Don't use the highest gears !

jeremyrundle

Here is a question that confuses me.

I recently spoke to a number of downhillers on tyheir MTBs today (yes I know its Christmas) boaring.

I asked bout their bikes and during the conversation it came up that they never use the top gears together.

As with mine I have 27 gears 3 on the main and 9 on the casette making 27, however they advised me against ever using number 3 and 9 together as it will place too much strain on the rear DR!

They must know but why, what is the point then.

getonyourbike

I don't have a clue what they're on about, if they meant 3 (big up front) and 1 (biggest on the cassette) I could understand that and teh chain crosses over a nasty angle and wears (stretches) the chain more, leading to a shorter life of the chain and cassette and chainings if the chain isn't replaced soon enough.

nwallace

Took me a while to stop using 46-36 on both of my Triples.
After a few chain breaks I finally got it.

Berk Bonebonce

Increased shearing pressure on a chain which is run at an angle, as in big at front and big at back, or small at front and small at rear.

jeremyrundle

Oh I think I understand now, whetever they mean I think they were saying don't use the highest gear on both, think I see now, as when I did the rear DR was pulled RIGHT forward and almost jammed!

desweller

FWIW the physically largest rear sprocket is the SMALLEST gear as it provides the smallest gear ratios, and the physically largest front sprocket is the LARGEST gear as it provides the largest gear ratios.

The Rookie

With Des, I think 'highest' and 'biggest' are getting confused here......

Simon

jeremyrundle

That is my fault, not knowing what I am trying to describe.

On my Saracen I would be third (where you have 1,2,3 on one side) and in (8 on the other side gear selector where you have 1,2,3, - 8) so like a car would go fastest.

I have tried that on the new bike and the rear DR jammed.

Hope that pathetic attempt at an explanation is better.

nicklouse

DHers dont have 3 rings on the front.

did you follow my link in your earlier post about how to use your gears? it asnswers this question.

also it sounds like your chain is too short.

The Rookie

When it's in '3', is it on the big ring at the front?

What direction are you trying to go into 3rd on the rear from fourth or from second? If its from fourth, if the rear mech is stretched out almost horizontal and the top jockey is being pulled into the cassette, as Nick says it sounds like the chain is too short. can you confirm it's trying to get into the 3rd largest gear (3rd from the spokes)?

Simon

smithaay

you dont wont too use the big gears you want too get a good cadence like 60-100 rpm
:P

jeremyrundle

The Beginner wrote:

When it's in '3', is it on the big ring at the front?

What direction are you trying to go into 3rd on the rear from fourth or from second? If its from fourth, if the rear mech is stretched out almost horizontal and the top jockey is being pulled into the cassette, as Nick says it sounds like the chain is too short. can you confirm it's trying to get into the 3rd largest gear (3rd from the spokes)?

Simon

Thanks I will take it back and get the chain checked.

Regards

warlock_the_great

It's all about the chain angle as has been mentioned. Don't use the 2 biggest or 2 smallest cogs. The gears are repeated elsewhere in the range anyway so....

Rockbuddy

Thing is, you may technically have 27 gears (3 x 9) on your bike but if you actually calculate your gear inches / ratios (http://www.sheldonbrown.com/gears) you'll see that you probably only have about 10-12 different gear combinations as there is so much overlap between the ratios. As people are saying here it is advisable to use the gears in the combination that crosses the chain the least. If you have a play with your gearing, depending on your set up, you'll find something like the biggest cog at the front and back is the same as the middle cog at the front and a couple of cogs down at the back, which is also the same as the smallest at the front and middle at the back. [/url]

jeremyrundle

Thanks, only I could see no reason to have 27 gears and not be able to use them, It is like buying a car with a six speed box but the garage telling you not to go above fifth.

I do understand now, funny, I am able to us all on my Saracens.

walkingbootweather

A useful guide in how to use gears?

http://www.bikeradar.com/forums/viewtopic.php?t=12647117

roger_merriman

jeremyrundle wrote:

Thanks, only I could see no reason to have 27 gears and not be able to use them, It is like buying a car with a six speed box but the garage telling you not to go above fifth.

I do understand now, funny, I am able to us all on my Saracens.

some set ups are more tolerant of crossing the chain than others.

it's better in many ways to say you've got 9 gears with 3 ratios, the ratios even on mountain bikes which have wide gaps between the ratios is never more than 3 gears so there is large over lap. the 27 speed etc is marketing fluff.

jeremyrundle

I tend to agree with you and thank you to all of you, at least I now know it is ME and not the bike.

walkingbootweather

For more on gear spread and useable gears see the last page of this link http://www.thorncycles.co.uk/thornpdf/ThornLivingWithARohloff.pdf. I was convinced and got a Rohloff hub bike giving 504% spread with 14 equally spaced gears. The explanation from Thorn is that a modern 27 speed mountain bike will actually only have 15 effectively different gears because the others are similar to those achieved with less tortuous chain line. Inspection of the supplied tables may suggest which gear combinations are optimal.