[Aargee]

I've this weird issue; I could redline in any of the 1st 5 gears & have touched 137 (85 mph) Kmph on 5th. Even if I'm in 10.5K RPM I'm in 5th gear, the 6th always starts from 8.5K RPM. Its a MC42 engine & not MC41.

I weight about 80 Kg (176 lb) & few guys out here using the same MC42 engine & weighing less than I do have peaked to 145 (90 mph).

My issue is I'm unable to redline on 6th gear; do any of you experience the same issue?

 

[Rick]

"the 6th always starts from 8.5K RPM"

You mean it 'stops' at 8.5K RPM and you can't rev higher? If you do mean 'start', please explain.

If you can't get to redline in 6th gear sounds like a warranty repair to me.

 

[Aargee]

You mean it 'stops' at 8.5K RPM and you can't rev higher? If you do mean 'start', please explain.

Ok will explain step by step as how I experimented...
1. Ride every gear upto 6K RPM before every up shift; so when I shift from 5-6th gear, the RPM for 6th starts from 5K RPM (1000 RPM less when I start 6th), which means, the speed of the vehicle is 80 Kmph. Now when I increase the speed gradually, all I can attain the top speed is 137 Kmph, which is 8.5K RPM

2. Ride every gear upto 7K RPM before every up shift; so when I shift from 5-6th gear, the RPM for 6K RPM starts from 6K RPM; which means the speed of the vehicle is 96 Kmph. If I accelerate (no matter hard or gradual) the top speed is 137 Kmph which is 8.5K RPM

3. Redline at every gear including 5th; now the RPM is 10.5; no matter how quick the gear is shifted from 5 to 6, the RPM falls back to 8.5K RPM. This means, the speed at 5th gear would be 137, on shifting to 6th, it starts from 135 & increases to 137 & sometimes upto 139.

These are my real time experiements.

If you can't get to redline in 6th gear sounds like a warranty repair to me.

Really?

 

[tygausa.com]

Weigh about the same as you. 4500 ft base elevation. Cannot get even close to redline in 6th gear...remember...it is a 250 beginner bike (though a great one at that).

WW

 

[Redline]

Don't shift gear when it hits the redline, go right into the redline until it can't go anyfurther (12,500 rpm).

Do this in fifth, with the throttle completely pinned. At 12,500rpm you should be seeing somewhere in the region of 150kph indicated. Very quick upshift to sixth gear, you should be seeing higher speeds than you previously have.

Don't be afraid to actually go well into the redline, get that baby up to 12,000rpm+ in 4th and 5th while pinning the throttle. Fun riding.

Eat some beans before you go, at 10,400rpm in 6th, fart.

 

[Aargee]

Don't shift gear when it hits the redline, go right into the redline until it can't go anyfurther (12,500 rpm)

The rev limiter cuts off a little past 11K RPM!!! Hope you're aware of it.

Do this in fifth, with the throttle...seeing higher speeds than you previously have.

Not more than 140; actually, I'm not alone, there're several guys who've reported this issue & that's why I mentioned the weight of the rider specifically. See the above post from tygausa; I'm beginning to think its the issue with the weight of the rider!!!

Don't be afraid to actually go well into the redline

I want to retain the bike for long, so I don't like to redline

Eat some beans before you go, at 10,400rpm in 6th, fart.

What has beans got to do? Seriously I don't understand

 

[Redline]

The rev limiter cuts off a little past 11K RPM!!! Hope you're aware of it.

Certainly not on my model in Thailand. All the way to 12.5 rpm if I wish.

Not more than 140;

Yes, probably not if you don't even go into the redline! Bloody 'ell!

I want to retain the bike for long, so I don't like to redline

Well there you go, forget about getting to redline in 6th if you're too afraid to go into it in 5th.

What has beans got to do? Seriously I don't understand

Beans make people fart. Maybe use them as a turbo as you're afraid to go past 10.5k rpm.

Only having a joke mate.

Were you the guy who lugged his bike around at under 4500rpm for the 1000km until it blew up?

It's a bike mate, go and bloody enjoy it.

 

[Aargee]

Certainly not on my model in Thailand. All the way to 12.5 rpm if I wish

And how much do you weigh?

Well there you go, forget about getting to redline in 6th if you're too afraid to go into it in 5th

Its not the question of being afraid, its just that I CHOOSE (read choose) not to redline. If I were to like redline, then I would've bought an inline like N250R which likes to scream always.

Were you the guy who lugged his bike around at under 4500rpm for the 1000km until it blew up?

