Sprockets and speed

[S4Mal]

The story so far : standard S4 came with 15T front sprocket, a little tall in the gearing dept I thought, especially around town. 14T front sprocket a real iimprovement :cool: 13T front sprocket is interesting but not as radical as I was expecting. Has anyone else found a good mix ? personally I think 25mph in 5th at 8000rpm could be something to aim for. :)

[SimonH]

Mal,
the gearing is too tall on the watercooled bikes in particular. My monster has a 748sp motor in it and the standard gearing (which is for a fully faired bike) is too high. I increased the rear sprocket by two teeth. Grant, who ran a similar bike, raised his by three teeth and it was fine.

SimonH

[JMo]

I would agree - too small on the front and it puts a lot of strain on the chain having to bend that much - better to go bigger on the rear. I know Renthal do a whole bunch of different rear sprokets (some in natty anodised bronze) - I presume yours is 38 or 38 at the rear at the moment? Have a look at what sort of gearing the 748/998 race guys us on short circuits...

xxx

[Rogerg]

been thinking of changing the sprocket(s) on my S4 for a while.

Is is a simple procudure (Idiots guide please) & what other bits will I need other than the sprocket(s) themselves?

Cheers all

[JMo]

Rog - normally you'd replace the chain and sprockets together, to minimise the wear that happens if you use old and new together... however, since your S4 has done less than a 1000 miles, I'd just go for a new rear sproket (a Renthal will cost you about £25).

The standard S4 gearing is 15 front 37 rear, and I believe you run a 525 chain on the S4 and 900/1000's (520 on the 620/750's)... so just order a sprocket (P&H do them) with whatever number teeth you want...

The rule of thumb is one tooth off the front is the same as three on the rear, but as I said above, I wouldn't go smaller on the front, to save chain wear...

So you'll want at least a 40 on the rear to make a difference - maybe even a 42 or 43 - and you'll still hit well over 120mph in top.

However, if you are adding teeth, you'll need a corrispondingly longer chain - so that will be an additional cost (which is why a lot of people just drop a tooth off the front, and use/shorten the original chain)...

xxx

[Rogerg]

cheers Jen,

bearing in mind we'll probably only do 3k a year at a push - will the chain wear really be problem if I just do the front?

[PaulS]

I've been using 15/39 on my S4 for some time now and have found it a significant improvement (particularly around town) over the original 15/37. You don't need to use a longer chain with the 39 and if you go much bigger than this you may find the front wheel reaching for the sky more frequently than you might want!

[JMo]

cheers Jen,

bearing in mind we'll probably only do 3k a year at a push - will the chain wear really be problem if I just do the front?

The problem with a smaller front sprocket is that the chain has to bend more each time it passes around the teeth, therefore it can wear the O rings more than with a larger sprocket... imagine how many times it does that at 100mph?!

As PaulS says - you'll probably notice a change of a couple of teeth - so why not go for the 39 on the rear (as he says, it should fit with the original chain), then go for a 14 on the front if it's not low enough - that would be the cheapest option...

I would agree that something as extreme as 15/42 or 15/43 would indeed give mighty wheelies - in every gear I imagine!

xxx

[Garry Hogan]

been thinking of changing the sprocket(s) on my S4 for a while.

Is is a simple procudure (Idiots guide please) & what other bits will I need other than the sprocket(s) themselves?

Cheers all
I changed the front sprocket on my 750 a while back and it were easy :D Just take off the front sprocket cover ( 2 allen keys ) and undo the 2 allen key headed bolts on the sprocket securing/clip thingy. Then loosen off the chain at the rear wheel a bit, then pull off the front sprocket. Now line up the new sprocket ( with the chain on it!! ) so the clip thingy will be in the right position for the allen keys, pop it on - re-tighten the allen keys and hey presto - a much improved Monstah :lol:

[Shauns4]

I've used a 14 front 39 rear on my S4 for about 5000 miles, no problems with the std length chain . Reduces the bike speed by approx. 11%, the top chain silder is the most vunerable point with the smaller front sprocket which is also still ok.

[S4Mal]

Thanks for the info guys - some interesting stuff. ref changing the front sprocket, I think its a good idea to use some thread locking liquid on the bolts as a 'belt and braces' measure.

[Rockhopper]

748's come with a 14 tooth front sprocket as standard. Its not an issue of how far the chain bends, its something to do with the actual tension on the chain which is increased by using a smaller front sprocket.

I changed my ST4's fropnt sprocket for a 14 tooth one last year. In 7000 miles i havent needed to adjust the chain once.

I think a 13 toother might make the chain rub on the swing arm though.