Spec'ing A Frame
 

I wish that people would give the fundamental measurements of a bike frame when they offer it for sale.

Wheelbase - a 39" wheelbase is a "responsive" bike, some would say "twitchy". A 42" is going to be a bit more "relaxed". Fork rake and trail would also help, but I understand these are more esoteric concepts. :-)

Stand-over Height - seat tube length is meaningless unless it is tied to a bottom bracket height and wheel diameter. What is critically important (to the family jewels) is stand over height. To some extent, I could care less about top tube length (within reason), as I can fit the bike with whatever stem length is required.

Frame's wheel size - absolutely essential to know so one can understand if they have the proper set of brakes to put on the frame. If a frame was designed for 27" wheel but you have 700c, the brakes you're planning/hoping to use may not work. You'll never know until you get your hands on the frame.

You can always ask. If the seller doesn't know, move on! :)

There's a lot of difference of opinion on what measurements are in fact the most important, and I think the reasons for most of them are at least as good as yours are. It boils down to personal preference. I think the best you can do is to ask for the numbers you want, AND for pictures, at least a side elevation that lets you see the proportions. Over time I've learned to guesstimate most of what I want to know based on that picture, combined with a few facts.

Also consider that many sellers don't know anywhere near what we on-line bike freaks know (yes, even us!), and will never give you the numbers you need. However, this doesn't diminish the desirability of what they're selling.

if 39 is 'twitchy' what would you call a 37.5 wheelbase?

I have to admit *blushing* I am guilty of this. I have a frame on ebay and I put the size but forgot to put any TT, WB, CS info on it.

even worse I listed a pair of hubs and never put the drilling :(

i agree with Road Fan, the 'important' measurements are different for different folks. Personally I'm not terribly concerned with standover height, I'm much more concerned with Top Tube length.

For me, seat tube and top tube. Wheelbase doesn't tell me much: the most stable, rock solid bike I've ever ridden has a 38.5" wheelbase (on a 63cm frame!).

SP
Bend, OR

I actually prefer to buy from sellers that can't seem to work a tape measure, can't take a good picture, can't read the model name off the frame, and are really slow to return emails. Why? Because those are often the best deals, sometimes incredible deals. One great deal I got was on a nice road bike, where the seller couldn't figure out how to put air in the tires (he thought they were defective, the bike had Presta valves).

A really sophisticated seller will likely know their values well too, and the price is almost always higher.

The bicycle market is very inefficient, the person with the most knowledge usually wins. I would rather be that person.

how about head and seat angles, as well ? Or seat post diameter :)

Realistically, I do not trust most sellers (on ebay or CL) to know how to measure a bike. Most (non-flipper) sellers (and a good amount of flippers) see a bike like something that needs to be sold, like a used window airconditioner or something that takes space. Unless they are enthusiasts. And in that case, expect higher prices.

Here is what I do: If I am to buy a bike for personal use from a CL ad, I always bring a measuring tape, and take it from there. If it is an ebay bike (and I bought just one bike and one frameset on ebay for personal use) I figure out the size and then I look up the charts, or base it on personal experience by eyeballing it. If it is a bike I do not intend to keep, I assume that it will not fit me and if it does, it is a bonus.

As usual, you offer excellent insights. That's exactly how I got great deals on the Team Miyata and Trek 660.

When I was preparing the list above, I was trying to get to the very fundamental measurements that all sellers should be able to make.

Simple things such as wheel base and how high off the ground the top tube is can be directly measured. Wheel size can be determined by reading the sidewall of the tire. Anyone of average intelligence can do these things.

1. Spin the crank to get the pedals out of the way, point the front wheel straight ahead and measure the wheelbase using a tape measure.

2. Measure the vertical height from the top of the top tube to the ground with that same tape measure.

3. Read the sidewall of the tire and report the tire size.


Tube lengths, frame angles, stay lengths, etc are more esoteric and did not make my list. Some of you know enough to report these but I do not expect the average Joe to do so.

It is probably because 98% of buyers don't give a crap about any of those measurements.

Just go look at the damn bike!

