Gearing change and wheelbase on a Single Speed…..

[sevenfourate]

Single Speed BMX with micro gearing: 30t front sprocket and 11t rear driver.

I want to lower the gearing / give it a bit more zip / reduce top speed.

If I remove 2 teeth on the the front sprocket OR add a 13t rear driver - along with a chain 2 links longer………will this mean in theory the rear wheel will still be in exactly the same place in the rear dropouts ?

 

[silva]

Adding teeth to front sprocket = increasing gear
Adding teeth to rear = decreasing gear
So in your case, leave the front sprocket, and 11t > 13t ?
Also, a tooth more or less differs between front and rear sprocket.
For ex, a case 3/1, rear + 2 teeth = front - 6 teeth.

 

[sevenfourate]

Adding teeth to front sprocket = increasing gear
Adding teeth to rear = decreasing gear
So in your case, leave the front sprocket, and 11t > 13t ?
Also, a tooth more or less differs between front and rear sprocket.
For ex, a case 3/1, rear + 2 teeth = front - 6 teeth.

Right. Got it…..thank you 🙏

I’d also forgotten about front / rear ratio when changing 🤦‍♂️ I’d like to make a fairly big change…..so as suggested adding 2 to the rear might be the best way to go.

So hypothetically: I’ve added 2 teeth to the rear. And fitted a chain 2 links longer:

Does that mean essentially the rear wheel will be in the same place in the dropouts / wheelbase won’t change ?

 

[Sharky]

I'm guessing that your rear dropouts are horizontal allowing the wheel to be moved fore/aft to take up any slack in the chain. You only need to add links if unable to move the wheel forward enough.

On my single speed road bike, I can cope with sprockets from 13 to 18, just by moving the wheel fore/aft and keeping the same chain length.

 

[sevenfourate]

I'm guessing that your rear dropouts are horizontal allowing the wheel to be moved fore/aft to take up any slack in the chain. You only need to add links if unable to move the wheel forward enough.

On my single speed road bike, I can cope with sprockets from 13 to 18, just by moving the wheel fore/aft and keeping the same chain length.

Thanks 🙏

I want to lower the gearing and keep exactly the same wheelbase / position of rear wheel in rear dropouts.

By definition of my requirements: I’ll have lost any adjustability via the dropouts. So all I have left to play with is gearing and chain length.

In my small brain - 2 teeth (On either front or rear) takes up 2 links of the chain. So if I add or remove 2 teeth [Rear and front respectively] and adjust the chain accordingly - nothing else ie: rear wheel position will need altering ?

 

[iandg]

You can still get 1/2 links if that helps

https://www.condorcycles.com/products/condor-1-2-x-1-8-inch-half-chain-link

 

[sevenfourate]

You can still get 1/2 links if that helps

https://www.condorcycles.com/products/condor-1-2-x-1-8-inch-half-chain-link

Cheers ! And complete 1/2 link chains of course:

https://www.customriders.com/bmx-pa...e=1&gbraid=0AAAAAD_iTgcqQtKuotYzmHkO7KpRaaLaj

…..Which is more often than not the ‘norm’ on these modern BMX’s with super short slots in the drop outs.

About to head to my LBS. I’ll inflict my question to them to get their thoughts. Maybe new gearing and a complete 1/2 link chain ? Would be as good of a chance as anything I can see or think of……

 

[silva]

Now 30t/11t=2.7
Wishes: lower gear equivalent to 2t rear, AND, same dropouts sleeves begin and end.
Requires gear change as much as can (teeth = stepwise not continuous) divided over front and rear sprocket. That is, sprocket diameters equally change, in opposite direction.
https://www.nitrochain.com/sprocket-diameters
1 tooth more/less = sprocket radius +/- 2 mm
So that the distance changes compensate eachother and thus do not alter the start/new chain position of the rear wheel.
So, 29t/12t=2.4, 28t/13t=2.1, 27t/14t=1.9

In a past I saw industrial specs half link chains designated as half strength of normal outer/inner link chains. It is possible that to compensate this, half link chain plates are made twice as thick, and thus heavier and maybe also the price tag.