Frame Considerations

gorgeous white painted, not the frame in discussion

You're a newbie and you've found out after a few rides that there's something wrong with your frame. Most of the time it's actually your inner wants are at play; and your head is telling you that a certain frame brand or design is much better than what you're having now. Well, if you want to switch to a new 'better' frame, that is your choice. The same also applies to a seasoned rider, but I trust that it would be more of a 'need' thingy.

Frame switching involves a lot of attention to details because that's the center of the build itself. All parts are connected to it. Okay, well, except for fork, stem, cockpit, front wheel, but you get my drift.

First off, there's the type of frame that you want to have, either a hardtail or full susser. You also may consider the material of the frame itself, be it carbon fiber, aluminium (of various grades), titanium, scandium, unobtainium (okay, that's too exotic). Then you have to look at the geometry that suits you. These are mighty important.

What's important just as well, but to a bit lesser degree (just a tiny bit) are the details on the frame.

You have to look at the:
headtube length
headtube construction (for the headset type)
BB shell length
BB type
RD dropout
V-brake bosses
disc brake mounting tabs
seatpost size
seattube size
cabling brackets
bottle cage bracket holes
bracket holes for pannier rack

I won't discuss about the frame types, materials and geometry. You have to look elsewhere for those. What's seldom being discussed are the other details as listed above (in no particular order of importance), and let's take a look at them. Here we go...

headtube length and headset type need to be looked at,
also note the cable brackets are on the top tube side for this frame

headtube length
If you're switching to a new frame and intend to use your existing expensive forks, then you have to measure the new frame's headtube length. Different frames would differ sligtly. You have to add spacers below your stem, or cut your precious fork's steerer tube to accommodate to a shorter headtube. If the fork's steerer tube is short by more than 5mm after stem is installed (without any spacers), that's a sure indication that the headtube length is much longer than your current. You have to look for other frames with about the same headtube length as your current one, then.

headtube construction (for the headset type)
If you intend to re-use your headset on a new frame, then the headtube diameter and type shall be looked upon. The 'standard' diameter size is for a 1 1/8" headset. The newer standard, usually for a much burlier frames is 1.5" e.g. freeride, downhill. [Update 17.08.2015: Also, it is now common for frames intended for 650B (27.5") and 29" wheels to have tapered 1.5" bottom with 1 1/8" top headset]. There's also the smaller 1" diameter, but these are no more common for mtb frames.

There are also many different headset types - normal, internal and integrated. You have to know what's on your current frame, and compare that with your replacement frame.

BB shell length for this frame is 68 mm, note the spacers used

BB shell length
Usually English thread BB are found on mtb frames, either 68 mm or 73 mm length. In the case of external BB, you need to put two 2.5 mm spacers on the drive side, and one spacer on the non-drive side if the frame's BB shell length is 68 mm. Keep the spacers neatly in your spares box if the BB shell length is 73 mm.

Check your BB spindle length in case it is the square taper or ISIS spline or Shimano Octalink. It has to match your BB length, or you'll have issues with your chainline/shifting.

RD dropout, note that there are no threaded holes provided for pannier rack mounting

[Added 17.08.2015]
BB type
There is a plethora of BB types now, as technology is expanding and components are refined to suite riding styles. Check what is your current BB type and the new frame you intend to use. If they are directly compatible, you don't have to spend $ for adapters (if available) to get a new BB altogether. Mind you, it goes without saying that the crankset follows the type of BB that you're using. So take some time to dwell into the subject and if you haven't, put the extra $ required in your budget.

RD dropout
Nowadays, frames come with replaceable RD hangers. Always get a spare RD hanger when you're getting a new frame, and put it safely in your riding bag as an emergency spare. Especially for long, epic rides, you'll never know when you'll need them.

who da boss?
also note that there are no pannier rack mounting holes on side of the seatstay

V-brake bosses
If you intend to run disc brakes on your bike (the norm now), then you can do without the bosses. However, if you're planning on using V-brakes, then obviously you have to have the bosses on the frame. Make sure that the bosses are there, or you have to make a separate purchase (seldom is the case, though). I've learnt that there are 2 sizes of bosses, so make sure you know which one to get.

disc brake tabs - a norm on modern frames

disc brake mounting tabs

If you intend to run V-brakes, then this is not important to you. However, it is best to have it for future upgrade should you feel the itch. Be careful while admiring a fellow rider's rig, and if you're feeling 'left out' as being the only rider in the pack with Vees (or cantilevers, for that matter). If you're using disc brakes, then you should check for the tabs. Nowadays frames come with the tabs, but do check when you're getting NOS (new old stock) frames sold cheap, or for that vintage quality.

seatpost size
You may need to lay rest your current seatpost if the size is not the same as your new frame's. Also applies to your seatpost clamp. Be careful also to note the seatpost size on your new frame, whether it is easily available currently.

A friend of mine has to source out on ebay and pay extra, because the seatpost for his frame is rare nowadays. Well, his is a vintage mtb frame, anyway.

Also, look at the seatpost clamp slit, whether it is on the forward or facing the rear tire. It is better if it is facing forward - reduced tendency for water or mud to seep in from rear tire spray while rolling.

the cable routing for the FD on this frame is from top,
the FD is XT down swing but can handle top routing as well

seattube size

This is directly related to the seatpost size, but the concern is more on the FD clamp. Usually the FD has spacers to adapt for different seattube diameters. You would need them if your new frame's seattube diameter is smaller than your current one.

I have tried using DIY spacers (inner tube, metal sheets), but of course, always the best path is to use the specific spacers supplied with your FD. Get them from the bike shop if you don't have them. Use your charm, and you could get them for free.

[Added 17.08.2015]
These days, added to the already many types of FD mounting for MTB is the direct mount type, borrowed from road bike norm. If your new frame has this, then you need to fork out extra $ for the new FD. Ask the seller (if bought secondhand) to have this in the package so you're saved from the hassle of getting a new one.

In the case of a full-susser, many frames are having specific type of FD mounting style. Some even require you to use a Shimano E-type which is uncommon and rare, if not hard to find at your LBS.

cabling brackets dictate your cable routing
my favourite - running on toptube sides or under it

cabling brackets
Look at your riding buddies' frames and you would see that their cable routings for brakes and shifters vary. Some have it railed on the top of the top tube, some have it a the sides of the top tube, some running beneath the downtube, and I've seen a frame with routing threaded into the top tube, on its sides.

There are advantages and disadvantages on routing the cables a certain way. Some would save you on cabling hoses but exposing your cables to dirt. Routing your shifter cables underneath the downtube (usually bare for a length) would certainly be the case. Check that the frame comes with the plasic guide on the bottom of BB shell if the routing is underneath the downtube. Routing the cable on top of the top tube would rob you the space to put a utility bag such as this Topeak Tri Bag.

Cable routing would also affect the type of FD clamp. Usually for bottom routed cable, the FD clamp would be the high type (down swing) and low clamp (top swing) for top routed. Anyway, check if your FD could handle both cable entries. You're $afe if it is. The same goes for E-type FD (Shimano). Note: those Shimano XTs in the links are of Dual Pull Technology - they can take either routing.

[Added 17.08.2015]
New generation MTB frames are having shifter cables routed through the inside of the frame itself. This in my opinion is a cost cutting exercise for the manufacturer. There are no extra parts for the cable routing brackets, only some rubber bits for covering the hole. This, however, in effect gives a much sleeker appearance and eliminates gunk and dirt attached to your cables - easier to clean your bike. However, do note that there might be some hassle in routing the cables, which is a once in a while job, anyway.

bottle cage bracket holes
This would essentially depend on your preference. Do you want your bike to be ultra light as it is? You could do away with the water bottles and use hydration pack instead. Or, do you want to have at least two bottle cages for touring? Perhaps you want at least one set of the holes to mount your hand pump bracket.

[Added 17.08.2015]
Take note also the location of the holes on the frame. Especially on small size frames where the front triangle is not big enough to mount a decent size of water bottle within it, the holes might be at the bottom of the downtube. A nice place to collect mud, sand and other stuff from the rolling front tire. Also applies for some full-susser frame designs, where the front triangle is packed with linkage and rear shock.

bracket holes for pannier rack
These are non essential for offroad riding, really. However, if you're considering to sport your bike with a pannier rack, they are needed. Check the seatstays for them, on both sides. Also inspect that there are at least one threaded hole near the slot for the rear wheel QR.


Wow... that's an awful lot of little details to look at, huh. Well, all for ensuring a good purcha$e, and minimal glitch in switching to that needed frame.

If I can part you a single tip, it would be best to buy a frameset, i.e. the frame with headset and seatpost clamp bundled together. Much better if it comes with the seatpost and spare RD hanger too. If you're buying a second hand item, ask the seller if he could throw in the FD as well. Saves you a lot of is$ues.

Thanks for taking your time reading up to this line.
Have a great day!
 
picture frame photo from Ikea
MTB frame in photos in case you're wondering is EPX Hollowpoint