Buy (or upgrade) only if it fits; both literally and in abstract.
That is, if it fits you perfectly on your body (apparel, especially) and also your riding style and discipline.
When shopping online, sometimes we'd encounter a deal that's too sweet to let it pass. Unless if you're positively sure that the items on sale would fit you nicely, then it is best to let it pass rather than having to re-sell it to your fortunate friend at a discounted price.
Fit
Your bike should fit you. So does everything else; especially things that are hugging your body - helmet, glasses, jersey, shorts, bibs, gloves, socks, shoes. Also the three parts on your bike that are in contact with your body - grips, saddle and pedals.
Take some time to study what's the correct bicycle size for you. The big frame may have enough clearance between your legs, but you may suffer from a stretchy riding position due to the long top tube distance.
That helmet on sale may look good in photo and have rave reviews over online forums, but your head might not fit nicely. That was my case, actually.
Brand conscious (or what's popular)
Giro helmets are respectable in design and in build. However, they just do not fit my head. I've tried so many different models on - Zen, Hex, and a couple others. My temple would hurt big time. Personally, MET suits me best. Perhaps Bell, too.
Fi'zi:k Gobi is a popular saddle; many swear by it, ratings and reviews are on the high side (with few saying it's not good for them). It suits with the high asking price, starting from RM300 (I can get a nice chair with that money, but won't be nice on the seatpost). I'm up with the good reviews, and put the saddle in my wishlist. Finally I got hold of a used item; abused but still intact. However, my butt hurts on the 25km offroad all the way. Some might say that a break-in is required like Brooks saddles, but I had no such problem with WTB Pure V. So...
Those are two examples from my personal experience which illustrate that not everything would suit everyone. You just have to try them out yourself and see if it fits you.
Try 'em out?
Unfortunately, we don't have such a scheme available locally. It's a trial and error thing. Well, reviews might not help you 100% so we're on a losing side (even if it's only partially). The next best solution is to try them out on a friend's bike, or borrow from them. However, I do not recommend you borrow or lend your apparel. Except maybe your helmet, gloves, shoes and glasses.
Bibshorts? No way!
What's your product size?
It's quite perplexing when your size on a certain brand would differ from another. Take, for example the size for a jersey. For brand X, you may have it in L size, but the other brand might suit you with their XL size. Some would say it's due to European or American or Asian sizing. Perhaps it's true, and the way to be sure is to get the chest measurement right - armpit-to-armpit measurement is a good indicator.
Here's an example, and in this case the brand is the same. I find that Shimano shoes are a bit strange in sizing. For my MT41, size 42 fits me nicely. When I tried out for MT087 at the shop, I need to get size 43. So, you have to try it out in the shop to make sure of your fitting.
In all cases, ask the shop if you can try the item out on you. Buy only if it fits.
Do you know that backpacks also do come in sizes depending on your torso length? Check out Osprey.
I tried it out in the shop, and man, with the correct size I didn't feel the bag on my back.
Take care, and ride safely.
Share the road.
photo taken from here