Sprockets - More Teeth On Rear = Faster Acceleration+ Top Speed?

Hi Duck,
Standard gearing on the Sprint ST 955 was 18/43 on the 1999 model, but they changed it to 19/43 for 2000 onwards, so depends on year whether you will need a 17 or 18 tooth front sprocket, my Sprint is a 1999 with standard sprockets & TBH the gearing feels OK to me.

JT sprockets are pretty good quality & value, I would stay away from any that don't have the rubber bush as without them transmission noise can be a bit intrusive.

The below link gives you an idea what to look for but beware as it says 1 tooth less than standard but not for which year model, so this could be either 17 or 18 tooth, best count the teeth on yours & then make sure you are getting 1 tooth less.


https://www.ebay.co.uk/i/2646417730...y2la0PwKpp9uTASwqcaOGbAIMyJQjKTBoCVRkQAvD_BwE

edit - OR THIS ONE
https://www.ebay.co.uk/itm/Triumph-...127434?hash=item42087b1c4a:g:D5oAAOSwa1Bdd4NA

 

I can’t help thinking this discussion is over simplifying things. Folks are basically saying that more teeth on rear/less on front amounts to faster acceleration and lower top speed and vice versa and also some comparison is made between the teeth count on different bikes.
Dealing briefly with the latter first - comparison is made difficult because the internal ratios between bikes are likely to be different, even with the same engine and thus any performance difference cannot be directly attributed to the tooth count.
Increasing teeth at the rear will only increase acceleration in first gear and indeed, may actually reduce overall acceleration. For example - take a bike with more teeth at the rear such that it’s first gear is lower than standard but second gear perhaps a little higher than the “standard setup” first gear. If both bikes accelerate to sixty - the modded bike will get off the line quicker but will need to change gear earlier but now finds itself in a taller gear than the Oem bike which is still pulling hard and hasn’t yet had to waste time changing gear and when it does, it drops nicely back to peak torque revs. From this point onwards, acceleration becomes a function of road wheel torque and as long as either bike has a gear available at all speeds that will allow Engine revs at or near peak torque, the acceleration will be the same or similar. The only difference will be the road speeds at which gear changes occur.
As for top speed - if a bike is nowhere near the redline in top and you want more speed, then perhaps changing down is more preferable to less teeth at the rear?
If a bike with Oem setup is just about capable of redlining in top, then less teeth on the rear will Cut top speed. Perversely, less teeth may well do the same because a higher top gear will reduce road wheel torque and the bike may simply not have enough power to overcome the rolling resistance at that speed and so top speed also reduces.
The reality is that manufacturers play around with all these factors when designing bikes - they will know the bike’s CD, or drag factor, they will have full knowledge of the engine’s power and torque characteristics and will use highly advanced software to optimise gearing which will be a function of both gearbox internals and sprocket tooth count.
If an owner increases or reduces tooth count, there is only a single certainty - that it will affect acceleration in first gear in a predictable way - all the rest is a lottery and amounts to trial and error but at least for road use, is most likely to be an unfruitful exercise me thinks!!
Standard sprockets all the way for me but no reason why folks shouldn’t tinker!!

 

I think you're missing the point of why most people adjust the teeth on sprockets. Having owned 2 V twin Aprilias I can absolutely say that they benefit from changing the gearing.
At low speed ie. around town without the change they are lumpy and difficult to ride smoothly, after the change....really easy.
Out of town it makes it much easier to save the wear on the front tyre as it's rarely on the ground and against what you seem to have said, acceleration was much better and as I rarely travel at 170+ I was happy to lose the top end for the extra fun.

 

I stand by what I wrote but whatever floats your boat. We all like to tinker with our bikes and so no reason you shouldn’t even if your reason is nothing more than saving on front tyre wear!!

 

I also think your over complicating the whole point...people are just talking about adding a couple of teeth to the rear sprocket regardless of whether the motor gearbox is capable of dealing with the change and in my experience i have yet to come across a bike that cant deal with a small change in overall gear ratio and that's with far less capable bikes that today's over powered offerings.
Back in the day we where always experimenting with overall gear ratios by changing the front or rear sprocket.

 

I think best to leave well alone....the standard gearing is the best compromise between acceleration,top speed and fuel consumption.

 

The key word there being 'compromise'.

 

Well your sprockets have no idea how many teeth they have - nor the ones inside the gearbox. They all just think they are circular levers........

For ‘normal’ use the manufacturers achieve pretty much the best compromise attuned to the motor output. For regular motorway pounding you might up a tooth on the gearbox but I’d get a car........

 

Would you care to interpolate?

 

Went one tooth up on the front of the Bonneville made me stop looking for 6th and now does a ton in 4th

 

verb
verb: interpolate; 3rd person present: interpolates; past tense: interpolated; past participle: interpolated; gerund or present participle: interpolating
1.
insert (something of a different nature) into something else.
"illustrations were interpolated in the text"

Ooh err misses.

Only time i have used interpolate is creating a ECU map.

 

Mathematically it’s about finding a middle value.

 

Yeah but i was wondering what the middle value of compromise was.

 

I had the exact same experience with mine. Most bikes I’ve had in recent years had the problem of being geared for low RPMs at highway speed, meaning a theoretical top speed in the stratosphere. Great for high speed tracks, suboptimal in the real world IMHO

 

Err..........that's what I've done with one more tooth theoretical higher top speed

 

Over simplifying, nobody could accuse you of the same!

Most bikes, not all, are over geared, gearing them down slightly IMHO makes for a better ride, not just for 0-60 standing times, but pulling better out of corners as well.
As a racer I am looking to get to revving out in top gear just before the breaking zone on the fastest straight, so I use many different sprocket combinations to achieve this depending on which track I am at.

 

You never raced cars, did ya? I was constantly changing rear axle gearing to fit the track I was racing that weekend. More straights and little elevation change, higher (numerically lower number) gearing for the axle. Steeper or twisty track needing more acceleration and torque, lower ( numerically higher) gearing needed. A 3.73 gear is a higher gear than a 4.88.

 

So are you saying that you went from 16 tooth to 17 tooth for the front sprocket? And if so, did you find that you could stay 1st, 2nd and 3rd gear slightly longer which would make for easier around town riding ?

 

I went up one tooth on the front of my speed Twin as first gear was to short, i might even try two later.

 

Factory bike sprocket/gearing may be less than optimum to overcome regulatory emission and noise standards and at a couple of standard MPH emission requirements. Bought an Enduro bike for the GF'S son, stock front sprocket was 13 tooth, switched to a 12 tooth for a much improved higher all around performance. Top speed loss was less than 0.5 mph. Cost $20 USD.