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Discussion Starter #1
If I went front the standard 17 inch rear to an 18 inch rear, how would that affect the gearing?

I'm trying to think my way through it, and I think that for a given engine speed, on the same sprockets, the rear wheel would cover ever so slightly more ground with every revolution, like going to a smaller rear cog.

But, similarly to a smaller rear sprocket, would acceleration and torque suffer?

Am I right in my first assumption, and what is the answer to my question, please?
 

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Hi,
I did a lot of calculations to find the right sprockets for my sons Varadero 125 when we put in a 180ccm engine...
I found a calcluation form xlsx. formate on a French site..it is set up for a Varadero 125..but all details can be easily modified to suit any motorcycle.

Just send me your e-mail address and I will forward it to You
arvid(....)at(....)lovik.net

Regards
Arf
Norway
 

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Discussion Starter #4
Looks intersting and thanks for the jpeg, but this information looks to be about sprocket sizes.

My question relates only to the effect of changing the rear wheel rim size.

Would your link help in understanding that?
 

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Ride any Road. Ask me...
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Bigger wheel = move distance per engine rev, extra 3.14" on an original 53.38", so + 5.9%.
Larger rear sprocket would reduce this, on a std 48 tooth, each tooth is worth just over 2%, same effect as smaller front, but on a std 15 tooth, each tooth is worth 6.7%

The % work either way, so larger front is +6.7%, just more than a larger wheel.

I'd think, as an 18" wheel is a "tyre choice" move, I'd run a 14t front with a 50t rear, giving an approx 5% down gearing effect, and the choice of full on enduro tyres! (Chain should be ok, as overall just +1 tooth in system.)

Any help?
 

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Discussion Starter #6
Any help?
Yes as in it's interesting, yet no as in this is not my question:....;)

All I want to know is, if I take my bike, as it is and change nothing except make the rear rim 18 inch instead of 17, what would the change in performance be.

I think that it would have a slightly higher top-end, but perhaps poorer acceleration, like changing to a smaller rear sprocket.

I want to know if my assumption is correct.
 

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I want to know if my assumption is correct.
Yes it is - as Mudwiz says 5.9% taller gearing (assuming the same profile tyre). This may or may not allow a higher top speed depending on the available power and the current gearing. What it will certainly do is bring the revs down for a given speed, give less acceleration in each gear and allow you to hold each gear to a greater speed (except top maybe). This will be just like changing to a smaller rear sprocket.
 

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It sounds like a sound plan if you're intending to bias the bike more towards the rough. I had in mind to do the same - the good thing is you can get a really strong wheel built at the same time.

As Mudwiz says, the gearing certainly would be better dropped to improve off road performance. It's a shame you'd have to drop to a 14 tooth front; I always figure the tighter turn on such a sprocket can't be good for the chain.
 

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Hi, By using the gearing, sprockets and the rear wheel dimensions, You can get the same gearing by changing as it is now by changing the front and/or the rear sprockets. just put in the data and it calculate everything automatic. Sprockets in ANY size are available...at least by piscopo in Germany.... on the Varadero with the 180 ccm engine, I changed the final gearing by changing from 15/43 sprockets (original with 125ccm engine) to 14/39 (180ccm engine)...then I had close to the same gearing in 5th gear (on the 125 ccm engine) in 4th gear 8on the 180 ccm engine)...so 5th was then mostly used for cruising and then saving the engine by riding with the same speed but with a lower rpm's ...like a 5th gear overdrive:)
I hope I have made myself understandable here...but when You see the file..it is just to put in the gearbox cogs, the output shaft cog , the rear wheel sprocket and the rear wheel size..
Regards
Arf
 
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