Leading Front Axle. What is the Difference?

[Guest]

I have a GS550L and am wondering what does the leading front axle do for ride quality/handling.

I just rode the bike Saturday for a 100 mile trip through the mountains (my back yard ). The bike handled GREAT and it was alot of fun. I'm just wondering what is the thoughts on leading axles or inline axles on the front forks.

Thanks!

[Zook]

Leading axles are more stable than a "regular" or trailing axle while in a straight line.
It give sthe wheel more of a caster effect by adding more rake.

[Steve]

On street bikes, it's more a matter of looks than function.

The L bikes were the biggest users of the leading forks, mostly because they could use longer forks that made them look like they were raked out there like the Harleys they were trying to copy.

Dirt bikes, on the other hand, have different needs. They want to get as much travel as possible, so they use longer fork tubes to get a longer stroke. Since that would really raise the front of the bike, they locate the axle part-way up the bottom tube to bring the overall bike height back down to a reasonable level.

Properly tuned with the correct springs and oil, I think you would be hard-pressed to tell the difference merely by riding.

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[Zook]

It really does affect stability. Even your car has a caster alignment setting. If it's not set correctly your car will wander twerribly.

With the leading axle the wheel will also tend to flop when turned.

[Nessism]

Motorcycle steering geometry is often misunderstood. The key characteristic in determining how a bike steers is the amount of Trail. More trail means more stability or slower steering.

Trail is a calculation determined by a) the Steering Head Angle, and b) Fork Offset. The Fork Offset is commonly set by the triple clamp and the inclined angle of the fork RELATIVE to the steering head angle.

A steeper Steering Head Angle reduces trail, thus increasing the speed of the steering. Contrary to common thinking, more Fork Offset REDUCES trail, thus increasing the speed of steering.

Leading axle forks have more Fork Offset than straight axle forks, thus they increase the speed of steering – or reduce stability to use a different descriptor.

The chassis engineer know this stuff so I’m sure Suzuki took this into account when they specified the steering head angle of the bikes. This discussion is only pertinent if one was looking to change their forks: if you took off your leading axle forks and installed a straight axle fork, the bike would steer more slowly.

Pretty interesting stuff.

[Mark M]

Leading axles are more stable than a "regular" or trailing axle while in a straight line.
It give sthe wheel more of a caster effect by adding more rake.

Zook, you've got that backwards. The leading axle reduces trail which is a less stable condition. It has nothing to do with the rake angle, which is set only by the steering head angle.

To the TS, it is a looks thing. The entire front end geometry must be designed to work together. This includes the triple clamp offset, the rake angle and the axle offset. The end goal is a set of rake and trail numbers that result in a stable, good handling bike. Whether the axle is offset (either forwards or back) or not does not matter, it is the end geometry that matters.

Edit: Nessism beat me to it!

Mark

[Steve]

Another detail to remember, it's not the angle of the fork tubes, it's the angle of the steering head, as Nessism mentioned.

The triple trees can alter the angle of the forks in relation to the steering head, so looks can be deceiving. If you draw a line straight through the steering head and project it to the ground, it will hit a spot just in front of the front tire contact patch. Draw a line straight down from the front axle. The distance from where that line hits the ground and where the line from the steering head hits the ground is your "trail" measurement. Higher numbers give more stability at the expense of increased steering effort. But using the diagram I have just put into words, you can see how simply moving the axle forward will shorten the trail and quicken the steering without changing anything else.

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[Colorado CJ]

So that's why it did so good in the twisties I though it would have been the other way around (slower steering) because of the "cruiser" moniker.

[RageZro]

A picture is worth a thousand words...



Less trail more high speed wobble, tank slapper.


Here's a good read if you really understand the trig of rake and trail, this experiment will mess with your head a bit though not to mention it will be the oddest looking BMW you will probably ever see... http://www.tonyfoale.com/Articles/RakeEx/RakeEx.htm

EDIT:
One thing that is overlooked is the fact that if you have changed the height of your rear shocks and/or tire diameter/aspect, then you have changed your rake, probably most will use shorter shocks which will increase your rake and slow you a bit in the curves.

[Steve]

Thanks, Rage, that's exactly what I was trying to describe.

That is definitely one strangely-crafted BMW, indeed. Nice to have the resources to play like that.

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[Zook]

You are right. I meant to say it added trail but gave the appearance of more rake, kicking that front wheel out there further.

[rphillips]

Suzuki must not like the idea, they used leading axels on the "80" & *81" GS 1100 "E", & took them away for "82" & "83" 1100 "E"'s. I've had both, & can't say I really noticed a difference.

[Nessism]

You are right. I meant to say it added trail but gave the appearance of more rake, kicking that front wheel out there further.

The leading axle fork reduces trail, not increases it.

[flyingace]

You are right. I meant to say it added trail but gave the appearance of more rake, kicking that front wheel out there further.

There is more rake in the L models. That's why they have leading axles - to reduce the added trail that increased rake would have created.

[Mark M]

That is definitely one strangely-crafted BMW, indeed. Nice to have the resources to play like that.

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Tony didn't play like that, it used to be his living. Now he has an honest day job, the slacker.

Mark