TiHabanero

This experiment with reviving an 81 Raleigh road frame has brought up a question. The frame angles on the bike are 74/74. The bike I moved the parts from (bike B) is 73 st/71 ht.
The fork on the Raleigh is 531. I don't know the offset.
The fork on the bike B is a Miyata cromo from an 85 912 with 45mm offset.

The ride quality between the two frames is significantly noticeable. The Raleigh has a harsher ride, especially on poor road surfaces. When I designed bike B it was purposeful as I wanted straight line stability (country roads don't have many sharp 90 degree turns). One added benefit with this has been a Cadillac like ride quality.
The question I have is three fold. 1) Does the head angle really make that much of a difference? 2) Does trail affect ride quality in terms of harshness? 3) Does head angle have an affect on harshness because it lays the fork out flatter which in turns provides more "suspension" or movement of the blades on rough surfaces?

guy153

It makes sense that this would be true. If you have a 71 HT then the fork is being bent more as opposed to being pushed on like a pillar or column. Curved blades probably also make a difference for this reason-- more bending and less pushing. The difference in stiffness between bending and column loading for a fork is practically infinite.

unterhausen

I always thought getting much suspension at all from a rigid fork was a pretty scary idea. Those steep head tube angle bikes we all wanted back then also seem like a bad idea.
I imagine bike b has considerably more trail. I don't think high trail is going to be more comfortable from a suspension point of view, but it might feel more solid. That could lead to it feeling more comfortable. Unless you stand out of the saddle.

8aaron8

I would add that, in my experience, the steeper seat tube angle plays a large role in comfort as it is pushing the riders weight over the front of the bike potentially increasing the stress on the torso and arms to keep you upright assuming your aren't trying to counteract that with a generous setback post. When your upper body is more engaged on a bike it often leads to more fatigue which can feel like harshness in the ride quality.

unterhausen

That's an interesting point about STA, and a lot of people don't have their fit dialed in to the point they know they have done that to themselves. I have wondered about the trend on mtb's to steepen the STA. Although I suppose the more upright position on an mtb would make it less important.

guy153

I think they may be ensteepening the STs on MTBs because they're so long at the front and often short CS. The steep ST puts the rider a bit more back in the middle.

unterhausen

As I understand it, the great ensteepening is because it makes it easier to climb steep hills. That's what my lbs advises anyway.

duanedr 

I believe the STA is steeper to allow shortening the rear end which helps in climbing. Shallower HTA and more rake would provide more compliance and stability. PVD used a 'trailing axle' design on a recent fork for exactly this purpose, he specifically said it puts the legs at more of angle and provides more compliance. Curved blades are longer so all else being equal they would have to flex more.

guy153

I'm not a huge fan of the really short CS on many MTBs now. I actually fell over backwards on one as I was trying out trying to get out of a bombhole.

I think it's supposed to make the handling more nimble or something. I don't see how it helps with climbing because putting it further back reduces the involuntary wheelies that are usually the limiting factor.

The MTB frame I made was a slack 29er but also with long CS. Can be hard to fit it on your car roof but it will go over anything like a monster truck.
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unterhausen

You don't need to steepen the STA to shorten the stays though, you can curve the seat tube. Although my elmariachi has the seat tube bent in such a way that it doesn't really improve clearance. And it moves the seat way back.

I am not the kind of mtb rider that is really pushing my bike going around corners, I'm too tentative. But I have to say I don't believe short chain stays offer that much just from the minor changes that are available. Although the turning radius of a unicycle is amazing, and maybe that's the desired effect. But they have all moved their front wheel way out front, so that must have more of an effect slowing turning.

Some company just showed a gravel bike with a yoke and dropped chainstays that had over an inch of clearance between the tire and seat tube. So why not just go with a normal chainstay? I guess it's the fashion.

TiHabanero

About chain stay length, it has been my recent experience with the 2 cm extra length on my home made bike does not affect climbing at all. 43.5cm vs. 41.5cm.
In no way am I a strong climber, never have been. I spin up climbs much better than muscle up them. Almost always seated on climbs. On the mountain bike I am the same way and have never noticed any difference in stay length on different bikes when climbing.

duanedr 

Right, there is probably a point of 'too short' which is possible with bent seat tube, dropped stays and especially with carbon but as you said...
As with most of this, it's down to differentiating a very mature product and making something that you can sell.

