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Bigger front and smaller rear sprockets?

  • Thread starter Thread starter Talon
  • Start date Start date
T

Talon

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So my chain and sprockets are trashed and I just got back from a 2000km roadtrip, well i just did like 1000+ km yesterday and the other 1000 a month ago on my 82 1100E... there's a story there with me ending up at my parent's house with no oil left in my bike and thinking i had a bad leak between the cylinders and the base, which only turned out to be a slightly weeping gasket which probably opened up quite a bit more when the bike got really hot while waiting in line for a toll booth (around 150ish c) then riding the bike back home after sitting for a month at the parent's house and it was 100% solid.

anyway i'm really not concerned with acceleration with this bike as i currently have a 2005 10R. I'd also like to get better gas mileage and run at a lower rpm all around, especially highway cruising speed. I've felt that the bike needed a 6th gear since i got it so i was thinking of going up in teeth on the front and dropping a few in the rear.

anybody else done this?
and is there a formula/program to figure out your final cruising speed and what rpm you would want to be at and what sprockets you would need to achieve that?

Ideally i think i'd want to be around 3k - 3.5k at around 110km/hr in 5th gear.

or even the transmission gearing ratios and tire circumference would work...

any drawbacks to this other then less acceleration?
and any recommendations on chains and sprockets?
 
What is your current engine speed?
Your stock sprockets are 15 and 42 teeth, giving a ratio of 2.8 to 1.
If you add 1 tooth to the front, it would be a 2.625 to 1 ratio.
Adding 2 teeth would be a 2.47 to 1 ratio.

If your stock engine speed at 110 k/h is 4000 rpm (close?), the new engine speeds would be:
with the 16-tooth front sprocket: 3750
with the 17-tooth front sprocket: 3529

Not sure if you have room to go with a sprocket much larger than this, so you would have to drop teeth from the rear sprocket. Dropping 3 teeth from the rear will change just a little more than adding 1 to the front, so let's figure a 16 and 39 combination. The new engine speed would be 3482.

Keep in mind that it's not just lower engine speed that will net you better gas mileage. If your new engine speed drops below the point where the engine is making sufficient torque, you will have to increase the throttle opening to compensate, negating any savings by running slower. You will also have to add more throttle during acceleration. You can probably get away with a 10% change in ratio, but I would not go any farther than that.

Changes in transmission ratios would be a nightmare. Unless you can find someone that can make the new gears, I don't think they exist, with the possible exception of gearsets made for racing, but they are all about acceleration and speed, the opposite of what you are trying to accomplish.

Change in tire size has pros and cons. You might be able to go with a larger tire which will have a larger rolling radius, but it will also be wider. A wider tire on the same width rim will get sqeezed into a tighter radius (cross-section) and will have a smaller contact patch when cornering. Not a good thing. Also not much change in engine speed. Going from a 130/90-17 to a 140/90-17 will only drop your engine speed about 2.7%, or 108 rpm.

.
 
i have a smaller rear sprocket on one of my 1000's, i think it's a 40 or 41, can't remember. i use the same chain and it's just moved back a little bit on the adjusters. i think it's great. still has plenty of power and it's nice for regular riding, especially long trips. my speedometer is probably not accurate but i reach a reasonable highway cruising speed at less than 4000 rpm. i use this bike when i go on longer rides and with my ol' lady. my other bike has the standard sprockets and i use that for riding with the guys where we tend to get a bit racier.

i haven't really checked for gas mileage difference but i'll try to and maybe repost.
 
well my current engine speed when crusing on the highway is around 4.5k - 5.5k i think. my tach bounces around a bit but i feel like i want to shift into a non existent 6th gear when i'm at crusing speed, which is usually around 110km - 120km

I'll probably try a 16 - 39 combination and see what its like.

i was just wondering the transmission ratios/tire size so i could do the math myself if i needed to :P
 
If you are changing the whole system I'd suggest an upgrade to a 530 chain and sprockets. That will give you more gearing choices, as well as less weight, rotational inertia, and wear.
 
The 530 conversion kit from Z1 includes the chain, sprockets and spacers if necessary....give Jeff a call. I went with a 116 link X-link chain, and 18-47 sprockets for a 2.61:1 ratio, which drops cruising rpm by about 300..... which looks like a small change on paper, but makes all the difference on the highway. I really like this ratio... the loss of acceleration seems negligible, and there is still great passing power in top gear, so no downshifting is needed. Also included, was a split (master) link. The Z1 site has all the formulae needed to figure out the correct sizes, to arrive at your desired cruising rpm.

Tony.
 
Hi Steve, great reply to the gearing question, that one would be one for the archive as it seems to be asked quite often. I am not about to change my gearing but now I now what the options are and the reason why the stock sprockets are the size they are, best overall to suit most riding situations, thanks for the info, cheers.
 
on a similar topic but slightly different, if that makes sense......i have somewhere the formula to work out sprocket sizes to maintain standard gearing when changing rear wheels and tyres for different sizes, ie gsxr rear wheel etc. someone let me know if this has already been posted if not i will dig it out and post it tomorrow after work. gotta sleep now as up at 6.
 
Shin-Ken 1074 said:
I am not about to change my gearing but now I now what the options are and the reason why the stock sprockets are the size they are, best overall to suit most riding situations, thanks for the info, cheers.
Click to expand...

I think these bikes are geared rather low in stock form to fare well in the 1/4 mile shoot-outs that the bike mags put them through....a decent E.T. helped with marketing, no doubt, though I'm not sure why the corresponding drop in top speed was ignored.Before the sprocket change, I too wished for a 6th gear for a more 'relaxed' highway cruise....though some here have gone in the other direction and geared lower than stock, which probably makes for some blistering acceleration.:-)

Tony.
 
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