You would end up with 2mm less rake than your current setup. (sorry i could not resist)

I just switched from 40 to 45 and could not really notice a difference.

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jg

http://www.phred.org/~josh/bike/trail.html

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Wilfried Heinle

Artificial Intelligence can never beat natural stupidity.

WHeinle's article explains it nicely. To explain it simply, going from 45 rake to 43 rake makes your bike slightly less quick-handling...but, you may not notice the difference.

I went from a 43 to a 40 after getting John Cobb's OK...bike handles fine (Kestrel Talon), as long as I don't get too far forward on it...it might be slightly more stable (has more trail) with a 40, but, the weight balance isn't as good in a forward position with the shorter wheelbase the 40 provides....again, theoretically. I don't know if I could tell a difference, because I never rode a 43 rake fork on this bike.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Thanks for all the replies. I'm not sure I completely get the theory, but if anything I'd rather my bike be a little more stable vs. quick handling when on the aerobars.

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jhc, the bike's trail will be "more stable" or "slower-reacting" going to the 43 from the 45, however, if you are worsening a weight-balance problem (of having too much weight on your front wheel due to a short BB-front axle distance) by shortening your wheelbase, the bike may not handle better.

Hope it's making sense....the first time I read about rake and trail, it seemed a little non-intuitive...once you understand the effect of head-tube angle in the mix, it makes sense. Good luck with it!

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

Will 2mm make a noticable difference in that respect? (seriously, I have no idea....thanks)

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jhc wrote, in regards to handling: Will 2mm make a noticable difference....



I doubt it. Only you will know, and only if you try it. If you currentlh have any handling problems on your bike due to too much weight on the front wheel, this would be the wrong way to try and correct the weight imbalance. But, if you don't have a weight distribution problem, a 2 mm shorter wheelbase probably won't result in enough of a weight shift to cause an imbalance that affects handling noticeably. IOW: sure, if you're getting a better performing, lighter fork that is a 43 instead of your stock 45, it will probably be fine. Hope this isn't too vague!

I had the opportunity to replace the stock Kestrel 43 with an all-carbon Litespeed 40 and did so. Very good trade, I think, but, I can't ride this bike steeper than 76 degrees without having a bit of a handling issue creep up. I use it as a road bike anyway, so, no problem. I'm a good bit heavier up top than most triathletes, therefore my weight distribution may not be the same as the majority, and this bike might handle fine for someone else at steeper angles than 76.

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Quid quid latine dictum sit altum videtur
(That which is said in Latin sounds profound)

It just depends on the geometry of the bike. Old-school builders would shriek in horror, but head tube geometries have gotten a bit "dumber", allowing for a little bit more liberal interpretation of what fork rake one needs. However, you do need to exercise caution, as there are a few bikes much less forgiving when it comes to the fork rake. Some crown heights are a lot higher/lower, so it can mess with the effective geometry of the front end (depending on which fork the frame was designed for).

And one big reason why there are "dumber" head angles: carbon forks don't always come from the mould in the rake or stack height they claim. I will not divulge my source of info, but there are a few forks that are off by as much as 3mm, whether it be by crown height or whatever.

You should read Slowman's writeup on this - it in the technical section of the web page, under geometry.

The addition of weight over the front of the bike changes the dynamic a bit - on my tri bike, I went from a 40mm to a 43mm fork, and the handling improved.