My last article on Fork Rake and Trail brought an email with the question:
“Why does bike designed for Motor Pace Racing have the fork raked backwards. Is it to increase trail?”
The Stayer bike as it is called, has a smaller front wheel, a steeper head angle, and reverse fork; all designed to get the rider closer to the motorcycle that is pacing him. There is a roller mounted behind the pace machine, set at a regulation distance. It is up to the rider to get as close to that roller as he can for maximum drafting effect.
If you look at the drawing on the left, you can visualize that a smaller wheel means less trail, a steeper head angle also means less trail, but the reverse fork increases trail to compensate. A stayer bike may have a little more trail than the average track bike, but not an excessive amount.
Another reason to have the fork reversed is that occasionally the rider will bump the roller on the back of the motorcycle. If he does the roller will spin and the fork will flex easier in the direction it is raked or bent, thus absorbing these slight bumps.
If you draw an imaginary line through the center of your bicycle’s steering tube (Steering Axis.) it will reach the ground at a point in front of where the wheel actually contacts the ground.
The difference between these two points is known as the trail. Trail assists steering; as you lean the bike to the left or right, the steering axis moves in that direction, and thereby turns the wheel in that direction as it pivots on the point of contact with the road.
Trail also assists the bike in holding a straight line. It works on the same principal as a castor wheel on a grocery cart, which goes in the direction it is pushed. (Or in theory it is supposed to.) This is why it is called “trail,” because the wheel trails along behind the steering axis.
Fork rake or offset is the distance between the steering axis and the wheel center. It doesn’t matter if the fork blade is curved forward in the traditional way, or if the fork blade is straight but angled forward from the crown. If the offset is the same the bike will handle the same.
You will see from the drawing above, if the head angle is made steeper then trail decreases because the steering axis moves closer to the wheel’s point of contact. Conversely, a shallow head angle will lengthen trail.
Less fork rake, increases trail, because the wheel center is moved back away from the steering axis. More fork rake means less trail because the wheel center is moved forward.
Bicycles built in the 1930s through the 1950s typically had as much as 3 ½ inches (9cm.) of fork rake resulting in very little trial, often zero. There was a theory at that time that trail made steering heavy and sluggish.
I remember writing an article for Cycling magazine in the 1970s; someone wrote to me saying my theories on trail were wrong, and sent me an early 1950s article from Cycling to prove it.
The old theory was that if you had the front wheel’s point of contact behind the steering axis, when the steering was turned 90 degrees the point of contact was then on the steering axis line. Therefore, the front end of the bike had dropped slightly, and to straighten up again, the steering had to lift the weight of the bike and rider; thus sluggish handling.
While this statement is true, in practice when riding, the front wheel never turns 90 degrees. In fact during normal cornering the front wheel turns very little, making this whole theory about the front of the bike going up and down irrelevant.
I started racing in the early 1950s and I can say from experience the bikes of that era did not handle and corner near as well as today’s designs. These bikes handled reasonably well because frames were built with much longer wheelbases, wheels and tires were heavier, and tires were fatter.
Road conditions at that time, especially in countries like Italy and France were often appalling. The long fork rake and the long wheelbase had a dampening affect on the rough road conditions.
[Typical European road conditions in the 1940s. Louison Bobet leads Gino Bartali (striped cap) and André Brulé in the 1948 Tour de France. Picture from The Wool Jersey.]
As road conditions improved, bikes were built with shorter wheelbases and at the same time tires became much narrower. It eventually became necessary to increase trail to keep the bike going straight.
There was a somewhat chicken and egg situation with regard to shortening wheelbases and adding trail. In my case I shortened the fork rake to shorten the wheelbase and found the resulting increase in trail was an improvement.
Other older established builders, still clinging to the little or no trail theory, shortened the fork rake but at the same time made the head angle steeper to maintain the trail status quo.
This made for some very squirrelly bikes being built in the 1970s, with 75 and 76 degree head angles and front wheels almost touching the down tube. Shorter chainstays to shorten the rear end of the bike were pretty much universally accepted.
A shorter wheelbase means the bike will turn on a tighter radius. Think of a school bus and a compact car, which one will turn tighter? The front wheel turns less on a short wheelbase bike on any given corner; this translates to having to lean less to get around a bend.
I think the big advantage I had was that I was still actively racing and could try out these changes, and experience the difference first hand. Eventually everyone agreed that trail was not a bad thing and head angles became sensible again.
