Hello, sorry in advance I've tried to search for this but no luck...

I'm looking to lower my front sprocket size to a Renthal 14T. Will that throw my speedo reading out? If so by how much? How can I get round this? And dropping 1T, am i going to need to expect about 1grand higher RPM in 6th gear?

Also, is it actually going to be THAT noticeable? (twisty road use/occasional track days)

Sorry about all the questions, I've never amended sprocket sizes on any of my bikes before so this is a real learning circle for me

Ok it's been a while since i've had to work out any gear ratios. However, if my math holds...

Presuming Stock NC30 tyre (150/60/18) stock Gearing: 15/40.

Redline (14,500rpm) Speeds:

1st: 65.5mph
2nd: 88.5mph
3rd: 106.5mph
4th: 120.5mph
5th: 133.5mph
6th: 145.4mph

As above but with 14t:


1st: 61.1mph
2nd: 82.6mph
3rd: 99.4mph
4th: 112.4mph
5th: 124.6mph
6th: 135.7mph

alexwitham wrote: Also, is it actually going to be THAT noticeable? (twisty road use/occasional track days)

Yes it is quite noticeable changing to a 14t front. Significantly better acceleration.

I always go for 14/44. I love the look of a big renthal sprocket on the back that is the size of a dinner plate. Revs out at about 100mph but loads of acceleration and to be honest I'm not that fussed about caning it at mega speeds on a straight road.
Now power out of a corner...............

And what is the maths to work it out?

mick.mh2racing wrote:And what is the maths to work it out?

Mick, I use this excel program:

http://www.dropbears.com/u/utilities/gearing.htm" onclick="window.open(this.href);return false;

All the info you need to input can be found in the haynes manuals. Useful file!

Thanks for the advice and responses there guys.

Will it make my speedo read the wrong MPH if i change the front sprocket?

And can i change the front sprocket down to a 14T will i also need to change my chain at the same time?

Thankoooo NC30 boffins!

alexwitham wrote:Thanks for the advice and responses there guys.

Will it make my speedo read the wrong MPH if i change the front sprocket?

And can i change the front sprocket down to a 14T will i also need to change my chain at the same time?

Thankoooo NC30 boffins!

Ooh a program :D Theres me with a calculator and the owners manual ^_^

You shouldn't need to change your chain. Only if you add / remove more than a couple of teeth will you need a shorter / longer chain.

Or if you switch to a narrower pitch sprocket (ie. 520 instead of 525)

If you look at the data i worked out you'll see that at given revs your mph's are different so your speedo will read differently.

What I advise people to do is ride around with a gps unit next to the speedo and either film it and do it later or make a mental note as your riding of what your speedometer is saying compared to the gps, then its' just a matter of marking the altered speeds on the speedo

Ok, so off I went to my local dealership and lucky me they had 1 Renthal 14T for the NC30 in stock, so I handed over the £20 sterling and sped off home.

Undertray off, loosened the pinch bolt, slackened the chain, off with the sprocket cover/speedo drive/clutch holder thingy and after spending a couple mins wriggling the old sprocket off she came. On with the 14T/sprocket cover/speedo drive/clutch holder thingy/fairing and key in ignition.

Off I wizzed and Oh God, what an absolutely awesome difference! Im so glad I went for this as the grin factor is just amazing from just a £20 Mod... Highly recommended!!!

Only question I have is, could someone accurately find out for me with the new gearing what my ACTUAL speed is at an indicated 30, 40, 50, 60, 70 and 100? Thank you very much.

Alex

Quite simply no, each bike could be different, best to use a GPS and work it out yourself.

Druid