New chain and sprockets, lacking power in 5th

[BlackStallion]

Just had a new chain and sprockets fitted today, and i was told the rear sprocket had 1 less tooth compared to my old one.

I've heard going down on sprocket teeth at the rear gives you more top speed, am i right?

Well i'm getting a bit better acceleration, and i hit 66mph in 4th gear today, when i could just hit 60mph with my old sprocket. However, when i change into 5th, the RPM drops, and there's no more power, it's like a useless gear now

Pretty gutted, because i used to be able to hit 73mph with my old sprocket. Looks like i won't be hitting 70 anymore

I'm wondering if it's anything to do with the front sprocket, maybe the teeth on that need changing if the teeth are different on the rear

Any ideas? I'm not sure with the whole sprocket thing...

[johnsmith222]

There's not really much you can do about this apart from getting a rear sprocket with 1 more tooth.

Less teeth in the rear sprocket means a higher top speed, but the bike needs enough power to actually get it there. It also means slower acceleration (I think you have "better acceleration" because you can use a lower gear to hit higher speeds. eg. before you were using 5th to do 65mph, now you're doing it in 4th. You may have lost a tooth in the rear, but the differences in ratios between 4th and 5th gear makes up for the missing tooth and some more).

Apparently losing 1 tooth on the front is like gaining 3 teeth in the rear. I would replace the rear sprocket for +1 tooth (back to the same as was on before) if I were you rather than losing a tooth on the front as you'd probably get a lower top speed than 66mph, but would be able to use 5th gear. The bike would feel like it pulled more but it sounds like top speed is important to you.

I'd just get a rear sprocket with 1 more tooth on there.

[BlackStallion]

Yeah, i guess going back to my previous sprocket would give me my top speed back

I just can't afford a new one right now, would be a waste of money really. I had no idea it was going to be 1 tooth less though. When i flicked into 5th, i was really looking forward for that extra little boost, but there was nothing there, and even with the throttle wide open, my speed was either staying the same, or dropping by 5mph sometimes, which i think is strange...

With being a 4 stroke, you need to ride for a good half an hour until the engine's warmed up fully, so it may just be the cold weather, because in the summer (my 125 much prefers warmer weather) after riding for a while, i could get a decent top speed out if my bike, compared to earlier the same day.

Just a guess...

I'll have to see when the weather becomes more "comfortably ridable"

[P.]

With my hyosung, not sure if thats the bike you are using, but anyway..
I used to let mine sit there and idle for like 2-3 mins.. then ride real careful... Always helped me and the bike was just kinda really crap for the whole journey if it wasnt warm!

That thing hit stupid speeds for a heavy v twin 125.

I found when i changed my chain and sprockets after they kinda "bed in" it was alot better... took about 100-150 miles, was adjusting quite a bit in that time.

But after that it felt back to normal.

[BlackStallion]

Read your sig mate, you had the Comet, which is a nice bike

I was told that i needed to give the chain and sprockets a chance to bed in, because the chain stretches rapidly, and needs to be adjusted every so often. I think you're right though, because i got straight on my bike after everything was fitted, and rode 70 miles back home, plus it was freezing!

The mechanic told me i'd get atleast a few extra mph out of the rear sprocket, but i guess i could ride in 4th from now on, it's a nice gear to ride in, and i've got to admit, for once tooth's difference, you can feel the improvement in acceleration, which i think is where i'm getting the advantage, but with the loss of top speed. Atleast i can overtake quicker now

I'll just have to see padwax mate, cheers

[BlackStallion]

This is the rear sprocket i've got
https://www.startright.co.uk/index.php?main_page=product_info&cPath=145_156&products_id=13902

Like it says, squeeze that extra few miles an hour

[P.]

yea i got all my bits from there
Comet was fantastic...wasnt learner legal though...bastard bike shop
Still, sounded nice, went fast enough for me to use motorways, great MPG, HUGE thing, big tyres, definitely made me a better rider, or atleast did the step to a bigger size bike before getting a much bigger cc.

Try bedding the chain and sprockets, letting it warm up substantially, should keep you going for a while!

Definitely watch the chain slack etc, that made a bit of difference to me...kept it relatively tight, about an inch movement.

[johnsmith222]

[BlackStallion]

[johnsmith222]

[G]

You're only going to get more top-speed if you're already revving-out in top gear generally - even some cases then you won't if the gearing is already 'perfect'.

[Ste]

Where's your speedo driven from, gearbox or front wheel? If it's gearbox one then changing the final drive gearing will mean your speedo is inaccurate.

Smaller sprocket at the back will give you worse acceleration and higher top speed if the bike has got the power to do so which it sounds like yours doesn't.

In plenty of cases down gearing a bike (which gives more acceleration) will also mean a faster top speed as the engine is then able to be go right to the red line in top gear.

[Vin]

Go on a diet, find a big long downhill, get flat on the tank you'll easily do a ton.

[BlackStallion]

[Ste]

With a smaller rear sprocket the speedo will be under reading, as it's only 1 tooth smaller than standard then it'll only be out by a small amount. But as the speedo will over read as standard, it might now be closer to being right.

It's possible to work out from the gear ratios what the speedo inaccuracy is and you can get little electric gadgets that correct your speedo, but it's more hassle than it's worth when your speedo is only out by a small amount cos you've already got a pretty good idea how fast you're going.

[BlackStallion]

Well, when my speedo read 73mph, i have to drop about 3mph for an accurate reading, so that's 70mph.

So if my speedo is saying 66mph in 4th, i'm really doing 63mph, even with the low power my engine delivers, i really thought it would still even say 70mph (really 67) but i'm still happy with the bike, and when i come to sell it, atleast it will have a relatively new chain and sprocket kit with hundreds/thousands of miles left in them

[Kwaks]

The "feel" of extra acceleration might just be the new chain being better adjusted and having less stretch applied.


Or as usual in my case its all in your head
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[chris-red]

Can you hit the redline in top gear? if you can drop a tooth on the rear, if you can't add some. This will get you more accelaration and a highier speed. My old GS wouldn't rev out so I dropped a tooth on the front (Same as adding to the rear) and the top speed went up by 10mph.
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[Kickstart]

Hi

While all the above is true, it sounds a bit strange for only changing the rear sprocket by 1 tooth. Going from 46 to 45 teeth is a tiny change. Even if you pulled the same revs in top the difference in speed would be under 1.5mph. I would doubt it is enough to knock ~10mph from your top speed.

If you could hit 60mph before in 4th then you should be hitting 61.3 now at the same revs. But as your speedo is driven off the gearbox it will still show exactly the same speed as before even if you are going a tad faster.

What size front sprocket is on there?

All the best

Keith
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[BlackStallion]