I think we are on totally different wavelengths in regards to this, jt. Are you suggesting I drive across town to look at any/every frame I'm interested in? Most are in a completely different part of the country (i.e., New Hampshire versus California), sometimes in different nations (Canada, UK).

When offering a bicycle for sale on Ebay, I always list the frame specs. Perhaps not every person would be interested, but many are. This thread is, perhaps, some evidence to support my opinion on this. I don't know about anyone else, for sure, but I would want to know those numbers before I buy a bike I cannot sit on and/or test ride.

Sorry, for some reason I thought we were primarily discussing local craigslist bikes.

Although uneducated sellers is not something I would really complain about anyway.

No apologies needed, this whole topic is just a rant, anyway. It's okay to rant in a rant thread.

Zaphod, there's probably something here I need to learn or remember:

Why are you more concerned about top tube length when stem length is so easily changed?

How do you avoid being concerned about stand over height?

Mike, I might be alone on this one and I don't pretend to have any scientific methods or anything backing me up....but here's my reasoning:

I feel like there's a difference in the ride of a smaller frame bike with a long stem versus a bike thats larger with a shorter stem. I like to stretch my upper body out when I ride, and I prefer the feel of a larger frame over a smaller one...so I prefer a long top tube.

You're right that I could take a 58cm frame and with a longer stem make the saddle to bar distance equal to that of a 61cm with a shorter stem. To me the larger frame would feel better, will have a little more give to it, and ya know everything on the frame is a little bigger too so I feel like it changes the ride...at least enough for me to prefer a larger frame.

I don't get concerned over standover height unless my feet don't reach the pedals when the seat is all the way down. I never stand flat footed on the ground with the bike straight up and down underneath me and I have yet to run into an emergency stop situation where I was required to come to a stop and stand in that position. I love my nads as much as any other dude...If I thought riding a big frame was endangering 'em I'd probably ride smaller frames. ;)

like I said though... this is my preference. I don't expect anybody else to feel the same way.

I can't answer for him but I really am not comfortable on a TT shorter than 570. To me the stem sort of goes with the head angle fork combo, not as a top tube fixer. Just my opinion.

Zaphod,

I wonder if the "feel" of the longer top tube derives from what must be a longer wheelbase that goes with that longer top tube. Long tube/short stem or short tube/long stem, either would let you stretch out your torso. One, however, would have the fronbt wheel a lot closer to the rear wheel than the other (all other things being equal).

On top of that, it may be that frames with long top tubes are generically designed with shallower angles, longer stays, etc, hence, they have a certain "feel" to them.

I had a bike with a 37.25" wheelbase. Can you say toe clip overlap? Actually for what is was intended for, it was great, but not my only bike at the time. Short rear triangle, if the builder had not filed a bit off the lower portion of the horizontal dropouts... I would have had to deflate a tire to change a rear wheel. As it was no Del Mundo's for that bike. High bottom bracket, this was when Campagnolo pedals reigned supreme, a high bottom bracket (11") was needed to get pedaling through a corner. Not needed today. While it was a great criterium weapon, I did not keep it. They had their place, their time has past.

Wheel base falls where it will after the other things are in place. To get a better handle on a bikes nature the front center dimension and top tube length tell me more.

There has been an evolution on what is the "correct" stem extension. Gios was one of the promoters of the short top tube, torsos did not suddenly become shorter, so they were pushing longer extensions. This places more weight over the front wheel, it changes the basic handling and envelope that one lives in between the wheels. Pinarello followed suit, even Colnago moved that way. DeRosa much later, and Merckx even later, and not for the full line. Better? Well, it is different, I tend to like normal angle bikes where my stem is 110mm and the seat in the correct position. Indeed everyone will be different.

Mike I wish I knew more about frame design and could say for certain what it is, but I'd say any combination of the things you listed could be the reason. Wheelbase makes alot of sense to me.

I also agree completely with ftwelder on this point
also I think really short and really long stems look silly.

that also makes a lot of sense as to why it would affect the handling.

I do recognize the flip side of the coin for racers...smaller frame, less material...lighter.

I follow Don't Ask, Don't Tell.