gearbasher

Without getting into the long reason why I'm asking this. But, for the same model steel frames, was a smaller rake used on the larger (i.e. 60cm +) frames than the smaller ones?

gugie 

This is my understanding. The more important parameter for handling is trail, which is typically a calculated number dependent mostly on head tube angle and fork offset (rake). Play around with some numbers in the link and see how it affects trail.

Smaller frames often have shorter top tubes. That brings the front wheel closer to toe overlap, so often the designer will decrease the head tube angle, pushing the wheel forward, which increases trail. To compensate you'll increase the rake to have the same trail as a larger frame.

I'm sure others will respond with their take, would be interested to see how some of the framebuilders on this respond.

Kontact

Gugie has it. The super weird fact of bike handling is that head tube angle affects handling much less than trail. So if you can make a bike with a 72.5 degree HTA have the same trail as a large bike with a 74 degree HTA, they will more act similarly on the road. And to maintain the same trail, the rake needs to shrink as the HTA gets steeper (74) and it needs to get larger as the HTA gets shallower (72).

In the old days of metal forks this was a normal part of geometry. Molded carbon forks have made having multiple rakes across a model size range too costly. Now you might see two rakes.

repechage

Reminds me the commentary of Brian Baylis long ago complaining of the handling of small frames he rode, “wheel barrow” he called them.

decades ago one could blame the UCI as there was a scantling that was designed to effectively prevent toeclip overlap as it was commonly called back then.
the rules have changed since.

the UCI did not like short people.

big frames… it gets complicated a different way, balancing handling and weight distribution.
A factor to note is that in a trail calculation, less rake can often increase trail, which is treacherous to note in isolation but can make the bike more “neutral” in handling.

Kontact

My '89 Cannondale had a very shallow HTA and a long rake. It handled very well. When was this?

gearbasher

Now that I have some time, I'll give the reason I'm asking. Years back I bought a 55cm, NOS, Guerciotti TSX frameset, It's probably early '90s. It came with a matching fork that was probably for a >60cm frame. When I contacted the shop about this, they said it was the fork they got with the frame and offered to send me a used, fully chromed, Guerciotti fork that would better fit the frame in exchange for the NOS one I got with the frame. I prefered the painted one, so I kept it and cut (many) more threads on the steerer so it would work with my frame, The bike handles fine. There is toe overlap, but I can live with that. The problem is: this frame beats the hell out of my shoulders, I own a 55cm Guerciotti PRX frame from the same era that has the same rake, but a shallower headtube angle (no toe overlap) and it's a lot easier on my upper body. So, should I hunt for a fork with more rake? Or, is it some other geometry features? Or, is it all in my head?

Insidious C. 

Here is an example as published by Specialized. The 83 Sequoia was offered in nine frame sizes. There were four combinations of HTA and fork rake as follows:

Seat Tube _________,,,,HTA ,,,Rake
470,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,73.5 ,,,51
510 ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,72 ,,,,,,51
540, 560 ,,,,,,,,,,,,,,,,,,,,,,,,72.5 ,,,47
580, 600, 625, 650, 685,,,73,,,,,,,45

edit: sorry it is messy and not very table-like

Kontact

Geometry doesn't account for this. Specifically, 4mm of fork rake or a 1 degree of HTA don't account for how the bike absorbs bumps. You could have the fork rake on your current bike reset by a frame builder (they will bend the fork arms more), and the only thing you will likely notice is that the bike might get easier to ride hands off. And you probably won't notice that.


Your problem likely comes down the composition of the frame or fork, the tire and/or pressure, the wheels or the shape and location of the bars/hoods. The bike is either transmitting more shock or you aren't fit to the bike well enough to weather it. Compare the fit of the two bikes. Try swapping wheels.

Rake isn't your problem.

gearbasher

Same bars, stem, saddle, brake levers, wheels and tires. Same saddle height and reach to the bars. The bar height on the bike in question is 1/2" higher than the more comfortable bike. I would think the higher bars would take pressure off my shoulders and not increase it. Maybe, I'll lower the bars and see. Also, the more comfortable one has a 3/8" longer wheel base. But, I don't think that would matter.

Kontact

Sitting up isn't always more comfortable. You might double check the bar width.

But the composition of the frame and/or fork might explain it as well. But stuff like this is usually fit.

Trakhak

Different wheelbases can make a surprisingly big difference in ride comfort. Longer-wheelbase bikes are often thought to provide more comfort than short-wheelbase bikes, other things being equal. It's not the wheelbase per se that makes the difference; it's the sum total of design choices that resulted in that wheelbase.

Classtime 

Compare saddle setback from BB. Back your bikes against a wall and measure horizontal distance from saddle to BB. I bet you ‘re more comfortable on the one with the bigger number. Go crazy and borrow your neighbor’s scale, put one under the front of your Kreiter Rollers and the other under the back while you get sweaty and comfortable at 90 rpm. Have your neighbor record the weight front and rear. Do that for both bikes.

gearbasher

I have no rollers. As far as setback and all other measurements, I took the bike I was most comfortable on and matched all my four other bikes to it. Setback was set before reach when I did it. So, the reach on all my bikes is slightly different. About a 5mm difference between the shortest reach and the longest reach. The uncomfortable one is the only one with higher bars. I'll try lowering them and see what happens.