Drive ratios between chain pitches

[Suzsmokeyallan]

Using logic, a 14/43 in a 530 should be the same ratio in all other pitches of chain if you maintain the same factors, in this case 14/43 tooth count.
Somehow this is supposedly not the case, does anyone have some solid information they care to share on this topic.

[tz375]

Allan,

That's an interesting question.

14:43 is the same ratio whether the chain is a 415 or a 630. The chain pitch makes no difference to the ratio but it does make a difference to suspension because the sprocket radii would be different.

[Suzsmokeyallan]

Thats my train of thinking too Richard but according to some info lurking around its not the case. This all came about because I want to upgrade the RE5 from the 630 to a 530 setup. Since its the same gearbox as a buffalo the same tooth count sprockets in 530 SHOULD give the same final drive ratio.
Uncle Rick has some info on this hes going to send me so once I get it I'll be able to see what its all about.

[H2RICK]

Info sent to you this AM, Allan, along with my thoughts on how the author justifies his conclusions.

[Suzsmokeyallan]

Ok Rick lets have some info from learned persons on this topic, heres the info giving rise to this idea. From the writers perspective its calculated as 18/49 from 15/41.

[tz375]

I'm not sure that I understand what it is that isn't clear...

What the guy is saying is that you can't just change from 630 to 530 because that would give you smaller sprockets and that might change suspension or cause the chain to drag on the swingarm.

So he suggests getting a front sprocket as close as possible to the original diameter and that of course has more, small teeth. What he should then have done was to work out the equivalent rear sprocket to get the same gearing.

15/41 is 2.7333.
18 teeth front at 2.7333 gives a rear of 49 teeth.

It's as close as you can get to the same ratio and same diameter sprockets.

[Suzsmokeyallan]

How does fitting smaller diameter sprockets change suspension? rubbing on the swingarm if the chain is too close would be an issue, but suspension???
The problem I have with this ratio is the very large size of the engine sprocket, go up too big in size and the 'spooling up' or higher gear acceleration will suffer.
If the bike has a 14 T as stock its best to leave it or go up one or maybe even two sizes, but to make a 14 an 18 is ridiculous.
The 18/49 ratio may be correct on paper, but due to which way torque is applied within the ratio, the engine may not be able to push it properly.

[h2okettle]

I don't know about the ratio figuring, but I am sure an 18 tooth will not fit.. my 16 tooth front with an oring 530 chain is very close.. I have heard of a 17 tooth on front, but not with an oring chain.. The later 77 I had came with a 15/40 cuz the different trans gearing.. My 73 GT750 came to me with a 630 chain and 15/47 sprockets.. I just changed them back to the 530 chain and 530 15/47 sprockets and it ran the same.. I too do not understand what the guy is saying, but then I am more of a rider than a wrencher.. I just keep my stuff going..

Allen..... Will ride for food

[tz375]

What are you reading that I'm missing?

The article was not about GT750's, it was explaining the rationale behind changing the number of teeth when swapping a long pitch chain to a shorter pitch chain. The numbers were illustrative of the effect of changing pitch and the impact on the number of teeth. The actual example was a GS series bike.

GT does not use a 630 chain with long pitch. The GT series run a 530 chain so a change to say a 525 or 520 is the same pitch but less width.

Remember that the first digit is the pitch in 1/8ths of an inch. So a 630 is 6 x 1/8 (3/4")
520 is 5/8" pitch, 428 is 4/8 (1/2"). So changing from a 630 to a 530 means there need to be more teeth to remain at the same size.

I don't recall anyone suggesting changing to an 18t front sprocket on a GT.

As for the suspension that's a little more subtle but it's related to the relative position of swingarm pivot in relation to the sprockets. Changing the diameter changes the leverage and changes the squat effect at the rear end under power or on the over run. It's covered in a couple of books but I don't recall whether it was John Robinson or Tony Foale. Maybe it was in Kevin Cameron's book on Sportbike prep.

[Cliff]

41/15=2.733:1 ratio, 49/18=2.722:1 ratio, 101/39=2.729 ratio, 30/11=2.727. It doesn't matter what the tooth counts are AS LONG AS the driven (rear sprocket) divided by drive (counter shaft sprocket) equals 2.72 or 2.73. The issue here is clearance. If you change to a larger or smaller sprocket is the the chain going to rub or hit somewhere? Same with the sprockets. Do you have the room to go smaller or larger??

[tz375]

OK. Let's try that again.

Remember that the original question was if the chain PITCH changes, is it simple to calculate the new size sprockets to go with that new pitch.

A 630 chain with 15 teeth is the same size as a 520 with 18 teeth. Not bigger or smaller, the same size. Where people are getting confused is they are reading 18 teeth in place of 15 teeth and are forgetting that we are talking about changing the chain pitch.

The problem is that we rarely change from a 630 to a 530 but we often change number of teeth with the same size chain and that is causing some of us to fixate on teeth, and to ignore the other part of the change - the size of the teeth.

So a 630 (big fat long link chain) with 15 teeth is the same diameter as a 530 (shorter thinner chain) with 18 teeth.

For more info, try these sites:

http://www.gizmology.net/sprockets.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

http://www.intobikes.co.uk/help/chain_and_sprocket" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

http://www.eurospares.com/graphics/engi ... andard.pdf" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

[Suzsmokeyallan]

Thanks for your input and time on this Richard, when I pull the side cover on the RE5 I'll see how the 14/43 530 combo looks for clearance across the top line of the swingarm pivot section.

[tz375]

Allan,

what chain and sprockets are stock on a US spec (or Euro spec) RE5?

Are you changing chain size or just gearing?

[Suzsmokeyallan]

RE5 stock chain is a 14/43 sprocket set in 630 size

[tz375]

If a stock RE5 is really 14/43 with a 630 chain, then changing it to 530 need larger sprockets with more teeth. grab a 15T GT sprocket and compare it for size. The difference should be clear between those two.

14/43 is quite low gearing though@ 3.071:1

17T front would need a 52 rear
or go 16:49 or decide if you want to change overall gearing at the same time