what are good training wheels

[Ox_Wagon]

Just when you think everything is sorted out Mavic comes along and brings out a new 2008 wheel set that CAN take compression force.

 

Interesting enough it is to improve the lateral stiffness of the wheel.  They have a nice website that sorts out the whole argument.  As they say in the movies ?I rest my case?.  <?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

 http://www.mavic.com/r-sys/

[Sean]

On a similar subject. Hendrik Potgieter has become suicide alley in the afternoons so have got myself an indoor trainer for during the week training. . My boet tells me I should get a different set of wheels (ok, just back wheel obviously) for use on the trainer, and save the usual wheels for the road.

Do you agree? Never used the indoor trainer before so not sure about the type of wear and tear?

[javadude]

It is better to get another back wheel, mainly to save your good road tyres from being shredded on the trainer. Its alot easier to quickly swap the back wheel than swapping tyres every time you need to use the trainer.

[Dicky DQ]

Forget what you have heard so far. Go for the stronget, heaviest cheapest you can get. They are training wheels after all. if you can affors the luxury of two sets, you will feel the difference when you change to your racing wheels.

 

What the hell get cast iron ones, if you can get them.

 

I know of ppl that pack weights into backpacks and the bottles for training.

 

Not me of course, I have about 15Kg of balast already.

[Ox_Wagon]

I agree. I only have one set of wheels that can be classified as training wheels. After breaking a few spokes (also carrying an extra 20kg) I asked my LBS to build me bomb proof wheels.  I originally purchased the wheels second hand with a group set. They have standard campy hubs, DRC st17 rear rim and Rigida china front rim.  The LBS re-spoked the wheels with strait gauge (2mm) DT spokes and also added brass washers to the hub side of the spokes (J bend side).  He basically build the wheel in a similar manner to a tandem wheel.  To this I added ultra cheap wire beaded Maxxis Detonator that I don?t mind to use on the trainer as well as the road.   I am a mtber with a tendency to ride a bit ham fisted, plowing through road debris and hitting cat eyes.  I would also consider, in hind sight, getting 25mm tires instead of 23mm.   So far I have had really good service from these wheels.<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Ox_Wagon2007-09-13 02:08:44

[Sean]

Makes sense. I will bite the bullet (again ) and go buy a spare wheel and tyre, and cluster of course.

Thanks Velo.

[NotSoBigBen]

Dick - have had similar issues, the problem is they ditch their additional weight come race day! And us?

[Johan Bornman]

I agree. I only have one set of wheels that can be classified as training wheels. After breaking a few spokes (also carrying an extra 20kg) I asked my LBS to build me bomb proof wheels.  I originally purchased the wheels second hand with a group set. They have standard campy hubs' date=' DRC st17 rear rim and Rigida china front rim.  The LBS re-spoked the wheels with strait gauge (2mm) DT spokes and also added brass washers to the hub side of the spokes (J bend side).  He basically build the wheel in a similar manner to a tandem wheel.  To this I added ultra cheap wire beaded Maxxis Detonator that I don?t mind to use on the trainer as well as the road.   I am a mtber with a tendency to ride a bit ham fisted, plowing through road debris and hitting cat eyes.  I would also consider, in hind sight, getting 25mm tires instead of 23mm.   So far I have had really good service from these wheels.<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[/quote']

 

Dear Ox Wgon. Your LBS is lazy. The only reason that straight-gauge spokes are still in use is for a) lazy builders and bn) people who have to build lots of wheels very quickly.

 

Straight-gauge spokes resist windup more than two times better than butted or reduced shank spokes, since the ability to resist torque goes up with the square of the diameter. It is much, much easier to build with straight gauge and therefore all lazy wheelbuilders do this. They do you no service, since they severely compromise the durability of the wheel.

 

Straight gauge spokes are not "stronger" but "weaker". I use quotation marks here because in tension, a thicker wire is obviously stonger, but spokes don't break in tension, they break from metal fatigue. Therefore your special wheels with straight-gauge spokes are unfortunately not so special. The fact that you say "so far, I have had really good service" out of them simply means you haven't done much mileage yet. Give it time. Wheels don't work the way you envisage them to work.

 

Brass washers are another remnant from the ark. They have no place in wheelbuilding unless you are using faulty DT-Swiss spokes with elbows that are too long (DT Swiss put millions of these into circulation before realising its mistake) or, you are building on a hub with a particularly thin flange, like a dikwiel's steel hub. They service no purpose in spoke durability at all.

 

Finally, none of the tricks you pull on your bike, such as hitting cat-eyes and plowing through road debris (where do you ride with this stuff piled up so high?) increases the tension on a spoke.

