VTR250 Rear Sprocket Selection

me55iah · 27-10-2006, 03:37 PM

Starting to look like the VTR needs new sprockets and chain so a quick call to Prestige honda reveals that I have options on the rear of 36, 38, 39, 40, 41 (std) all the way up to 53 teeth.
The question is....how many teeth should I drop and how much impact should I expect as I trade off acceleration against top end speed??
I'm pretty happy to lose a little acceleration to gain slightly lower revs at say 110km/h.

Suggestions please on a postcard.....

lee · 27-10-2006, 04:40 PM

Umm, if you plan on dropping teeth on the rear, I hope you enjoy slow rides.

Dejavu · 27-10-2006, 05:37 PM

Quote:

Umm, if you plan on dropping teeth on the rear, I hope you enjoy slow rides.
[/b]

the VTR 25o peaks out too early and hits revlimiter in top gear so gearing down on the rear is a great way too get a higher top speed with less engine stress ie not reving its tits off

in that respect i'd go a 38 rear for best of both worlds

Ev · 27-10-2006, 06:06 PM

Quote:

Umm, if you plan on dropping teeth on the rear, I hope you enjoy slow rides.
[/b]

While I agree with the above sentiment.

I was wondering if you could maybe instead go up at the front sprocket(?available), that way if you change your mind it will be easier ? cheaper to go back to stock... as an added bonus this will also result in less chain / sprocket wear than stock.

me55iah · 27-10-2006, 08:28 PM

Sadly there is no variance for the front (through Honda anyway)
I was under the impression (please correct me if I'm wrong) that dropping 3ish teeth from the rear would mean higher speed for a given rev speed. For some reason I keep looking for 6th (old habits) and the only other option I can see would be to bash a 6-speed box onto the thing.

which is NOT gonna happen 'til after Lotto!

GORCAT · 27-10-2006, 09:20 PM

Quote:

Sadly there is no variance for the front (through Honda anyway)
[/b]

Pop down to Motorcycle Masters at Kewdale and ask the guys there if there is an alternate front sprocket, Honda (and other manufacturers) make a whole range of bikes and the output shaft diameter and splines are identical on a lot of them. Some may require a little adjustment for width but I'm sure it can be done.

Gooseman · 16-11-2006, 08:43 PM

Once i get my vtr250 sorted I'll be getting a smaller rear for it

You are right that it peaks too early! well right! I've looked at the dyno, and the torque peaks at something silly like 4,600RPM @ 16nm. 7-9000RPM @13nm and 9,500-12,000RPM @12,000nm.
So as i see it, aiming for your usual freeway/highway speed to be between the 7-9000rpm range would be a good plan, but once i get ready to set it up i'll get it running at about 4,600rpm@100km/h just to see the results/ridability. I'd expect 8k@100km/h to be on the ball though, as there may not be enough power at 4,6k

Ev · 16-11-2006, 09:30 PM

Quote:

Once i get my vtr250 sorted I'll be getting a smaller rear for it
[/b]

I have serious doubts about this being a good idea, I would be interested if anyone could speak with experience on this matter.

Maybe at 110 it could work out(only one good way to know and I cannot remember my machine stock at that speed)), but for the rest of the riding time your gonna have a bike that is not a pleasure to ride, requiring you to constantly wring its neck to accelerate effectively.

I was glad to add teeth, and actually feel some throttle response around 100, in fact my bike felt too sluggish around 4-5k and with the stock gearing I was always revving it higher to compensate, so find my bike more driveable now, not having to kick down gears for acceleration.

Gooseman · 19-11-2006, 09:14 PM

vfrev, what's your top speed atm?

Ev · 20-11-2006, 08:02 AM

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vfrev, what's your top speed atm?
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145 was near the top maybe 1000rpm left till redline,premium unleaded(I now suspect ULP is better in VTR) , no engine related modifications, did not have much drive at that speed and would suspect that with normal or higher gearing, the engine would be running out of puff... unless you have power modifications ie bigger jets,pipe etc.

PS: I am quite cautious in my riding and prefer to keep the VTR250 below 130, as I just don't find it confidence inspiring above that speed, in fact I don't find the bike very inspiring after 80kmh in comparison to other bikes out there. ohhh and I still like it though and would not have another 250(cept a spada maybe)

Absent-minded · 30-11-2006, 12:43 PM

yeah i find it tops out a little too early, im sitting on 100km/h ad 7000rpm, and does anyone else seem to have a flat spot about 8000??

tigerleo · 30-11-2006, 10:11 PM

No flat spot on mine at 8k RPM - but I had Russel at Dyno Time shim the jets to smooth the throttle response...

The Roo pipe gave a pronounced flat spot at around 4.5 to 5.5K RPM (or there abouts) - and also just off idle. Perhaps the Megacycle exhaust is giving you a flat spot, just in a different place?

Absent-minded · 01-12-2006, 10:34 AM

Na tiger, the flat spot was quite noticeable before the pipe but the pipe smoothed it out a little bit, i generally just try and skip that part of the rev range,

Cbr1k · 01-12-2006, 11:52 AM

If you want to calculate your gearing and the resulting speed changes download the attached Excell Spreadsheet.

To use just enter all the data in the Pink Cells. It is setup for my bike so you'll have to get the data from a Service manual or wherever.

http://www.iinet.net.au/~cbr/Gearing.xls

Cheers
Big Rob