701 rallybike – gearing.

“You know what really grinds my gears? – Gearing does!” :

Said Peter Griffin – never.

It is what makes the bike move though. Gearing is one of the cheapest ways to make the bike perform a lot better. Best bang for Buck so to speak.

The possibilty is there for most of motorcycles, that have chain drive. Due to the EU regulations they are mostly geared extremely long/tall. This creates a motorcycle that has low rpm during a testride in some particular speed and gear they need, just to comply the regulations. As an example can be talked about some enduro bikes or also the 950-990 bikes. They were designed by the engineers to be run with 16/45 gearing. This did however not fulfill the requirements of the treehuggers and so the bike comes from factory delivered with 17/42 gearing. That is way too tall for any offroad application or performance usage. It is good practice to change at least the front sprocket ASAP. Well, it is cost effective.

With this type of gearing systems we have limitations. We want the bike to have plenty of top speed and low gearing for the first 2 gears to be able to crawl in offroad conditions. On a lot of enduro bikes the gearbox is a narrow band box. On some versions it is differently geared and on some, it is wide band.

For the 701 – it is actually quite narrow geared. So if one chooses to shorten the gearing, it will also rob You from top end speed. But how much ? well – there is plenty of help for that. Try https://www.gearingcommander.com/  . Point is to find a good compromise between top speed and low down torque and the size of sprockets/chain.

We went from the oem 16/46 to a 15/48, keeping the size change to minimum and bringing the speed down from 187 to a manageable 160km/h. We will gain torque. for a rallybike very important component. Torque is what helps to get You out of mud and sand, helps You go over logs and stones and helps to get the front end light for any high speed pothole avoidance.

Sprockets and chain go together as a system. When worn, should be replaced as such. We use what works and is also cost-effective. Special steel sprockets or OEM front(especially important for some bikes for fitment). And the strongest chain one can get for that particular size spec. Why so – well the gearing feel is only as good as the components doing the power transfer. In ideal conditions the chain drive is about 98% efficient. If parts are not up to the job, the power and feel will go down. The slack in chain and worn out links or worn out sprockets can cause up to 10mm of slack movement in the chain. This means (depending on the sizes) up to 10-15cm rear wheel movement, that is not controlled by You. This also happens during fast oscillations over rough terrain and causes suspension chatter/upset for the rider. The transition from off-gas to full power will feel like sluggish jolt and the bike looses traction also during small oscillations.

The drive is also something that will change the stability of a bike if adressed so. On the rear swingarm there is a longer positioning hole for the axle. This is there for many reasons and one of them can be to make the wheelbase longer – the effective length of the swing longer – and therefore to soften up the rear shock/spring effect. We like that on a rallybike. This will give comfort and high speed stability. Make room for a bigger tyre in the swingarm and will make it easyer to install/remove the wheel.

And the chain is golden. Thats just pretty. We like.

 

 

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