Renthal Vs AFAM

I own a Gixxer K4 600, and soon I want to change the chain and sprocket, losing a tooth in the front sprocket for fast acceleration, the questions are how much mph will I be losing at the top end & who’s better Renthal of AFAM? (or is there someother company I should be looking at)


The change in top speed (in each gear) depends on how many teeth were in the original front sprocket. So if you go from a 15-tooth front sprocket to a 14 then top speed will be reduced by 1/15 (6.7%).

I’d go with Renthal - their stuff seems to be better quality.


I run with AFAM sprockets on my gixxer and have had no trouble, specifically the hard-anodised race range. Renthal are top as well, I’ve used them before. Duncan’s got the speed change covered.

Duncan how did you work that out can you explain in a litlle more detail please cheers

If you switch from a 15-tooth front sprocket to a 14, that is a 1/15 change (6.7%)
If you switch from a 15-tooth front sprocket to a 13, that is a 2/15 change (13.3%)
If you switch from a 15-tooth front sprocket to a 12, that is a 3/15 change (20%)

If you replace the front sprocket with a smaller one you lower the gearing and lower the top speed in each gear. The front sprocket has to turn further for each revolution of the rear which gives greater mechanical advantage.

If you replace the rear sprocket with a larger one you lower the gearing and lower the top speed in each gear. So if your front sprocket has 15 teeth and your rear has 45 and you want to lower the gearing by 6.7%, you could replace the front sprocket by a 14 tooth item or replace the rear sprocket by one with 48 teeth.

If you were to change the sizes of both front and rear it is a bit tricky and you will need to wrap a wet towel round your head and think very slowly.

Is that any clearer?


Where’s the towel… I have -1 on the front, and +2 on the rear. It goes quick, quickly. It’s a bit much for a gixxer thou, but -1 off the front on most bikes feels great! A very cheap mod for more acceleration. It’s not like we use the top-end speed anyhow. I’ve yet to top my gixxer out at the track.

Well I have my Renthals and new DID chain ready to fit up to my bike when I get a chance. I’ve gone for the -1 at the front and +1 at the rear, hehehe should give it bit more of a kick.

This should be quite handy for me because when I go to work I never hit the power band so I could do with a little more power low down.

Jay, run it like that at Silverstone and by the end of the day you should easily be banging the limiter down the hangar straight, if not, you may require bigger nadgers.

Should be fine Chuffster, I don’t remember the top speed there before on my stock-gearing 750, but think it was about 160-170mph, which the K5 is still capable of with this gearing.

Think ill go for an AFAM set with -1 at the front and keeping the back standard.
Am I right when saying the mileage is recorded by the front wheel, so there shouldn’t be a problem with my bike reading a higher mileage than it’s doing?
And is this a job I can do myself with the help of a service manual and a Snap-on set, or should I leave this job to the pro’s?

Thanks once again LB

Speedo is run off the drive-shaft (or there abouts) on a gixxer mate, not the front-wheel, that’s Fireblades and other funny bikes

errr so does that mean I will or won’t have a problem Jay

You will have a problem and you need a speedo healer to sort it out (little yellow box that needs to be wired in).

Bikes which have it on the front dont have these problems as they are usaly always the same size tyre, as jay said all GSXRs (modern) have it on the output shaft and gets affected by the sprocket change.

The speedo pick-up counts the number of revolutions the front sprocket makes & converts that into MPH, if you reduce the size of the sprocket, you’ll be going slower for the same number of sprocket revolutions, so the speedo will display a faster speed than you’re actually doing.

You can get electronic boxes that plug in & allow you to adjust for changes in sprockets.

You can change a chain & sprockets without a chain breaker/riveter, but it’s a lot easier doing it with one.

If all you want to do is change the front sprocket & the chain itself is OK, then you don’t need to change it as well, just do the sprocket. Front sprockets are much of a muchness, they’re steel & you don’t see them once they’re on, so one decent brand is pretty much the same as the next.

Yeah it is cheers Duncan

DA, for most gearing changes, it’s not even necessary to get the speedo corrected, I think it’s a personal decision. I never have done, though with my gearing, it does over-read by a bit, but hey, it keeps me the right side of the speed limit

Assuming you’ve gone to a 14 from a 15 front sprocket then what used to look like 30mph will now look like 32 and what used to look like 60mph is now 64. But your speedo was wrong before so it makes little difference.


Plus you get 7% more torque if you -1 @ the front, and it doesnt effect top speed really it just moves the rev counter up a touch. Its also better for two up. Renthal or afam? doesnt matter! there both top notch…

Going to get the Afam set and the lil yellow box to adjust the speedo, sorry for the late reply but safe for all the help