Gear ratio adjustment for 15 year old

leshere

Hi it is Cycling daddy here...who knows little.
Not sure if this is the right forum??
I understand about ratio for Junior riders (I think) . On my sons bike the easiest option seems to be to limit him to the smaller chain-wheel (if the chain-wheel is the roundish spiky thing near the pedals). This would allow him to use the full cassette (10 round spiky things in the middle of the back wheel). However often the limitation is made by adjusting the stop on the cassette.
Is it OK to do it either way or is there an advantage to limiting at the cassette end?
If I do limit to the small chain wheel can I remove the front deraillieur or does the cage serve some purpose other than kicking the chain back and forth? At the moment it is hard to stop it rubbing wither at one end or the other.

Many thanks for help so far and all the encouragement...cycling seems to be quite mad very friendly and terribly expensive.

Pross

A lot will depend on what chainrings the bike is fitted with and the range of the sprocket sizes on the cassette. The restriction for under 16 riders is 6.93m for road and track racing i.e. if you put the bike over a line with the cranks in the 6 o'clock position / largest gear selection and push it backwards by time the cranks return to the same position the bike cannot have travelled more than 6.93m. You can be under that by any amount but you want to be as close as possible.

If the chainset is a standard 53 x 39 (i.e. the largest chainring has 53 teeth and the smallest has 39 teeth) you can achieve a gear of 6.8m by using a cassette with a 12 tooth smallest sprocket and limiting the front mech so that it can only use the smaller chainring but this will leave you cross chaining to get the biggest gear (which is inefficient and likely to leave the chain rubbing and placing more strain on the chain, chainrings and cassette). You could also go for leaving the front mech in operation and screwing the rear mech limit screw in so that the smallest sprocket that can be used is the 16 tooth. Both of these options will leave you with reduced gear options. The best solution is possibly to buy a cassette with a smallest sprocket of 15 teeth and screw the rear mech in to limit it to the 16 or to get a 52 tooth chainring and 15 up cassette which would give you access to all gears with a maximum size of 6.8m.

If using a compact chainset the cassette sizes will vary. The above assumes a wheel size of 700c with 23mm tyres.

Sorry if this is confusing, there are just so many options and none are perfect.

Some additional information can be found here http://www.britishcycling.org.uk/zuvvi/media/bc_files/volunteer/Commissaire_Quick_Guide_RIDERS-PARENTS.pdf

rpd_steve

The idea of restricted gearing is to prevent juniors from trying to push grar ratios which could harm musscle development. The level of restriction depends on his age, and type of racing. You can see the exact restriction here:

http://www.britishcycling.org.uk/zuvvi/ ... SSAIRE.pdf

You are indeed correct that the front cogs are called the chainset or crankset and the rear are called a cassette. Cassettes are often refered to as 11-23, 11-25, 12-25 etc. This means that the smallest cog on the cassette has 11 teeth and the largest 23 teeth for example. This defines the range of the gears avalible to your son. This works in conjuntion with the chainset, which are either a standard double, 53 teeth and 39 teeth or a 'compact' with 50 teeth and 34 teeth.

Blocking off a chain ring is not good practice in general. You always want to run the chain in as strait a line as possible to reduce wear on the chain and gears, reduce noise and improve efficency. So the small chain ring (front) is used with the big 6 or 7 cogs on the cassette and vice versa - hence avoiding maximum 'chain cross'.

Jnr gearing can normally be obtained with a smallest cog of 14 - but is you let me know your sons age, type or racing and the number of teeth on each of his rear cogs then i will let you know what gears need to be 'blocked off'. This normally means the smallest 2 on the back. This can be donr by winding in the limit screw of the rear derailer. The shifter on the handlebars will still click if he trys to change but it wont do anything.

This method is more preferable to using only one chainring as he still gets a full range of gears within his allowed range - there are no gaps where he may finf that for 10 mph his legs are too slow in one gear and too fast in the next gear for example. It also teaches him good gear technique young which is a good thing.

Let me know if you need help on what to do next.

Pross

Just to prove a point on the complexity - I messed up in my post above. A 52 front and 15 rear gives too high a gear, to ensure a full set of gears you would need a 49 front and 15 rear.

leshere

Thanks the chain rings are 53 and 39 the crank is 175 I think not sure what that makes it all. The cassette starts at 12 but need to take it out to read the larger rings. He is 15 or A
L

Pross

leshere wrote:

Thanks the chain rings are 53 and 39 the crank is 175 I think not sure what that makes it all. The cassette starts at 12 but need to take it out to read the larger rings. He is 15 or A
L

In that case you will need to wind the rear mech limit screw in so that nothing bigger than a 16 can be selected. That will probably mean blocking off the 4 smallest sprockets (depending on the cassette you may not have a 16 and will end up running with an even lower gear than the restriction). My suggestion would be to buy a 15 up cassette (i.e. any cassette which has a smallest sprocket of 15 teeth) as you will then only have to block off the smallest sprocket. It will also have the benefit of keeping the gaps between teeth smaller and / or allowing the biggest sprocket to be larger to give an easier gear for climbing.

johnmiosh

Download the rabbit gear calculator.

http://software.bareknucklebrigade.com/

You will then be able to compare easily the gear sizes of what you have now with the suggestion above.

Feed in the chain ring (front spiky bit), sprocket, (back spiky bit) and tyre size (probably 700 x 23). and it will tell you the distance moved as per pross's example above. The answer appears in the box marked development (m).

leshere

Ahh that is what I wondered. I found a BBB CASSETTE 10 SPEED SHIMANO 16-25 would that be right? Thanks I live I learn

BruceG

Hi There
Been there and done that with this. My son is the same age as yours so a Youth Cat A, and as already mentioned the highest gear allowed is 6.93. You can try winding in the limit screws on the rear derailleur, however you will find that you cannot get enough movement to block off the required gears. You can also set the bike up so that only the smaller chain ring is available at the front, this is easily done by setting the cable with bags of slack so that the changer becomes inoperative, however you run ito cross chaing and noise issues as already mentioned. And I have done all of this and to be frank they just become a compromise, in the end I bit the bullet and bought the cassette and chain rings to to the job. Now the ratio you want to aim for is a 52 tooth chain ring with a 16 - 25 cassette, this will give you a gear length of 6.84, you can do it with a 53 tooth chainring but that means the smallest cassette size is 17 and that will give you 6.56, and you cannot buy a cassette starting at 17 so you are back to restricting the derailleur again.
My advice to you is do what I did, yep it is a little costly, however I sold the other parts to meet some of the cost, and when my son moves up a catagory at the end of this year I will sell on his 16 -25 cassette to recover some of the costs.
Of course this is based on my experience and relates the best experince/soluton I found, hope your lad enjoys his racing as much as mine

Bruce

BruceG

leshere wrote:

Ahh that is what I wondered. I found a BBB CASSETTE 10 SPEED SHIMANO 16-25 would that be right? Thanks I live I learn

Yes thats the one, you will need a 52 chainring though

leshere

Thanks very much as you say bite the bullet and go for it hoping to sell the set on at the end of the year. Cycling is not...really not...cheap