I want to buy a back rack online. How can I be sure that it will fit my bike without testing it first? Is there any standard for racks that I can ask the seller about? What are the chances that I won't be able to mount it?
Assuming you have braze-ons for a rack on your frame, you should be abl to get a rack fairly easily.
Racks are made with the basic characteristics of the bike in mind. You need to pay attention to:
Your best option, if you are unsure, is to ask your LBS. They will want to see the bike, but will usually have a functional rack in stock, and install it for you. The costs are usually not excessive, and the saved hassle is worth it, unless you just prefer DIY.
Hope that helps.
There are two standard ways that a rear rack fits onto the bike: 3 point fixing and 4 point fixing. Most but not all racks on the marketplace come with a small bag of parts for the fit.
The most important question is if your bike actually has eyelets. These small holes on the rear dropouts are crucial if you want to fit full mudguards or a rack. If you do not have these then it is not the end of the world, you will just have to have a more expensive solution. One of the rack manufacturers does a kit:
That will set you back a minor fortune and you will not be able to get it in your typical LBS.
More commonly available at the LBS is the rack that bolts onto your seatpost. I have not tried one of these myself however I do know that they get knocked rather easily and can sway from side to side. Plus I think you can only carry ten kilograms or so with one. The market leader for such racks in the UK is Topeak. Here there is a lot to get right, they do gazillions of different models to suit different frame sizes and bike types. No disrespect to the product, but avoid if you can:
Okay, that is the 'no eyelet' scenario out of the way.
If you are lucky then you will have two eyelets either side on the rear dropout and eyelets on the seat stays above the bridge/brakes and on either side. These are so that you can mount mudguards and a rear rack. If you are lucky enough to have the full eyelet collection then you can get a 4-point fixing rack.
If you only have the single eyelets on the dropouts and no extra eyelets on the seat stays then that is not too bad, you can still go for 4-point rack but you will need to make sure that the rack comes with 'P' clips. The 'P' clips go round the seat stays and provide the equivalent of the eyelets.
Alternatively, and for cleaner lines, you can go for 3-point fixing. This is where the rack connects to the two eyelets at the bottom and to the mudguard bridge in between the seat stays.
As mentioned the rack, whether 3 or 4 point should come with a fitting kit. This will include everything needed to get it onto the frame. Care must be taken when fitting the rack to use the correct bolts and to not have an extra long one on the right-hand dropout as this can interfere with the freehub cassette and chain.
With a steel frame you are well advised to grease the bolts before putting them in, use of washers will not hurt either. Rack bolts are very prone to coming undone due to vibration and once the rack has bedded in you will need to check the bolts are as tight as you intended them to be. 'Loctite' on the screws can be applied if there is not any on them already.
Racks can come in 700c and 26" sizes. Most are universal and designed to fit either wheel size. If you have no mudguards then you may want to consider a rack with a built in mudguard. Here is one example:
That is the once popular Blackburn MTN-1. Note that it has six holes drilled at the front, these are for the fitting kit and it comes with bits and bobs including P-clips to suit 3 as well as 4 point fixing.
What is poor about the Blackburn MTN-1 is that the loops at the bottom to hold on the pannier may not suit your panniers.
Another design feature missing from the MTN-1 is a bracket at the back for a light or reflector. This model by Topeak has one of them:
Although the light to go on there will be quite pricey and hard to find in a LBS, it will be a neat solution.
That particular Topeak rack also shows yet another design consideration: the problem of the disk brake. If you have rear disk brake then you will need a rack specifically designed for that. It sticks out more and is less elegant than a regular rack.
Also of note with that Topeak rack is the top and how it appears to have extra edges to the middle bit. This is to suit Topeak's range of top-bags. They slot into the groove and click in place making them very secure and not wobbly.
I advise checking out the Topeak rack and bag combinations for yourself in a LBS. Although they have lots of fancy compartments and are very well made, sometimes a 'really heavy handbag' is next to no use if you want to carry a notebook computer, or some shopping or a tent or a sleeping bag or a stove. Fine if you want to commute in with a change of clothes and have compartments for other nik-naks you need for work, but still rather heavy and expensive. Plus you are locking in to their system and it is not universal with other bags.
Personally I don't bother with panniers and racks anymore. Panniers can wobble about and leave heel clearance to be a problem. Nowadays I use a 1950's style and unashamedly retro saddle bag. I ride in the seat and prefer to have the extra weight next to my own centre of gravity. (Panniers give light handling on the front wheel that I don't like.) As a consequence I am the proud owner of a Carradice 'Long Flap' bag and SQR bracket. This is very easy to take on and off plus it has pockets either side for tools in one and luxury ready eats in the other that can be easily accessed. I can get a notebook computer in, full touring kit, a weeks worth of clothes for the office, several shopping bags worth of groceries and a small Tardis, admittedly not at the same time.
In addition to the above benefits, no eyelets get used to mount it and girls do comment on what a nice bag it is as it is a bit hand-bag looking. The 'cotton-duck' material is also brilliant as it swells in the wet to become properly waterproof.
A standard rack will fit a standard (full-sized, non-suspension, diamond frame) bike with rack eyelets. Beyond that you're on your own.