Engine Braking - Guy Martin

Talk about all things motorcycling and non-motorcycling, not directly related to racing. No Politics.
Post Reply
mehow
Posts: 3
Joined: Mon May 06, 2013 1:46 am

Engine Braking - Guy Martin

Post by mehow »

I hope it's okay to post the following link:

https://youtu.be/sjZXaUwYoog

At 1:20 Guy Martin starts talking about a box full of neutrals and how you need engine braking to make the bike turn in.

Can someone please explain why the same thing couldn't be accomplished with the rear brake?

Thanks!

kenup283
Posts: 1334
Joined: Thu Jun 27, 2013 4:40 am

Re: Engine Braking - Guy Martin

Post by kenup283 »

Bikes need power to hold their lean angle and complete the turn. If have only brakes to slow then to keep from falling over into the turn the bakance of forces mandates lean angle to be reduced as go around the corner. This causes you to run wide. With the engine is engaged then the speed needed to keep the lean angle and hold the radius of line the bike is on allows it to complete the turn. While not a technically corect analogy if you have any expirence with JetSkis they need power to turn, turning the handlebars does nothing if power is not applied. In a similar way turning the bars on a bike does nothing to turn the bike, only lean angle can do that and power from the engine is needed to hold a steady lean angle.

User avatar
Tourn46
Posts: 3403
Joined: Sun May 15, 2011 5:09 pm
Location: UK

Re: Engine Braking - Guy Martin

Post by Tourn46 »

mehow wrote:I hope it's okay to post the following link:

https://youtu.be/sjZXaUwYoog

At 1:20 Guy Martin starts talking about a box full of neutrals and how you need engine braking to make the bike turn in.

Can someone please explain why the same thing couldn't be accomplished with the rear brake?

Thanks!
I don't know if you ride or not (but even in a car it will be demonstrated), drive along in gear and release the throttle, you'll slow down because the revs will drop and the wheel being driven by the engine will slow down, drive along and go into neutral and release the throttle, you'll just freewheel and not really slow down as there isn't really a connection to the engine, so although the engine revs drop, this isn't transferred to the wheel.

Another important factor is that you have to also acknowledge that Guy wasn't expecting it to happen, by the time he realised there was no engine braking, tried to fix it, he'd have been half way around the corner too - especially at the speeds these guys do! I've hit a neutral before going into a corner and it's horrible... I'm glad nobody was coming in the other direction!

User avatar
bobkarol
Posts: 10
Joined: Thu Jul 05, 2018 5:19 am
Location: Navarro, California, USA
Contact:

Re: Engine Braking - Guy Martin

Post by bobkarol »

I agree with Tourn46. If you miss shifting a gear while slowing in a turn, it takes a couple of seconds to realize it and recover. The bike runs wider than your intended line, because the engine isn't contributing any drag to help tighten your line. The more you slow while following a constant radius line the faster the bike will lift. The reason for using engine braking is to smoothly control the drag on the rear wheel and to be in the correct gear when you are ready to accelerate. You can follow the same corner-tightening line by trail-braking alone. You learn this in down-hill coasting races on a mountain road with the gearbox in neutral. This teaches you the reflexive technique for holding your line, if you hit neutral in a corner.
Last edited by bobkarol on Fri Jul 06, 2018 4:54 pm, edited 1 time in total.

User avatar
bobkarol
Posts: 10
Joined: Thu Jul 05, 2018 5:19 am
Location: Navarro, California, USA
Contact:

Re: Engine Braking - Guy Martin

Post by bobkarol »

"..turning the bars on a bike does nothing to turn the bike, only lean angle can do that," overlooks the process of turning the bars to turn the front wheel. The front wheel is turned to offset the bike's Cg and cause it to lean into the corner. Because the bike is an unstable platform, the purpose for leaning while cornering is to use gravity to counterbalance centrifugal force pulling the Cg outward. While cornering, the front wheel is turned in the direction you want to go, just like any other vehicle. Also, "...and power from the engine is needed to hold a steady lean angle," disregards the fact that you can coast a bike in neutral and by steering maintain a steady lean angle. As the bike gradually slows at the lean angle you maintain, your line will tighten.
Last edited by bobkarol on Fri Jul 06, 2018 5:27 pm, edited 2 times in total.

User avatar
bobkarol
Posts: 10
Joined: Thu Jul 05, 2018 5:19 am
Location: Navarro, California, USA
Contact:

Re: Engine Braking - Guy Martin

Post by bobkarol »

A final note: Coordinating either the power or the braking force you apply with the lean angle you choose defines the future radius of your line. How you do that depends on the configuration of the corner and where ahead you want to place your bike.

Post Reply