17" Rim V's 18" Rim (Sprocket size?)

[Poacher886]

Hi,
I raised this question in my thread about wheel bearings, but thought this needs a thread headed correctly.

My 92 Trident has a standard 18" Rim with a standard 46T rear sprocket. In a bid to lift the accelaration i was going to put a 48T rear sprocket on it. No problems there.

Late last year i managed to get a 17" wider rim of a 96 Daytona / Speed 3 etc etc... I now intend to put this on my Trident, but im a bit confused about the rear sprocket.??

Firstly will the sprocket of my Trident fit the Daytona wheel...im guessing there the same fitment? and secondly, i was supprised to read that the standard sprocket size on the Daytona / speed 3 etc is only about 42-43T!! this supprises me, because by my calculations, the smaller wheel will offer less accelaration than the 18" wheel on the trident!.

So now im a bit confused...what sprocket should i put on the 17" rim, to give me similar acceleration to a 48T on the 18" Rim????


Any ideas / thoughts

Thanks.

[daytona 750]

i have done the same conversion on my daytona, and kept my original sprocket, and didnt notice any difference in acceleration to be honest

im not sure if the different models hjad different gearing?

i didnt really have a reference point for my rear sprocket as so far as i am aware they never put a 17 inch wheel on a 750 6 speed motor

[Poacher886]

But in theory, the 17" Rim would require a larger sprocket than the 18" Rim in order to maintain the same acceleration yes!

Thus i would need a 50T or something on the rear of the 17" Rim to equal a 48T on the 18" Rim....

????

[Roden]

17" wheels had a 43T sprocket as original, 45T is what most people install for more pep but you will find it revving a bit harder at cruising speeds.

I have a 45T rear and I really like it for the type of riding I do. If I was off on a long trip though, I would be tempted to put a 43 back on just for the extra legs on the highway.

I think the differing sizes would be because of the different rolling diameters of the two wheels. The 17" doesn't travel as far in one revolution as the 18", hence the ratio is stepped up to maintain similar revs at x speed? Maybe....

Cheers,

Roden

[sailfish]

Originally Posted by Roden

I think the differing sizes would be because of the different rolling diameters of the two wheels. The 17" doesn't travel as far in one revolution as the 18", hence the ratio is stepped up to maintain similar revs at x speed? Maybe....

Yes, the rear tire circumference ultimately determines how fast your engine will turn so you'll need to know that value for each tire. Tire manufacturers usually provide that information on their websites.

[Poacher886]

Originally Posted by Roden

I think the differing sizes would be because of the different rolling diameters of the two wheels. The 17" doesn't travel as far in one revolution as the 18", hence the ratio is stepped up to maintain similar revs at x speed? Maybe....

Roden

But this is what i dont understand...the 17" wheel is already struggerling to keep up with the 18" wheel, yet they put a smaller rear sprocket on it to make it even slower????

While i understand it will drop the revs and alow for a longer gear, you would hardly make the early speed triple "slower" than the standard trident!!

Seems strange to me.

[sailfish]

Originally Posted by Poacher886

Firstly will the sprocket of my Trident fit the Daytona wheel...im guessing there the same fitment? and secondly, i was supprised to read that the standard sprocket size on the Daytona / speed 3 etc is only about 42-43T!! this supprises me, because by my calculations, the smaller wheel will offer less accelaration than the 18" wheel on the trident!

In terms of wheel size only, the 17" will give you more acceleration than the 18" allowing that the sprockets are identical.

[GeoffE]

Hi,

A couple of bits that may help?

The standard tyre on the Trident is 160/60-18 with a circumference of approx 80.3".
The standard tyre on the Daytona/Speed Triple is 180/55-17, circumference approx 77.9".
(The standard tyre on the Sprint/Trophy is 170/60-17, circumference approx 78.6")

The Owners Handbook lists the sprockets & links fitted as standard for that sales market.
The UK Handbook notes the Trident 900 as 46/17 with a 112 link chain.
The Daytona 900/Speed Triple are noted as 43/17 with a 110 link chain.
(The Sprint is noted also as 43/17 with a 110 link chain).

I find Renthal's gear ratio table useful (http://www.renthal.com/File/gearing_ratios.asp), and it may help you if considering a higher/lower ratio, and seeing acceleration viz top speed.

So the Daytona 900/Speed Triple (and Sprint) have a higher gear (less teeth/rotation), but a smaller wheel circumference, to the Trident 900. I suspect that if we did all the sums, the performance of both Trident 900 (18") & the Sprint (17") standard set-ups would be about the same? With the Daytona 900/Speed Triple standard set-ups (and their 180/55-17 tyre) perhaps slightly nippier?

(Fyi, my Sprint currently has the 170/60-17 rear tyre, but I will certainly try the 180/55-17 next time).

Geoff

[Poacher886]

Originally Posted by sailfish

In terms of wheel size only, the 17" will give you more acceleration than the 18" allowing that the sprockets are identical.

@Sailfish. This is wrong, its the other way round. Imagine getting a big wheel and rolling it along the ground for one revolution, then do the same with a smaller wheel.....now which ones gone the furthest!...the bigger wheel. This is why the original push-bikes (penny farthings) had a huge wheel, the same princible, of course now we use gears, but the effect is the same.

@GeoffE, thanks for the info...the renthral gear selector, is for "gearbox" sprockets though! so not much use for the final drive versus wheel size.

[Roden]

Originally Posted by Poacher886

@Sailfish. This is wrong, its the other way round. Imagine getting a big wheel and rolling it along the ground for one revolution, then do the same with a smaller wheel.....now which ones gone the furthest!...the bigger wheel. This is why the original push-bikes (penny farthings) had a huge wheel, the same princible, of course now we use gears, but the effect is the same.

@GeoffE, thanks for the info...the renthral gear selector, is for "gearbox" sprockets though! so not much use for the final drive versus wheel size.

Poacher, I think you will find that Sailfish is correct. The smaller circumference of the 17" rim does indeed mean that it doesn't travel as far in one revolution as the 18" wheel. So, given that the sprockets are the same, the engine would have to carry more revs with the 17 incher, to travel the same distance as the 18 incher in the same time frame! Hence the 43T sprocket fitted to the 17' wheeled bikes.

Phew. Does that make sense?

Cheers,

Roden