I think I've read on this forum most people saying around 2500 minimum. I'm in 5th around 40-45 mph if that helps you. I don't have a tach but that speed should match close to that rpm. My bike pulls just fine in 5th at 45ish mph.

I have had many bikes.
I'm in the process of buying a 2007 S40.
I wanted the S40, to feel 30BHP on a 350LBS bike.
My only complaint will be, I'll ride it every other day a good 20 minutes of interstate riding.
Speeds of 75 to 85MPH GPS verified.
I am currently doing that on a Rebel 250, and needed more power.
The S40 stock is not a fun bike to do this with, but I'm looking for modifications to make it possible.

I have no problems whatsoever with side winds, or the light weightedness of the bike.
My only issue will be speed (to go between 75 to 85MPH) by looking at some minor performance enhancements, and reducing vibrations through a gearing mod (25t pulley seems intriguing).

Stock the bike does fine at 75MPH, but I occasionally want to peak at 90MPH. The Rebel 250 doesn't do 90. At least not on GPS. It does sometimes go to 90MPH on the speedo (which is around 85MPH GPS).

So I'm looking for a replacement Rebel 250 with just a tad more power and top speed (5 MPH more top speed is good enough).

I read hundreds of posts about a bigger bike, but it's not what I want.
Unless I get a supermoto (which is both costly, and doesn't sit very well), there are only a few bikes with >300cc engine, and <400LBS weight, and an upright seating position.
Add to that a <$2k pricepoint, and the only bike left is a second hand S40.

KTM KLR650 is over 400LBS.
Yamaha FZ-07 is too much bike for me, and too expensive
Yamaha SR400, too expensive, and low quality.
Rebel 450 is nowhere to be found anymore (around these areas).
CB300F is more expensive, and reaches about the same top speed, without the added benefit of the S40's nice acceleration.

That's in a nutshell my story.
So now I'm looking to improve the only issue the S40 is lacking in for me, is top speed....

This question on lowest RPM for cruising was just asked to see how a 25t pulley would affect gearing when riding in town.
I ride a lot between 40 and 45MPH; which is currently possible on an S40 in final gear (it does 2750-3000 RPM).
With a 25t front pulley, I'll have to ride in 4th gear when going under 45MPH; which will affect MPG in a negative way.
Then again, the newer gearing will work well for speeds between 45-85MPH, which is where I'll be riding the bike more frequently in.

I just want it to do 85MPH on the interstate when I need to, without falling apart.
The 25t front pulley will be a given mod; I'm just not sure if the stock bike will pull the load easily. I could do a port job, and have more high rev power; since the S40 has sufficient low end power....
The 25t pulley will shift the optimal "75MPH" speed to 81MPH.

A higher compression cylinder will seem interesting, as it will increase efficiency (MPG), and power.
Seeing the low compression of the 650, I wouldn't mind increasing it a tad..

Sorry about the many questions...
There's a lot that I try to accomplish,therefor I have so many of them.

Hyosung GV250 is 341 lbs stock and will happily do 90+ with no mods, but with high flow muff/filter/jets and 1 up (front) and 3 down (rear) on the sprockets as well as a proper chain it will do 100 mph any day no problem and weighs 322 lbs.  I'm not guessing or number crunching.  I had one and this setup is what I ran.  It is certainly not as torquey as the S40 but it'll get off the line faster than most cars and going 90 mph is smooth and comfortable any time.  Given what you're looking for I'd say you might want to look into this option.  The cost difference is minor.

MeeLee wrote on 01/29/16 at 23:02:07:


The 25t pulley effectively makes your new 4th gear (with 25t pulley) equal to the old (with stock pulley) 5th gear ratio. You shouldn't have any issues.

$2k or less can still net a nice Ninja 500 used, which has a fairly upright riding position , even for my old body, aside from my knees, and will utterly smoke the S40 anywhere but off the line, and do so with very little vibration
or if you must have a cruiser, there's the now discontinued Vulcan 500, with a detuned Ninja 500 engine, that will still eat the S40 alive anywhere above say 45 MPH
both of these are quality bikes with a 6 speed transmission, and far better suited than the S40  for high speed  freeway riding
S40s are great ion town cruisers, and fine backroad mounts, but they aren't great interstate bombers
unless you keep it down to 65-70, which work fine if you stay in the slow lane, even in texas, where everyone likes to go 90+

MeeLee

I had a 250 Rebel years ago and mine topped out about 75 on most days.

It also slowed down going up hills .  

My S-40 with 140/90 tire and 25 tooth pulley will gain speed going up those same hills.  

OldRider has a 300 Ninja that must be great on the Super-Slab , he rode it to a Dragon Run just for a one day ride all the way from Florida.  

which is why I recommend an older 500 instead of the 250, it's not buzzy at highway speeds if it's running right, it hums happily along at anything from 70-100 mph
the 300 is injected, and is supposed to match the performance of the old 500, but revs higher to do it, and might not be doable on a 2K budget