

Use a 2.0mm allen key to undo the grub screw on the left side. Use a 17mm spanner to adjust the bearing preload adjuster so there is just no play. screw down the grub screw. Be gentle with it as grub screws are easily rounded of. It only has to be secure so the adjuster does not unwind by itself. 

The adjustment is best carried out withthe wheel clamped by the QR in the frame as QR pressure loads the bearings. 

Proceeddure for the fornt and rear hub is the same. 

Freehub change:

If you chanaging your freehub due to notching then so you cassette lockring up tighter. 40Nm is the minimum required. Miche cassettes also notch shimano pattern bodies less so there your other solution. 

Undo the end caps with two 5mm aleen keys in each end cap noting the direction arrows on the left end cap. Remove the axle and change freehub. 

Assembly is the reverse of disassembly but bearing preload may need to be set again. 

Bearing Replacement

The freehub bearings can be replaced but most users will lack the bearing extraction tools to make this possible. walking the bearings out will likely damage the freehub or get the bearing stuck. 

Main shell bearings should be extracted with bearing extracter or kocked out carefully. A bearing press should be used to press in new bearings. The Miche supplied 6001C3 bearing shoudl be used. a standard 6001 bearing will fit but will wear out faster because its not a clearance bearing.

 

28 Apr

Tubeless pinch flats

Posted by Bold Apps

Yes it can happen. On 300km audax on saturday 27th April, about 60km in, I hit a big stone and the IRC Formula Pro tyre I had mounted lost air very rapidly. The puncture was a This 5mm cut along above the bead. It is not a puncture that cannot be easily fixed by inserting a tube as it is not easy to boot that area. 

A 3.5mm Maxalami plug did fix the hole but the tyre developed a hernia and the plug pushes out above ~15psi. So I rode 8 miles home to swapped wheels. Incidentally the tyre still is inflated to that pressure 24 hrs later and it would have got me further. 

I bring this up because I get the odd email about this sort of failure from time to time. The customer normally find the tyre fails without warning and thinks its the tyres fault. That's unlikely but hitting a stone or pothole at some point and thinking all is well is likely. This can weaken the tyre and it then fails at a later date. 

These failures do happen to other brands of tyres too. IRC normally replace  the tyre even though it strictly is not a warranty. The Formula Pro X-Guard tyre due to the puncture protection belt does seem to fail seem to fail so if you ride on back lanes that are full of holes or venture down bridleways/gravel sometimes the X-Guard tyres are a better bet.

The IRC Formula Pro RBCC is a race tyre and while normally long lived and reliable they are not invunerable and more easily damaged than its hardier brother. This however this is the case with all race tyres. We all want nice fast rolling tyres but in reality these are racing tyres. 

A weakened tyre should have telltale bulges or other deformaties.  Tubeless tyres are should therefore be inspected. Just because it's holding air dies not mean all is well. The moral is check your tyres. 

My failure did happen after I spent a few rides bouncing down bridleways. Did this weaken the tyre, I don't know. I did hit the stone fast and just before I hit it I did think that's looks sharp and I hope... Bang.

The other morale is carry Maxalami plugs. There is nothing that can't be fixed even if it temporary, that is fixable with these plugs. A tube is not the answer as there is no way you'll get a boot to stay put just above the bead when mounting the tyre.

 

 

14 Mar

ENVE rims - warning

Posted by Bold Apps

The bead hooks on the ENVE SES road rims (rim or disc brake) are simply not conforming to any standard. The bead hook is not properly shaped and as a result can cut into tyre just above the bead. It won't happen to every tyre but how much contact the tyre has with the "sharp" edge will be important as will the type of tyre. That means tyre pressure is important (too low and the risk of cutting should increases) as is the amount of tyre deformation caused by cornering. Tyres with reinforcement at the bead will be less prone to cutting as would low TPI tyres. Let me emphaise that all tyres are susceptible to damage though. The rim bead hook design is at fault not the tyre. No tyre is actually safe to use on these rims due to the increased risk of failure. 

In my opinion no tyre should be used with these rims. I noticed this 18 months ago but I refrained from publishing due to lack of proof (sample size too small). Some warranties for IRC tyres on these rims have cropped up. 

If you suffer a tyre failure on an ENVE rim I therefore cannot consider a warranty issue. Your tyre maybe replaced as good will but in my opinion you should be returning your wheels to ENVE for a refund. 

I think there are issues with DT Swiss road rims too but that is due to the size of the bead hook (too small) and the wrong orientation. Tyres with reinforcement at the bead are best used.

 

 


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