Frames I built had around 2 ½ inches (6.3cm.) of trail. In the early 1970s I did experiment with more trail but found that the bike felt sluggish and had a tendency to wander when climbing or sprinting out of the saddle.
As with any design aspect, more is not necessarily better; for a road bike with a 73 degree head angle the optimum trail seems to be around 2 to 2 ½ inches (5 to 6.3cm.)
Addendum. Nov 15, 2008.
There seems to be some confusion over the term “Fork rake,” which I can understand. The dictionary definition for rake is “The angle of inclination from the vertical.” However, when referring to bicycles, rake and offset are different terms for the same thing. Both are the term for the distance the wheel center is set from the steering axis, regardless of the head angle.
This probably came about because early framebuilders were artisans, not scholars. To add to the confusion, a bicycle head angle is measured from the horizontal, not the vertical. Back in the day when all bicycles had perfectly level top tubes, it was the angle measured from above the top tube to an imaginary extension of the head tube.
Last week I was contacted for an interview with an online magazine from Hamburg, Germany.
Okay, so it’s not the New York Times, but it is the coolest looking eZine I have ever seen.
It is called BETA-SWAY “Urban Sport Guerilleros Monthly.” Its sports related content includes cycling.
Written in English, the photography is outstanding, as is the layout. Check what happens when you click and drag the bottom right corner of each page.
English was obviously a second language for the interviewer, Carlos Pinto, but I think because of this some of the questions were different from the usual stuff that is asked.
I certainly enjoyed responding. Check it out here. The interview is on page 24 of the May issue.
From time to time, I get emails asking for information on framebuilder Mike Melton. I always respond that I have no idea where Mike is now. However, here is the little I do know.
I met Mike in 1980 a year after I came to the US and I was working for Paris Sport. I was building some aero-bikes for the US National Team. Time was running short and Mike Fraysee of Paris Sport brought Mike Melton in to assist me.
Mike was an established and well-respected American framebuilder from Columbia, South Carolina. We worked together for a week and obviously got to know each other pretty well during that time.
Afterwards we went our separate ways and usually met up at least once a year at the various bicycle trade shows. Mike continued his connection with the US team when he later went to work for Huffy and built frames for the 1984 Olympics in Los Angeles.
In the years that followed he would design and build some carbon fiber frames for the US team and was somewhat of a pioneer, in building frames using that material.
Below is a picture of an earlier 1982 steel tube Aero frame that Mike Melton built for John Marino for his winning “Race Across America” ride.
I have not heard anything of Mike since the late 1980s and I would love to renew our contact. I recently received a request for info from Matthew Marion who sent me the photos of his red Melton frame you see here.
I believe Mike is a few years younger than I am so he may or may not be retired now.
If he wishes his whereabouts to remain unknown, I will of course respect that. However, he may not even know that his past work still has a following and their owners treasure the fine crafted frames he built.
Update 1/29/11: Mike Melton died on January 26th, 2011, after a long illness resuling from a rare neurological disease believed to be spinal cerebella ataxia, similar to ALS or Lou Gehrig’s disease.
Early last December I rode my bike to Folly Beach. A long narrow barrier island, close to Charleston, known to the locals as “The Edge of America.” It was a beautiful sunny day, temperature in the eighties, with a cooling breeze.
I stopped to take some pictures of my bike on the pier; they were never posted here (until now) because two days later I would be involved in an accident and my frame was wrecked.
Just five weeks ago I started riding again; I’ve been riding three days a week, 25 to 30 miles each day.
Yesterday was an almost identical day to the one when I last rode to Folly Beach. Temperature 81 degrees, with a light breeze; perfect riding weather.
That day last December I was flying, I really felt I was starting to find form. I decided to do the ride again to compare my fitness level with that before my accident.
I didn’t take the direct route because Folly Road is narrow and highly congested, especially on a warm, sunny day when everyone heads to the beach. Instead I headed south on Savannah Hwy. actually going away from Folly Beach.
Left on Main Road an over the Stono River bridge. Left again on Rivers to Maybank where another left took me over the Stono River for a second time. Then a right on Riverland Avenue; a pleasant road to ride on, shaded by old growth live oak trees.
A long way around but worth it because when Riverland finally merges with Folly Road, the road is much wider at this point and in a few miles there is a bike lane.
A turn around at Folly Beach without stopping and I headed back the exact same route. About fifty miles round trip done in three hours; 15 minutes slower than when I did the same ride last December.
It appears I have not quite reached my previous form, but I’m getting there.