How to convert 17" bike to 18" without changing the frame

Question

I bought an Author Basic (2012) with a 17" frame.

But I have some back aches after 2 or more hours of cycling (just cycling or with little jumping) and sometimes I feel a little unsure while riding (discomfort).

I think it's about frame size. My preferred frame size is 18" and I figured this out later. I can't give the bike back to the store.

When I had Mongoose Tyax Comp (2010) in size S with Kenda Small Block Eight tires I felt more comfortable and self-assured than on my current bike.

So what can I do now?

My brother says that I can lift my seat back a little + buy new longer stem and it can help to win couple inches but I don't know if it can really help.

Or maybe there are some different and more convenient way?

I have no money to buy new bike or new frame, so I'm hoping to find a tweak or solution for my current bike.

Answer 1

Without being able to get a larger frame, your brothers suggestions are about the best you'll be able to do.

Do you feel too compact on the bike (arms/hands feel close to your knees when pedaling)?

• pushing the seat back and longer stem will allow you to stretch out.
• You can purchase a longer seat post if needed, they even make offset seat posts that would allow you to move the seat a little further back.

Do you feel like your are leaning over too much on the bike (handle bars seem too low and you need to crouch over to reach them)?

• There are all sorts of stems in a wide variety of lengths available, even riser stems that raise the height of the handle bars so you are not leaning over as much.
• You can also purchase riser handlebars that would provide some additional height to the front end of the bike.

I switched out from flat handlebars to riser handlebars on my mountain bike and felt much more comfortable. These new handlebars were also wider which have made me feel much more stable on the trails.

Answer 2

If you still have your old bike grab a tapemeasure and take a few measurements. Start with center of the pedal to top of the saddle while the crank arm is aligned with the seatpost. If your new bike is shorter and the seatpost is at the max look for a 400mm or longer post to get more leg extension. because of the seatpost angle this will push you back away from the bars. Measure from the back of the saddle to the center of the bars. This will give you some idea how far you need to as @Glenn suggests extend the stem or increase seatpost setback. With a few measurements you will save time and aggravation of installing stems and bars and being unsatisfied with the fit. This wont be exact but will get you closer than just quessing how much you need to extend.

Answer 3

Surprisingly small changes can make a big difference in your comfort on a bike. If your frame is only an inch or so too small you can probably make it fit – or at least significantly improve the fit. I know this from long experience being too tall for common off-the-shelf bikes and too poor to get a custom frame built. You're getting some good advice, and you could almost certainly (in the US at least) spend less on getting a bike that fits by selling your current bike and buying a used bike in the right size – but you know your constraints better than we do…

A frame that is too small will likely put you in a position where you are leaning forward more than you want to – this may strain your back and put more weight on your hands and arms than is comfortable. A small frame will also have a shorter top tube than a frame that fits you. To adjust the fit you will need to:

• Raise your seat, this may require a longer seat post to maintain a safe insertion into the seat tube.

• Raise the handle bars. Your steering tube may have been cut off, so it won't be as easy to adjust the fit as it would be with a quill stem. But you can get a stem riser which will help – it should provide you with 75 to 100 mm of extra height.

  

• Get a longer stem. This will "lengthen" the top tube for you. It looks like as you raise the bars on that bike (based on the geometry of the 2013 model) they will move closer to the seat which will make the frame feel even more cramped.

Those changes could easily run to $100 or so in the US. After you've done that it is likely that your weight distribution on the bike may have shifted so you will want to experiment with the position of the seat to see where you want to be. You may be able to start this by just shifting yourself a bit forward and back to see where the bike feels better. After you get a feel for it you can move the seat forward or back to match. Doing this will also change the effective top tube length (and thus the length of the stem you need) so you may want to hold off on buying a new stem until you get a better feel for where you want to finally end up.

If you have access to a bike that you're comfortable on you may be able to simplify the process by taking measurements from it.

Answer 4

The answer is do your research before buying. Now you're throwing good money after bad trying to fix a problem that you should have detected before buying the bike. I suggest selling it, and buy a suitable bike.

But, as a tall and leggy guy I know how hard it is to find stuff that fits. I routinely bent seatposts and have cracked a frame by having the seatpost up at maximum extension.

You can buy seatposts up to 400mm or 450mm long, but they tend to poke up so far that your body weight combined wiht the leverage will bend the pole. My fix was to find a second steel pole with an outer diametre just smaller than the inner diameter of my seat pole, and hammer it in using grease. Downside, my seat pole is ridiculously heavy and long, but they don't bend now. Doesn't look wrong when fitted though, just looks long.

You can get seat posts that have a setback, to hold the saddle further aft but this moves your center of mass backwards, increasing the wheelie effect and making steep hillclimbs a little harder.

Sorry for being blunt, but you're doing the same wrong things I used to do. Save up and get a right-sized bike.

Edit: adding pic of extended seat pole: