I have measured many a wheel base on old 10 speeds - my new Trek 7.3 FX etc. All seem to have a 42" wheel base. Wheel base is directly associated with the frame/front fork. "If" I were thinking of building my own bike is 42" the norm for a wheel base and if it is, why? Thanks

wheel base is a result not a goal, usually the rear triangle on a bike is going to be very similar from one size to the next but as you increase things like top tube length the wheelbase will increase, other things that will affect the wheelbase are things like headtube angle , seattube angle , chainstay length and fork rake,

just for fun you could pluck some frame geometry off of the internet (Surly lists all thier geometry) and do a practice draft or two on some big paper just so you could see all the points there is to hit, you dont have to get too involved if you dont want , most of the time I just draw centerlines for the general layout. If you are going to use lugs then you will need to know the angles before you start, hope this helps.......

Agreed. Wheelbase is largely a by-product of other decisions.

I personally do not pay any attention to wheelbase and have only the vaguest idea what it might be on the frames that have built.

I think wheelbase often is a target in bikes. On comfort bikes and some kinds of touring bikes long wheel base can be important to the ride. On stuff like some MTBs, or road bikes that need to be highly maneuverable, or are optimized for climbing in certain regards, a short wheel base can be an advantage, or at least a goal. But as others have said it is also a natural result of other decisions. Once you do know what specific style you want to emulate, you can study current catalogs online, and also study vintage bikes which may be better or worse depending on your needs and the influence of various fads on current or past designs.

Good point PP1, perhaps my choice of words was a bit loose and six-jours choice of "by-product" was more suitable, you certainly can set out to have a longer or shorter wheelbase for various reasons but I read the post like there was a specific number being used to start the process of drafting a frame and I was just pointing to information that would quickly dispell that for him, It's all good.

Great info here. I was looking at wheel base from a build up approach. Ergo,
changing the front fork on say an old 10 speed. My looking at all of this is the
handling prperties that will be lost or gained but you guys answered all my
questions. Thanks

I really have a hard time imagining why you would worry about the wheelbase in designing a frame. The chainstay length, frame angles and fork rake, yes, but the top tube length is much more important than wheelbase.

What about a bike that uses a bent seat tube to tuck the rear wheel in tighter? That seems pretty obviously to be a wheelbase play. At the other extreme some of the Rans recumbents seem to be an obvious attempt to maximize wheel base for ride reasons.

Another comon, though possibly fictitious wheelbase issue is when every bike in a range has the same wheelbase, That is actually kinda hard to do. But I guess some makers assume they can't sell a touring bike (etc...) unless it has a 43" wheelbade, 4X0 chainstays, and 73/73 angles, yet every bike is 43" inches in wheel base, or so they say. If wheel base was just a result of the overall process, the numbers wouldn't be rounded, or the same in every size. I am not recomending this approach, but it seems to exist at some level.

I don't actually design for a number since even when I am concerned about it, it is normally an exercise in getting more, rather than a particular number.

the bent seat tube allows shorter chainstays.

Once a bike is above 19", most manufacturers will use the same fork and chainstay length, and seat tube/head tube angle for a given model. So wheelbase is determined by top tube length. I just think the OP's sample was too small. Think about the ridiculousness of a 25" frame having the same wheelbase as a 21" frame. Most production bikes have less TT variation than ST variation, but it's there.
I just happened to have a Waterford geometry page open, here are some wheelbases for one of their frames:
480 940
500 977
520 979
560 995
580 1000
640 1029
That's almost 4" difference between the biggest and smallest frames, but
only an inch if you throw out the ends of the height spectrum.

Anyone remember the "Rigi"? It had two 1/2" tubes in place of the conventional seattube. The rear wheel projected between those two tubes, allowing the chainstays to be as short as possible without putting the cranks through the rear axle.

Yeah, 'bents are a breed apart:

Yeah, was supposed to be the hot setup for crits. I had one. It sucked. I'd still like to have it back now, though.

Yeah, I'd like to have the mint condition Paramount track bike I had 25 years ago. C'est la Vie! I have a Steelman now: https://home.comcast.net/~jeff_wills/steelman/index.htm

There is a recumbent like that here in town. A guy here collects any strange bike he can get his hands on, he has a conference table bike.