what is the relationship between frame geometry, speed and comfort?
 

Hello all

What is the relationship between frame geometry, speed, and comfort?

I am touring on a vintage mountain bike with an enormous wheel base. The chainstays are quite long, the distance between the front of the rear wheel and the seat tube is almost twice the width of my hand.

The bike is incredibly comfortable. Fits me like a glove. Perfect body posture, everything.

But, I'm slow. Way slower than I ought to be.

I noticed this in a sort of a controlled experiment, when i first got the bike. I would ride with a friend who wasn't in very good biking shape. She rode the same bike, a hybrid, every day. I would ride my mtb, a 1983 Diamond Back Ridge Runner, or a vintage Raleigh 12 speed road bike.

I without a doubt went faster on the Raleigh. WAY faster. With way less effort. And I've noticed this to be true in all sort of different scenarios, the feeling that I ought to be going faster when on the mtb, but not knowing exactly why.

My own, completely unfounded theory, is that the mtb is so comfortable because the frame is designed to absorb shock. And there must be something about the frame geometry, what with the wheel base and all, that makes it harder to engage the right muscles to go faster with less effort. (???)

But I'd love a better explanation!

Thanks!

We Get Older :50:. stop worrying about speed death will come soon enough.


Buy Expensive Tires.

Actually, age was one of the control variables in the experiment, as I didn't age more than a day or two between riding the road bike v. the mountain bike. So it really didn't account for anything there.

That's a dumb answer btw.

Push a Big Gear Then, HTFU. Fast is Work, work harder .. drop the excuses of your bike .

My rule of thumb. At the same effort level, cruising speed on a road bike with drop bars is 2 mph faster than on a mtb with slicks, which in turn is 2 mph faster than the same mtb with fat knobby tires.

The mtb that I was riding when I developed this (empirical) rule was a high end hardtail with light weight and tight geometry (for a mtb), pretty aggressive fit (bars narrow and 3" lower than saddle, bar ends). A mtb such as you described would likely be slower yet.

The reasons include, I think, aero resistance/body position and rolling resistance.

This is why I took to Mountain biking...

This n that is faster or slower,, bla bla bla,,,etc

After your first successful ride on a pump track or after you find the flow on a true single track, cars buzzing past your hips fast enough to turn your bones into cottage cheese just don't make sense to me no mo'

Some frames are much slower than others. The enlightened ones will argue all day about whether or not this is so and if so or not, why? It is, however, true. It's not really geometry. I've ridden slow and fast road frames with very similar geometry. Though geometry will have an effect, I don't think it overwhelms the other factors such as tubing size, material, joining, etc. Wheels and tires have large effects also.

All that said, very fast bikes can be very comfortable. It's not mutually exclusive at all.

Chill out turbo, he read your question differently than your intent.

It's not about excuses, but explanations. I am interested in the way the same amount of effort on different bikes brings about such different results.

Pretty much everyone I talk to online or off agrees that mtbs are like pulling anchors relative to road or touring bikes, and there are tons of reasons, from aerodynamics to tyre widths to frame geometry.

I'm interested in whether the "relaxed" frame geometry actually encourages the use of different muscle groups, and people seem to think not, it's more the other factors.

i cycle on empty country roads, no tracks, no cars, no cottage cheese.

This thread actually answers the question pretty well:

http://www.bikeforums.net/touring/52...ng-frames.html

in particular,

"Different styles of riding require different positions... if you're a triathlete as opposed to a pure cyclist, you will ideally want a position that takes advantage of your strongest muscle groups (e.g. hamstrings iirc). As a result, TT frames have very steep seat tube angles (e.g. 78º).

Touring bikes have slacker angles primarily for positional comfort. Also, the more upright position gives you a better view, albeit at the expense of worse aerodynamics. The design also adds a little bit of flex (and therefore comfort), since the seat tube will be longer. IIRC slacker angles also uses the quads more, which is better for seated climbing."

Because the mtb I'm using as a touring bike has a very slack seat tube, and a very long wheelbase it is both comfortable and slower, because I'm using primarily my quadriceps. So I'm powering up hills very efficiently but when on the flats I'm a lot slower even if I'm exerting myself the same.

So the answer to my original question is pretty much just that.

For those interested, and as this is the bike fitting forum I think this is relevant, this article about frame geometry is of some interest as well:

http://www.cyclingabout.com/understanding-bicycle-frame-geometry/

thanks for all the advice, appreciated!

For TT and tri bikes the steep seat tube angle is to provide a position that opens the hip angle as much as possible with the back flat and level. Hence both TT and tri bikes use similar seat tube angles, even though there's no running necessary after a TT. Even with the steep seat tube angle, you still see riders "on the rivet" on TT events because the UCI limits saddle position w/r to the BB.

Your first quote also has the muscle group thing wrong: it doesn't make any difference, road or tri bike. Muscle usage is the same.
different muscles used on tri vs. road bike: newbie question

If your hip angle is open, you can use any muscle groups you want, no matter your seat tube angle or saddle setback. When my quads go out I can still pedal almost entirely with my hams and glutes and vice versa. Your pedaling technique should allow you to trade back and forth.

Your MTB is likely slower because the frame is more flexible, little or nothing to do with frame geometry. Stiffer frames are faster. MTB frames are notably flexible. Road frames are stiff. That's also the reason you find it comfortable. And of course a modern road frame will also climb much faster than any MTB.

Well, go figure... I don't know a damn thing about tri bikes, my interest is in road v. touring v. mtb. Looking all over the internet I get all sorts of contradictory theories about how the body and the cycle frame interact.

Looking at pictures of my frame v. basically any touring frame, the seatpost is at a dramatically different angle, the chainstays are way longer, my knees are riding higher, my quads are like iron rods and I feel like I'm dragging anchor relative to the experience of bikes with tighter geometry. So I'm still pretty convinced that my body is actually engaging differently because of the frame dimensions.

I guess the mtb frames are designed to absorb shock in all sorts of different ways, and I can add flexibility to the list of reasons I'm dragging anchor here. Damn comfy bike though. Kind of worth it.

At speeds above 15 mph or so, the difference in aero drag between an upright position and a flat back position will dwarf the effect of any other factor. You haven't said what your position is on the MTB. If the handlebars are higher than the saddle, I suspect the main thing slowing you down is aero drag.

I prefer a bike with a slightly longer wheelbase because I find them more stable and less "twitchy." I'm an avid recreational cyclist, not a competitor, so stability improves both comfort and control. I had a shorter wheelbase bike that was faster. I assumed one of the reasons for this was weight and I assume that a shorter wheelbase uses less material and is thus lighter. I did not like the short wheelbase bike because it felt less stable, and thus I would not push it as much as my other bike - particularly downhill or in windy conditions.

The number ONE factor and number TWO factor for going slower on your mountain bike are wind resistance and tire resistance. If its an old bike with an inefficient drivetrain then this is important too.

Seat tube angle of a particular number doesn't mean anything. My road bike has an effective seat tube angle of about 69 degrees and I'm faster on this bike than it the seat tube angle was steeper. Seat tube angle needs to relate to your personal fit on the bike.

The OP has given us very little information to go on so there is not much else we can advise him on.

Anthony

Have you equalized your saddle height, angle (nose up/down), and saddle setback between the two or more frames that you have? I find that tends to make all my bikes feel and ride the same with similar efficiency.