I'm wondering what is the "sweet numbers" for the street bike? looking to replace sprockets on my MC18, should I just go stock?

Gearing on a street bike would all come down to personal prefrance. If you feel like you need some more top end/accelleration start changing sizes.
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Cheers,
Dave.

I never rode the bike past the parking lot: rear brake locked up before I made it 200 meters, it came in terrible shape and currently being rebuilt. Chain and sprockets look wasted, tires are cracked and no oil left in the forks or shock.

Almost as bad as mine started. Mind you I have been no further than the end of the driveway. I had taken a risk with an engine i sourced. Turned out the centre crank seal was buggered. So engine is coming out again tonight. I stuck with a stock setup. The plan was to see how that suits me and go from there.
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Cheers,
Dave.

I did a quick Excel spreadsheet of the MC18 gearing.
You can alter the sprocket teeth and rear wheel circumference (the blue cells in the spreadsheet) to suit what you have, to see what you'll get.

For what its worth, I like to use 16 tooth front and 42 tooth rear for the road.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

My crappy Mac does not like Excel

Ordered 42t rear, converting to 17" wheel so perhaps will try 16t front if the gearing too short. From what I can gather the stock size is 15t?

Yes standard gearing is 15 tooth front, 42 tooth rear. See here for the gearing specs I used.

If you install Open Office Aqua (free and open source) for Mac OSX 10.3 and later you will be able to open this .ods MC18 gearing spreadsheet which is the same as the MS Excel one I posted above. Hope that helps?

Also, (in New Zealand at least) Honda did issue all NSR250 R5k owners with a 16 tooth front sprocket as a bit of an "afterthought". I know this, because I owned an MC18 back in 1990 and went into my local Honda dealer to get the 16T front sprocket.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

With standard gearing 45hp is about right (180-185kph) but once derestricted the bike is working too hard. 16tooth fronts are very hard to come by (Tuckerbag has found a source at reasonable cost) but seem ideal with the extra power. Puts you comfortably over 200KPH assuming you can reach 12000 rpm in top. 3 Tooth off in the rear sprocket should be a close equivalent although I would be tempted to take 4 off just for the giggle in trying to reach a silly top speed.

in my experience 60 hp is only good for just about 200kph not sure taller gear will achieve higher speed.

My Triumph D6 would reach 150 mph indicated but on GPS only 135 mph (216 kph) Ducati 900 with only 80 hp but being narrower and more aerodynamic was good for 220. RG500 nearly pegs the needle (250+ indicated) but on GPS only about 220 and that's with about 100hp at the wheel

I had a 38 rear 15 front on my 18, great on the open round but a pain in town. Also tried a 14 front which gave excellent excelleration but was a bit manic. Now on 15 front 42 rear.
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it wouldn't be fun if it was easy!

dunkenb wrote:
I had a 38 rear 15 front on my 18, great on the open round but a pain in town.

Hahaha! No idea what a pain round town is, eh Steve?!

We ran some silly gearing on the MC21's just for a laugh. 16T fronts, small rears and an HRC transmission... try almost 70mph in first!
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Andy.
NSR-WORLD.COM

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Bill was the best I think his was 16/36. Used to love it but then is is only about 50kg!
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If I have to take the carbs off once more...