Hal Fisher

I was a the bike shop the other day while I still decide on which bike to get (my price point has moved up to the under $600 range because I want a really good stock fork shock right away). I just returned a 17" Schwinn Mesa and decided I should at least try a bike with a good fork on it. What they had there was an Iron Horse with a great marzocchi mx comp but it only had a 15.5" frame. I thought it was going to feel really small but I decided what the heck, better smaller than too big. When I got on it right away I thought there must be a mistake, this bike felt bigger than the 17" mesa but it was supposed to be just a 15.5? I thought at first the neck must just be way longer but when I checked it wasn't. I just couldn't figure out why the supposed shorter framed Iron Horse Warrior 3.0 with it;s 15.5" frame felt much larger than the Schwinn Mesa 17".

Well I got home and started researching what you guys felt would make a good bike in the $500 range and noticed quite a few people mentioned Gary Fisher bikes. I went on his website and after looking at a few (marlin, piranha) I noticed a caption stating his geometry is set up to make for faster uphill and better controlled downhill riding. I then started looking at the angles of the frame and noticed he uses an angle of about 92o on the underside angle (this is a guesstimate and using "o" as a degree indicator) for attaching the seat tube and top tube (not sure about the names of these). I then checked the angles of the Mesa which is more than that at about 95o and the Iron Horse is way less at a guesstimated 86o. This all then made perfect sense why the shorter framed IH felt longer than the longer framed Mesa. The difference is the opposite angles that the top of the frames angles have. The seat on a frame that has a lower angle of 86o is going to have a top angle of 94o (IH) making the seat sit much further back from the steering head than a bike like a Mesa that has a top angle of about 85o (all these angle degrees are just approximated).

Now I am sure a lot of you already know this and can give extremely accurate descriptions and actual angles and a better explanation on all this, but I just wanted to point this out for someone who stumbles on to this same odd predicament, wondering why they seem to fit differently on the same sized bikes from 2 different manufactures.

Hal Fisher

I am now pondering how the wheelbase effects the uphill and downhill dynamics.

I would think a longer wheelbase would benefit downhill while a shorter one would benefit uphill. So I guess a frame that has optimal dimensions in the middle would render the best possible for either uphill or downhill. If I am missing something somewhere please advise.

C Law

yup. all bike brands, and models in the same brand, ride fit and feel a bit different.

Hal Fisher

My analysis (can barely be called that) was an attempt at maybe a little deeper understanding than what you state. My explaination leaves room for changing just the size of the bike and going with something a little bigger or smaller may yield desirable ergonomics instead of believing, like I once did, that you always fit a certain size downtube and either the model bike works for you or doesn't.

Hal

C Law

yup

It's difficult to have a forum discussion on frame geometry if you don't know the names of the frame tubing (click here) .

I think what you are saying is that top tube length is (generally) the most important measurement to use to fit a bicycle and not the seat tube height (as was the standard measurement used to fit say..10 years ago) . Also, you are saying that company A's 17 inch frame does not equal company B's 17 inch frame. If you are saying that, I would agree with you

also keep in mind, you can't predict overall feel of a frame by using one tube or angle measurement alone. It is all interelated.

Hal Fisher

Actually, I was far closer to the real names than I thought (this obviously isn't microbiology). What I really lack are the names for the inside and outside angles of the frame, anyone have those handy (anyone cad frames)?

shiggy

The angles between the tubes as you are measuring are fairly meaningless. The head tube angle and seat tube angle are measured relative to the ground and effective top tube lengths are parallel to the ground.

There are books written, classes taught and careers devoted to how they (and many other factors) relate to the ergonomics and fit of bicycles.

Hal Fisher

I kind of think the angles do mean something but thank you anyway mister contarian.

Hal

shiggy

Go do some more research.

Yes, the seat tube angle and head tube angle do mean something as far as the ergo and handling of the bike goes.

The angle between the top tube and the seat, seat tube and down tube and such are only important if you are constructing the frame and are a product of the other factors of frame design, function and fit.


https://www.salsacycles.com/alacarte.html

twochins

hal dog, i think headtube angle and wheelbase, and maybe toptube, are pretty important...but in any case of bike your looking at, take it for a spin and make sure it fits well....you're absolutely on the right track though, the bike needs to fit you like a shoe to work well on the trail