Disc rotors .. swopping??

[MTB0007]

Hi

Maybe a doff question...

Can one upgrade your wheels with disc rotors at 160mm, to a wheelset with 180mm disc rotors.... both are Shimano rotors...

If anything what can be done to do this..?

Help please... In my mind it would not work..

[AndreZA]

The size of the rotors has nothing to do with the wheels BUT some flimsy wheels will break if you fit 180mm+ rotors due to the greatr stopping power. If you go for bigger rotors youwill need frame/fork adapters to move the calipers so that the bigger rotors fit.

 

 

[MTB0007]

Makes lots of sense,now thanks..

Also explains why on these cheaper wheels, that my bike came with the rotors are 160mm..

I am asuming the spacers/adaptors, are avail in most LBS....

Thanks Mampara

[AndreZA]

You do not need anything bigger then 160mm. You can actually go smaller at the back. A 140 looks super nice on the back. Almost the same size as the casette. I'm assuming you do cross country riding and not freeride or trails.

 

Yes, the adapters are availble everywhere.

 

 

[MTB0007]

Yep Cross ..

Did Freeride until last year - broke my hand and had to have two ops to sort it...

Still hurts when I jump around.. which is why I moved to Road in Jan...

But the wild road (motorists) users, and the call of the wild ... has lured me back.....

I will look into the smaller rotor, for the back..

These rotors look, as if they are riveted,?? How would one change them?

[AndreZA]

Normally they screw onto the hub with torx bolts (T25). You will need a special tool for that. Otherwise if they are shimano wheels, sometimes Mavic als have it, they screw on with a big bolt. If they have the two piece system you do not touch the rivits/bolts that is in the middle, only the once that attches it to the hub.

 

6bolt

http://www.mtb-bitz.co.uk/images/gusset_r-series_disc_MED.jpg

 

6bolt 2 piece

http://www.monkamoo.com/Buy%20Images/hopemono6tibuy.jpg

 

centrelock two piece

http://www.shimano.com.au/publish/content/global_cycle/en/au/index/products/mountain/xtr/product.image.+media+images+cycling+products+bikecomponents+SM+SM-RT97M_600x450_v1_m56577569830637395_dot_jpg.bm.512.384.gif

 

[Johan Bornman]

The size of the rotors has nothing to do with the wheels BUT some flimsy wheels will break if you fit 180mm+ rotors due to the greatr stopping power. If you go for bigger rotors youwill need frame/fork adapters to move the calipers so that the bigger rotors fit.

 

 

I'd love to be proven wrong on this one but my experience on the issue is not the same.

 

I have never seen a wheel "break" due to too much torque applied at the hub aka too much "stopping power."

 

The scenarios are as follows:

 

1) The spokes rip out of the rims

2) The spokes rip out of the hubs.

3) The spokes break.

4) The wheel collapses and tacoes.

 

The latter I can't foresee since torque applies even tension and relieves even tension right around the rim. In other words, total tension remains the same, no matter how hard you brake or accellerate. Since total tension remains the same, we know the wheel tension remains balanced and therefore a taco is unlikely, if not impossible.

 

For the spokes to rip out of the rims, we'll have to rip all 16 pulling spokes out at once, since once again, we know the tension in all the pulling spokes remain balanced between spokes (even though invidvidual tension goes up ) and the tension in all the pushing spokes remain the same (even though individual tension goes down.

 

For the spokes to rip out of the hubs, the same argument as above is valid.

 

For the spokes to break, you'll have to exceed the maximum tensile strength of one spoke and multiply it by half the spoke compliment i.e.

16 spokes, convert that to torque and convert that to stopping force. Even a thumbsuck with one eye closed and Ramstein playing full blast in my headphones tells me that this is one awsome force. The breaking tension of a 1.8mm DT spoke is 250kgs (source: The Bicycle Wheel). Multiply that by 16 and you get a total load of 4000kgs or four tons.  Apply that load over 250mm of spoke and you have a torque of 1000NM. If I'm correct, that's more than any sports car can produce. Assuming that the centre of the wheel is 1 m from the centre of gravity of you on your bike, you have a force of one ton on your two wrists at the moment of spoke breakage.

 

Methings your wrists will snap first. Actually, they won't, your neck will break first since the bike will overturn with such a moerrova speed that your riding compation will observe you as being in a spin-dryer on your bike. Of course this spin dryer will only do 1/4 revolution before things get ugly.

 

OK, theatrics aside. What will happen in a case of theoretical "too much stopping power" is a faceplant. Your wheels are safe but not your nose.

 

 

 PS - I have no doubt that the calculators and physics text books are now being consulted.

 

 

Johan Bornman2008-08-29 08:09:41

[Piernas Flacas]

One learns something new every day. Thanks Mampara

[MTB0007]

Ok

Thanks just checked.. these are the Shimano big "screw thread" type

Spanners, wont be a problem..

