fork rake

[steveO:K]

I have just replaced the front fork on my road bike.

 

The manufacturer recommends a fork rake of 43mm, the fork i bought has a rake of 40mm.

 

How adversely will this affect the handling if at all?

 

 

 

 

 

[Canaris]

probably improve handling.  make it less "twitchy"

[steveO:K]

Interesting! I thought that with a shorter wheelbase it might be more twitchy

 

thanks

 

[Johan Bornman]

I have just replaced the front fork on my road bike.

The manufacturer recommends a fork rake of 43mm' date=' the fork i bought has a rake of 40mm.

How adversely will this affect the handling if at all?




[/quote']

 

Forks don't have rake. Frames have rake and rake is the same as head tube angle. Rake is simply the inclination from the horizontal and is expressed in degrees. Typically, 70-something degrees but going smaller on downhill bikes, I'm told.

 

Rake has a direct affect on a fork's trail, as does one other variable I'll deal with in a moment. Trail is the distance between the imaginary point if you would put a straight-edge along the head tube (hugging the angle) where it meets the road and the plumb line from the hub down to the road. If you draw a little diagram you'll see that the head tube line lies ahead of the real contact patch epicentre.

 

If this distance is too small, the bike wants to zig-zag when you stand and pedal. That's the only noticeable effect within the angles of most road and mountain bikes. This phenomena is called lean steer. Not lean as in a skinny person but lean as in "Steer by itself when the bike is leaned).

 

In order to make that distance longer and the bike thus more stable when standing, the fork is given some offset. Offset can be done by way of a curve in the fork, or in the case of straight forks by fiddling with the fork's departure angle at the crown or as is the case with MTBs, by building the offset into the crown itself by putting the stanchions a tad ahead of the steerer tube.

 

Offset makes the bike more stable but note that rake does affect the offset.

 

Lots of people including fork manufacturers confuse rake with offset so you are not to be blamed for having been fooled.

 

Your new fork has a smaller offset which will make its trail 3mm shorter. Trail is typically 15 times more, so if you really pay attention, you'll feel a difference of 6.6% when standing out of the saddle. I can't give you a more accurate answer than that.

 

Let us know if you can feel 6.6%

 

 

PS: Note that a bicycle only has one fork and it's always in front.

 

 

Johan Bornman2009-01-16 08:26:03

[steveO:K]

Thanks JB, sorry about the incorrect terminology.

 

The response makes perfect sense.

 

I think i can handle 6.6%, just as long as i dont fall while trying to read the newspaper and ride simultameously.( i have seen somebody doing this)

 

[Johan Bornman]

Thanks JB' date=' sorry about the incorrect terminology.

The response makes perfect sense.

I think i can handle 6.6%, just as long as i dont fall while trying to read the newspaper and ride simultameously.( i have seen somebody doing this)
[/quote']

 

It's a pleasure. No need to apologise. There is no crime in asking.

[lowracer]

And to confuse the issue, rake, trail and offset means different things to motorcyclists and bicyclists. lowracer2009-01-16 09:02:05

[Johan Bornman]

And to confuse the issue' date=' rake, trail and offset means different things to motorcyclists and bicyclists. [/quote']

 

Absolutely not. Not unless they are as confused as half the bicycle guys.

 

Rake is a standard English word for "at an angle".

 

Offset is....err, offset and trail means "to lag behind" amongst other non-relavant things.

 

Not much scope for confusion here.

 

 

 

[Guest Agteros]

Is a rake not that thing to use for raking leaves off the grass?