1

I have a SEKAI sprint 1000 bike which is a tiny bit big for me as I have problems reaching with my feet to the ground. The existing seat is already down to the lowest level so can't reduce the height any further. What I am thinking is to change the wheel to a smaller size. The current size is 27 1/4" (rim). Can I install smaller wheel on this bike without having replace virtually everything?

If there is a seat available which has slightly lower seat frame so that if I replace the seat then it goes a bit lower (hope this makes sense?)

  • 3
    It needs to be noted that basic sizing for a conventional "diamond frame" bike can be roughly determined by "standover height" -- you should be able to stand flat-footed on the ground while straddling the top tube, with "comfortable" clearance. (For less conventional frames you have to imagine where the top tube would be if it ran horizontally from the front connection.) There are of course several other measures for good bike fit, but this is the most basic. – Daniel R Hicks Aug 13 '13 at 11:37
  • 3
    And a way to roughly set seat height on a road bike is to have someone hold the bike while you sit on it and pedal backwards (assuming a bike with a freewheel). Do this with your HEELS on the pedals. With your heels on the pedals your knees should just barely get to perfectly straight, without having to rock in the seat. Then, when you adopt the normal stance of toes on the pedals your knees will be slightly bent. Once adjusted this way you may find you want to go up/down a half inch or so, but you shouldn't need much more. (Of course, off-road bikes may need to be set up different.) – Daniel R Hicks Aug 13 '13 at 11:43
  • 3
    You can use a smaller width tire with the same rims, and generally not need to adjust anything. This might gain you a half inch or so, depending on your current tire and rim. Otherwise, installing smaller wheels just isn't worth it. It would cost $100-300 for the new wheels and tires, and you'd still have a problem with the brakes. And only gain about an inch. – Daniel R Hicks Aug 13 '13 at 11:46
  • @Daniel R Hicks. It passes standover height test. and the tyres are already small not sure if I can get smaller (thinner) tyres then these ones. It looks like the seat needs to be adjusted. I remember having pain between the legs after few minutes of ride (not in genetals but behind it on the boans). Looks like the seat's tilt needs to be adjusted so it does not cause injury while climbing up or down! This is the reason why I thought its too high as my legs are not completely grounded when I sit on the seat. – daehaai Aug 13 '13 at 12:24
4

The first problem with changing the wheel size is surely the brakes. Assuming they're rim brakes, they won't be in the right place for a smaller wheel.

In any case, is it the distance to the ground that is an issue or the distance to the pedals? If it's the latter, then changing the wheel size won't help, however, you might get an extra 5 or 10 mm by using shorter cranks - if this is appropriate for your height.

I would imagine that it's probably better and not much more expensive to trade the whole bike in for one which fits you.

  • The issue is with distance to the ground (only by a couple of inch max). You are right break would be an issue. I really would like this bike and don't want change just for a couple of inch of height. Any recommendation on seat that I could purchase to help this (even for 1/2 inch)? – daehaai Aug 13 '13 at 9:43
  • 10
    Do you mean distance to the ground when stopped? It is absolutely normal (actually even necessary) not to be able to reach the ground from sitting on the saddle (if you do then your fitting is terrible and might even have issues on your knees), usually you get off your saddle to stand up and sit on it once you start pedalling. – pedromarce Aug 13 '13 at 10:25
2

As many others have stated it is possible to mount smaller wheels. The issue will be mainly a cost versus return on investment. The brakes may be able to be adjusted to reach and the frame may be spread to fit the wider hubs. The google images I have seen of a SEKAI sprint 1000 appear to be an older 10 speed. It most likely is equipped with a 5 gear freewheel using a 5 speed chain. The more modern and smaller diameter 700 c and 650b size wheels will most likely use a cassette with at least a 8 gears. This means your old crank, derailleurs and chain may be incompatable with the new wheel. The 8 speed chain may be too narrow to fit on your present crank and your old chain may be too wide to fit on the cassette

  • 700c brakes with longer reach brakes is a fairly common swap, and there are other questions about it (gives wider range of available rims and tyres). Finding a new wheel with a 7-speed hub might take a bit of looking, but 7-speed freehubs (and 6-speed and lower freewheels) are still available. – armb Aug 13 '13 at 15:18
  • 650b wheels is another matter. A more important issue with the cranks is that if you lower a bike by using smaller wheels, the bottom bracket is closer to the ground, and you risk pedal strike. 27 inch to 700c you can probably get away with, but more than that, you may well need shorter cranks. – armb Aug 13 '13 at 15:21
2

The question I would want to know is...how old are you and how tall you currently are? If you are young, like early teens, it's likely you'll be growing a few more inches, so you may not need to convert the bike wheels to a smaller size, ( that's asking for more problems with braking accuracy on the rims ), and trying to find a different seat. This may cause your riding position to be way off in the saddle to pedal height. As other posters indicated, you'll be changing parts to try and fit a bike to your body size, and spend money and time accomplishing this task. You may be able to find a bike that fits you that can be ridden for a season or two until you grow into this bike. If you are much older than early teens and have reached your growth potential, I'd consider finding a bike of the proper frame size so you can enjoy the bike rather than curse at its short comings and spend money on something you may not be happy with as far as results.

0

20 inch wheels on full suspension 'trial' frame and MTB frame with high Bottom Bracket. But the frame must have disc brake mounts, very difficult to change rim brakes position. And you may need shorter crank arms. A 17” (rim) moped tire on the rear may help with a 16” (rim) on the front.

Bicycle wheels and motorbike wheels are measured differently, a motor cycle wheel is measured at the tire bead surface and its diameter is the actual number of inches it is stated to be, a pedal bike rim is measured at the outside diameter of its tire.

Lowering the rear axle with the suspension will also shorten the steering trail, making it easier to turn sharp corners.

I put a 19 inch moped tire on a motorcycle rim, (tire being 23.25” O.D.) In place of my 24 inch bicycle tire. It increased the trail of the steering a very small amount, but still rideable. You can use a 16 inch motorcycle tire (20 inch O.D.) on a BMX rim.

Changing a bike with 26” tires to 24” tires would be easy, if it has disc brakes. It will lower the crank only one inch.

large frame with smaller wheels build your own frame

  • 1
    Welcome to Bicycles @Nohj. We recommend that new members take the tour to make best use of the site. It's not a discussion site. – andy256 Nov 13 '16 at 22:19
  • Its a perfectly valid answer, voting to keep. Could do with some more detail though - we like the answers to be self contained rather than depending on some other website. OP, could you please use EDIT to expand your answer? Maybe add a couple of pictures to show how it looks ? – Criggie Nov 13 '16 at 23:05

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.