I have just started as National Sales Manager for WEBCO, tools...

But I need to do a Bicycle Maint.. course...

These things (Bikes) change so fast.. Know of a Course?

[Johan Bornman]

I've just thougt of another scenario:

 

The hub can shear off where the rotor connects or even in the middle of the hub if it is not beefy enough to transmit torque from the left to the right.

 

My money is still on the faceplant. The hubs will have to be very, very flimsy for it to sheer. The hub's ability to transmit torque is inversely proportional to its diameter. Even in the days of bikes with hubs with very, very thin diameters, they never sheared from hard accelleration input by track sprinters. Braking applies much more torque than accelleration but in my opinion nowhere near enough to shear the hub.

 

If the engineers here have access to shear data, let me have that for aluminium please and I'll calculate the capacity for a few hubs I have on hand.

 

 

 

 

[Johan Bornman]

Ok

 

These things (Bikes) change so fast.. Know of a Course?

 

Some of my fellow hubbers should be able to steer you in the right direction.

 

 

[AndreZA]

These things (Bikes) change so fast.. Know of a Course?

 

Parks big blue book or

 

Talk to Johan Bornman, he gives classes.

 

 

[MTB0007]

The size of the rotors has nothing to do with the wheels BUT some flimsy wheels will break if you fit 180mm+ rotors due to the greatr stopping power. If you go for bigger rotors youwill need frame/fork adapters to move the calipers so that the bigger rotors fit.

 

 

I'd love to be proven wrong on this one but my experience on the issue is not the same.

 

I have never seen a wheel "break" due to too much torque applied at the hub aka too much "stopping power."

 

The scenarios are as follows:

 

1) The spokes rip out of the rims

2) The spokes rip out of the hubs.

3) The spokes break.

4) The wheel collapses and tacoes.

 

The latter I can't foresee since torque applies even tension and relieves even tension right around the rim. In other words' date=' total tension remains the same, no matter how hard you brake or accellerate. Since total tension remains the same, we know the wheel tension remains balanced and therefore a taco is unlikely, if not impossible.

 

For the spokes to rip out of the rims, we'll have to rip all 16 pulling spokes out at once, since once again, we know the tension in all the pulling spokes remain balanced between spokes (even though invidvidual tension goes up ) and the tension in all the pushing spokes remain the same (even though individual tension goes down.

 

For the spokes to rip out of the hubs, the same argument as above is valid.

 

For the spokes to break, you'll have to exceed the maximum tensile strength of one spoke and multiply it by half the spoke compliment i.e.

16 spokes, convert that to torque and convert that to stopping force. Even a thumbsuck with one eye closed and Ramstein playing full blast in my headphones tells me that this is one awsome force. The breaking tension of a 1.8mm DT spoke is 250kgs (source: The Bicycle Wheel). Multiply that by 16 and you get a total load of 4000kgs or four tons.  Apply that load over 250mm of spoke and you have a torque of 1000NM. If I'm correct, that's more than any sports car can produce. Assuming that the centre of the wheel is 1 m from the centre of gravity of you on your bike, you have a force of one ton on your two wrists at the moment of spoke breakage.

 

Methings your wrists will snap first. Actually, they won't, your neck will break first since the bike will overturn with such a moerrova speed that your riding compation will observe you as being in a spin-dryer on your bike. Of course this spin dryer will only do 1/4 revolution before things get ugly.

 

OK, theatrics aside. What will happen in a case of theoretical "too much stopping power" is a faceplant. Your wheels are safe but not your nose.

 

 

 PS - I have no doubt that the calculators and physics text books are now being consulted.

 

 

[/quote']

Hi Johan

 

I would not argue, its Friday.. and Im tired..

 

I think the force, vs Flimsy wheels is an easier win,

If only cos - if i was to expain to my wife why I want new , better, more expensive wheels..

All the text book stuff although good, and Impressive and obvously to the tech, people totally true.... 

If - I used it I would loose my beautiful wife's attention ...

 

I choose Mampara's theory, cos its easier to sell to my beautiful wife..

And she would want safe...

 

[steven]

If you upgrade to 180mm rotors from 160mm , you will need to get an apapter which will give you the extra clearance for the 180mm rotors which are available as a stock item from Coolheat.

 

rgds sm

www.coolheat.co.za

 

[singletrackmind]

can you get a 140mm adapter for formula oro brakes? would like to change my rear to that and stick with the 160mm on front

[steven]

Not sure whom the agent or importer is for Formula One brakes and suggest you contact your Lbs whom can inquire.Shimano have a large range of parts and backup so perhaps if you cannot get your adapter change to the new economical Brm486 range

 

rgds sm

 

www.coolheat.co.za