Two questions on replacement fork

For discussions about bikes and equipment.
Post Reply
belgiangoth
Posts: 1657
Joined: 29 Mar 2007, 4:10pm

Two questions on replacement fork

Post by belgiangoth »

1 - For my Pompino, I would like a new set of forks in steel that are not as massively heavy as the ones the frame comes with, would even consider a custom job. What are the dimensions/rake, trail, stuff that I need to consider and measure for a replacement?

2 - For my Carlton Track bike - it's a threaded fork and I have some toe overlap, in a bid to get rid of this and maybe fit some mudguards I was looking to change forks so that I could have maybe a cm more space - is this looking to give the bike crazy handling? I expect the handling is pretty "sharp" as is being a track bike so making it a bit more "soft" should be ok? (As I am a rather soft rider myself). Again, what are the measurements I need to bear in mind?

thanks
If I had a baby elephant, I would put it on a recumbent trike so that it would become invisible.
Brucey
Posts: 44522
Joined: 4 Jan 2012, 6:25pm

Re: Two questions on replacement fork

Post by Brucey »

belgiangoth wrote:1 - For my Pompino, I would like a new set of forks in steel that are not as massively heavy as the ones the frame comes with, would even consider a custom job. What are the dimensions/rake, trail, stuff that I need to consider and measure for a replacement?


-dropout to crown race height, steerer diameter and length, tyre clearance, brake mountings, offset

2 - For my Carlton Track bike - it's a threaded fork and I have some toe overlap, in a bid to get rid of this and maybe fit some mudguards I was looking to change forks so that I could have maybe a cm more space - is this looking to give the bike crazy handling? I expect the handling is pretty "sharp" as is being a track bike so making it a bit more "soft" should be ok? (As I am a rather soft rider myself). Again, what are the measurements I need to bear in mind?


work out the trail that you have at the moment; if it is generous (and it might be on a track bike) you could get an otherwise similar fork with 1cm more offset and the bike will still steer OK. Not the same, but OK. Note that an increased crown height will also increase the trail slightly, for any given offset.

Handy trail table and interesting article here;

http://johnforester.com/Articles/BicycleEng/Kvale%20Geometry.pdf

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
User avatar
531colin
Posts: 16083
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Two questions on replacement fork

Post by 531colin »

However, its just as likely your track bike has "lively" handling......and if you add 10mm to the fork offset you will reduce the trail and make the handling even more lively....more likely to be upset by road surface imperfections, wind, and accidental rider input, eg looking over your shoulder.

....."rules of thumb"......
In round terms, one degree change in head angle has about the same effect as 10mm change in fork offset (for 700 wheels)
....one degree makes a noticeable change in handling, eg from "lively" to "relatively stable"
20mm change in fork length (axle to crown race seat) gives a one degree change in head angle.

So, if you want 10mm more toe clearance on the track bike, get a fork that's 20mm longer and has 10mm more offset, and the handling will be much the same as it is now. .....the reduction in trail given by the increased offset is about balanced out by the increase in trail from the longer fork.
Post Reply