Maths gurus - gearing question for you!

[GuzziHero]

Right, just did a chain and sprocket change on my Haotian HT-100 but the new sprockets have different teeth numbers than the old ones. I was someone with more maths skill than me could work out what effect this ratio change would have on the bike.

 

The bike usually hits a top speed of 50mph in 4th (top).

 

The original sprocket sizes are: 14 tooth front, 36 tooth rear.

 

The new sprocket sizes are: 15 tooth front, 39 tooth rear.

 

Now its a 4hp bike, so I can't imagine it makes a lot of difference, but it would be interesting to know whether the mathematical difference equals the difference I think it has made. I'll reveal that if/when I have an answer

[Spudgun]

The maths says the bike should go 1.5MPH faster.

[GuzziHero]

Ahh, thats interesting. I thought it was acellerating slightly better which would give a lower top speed

 

Cheers!

[Spudgun]

The difference between the gearing is a factor of 0.03. In reality, it's so small, it's not really noticable. To get something noticable, you need to add around 10 teeth to the rear sprocket. I did this on an old BSA Bantam (47T to 58T). It was slower, but it accelerated faster and it would climb up walls.

[Chris North]

From what I've read, adding one tooth to the front would be the equivalent of subtracting 3.5 from the rear. Never tested it though, and I'm not really a bike nut or a math whiz...

[GuzziHero]

So +1 front = -3 rear. So I've added 3 to the rear...its honours even, pretty much

 

It shouldnt be noticeable but the old chain and sprocket were size 428, the new ones 420. Same pitch, but shorter roller lengths (henceforth thinner sprockets). Slightly reduced mass but I can't imagine that would make a flea's pecker worth of difference.

 

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Oh...just found this:

 

http://www.sprocketcalculator.com/

 

Which says a top speed of -1.1% and a torque increase of the same.

[Stealthbomber]

The bike usually hits a top speed of 50mph in 4th (top).

 

The original sprocket sizes are: 14 tooth front, 36 tooth rear.

 

The new sprocket sizes are: 15 tooth front, 39 tooth rear.

 

In case you ever need to do it manually, you just divide the rear sprocket by the front to give the overall final-drive ratio.

 

36/14 = 2.571

39/15 = 2.6

 

Soooo...

 

Previously your output sprocket was turning 2.571 times for every rotation of the rear wheel.

Now your output sprocket is turning 2.6 times for every rotation of the rear wheel.

 

Thus, as has been said, your overall gearing is very slightly lower.

 

For future reference, you can achieve the same effect (on a ped) by having a bowl of all-bran for breakfast rather than a fry-up or having a good dump before riding it.

[GuzziHero]

Spudgun said it was geared slightly higher. That convertulator says lower.

 

And its not a moped Its a step-thru motorcycle It has a front mounted engine, manual gears and a chain and everything! That said however, I usually call it a scooter for simplicity.

 

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Slightly off topic BUT...

 

Do you feel with your bike/s that each model has a 'comfy speed'...that is a speed at which you feel comfy entering almost any corner and know that the bike will handle whatever you do on the other side, be it brake more or accelerate?

 

I find each of my bikes has a comfort zone at a different speed. FZR was about 80. Guzzi V50 was about 85. California is 58. Griso is 64. RXS100 was 65. Haotian is...50. In fact, in town I corner faster round town on that thing than I do on any litrebike.

 

Just wondered if you had the same experience.