Fredo76

I built my tall frame years ago with 75/75 angles. In my old age, I think I would go with 73/75, keeping the 75 seat tube angle because the frame is so tall, but relaxing the head tube angle to gain stability and lessen twitchiness.

ThermionicScott 

That's thought-provoking... I've read that the rear triangle of a steel bike is pretty rigid no matter what you do with it. (That was the point of using a triangle in the first place, right? )

Anecdotally, it seems that when I've felt the most beat-up on long rides, it was also the case that I hadn't been taking in enough calories. Perhaps some of what I've attributed to too stiff a frame or too narrow of tires is just my "suspension" being out of gas, and that's why the more experienced riders I've been with didn't have the same issues, at least to the same degree...

unterhausen

Wolftooth just announced a headset that will allow +/- 2 degrees change in HTA. Which is a little more than the angleset. Should be interesting to try out.

xroadcharlie

I had no idea how head tube angle and trail could change how a bike handles until I switched bikes with a friend last night. It may also account for some difference in ride quality.

I was riding my Giant Sedona comfort bike and my friend has a Specialized low entry cruiser style bike. The steering on my Sedona, Which I believe is based on a mountain bike frame is so much more sensitive my friend almost had trouble keeping it straight. And I noticed immediately how more relaxed the handling of the cruiser bike was. I'm guessing these two bikes are at the extreme ends of spectrum for handling. I'm good with both bikes, but was shocked at the effect different fork geometry can have.

I do find my Sedona less then reassuring on the rare occasion i approach about 35 kph. It feels unstable. I don't know the numbers on these bikes fork geometry, but I can see clearly the Specialized fork extends farther then on my Sedona.

bty, I really enjoyed the Specialized low entry cruiser. I might consider one next time. It makes getting on and off the bike SO much easier, especially with a trunk bag or panniers.

Cynikal 

Cool idea, too bad it's only for tapered steer tubes.

unterhausen

You're just going to have to make a test frame with a tapered head tube. What angle head tube would you choose? I think 72 degrees might be interesting.

Road Fan

Well, it's really been decades since bike designers have known that trail affects handling, and that seat tube angle affects ride. I think the main reason a shallower STA improves ride is because it better places the rider's CG with respect to the BB. If your butt is farther back from the BB plumb line you have less weight on your hands. When you see or know a bump is coming you can lift your whole body up without pulling the bars, and hence your hands are not directly exposed to the jounce (sorry, automotive term) of the front wheel. In any case the jerk on your hands is smaller than with more weight on your hands. The push up at your butt as the rear wheel hits the bump can be reduced by long chain stays (just based on leverage), but I think the biggest insulation from rear end shock is lifting your butt and your hands (temporarily) out of contact with the bike. So long chain stays, a very laid-back seat tube or very high setback seat post, and a fork/head that allows a lot of elastic bending moment between the front wheel and the fork crown should together result in an improvement in comfort compared to the "crit geometry." Now how do you do all this without compromising lateral handling integrity and tracking accuracy? I can't afford to get an in-depth look at say, some Weigles, some Singers, and some BG Herses.

But I bought a Trek 720 to test this rear end stuff (47 cm chainstays) and trail around 55 mm. We'll see how I like it!

At least with my bikes this is how it feels, and I like it. OTOH, my Masi and Mondonico (actually two of those) are both rather comfortable and have STAs around 74 - 75 degrees, but very light, flexy main tubes. One of the Mondos has ELOS and the other has "pretty light" standard diameter, but it was not claimed to be SL when it was new. All three of those bikes have trail around 60 mm.

guy153

I think STA has a lot to do with riding position. If you want a more upright position then slacker ST is better-- you're basically rotating everything backwards. Upright position also goes with more weight on your butt, squishier wider seat, and therefore you want your legs coming out forwards a bit more, which the slacker STA gives you.

Old-school "roadsters" often had a STA of around 70 degrees which is what I used on my extreme rad-yet-trad opafiets-style build.