Fork Length

Sheppy

I realise this has been touched on in similar threads but having looked at the effect of putting on a longer fork I was wondering whether there was more to it than angles.

i.e. I have a Trance 3 with the standard Tora 100mm fork. The head angle is 70.5. If I were to put say a 130mm Revelation on it instead, I would lengthen the fork overall by 30mm. This would decrease the head angle to 69 degrees. It would also lengthen the wheel base by a mere 10mm. It would be the equivalent on riding up a 1.5 degree angle instead of on the dead flat.

Two things,
1. Clearly I have too much time to work all these angles out
2. These changes seem very insignificant to me (assuming they are right!), are there other reasons for not doing it?

Can anyone offer me any more insight into this?

nicklouse

not like riding up a hill.

and as you have a fully thing change.

also have you taken all the sag(s) into consideration. Also how do the makers measure the head angle?

Sheppy

not like riding up a hill.

Hmm, that is true, you have also increased the wheelbase by 10mm, I take that back.

also have you taken all the sag(s) into consideration. Also how do the makers measure the head angle?

No, I haven't taken sag into account as the manufacturers don't when they quote the angle in the specs. The angle is measured between the fork and the horizontal, the Giant website shows it well.

Maybe I'm just being a bit nerdy and too tied up in numbers here... :oops:

Anonymous

a fork that has 30mm more travel isn't neccesarilly 30mm longer from axle to steerer. it might be more, it could even be less.
My old 150mm travel junior T (2001 model) is exactly the same length, axle to steerer, as a new 160mm Marzocchi 55.

Marzocchi 66s are much longer than equivalent travel forks from other manufacturers.

You'd have to get the length of the fork measured, to calculate head angles.

nicklouse

Sheppy wrote:

No, I haven't taken sag into account as the manufacturers don't when they quote the angle in the specs. The angle is measured between the fork and the horizontal, the Giant website shows it well.

Maybe I'm just being a bit nerdy and too tied up in numbers here... :oops:

not quite true,

many manufactures use many different ways, some use a fixed length fork/shock for the angles others use fully extended and others use a % sag...

as a general rule of thumb changing the axle to crown race length by 1 inch changes the head angle by 1 degree. this is on a bike of average wheel base and does not consider any change in the rear.

Sheppy

a fork that has 30mm more travel isn't neccesarilly 30mm longer from axle to steerer. it might be more, it could even be less.
My old 150mm travel junior T (2001 model) is exactly the same length, axle to steerer, as a new 160mm Marzocchi 55.

Marzocchi 66s are much longer than equivalent travel forks from other manufacturers.

You'd have to get the length of the fork measured, to calculate head angles.

I took the fork length measurements from the Rockshox spec sheet. Mainly because I was expecting it to be variable but apparently it is just 30mm.
Couldn't find any from Fox

as a general rule of thumb changing the axle to crown race length by 1 inch changes the head angle by 1 degree. this is on a bike of average wheel base and does not consider any change in the rear.

That would pretty much tie up with my calculations...
I just assumed sag would not be included because otherwise it would be extremely tough to measure on a full susser.

Thanks for the info guys, I'm very interested in hearing more views/info on it.
I guess what I'm really interested in is if it will feel much different if anyone has done something similar before?

supersonic

Does giant warranty a 130mm fork with this frame?

grantway

Sheppy what is it you are trying to do? Is it you would like to have more travel
but Dont want to upset the balance of the bike?

If so buy a fork that has adjustable travel say 100-120-140.

For a start you have the 100 which keeps your bike balanced with you
rear shock, then you have 120-140 to enjoy the downs.

But I would be worried as Supersonic says, do Giant warranty a longer fork
has the bike spec warranty is a 100mm travel fork.

Does Giant have a technical back up over here to call and ask or
what does your LBS say?

Sheppy

Sheppy what is it you are trying to do? Is it you would like to have more travel
but Dont want to upset the balance of the bike?

Yes that's exactly it. I was thinking I would get the U-turn version of the revelation but then I had the thought that perhaps I would only ever use it in the max travel setting so why not get a fixed length 120 (Fox F120 ). The changes in angles and lengths are so small I wanted someone to convince me I needed an adjustable... I notice that the extended fork would put it to the same angle as something like a Stumpjumper FSR. Also there are quite a few bikes with adjustable forks as standard which would cover the same range as travel as I am proposing except they have more rear travel.

I just like to try different things. I'm quite a coward when it comes to drops etc so I'm not particularly concerned about the warranty anyway