Swapping forks and handling

[JasonF]

I love everything about my Vamoots except the poor tire clearance. Although advertised as good for 28's, I can't get any 28 to fit using Moots' standard road fork. Even after going through the previously-discussed solutions like extra caliper spacers, using Ultegra brakes, etc, etc…

Attached is an example: narrowish Neutron rim, Spec Roubaix 28mm tire. The culprit is the fact that the caliper bolt drilling is pegged at the lowest part of the fork so even an Ultegra 6800 caliper doesn't provide more than 2mm of clearance.

So I'm considering a Seven 5E fork. I have experience with the 5E from an Axiom I used to own and know it will fit any 28 with ease, and maybe a true 30 and/or narrow 32. It's a good fork but expensive.

My question involves rake and axle-to-crown changes:

1. The Moots fork has a 50mm rake. The Seven is either a 48mm or 51mm. Using a 27mm Open Pave tire, that means my trail on the Moots fork is 59mm. Going with the 48mm 5E results in a trail of 61mm and the 51mm 5E results in a trail of 57mm. Will going with either fork dramatically change the handling of the Vamoots, which I consider the best handling bike I have ever owned? Is it safe to assume that the 61mm trail bike will be slightly more stable and the 57mm trail a touch quicker?

2. The Moots' fork has an axle-to-crown of 370mm. The Seven A2C is 375. Will the difference be that noticeable? The front end will be higher using the Seven fork and will change the head angle, but will it be a huge difference?

Thanks in advance, since the Seven fork is expensive ($550) I want to know what I'm getting into geometry-wise.

[drewellison]

I recently went through a fork change on one of my bikes. I dropped the front end about 8mm, steepened the angles a bit, and it changed my position and handling on the bike enough that I could tell the difference - not drastic but noticeable and better IMHO.

I did a lot of internet research on fork lengths and, very generally speaking, American made/branded forks are longer and Italian lengths are shorter. My bike is Italian steel and came to me with an American CF fork. By changing the fork, I think I brought it closer back to how the geometry was intended.

Here's a great reference on fork lengths and how much changing the axle-crown length will change the angles.

http://www.sheldonbrown.com/rinard/forklengths.htm

[tv_vt]

Are you talking about the standard Seven 5e fork, or the commuter version?
You could get the commuter version with tons of clearance - just need to make a calculation on which rake would work best, allowing for the taller axle-to-crown length compared to your Moots fork. Bet Seven could help you with that.

Those forks come in multiple rakes - you can replicate your current handling characteristics by adjusting the rake to compensate for the change in a-c length.

The new Seven fork will change your head tube angle, probably making it shallower (since it will probably be a taller fork, raising the front end of bike slightly). Once you figure out what the new HT angle is (using the link to Sheldon B above), then plug in the new vs old HT angle on this website ( http://www.yojimg.net/bike/web_tools/trailcalc.php ) to figure out what change in fork rake gives you the closest trail to what you have on your bike now.

PS. if you go with the standard 5e fork, I'd choose the 48 rake over the 51, based on your #1 comments. 59 to 61mm change in trail should be fine.

PPS. I have the Seven 5e commuter fork on my Hampsten SB and think it is fantastic. Really a great fork.

[tigoat]

It will change the head tube angle by about 0.33 degree with this taller fork swap. Geometry wise as a whole, you might notice a slight difference at first but after a while you will get used to it. I don't see anything wrong with this new front end geometry in terms of handling.

However, most people don't realize that when you swap forks, especially if they are different in geometry and stiffness, it might affect the front end respond even though it has little to do with the geometry change of the bike as a whole. Hope this explanation make some sense.

[JasonF]

Excellent, thanks so much for the tips - it is the standard (short reach) 5E fork and I'll have to crunch some numbers to make sure the handling doesn't stray too far.

[Peter P.]

1. The Moots fork has a 50mm rake. The Seven is either a 48mm or 51mm. Using a 27mm Open Pave tire, that means my trail on the Moots fork is 59mm. Going with the 48mm 5E results in a trail of 61mm and the 51mm 5E results in a trail of 57mm. Will going with either fork dramatically change the handling of the Vamoots, which I consider the best handling bike I have ever owned? Is it safe to assume that the 61mm trail bike will be slightly more stable and the 57mm trail a touch quicker?

Yes; you've got the changes right regarding how they will feel. My experience has been, 5mm differences become obvious; the numbers you'll see; probably not.

2. The Moots' fork has an axle-to-crown of 370mm. The Seven A2C is 375. Will the difference be that noticeable? The front end will be higher using the Seven fork and will change the head angle, but will it be a huge difference?

Again, I've had experience with swapping forks. I think you WILL notice a difference. My solution would be to choose the 51mm rake version because I think the longer rake (1mm!) may mitigate the wheel flop you may notice with a taller fork. At least that's what I noticed with my bike.

I would suggest you buy and install the Seven fork, but leave the steerer full-length regardless of how much needs to be cut. Buy as many spacers as needed to take up the slack but install the stem at the normal height. Ride the bike as is to ensure it's what you want. Then, at the absolute worst, you have a failed experiment with a fork you could easily resell. If you decide to keep it, THEN you cut it and make a necklace with all the extra spacers!