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17T 520 sprocket upgrade for Yamaha XVS250

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john24ssj
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PostPosted: 16:29 - 24 Jun 2017    Post subject: 17T 520 sprocket upgrade for Yamaha XVS250 Reply with quote

Hi everyone,

I just got XVS250 with the stock 20/56 sprockets and a 428 chain and the gearing is way too low. 1st gear is pretty much useless, I mostly take off using 2nd. I found loads of info about XV250 mod which I though I was doing (did not realise XVS250 and XV250 were different) until I realised it does not work. The rear 42T sprocket fitted the wheel hub perfectly but of course I realised the chain being 428 would not fit the sprocket and the front one was not fitting either into the splines Sad

So I got 1/3 of the mod which is the rear sprocket at 42T JTR857 but I can't find a 17T front sprocket what would fit the right z-14 splines
https://i.imgur.com/YqQvJoS.png
that XVS250 needs at 520 pitch.

Can anyone recommend a 17T 520 front sprocket that would fit the XVS250?

Thanks
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Matt B
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PostPosted: 09:17 - 26 Jun 2017    Post subject: Reply with quote

I have no idea what you think you are trying to achieve with this. Do you properly understand the way final drive ratios work?

If you wanted to raise the gearing then fitting a smaller rear sprocket or a larger front would achieve that. You should not need to mess around with both and not by that amount.
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bamt
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PostPosted: 09:40 - 26 Jun 2017    Post subject: Reply with quote

The virago 250 does have rubbish gearing as standard, there's a lot of discussion about this on the virago tech forum. On Mrs Bamt's I went one bigger on the front and about 3 smaller on the rear - chosen based on examining gear tables, reading the experiences of others and choosing a pair that left the rear wheel in pretty much the standard position so full adjustability each way to get the chain properly adjusted without hitting the stops. It's pretty perfect now.

It does sound drastic, but as long as you aren't a riding a heavily loaded bike in the mountains it is far more rideable, and you aren't having to knock it up a great almost as soon as you've rolled off the line (iirc it now redlines about an indicated 25-30mph in 1st, rather than an indicated 15mph).

I'll check what I actually bought, ours is a 1996.
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bamt
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PostPosted: 10:14 - 26 Jun 2017    Post subject: Reply with quote

Hmm, hadn't noticed the original gearing on OP's bike. Ours was 16/43 iirc. Having checked I took it to 17/40 (JTF569.17, JTR857.40). Possibly not much use though as it looks like a completely different setup, which surprised me as I thought they were pretty much unchanged through their life.
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john24ssj
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Joined: 08 Aug 2014
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PostPosted: 11:51 - 26 Jun 2017    Post subject: Reply with quote

Matt B wrote:
I have no idea what you think you are trying to achieve with this. Do you properly understand the way final drive ratios work?

If you wanted to raise the gearing then fitting a smaller rear sprocket or a larger front would achieve that. You should not need to mess around with both and not by that amount.


Yes I do understand how ratios work perfectly fine Smile
Current ratio is 2.8 (20T front / 56T rear). Sadly with the 428 chain pitch 20T is the biggest and 56T is the smallest sprocket they make for XVS250 thus I can not lower it from 2.8 but can only increase it (which is not what I want):

https://i.imgur.com/dFB7Y4Wl.png


Now another option is to change to 520 pitch sprockets which give a far better flexibility but I am struggling to find a 16T or even a 17T front sprocket that would match the Z-14 spline cut-out. My perfect ratio would be 2.4 (17T front and 42T rear) as mentioned by bamt I don't want to be hitting the stops.




bamt wrote:
Hmm, hadn't noticed the original gearing on OP's bike. Ours was 16/43 iirc. Having checked I took it to 17/40 (JTF569.17, JTR857.40). Possibly not much use though as it looks like a completely different setup, which surprised me as I thought they were pretty much unchanged through their life.


Yep that's the issue I am having Sad the splines do not match so in theory the best I can to is 15T front and 38T rear but I am worried about clearances not hitting anything :S
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The Shaggy D.A.
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PostPosted: 12:16 - 26 Jun 2017    Post subject: Reply with quote

Bamt, after you made the swap, what was the top end & mpg like?
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bamt
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PostPosted: 13:23 - 26 Jun 2017    Post subject: Reply with quote

On a suitable private road the bike might allegedly cruise happily at an indicated 85 (which could be anything in reality, but certainly towards the top end of what you'd want the brakes and suspension to handle).

Certainly I was comfortable on the motorway, whereas a 125 is just scary. I got mid-80s mpg, but only measured over about 70 miles between closest fuel stations to the start and end of a 90 mile round trip mixed A road and motorway commute (not hanging around). No idea what it did before, as normally it has short bimbles by Mrs Bamt and I keep it topped up from a Jerry can.
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john24ssj
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Joined: 08 Aug 2014
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PostPosted: 08:34 - 28 Jun 2017    Post subject: Reply with quote

Found the solution!
Got in touch with jtsprockets directly and they showed me that there is a XVS125 conversion kit to 520 which also applied to the XVS250. The front would be 15T and rear 38T giving me the ratio of 2.53 which is close enough to what I initially wanted.

I bought the parts and hopefully all goes well. I will report back with my findings later Smile
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