You got half the things right; the engine blew, but I didn't lug the engine

It's a bike mate, go and bloody enjoy it.

Yes, I'm, hope you didn't see my TLog - http://www.cbr250.net/forum/honda-c...ourteen-days-hands-solo-ride-north-india.html

 

[Redline]

And how much do you weigh?

About 75kg.
175cm tall.

I'm European, not Thai. I'm not sure what you think the rider's weight has to do with a rev limiter cutting in or not though.

Its not the question of being afraid, its just that I CHOOSE (read choose) not to redline. If I were to like redline, then I would've bought an inline like N250R which likes to scream always.

So you don't want to, or even like redlining, but you're not happy with 137kph indicated?

Buy another bike, not a single-cylinder 250cc.

You got half the things right; the engine blew, but I didn't lug the engine

I thought you kept it below a very low RPM for a long long time. Was it 5,500 you refused to go over? For the first 1000km? I forget the exact info.

 

[sendler]

149kph

I can hit 149 kph actual at 9600 rpm indicated

 

[Aufitt]

We'll never redline in top with standard gearing.. it would be over 170kph.

Just go up 2 teeth on the rear sprocket and enjoy better accelaration and a fractionally better top speed anyway.

All bikes are on the tall side to pass ride by noise testing.. especially 23hp thai commuter bikes.

 

[Redline]

Just go up 2 teeth on the rear sprocket and enjoy better accelaration and a fractionally better top speed anyway.

So that will improve both top-end and acceleration?

 

[jkv357]

Aufitt got it - it's the gearing.

The CBR doesn't have enough power to pull the stock top gear to reline - no matter what you do or weight or...

You need to gear-down, as Aufitt said, to get your top gear RPMs higher and get the engine closer to peak power. If you do, your cruise RPMs will be higher as well, which could be a pain. Most cycles will not pull top gear to redline, usually because typical highway cruise gets too hectic.

As far as reving, there's usually no reason to hit the rev limiter - even if you are trying for max acceleration. I'll look for a dyno chart (EDIT -http://sites.google.com/site/tommyscivicpage/Home/Untitled.jpg, from that dyno chart I'd shift at 10,000RPMs most of the time - slighly higher from 5th to 6th) , but generally if you just slightly (500 RPM) exceed the RPM where max HP is made before shifting you will stay close to the power peak for the most time - giving you best acceleration. Don't be afraid to spin the CBR's engine - it's designed to live comfortably at higher RPMs. Use a quality oil (synthetic is always my choice) and change it often enough - more often than the manual suggests IMO.

Really, unless you change your gearing significantly or do a lot of mods the CBR isn't going to be much faster. You just have to deal with that or buy something bigger.

 

[jkv357]

So that will improve both top-end and acceleration?

Not typically, but in this case - yes.

 

[Redline]

If you can't get to redline in 6th gear sounds like a warranty repair to me.

I have to guess that you're talking out of your ass.

I don't think I've heard of anyone hitting redline in 6th on this bike. Certainly not in stock form anyway.

 

[Redline]

^^ What case? The CBR250R will get both increased acceleration and top-end with +2 on the rear sprocket?

 

[jkv357]

^^ What case? The CBR250R will get both increased acceleration and top-end with +2 on the rear sprocket?

The gap from 5th to 6th is pretty large. For maximum top speed you'd need to find the gearing that put the engine at 10,000RPMs in top gear. You are fighting aerodynamic drag at that point, and there is a speed that your maximum power will not take you past based on the aerodynamics of the particular cycle.

Basically you'd need to test with different gearing to come up with the optimum combination that would put you right at the power peak at the highest speed.

 

[Redline]

Okay, not sure that explains how it will improve both of them though.

 

[jkv357]

Okay, not sure that explains how it will improve both of them though.

I guess it didn't, so -

Adding teeth to the rear sprocket or subtracting from the front (lower gearing) will increase acceleration. The engine will pull through each gear quicker and easier. You'll be shifting more often and not going as far in each gear, but your acceleration will be better. Same as a bicycle with multiple gears - it's easier to accelerate with a larger rear gear, but you are peddling faster for the speed you are going.

Because of the tall 6th gear, the same change will get your RPMs closer to the power peak in top gear as you near top speed - as described above.

 

[TheMente]

You mean that "lighter" rear sprocket will allow 6th gear to rev higher so improve top end speed?
But will make all the other gears shorter.

I don't think is worthy, considering how often I find myself struggling to go faster in 6th gear than how often I use other gears at "standard" speeds...