 

JB

[Johan Bornman]

Ok' date=' let?s try again?.<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

 

The figures below show the interface between a spoke and high end aero rim.  In figure A the spoke is under tension in other words pulling. Everything is fine in that the spoke is pulling the internal nipple in to the rim. In figure B the spoke is in compression or pushing (standing).  In this case the nipple is pushed away from the rim wall. So the only way it would be able to support weight is if it hits the underside of the face that the tubbies are glued to. Not good.

 

In short, all spokes, due to pre-tensioning, should always be under tension.  The amount of tension varies as the wheel rotate with the top spokes experiencing a higher tension than the bottom spokes.  Spokes should preferably never see a compression (pushing) loading as they will simply flop around loosely.        

[/quote']

 

OK, I'm back in town and like you say, lets try again.

 

Your figure A is correct in that it indicates a pull inthe direction of the arrow. Lets assume the force of that pull is 100 units.

 

B is incorrect in that the pull is now only 50 units instead of 100, because we're now pushing on that spoke with a force of 50 Units. 100 - 50 = 50, is the point I'm making and which Lefty seems to want to extend beyond high school physics for reasons of his own.

 

Try and visualise this differently.

 

Hold the wheel by the QR in your left hand, with the QR pointing vertically and the wheel lies horizontally. Now apply a force with your right hand on the tyre, pushing towards the hub. It should become apparent to you that the force is now between your two hands and that the far left side of the wheel experiences no change in force (tension).

 

When you build wheels this is even more apparent. When you have a hop in an area of a wheel, you get it out by tightening the spokes at the hop, not on the opposite side of the wheel.

 

Try this at home on your wife's wheel. Mark say six adjacent spokes and now loosen each one of those spokes by a known number of turns. Note the hop. Now return the tension to its previous state and see the hop disappear.

 

Now imagine this happening as you ride.

 

By now you should have a clear picture of what goes on in there.

 

It's a little bit like those pictures you could find in the centre of Huisgenoot ten year agao. They looked like a random bunch of geometric patterns and if you stared at them long enough you'd see a camel in front of a pyramid. Some people managed to see this quite easily, others needed copious amounts of cough medicine to make it work.

 

JB

 

PS, your picture shows a low end aero rim. A high end rim would have double walls with the spoke pulling on the inside one.    Have a look at the anatomy of a CPX 33.

 

 

 

 

[Dicky DQ]

I am Doff - so please let me know if my summation is correct:

 

Wheels are buit and the spokes are tensioned to produce a true round wheel. Theoretically all spokes on a side should have a similar tension...

 

Once you put weight on the hub the following should happen........ based on my limted engineering experience:

 

From the horisontal spokes to the top on the wheel varying amouns of tension is applied to the spokes, depending on thier position.

 

All wheels/rims hang from the spokes, there is never compresion pressure applied to the spoke. Unless you hit something which causes the rim to deform at a specific point at the road contact point.

 

[Johan Bornman]

I am Doff - so please let me know if my summation is correct:

 

Wheels are buit and the spokes are tensioned to produce a true round wheel. Theoretically all spokes on a side should have a similar tension...

 

Once you put weight on the hub the following should happen........ based on my limted engineering experience:

 

From the horisontal spokes to the top on the wheel varying amouns of tension is applied to the spokes' date=' depending on thier position.

 

All wheels/rims hang from the spokes, there is never compresion pressure applied to the spoke. Unless you hit something which causes the rim to deform at a specific point at the road contact point.

 

[/quote']

 

I doubt you are doff, its just that the way a spoked wheel supports a load is not obvious. Your summation is the classic intuitive one.

 

First, lets deal with the uniform tension. Like you say, in theory, the tension should be even, but it never is for a really true wheel. Rims are not perfectly round to start off with and the joint is nowadays welded, which makes the rims either hard or soft in that heat-affected zone, depending on whether they were quenched to cool or not. This means that spokes in that zone are always at a different tension from the others.

 

But that's neither here nor there for the big one: the way tension changes in a wheel when it is loaded. The load is applied at the hub towards the road and the road pushes back with an equal but opposite force. Therefore the tension in the bottom spokes reduce, whilst the top spoke tension remains unchanged. The number of spokes that are affected in this way depends on the stiffness of the rim and the amount of spokes in the wheel. It is usually a few spokes - 3 or four.

 

It is easy to prove. As I explained earlier on in this thread, just get on and off your bike and have someone play guitar with the bottom and top spokes.

 

Unfortunately no-one seems to want to do that.

 

JB

[GoLefty!!]

This looks like a fun fight I missed! Bugger! Yo Lefty' date=' what's up, why didn't you come to Ceres, was just like last year except harder and cooler!

[/quote']

 

 

Yeah I missed Ceres this year. Was down with a touch of the Bronchitis after some travels in the north of the continent. Dust , heat, and stunning women do make me short of breath...

 

Not sure what the next event is going to be, prehaps Lourensford.

 

Where you been?