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Bigger front & Smaller rear sprockets on Bros 400

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UnspeedySam
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PostPosted: 14:52 - 26 May 2011    Post subject: Bigger front & Smaller rear sprockets on Bros 400 Reply with quote

So I'm going touring on my Bros this summer (as soon as I get it fixed) and one thing that worries me is how high the revs are at motorway speeds.

If I go up one tooth on the front (16 -> 17) and/or down one tooth on the rear (44 -> 43) how much difference is this likely to make to the gearing? Am I likely to have issues holding my speed in 5th or is it likely to have the intended effect?
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Riding: BMW R1150RT `02 bought mildly crashed
Fixing: Also the BMW as I get less broken bits
Gone: ZZR600 '00, TRX850 '97, RXS100 '93, JS125-6B '07, BMW R1100RS '93, Kawasaki ZX-6R-J2 '01, Honda Bros NT400 NC25 '88
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Paddy Blake
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PostPosted: 15:53 - 26 May 2011    Post subject: Reply with quote

I would be a bit worried if you are carrying a lot of stuff on the bike
and what you intend to do with the gearing that it might lack power it
top gear.
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UnspeedySam
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PostPosted: 16:09 - 26 May 2011    Post subject: Reply with quote

Yeah that's my concern. I was just wondering if anyone had a vague idea of how severely it's likely to affect acceleration and top gear performance.

I could go of course get myself some conical air filters, remove my exhaust baffle and rejet the carb to compensate...although I have no idea how much difference that would be likely to make either...
____________________
Riding: BMW R1150RT `02 bought mildly crashed
Fixing: Also the BMW as I get less broken bits
Gone: ZZR600 '00, TRX850 '97, RXS100 '93, JS125-6B '07, BMW R1100RS '93, Kawasaki ZX-6R-J2 '01, Honda Bros NT400 NC25 '88
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Paddy Blake
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PostPosted: 19:12 - 26 May 2011    Post subject: Reply with quote

I am trying to do the sums on this and am probably wrong.

Standard.
16f 44r =36% Front is 36% of the rear.

New.
17f 43r=40%

So say you were doing 80mph at 8000 rpm then with the new settings
you would be doing 80mph + 4% 83.2mph at 8000rpm.
That does not seem right though.

There has got to be some way to work it out on paper.
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Nexus Icon
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PostPosted: 19:17 - 26 May 2011    Post subject: Reply with quote

Try this...

https://www.gearingcommander.com/
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Paddy Blake
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PostPosted: 19:19 - 26 May 2011    Post subject: Reply with quote

Ok the increase in the front is 6% and decrease in the rear is 2%.
So it could be going up from 80mph to(80+8%) 86.4mph.

That seems more like it. Smile
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UnspeedySam
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PostPosted: 19:39 - 26 May 2011    Post subject: Reply with quote

According to that I should get a reduction of about 550rpm (6809 down to 6263) at 80mph in 5th. Not sure if it's worth my £40 or sacrificing acceleration...

Opinions?

edit: I'm sure the figures they have for the bike are low...but I haven't ridden it in a month so honestly don't remember what the figures are. Still gives an idea of the difference though.
____________________
Riding: BMW R1150RT `02 bought mildly crashed
Fixing: Also the BMW as I get less broken bits
Gone: ZZR600 '00, TRX850 '97, RXS100 '93, JS125-6B '07, BMW R1100RS '93, Kawasaki ZX-6R-J2 '01, Honda Bros NT400 NC25 '88
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