Track Rake vs. Road Rake
 

My track bike handles best on a smooth track when it has the stock fork with a short 38mm rake. If I ride this same bike as a single speed on the road, it handles better with a 45mm road fork. This is assuming the same frame geometry, head tube angle, tires, etc.

A short rake increases trail and makes a bike track straighter hands-free, when ridden on an ideal smooth surface. Old time photos of track motor pacing show specially modified bikes with backwards forks (negative rake). I used to think this was to allow the bicycle to more closely follow the pacing vehicle, but it was most likely done to improve high speed tracking and stability.

Then why do road bikes have longer fork rakes and touring bikes have fork rakes that are longer still? My theory is that because of imperfections in the pavement, a longer rake (and thus shorter trail) makes the bike less "twitchy" because of decreased "bump steer". When the front tire hits a bump or crack in the road, the force is usually unevenly applied (more on one side of the tire than the other). This causes a slight deflection of the tire that changes steering (I am going to call this "bump steer", but that term may have different meanings in the motorcycle and auto industry). A bike with a long rake will have a shorter trail and thus a shorter lever arm in which a bump can change the steering. Thus a longer rake decreases the bump steer effect and a road bike will feel more stable and less twitchy than if this same bike had a short raked fork.

This would explain why my track bike handles best on the road when it has a 45mm road fork. It would explain the fork geometry trends of current and traditional track, road, and touring bikes. It would explain why a carbon fork feels better on the road as it absorbs some deflection energy and decreases bump steer, in addition to the vibration dampening effect. It would suggest that when we convert a track bike for road use (either fixed or SS), we should install a road fork if we want optimal handling.

Is my theory correct or is it a load of hogwash?

I had heard that the old photos of track riders posing with their bikes with reverse rake actually turned their forks around on purpose. Misinformation for their rivals, cloak and dagger stuff. It was not meant to ride with, but a strategic red-herring.

Our I could be (and probably are) wrong.

yeah, that sounds like some myth. the stayer bikes do have negative rake.

I'm guessing the lack of rake, and the tighter steering help more on a banked surface. To an extent.

Yes, I agree. Decreased rake would help a track bike maintain a steady line on the banking and decrease oversteer. Another possible reason for a track bike's short rake (and thus long trail) is so it will auto steer straighter (i.e. steer truer) when applying maximum effort when sprinting on a smooth surface, and thus minimize steering input from excess body motion.

stayer bikes often had negative rake so they could get as close to the motorcycle as possible and tuck into the air pocket for drafting to make the speed record attempt easier
drafting in the ideal part of an air pocket can increase your efficiency by up to 40% thus increasing speed

True, a reverse fork rake does allow the stayer to draft a few inches closer. I think it must also increase trail and make the stayer bike more stable at high speed (on a smooth surface).

Dave Moulton says stayer forks are mostly for drafting. The bikes do wind up with a bit more trail as well but not a huge amoount.

While we're on the subject... my bike is a conversion with a road fork and a long rake, pretty standard road geometry for 20 years ago and just inching into touring land. I love it on the road, but I've never raced it on the track. Someone told me a little while ago that if I put it on the track and went too fast through the banks, the centrifugal forces could actually bend the fork!

Is that possible? Is it likely?

cromepista - i think your thinking is not taking in to account the effect of headtube angle. a bike with a steeper headtube angle (your track bike, probably) is going to require less rake in order to achieve the same amount of trail as, say, a slacker road bike with a more raked fork.

you can have two bikes with the same amount of trail, and they'll differ in headtube angle and rake - this will also affect the handling.

Hogwash, road bikes have more rake but also shallower HT angles.

Your bump steer concept is completely backwards. More trail will result in less "bump steer."

But I am talking about how my one bike (a Pista) handles better on the road with a road fork (45mm rake) than it does with its stock shallow raked track fork. Both forks have the same tire clearance (i.e. the track fork legs are not shorter). The head tube angle is the same with either fork.