- - - TRY to modify the height of a BMX 20 inches bike - - -

[Mattley]

Hi everybody,
I have a bmx bicycle (20 inches wheel). Since my height is 176cm, I can't go on it.
So I would like to modify the height of the frame.
The height from the floor to the handlebar is 90cm (see the picture attached), I need to increase it up to 104cm, so 14,5cm is missing.
I thought to replace the current fork with a longer one.
Could you give me any tips? Do you think it can work?
Thanks in advance
Matteo

 

[Bob E.]

Search for bicycle ape hangers

 

[Wildcat]

One of these will get you up to 18.0 cm height extension, but your brake cables may need to be lengthened, which means new ones.

 

[Mattley]

Thanks, I bought a bike stem extender, but the size is wrong, was able to increase the height from 90cm to 97cm but I need to increase up to 104cm. (picuture attach)

After extending the brake cable, I have to change the screw "diameter" (picuture attach).

My question is: Can I extend the fork size? Do you think it can work?

 

[Wildcat]

You can post the pics full size.
They don't make fork extensions that are reliable, but you could add longer forks, a 24" or 26" fork would give you more height but change the angles of the frame which would make it handle differently. Brakes on the front would be a challenge also. I would recommend getting another bike to avoid sinking more money into this one that might not suit you after all. That's always a good solution, another bike!

 

[Mattley]

Could you tell me the maximum angle? or fork length?
Attach example fork 26 41,5cm they are increase 8,5cm from 33cm, are they many?
Thanks in advance

 

[Wildcat]

All I know is that a 24" fork is about 2" longer and a 26" fork is 3" longer than a 20" fork.

 

[horsefarmer]

This 20" bike has a fork from a 26" lightweight...
https://ratrodbikes.com/forum/index.php?threads/columbia-powder-puff-racer-done.112607/

 

[Mattley]

Hi horsefarmer,
Thanks for your message. Could you please tell me the length of the fork?
regards

 

[RustyGold]

There are BMX bikes available with 22", 24", 26", 27.5", and 29" wheels...why so focused on stretching a 20" bike beyond it's design intentions. Also, if you really want to stick with 20", there are plenty of long frames available to stretch out the cockpit...5'10" really isn't too big for a 20"...but, if you are focused on seat height, you should probably be looking at 26" or bigger bmx bikes.

 

[AndyA]

Cousin Mattley:
Like Wildcat and Dr. Gold say, you'll probably be happier with a bigger bike. Pics are examples of some 24" bikes fitted for folks around 5'-10". These are not BMX-style frames but you could probably find a 24" MTB to convert to single speed (or keep the derailleurs if you want). Regarding longer forks, I tried a 26" fork on the black bike (Sun Retro) and it looked kinda cool, but the handling was squirrelly so it wasn't much fun to ride. Went back to the stock fork. Have fun!

 

[Mattley]

Thanks for your message.
The project continues on the 20 inch bike
One day I will explain to you why I insist on this size.
In a world preview, I show you the bike of the future (see the picture attached)
The fork in the picuter is 470 mm. I think it is too long.

Who knows the minimum and maximum angles of a frame that assure the stability and safeness of the bike? Is there a book on bike geometry?

I don't know whether to try to install a 24 or 26 fork. What do you think?

Thanks again
Take care. Best regards

 

[Mattley]

 

[MattiThundrrr]

It can make for some interesting handling. I have a 26 inch fork and wheel on a little bike with a 20 inch wheel, it is really funky to ride.
This is about mountain bikes, but the paragraphs on geometry and handling can give you an introduction to the concepts you are playing with
https://www.singletracks.com/mtb-gear/considering-upgrading-to-a-longer-mtb-fork-read-this-first/Sheldon goes deeper
https://www.sheldonbrown.com/rinard/forklengths.htmAnd here is a link to the build of my monstrosity.
https://www.ratrodbikes.com/forum/index.php?threads/the-wonky-donkey.109555/

 

[Wildcat]

I like that Orange dyno!
Time to get serious. How much increase in height (IH) is needed?
That is the height now (HN) subtracted from the new height needed (NHN).
NHN = 104cm
HN = 90cm
IH =14cm

The 20" fork tine length (20FTL) is 32cm. I measured my 26"BMX forks, the standard size. Both of mine measure (26FTL) at 40cm. 26FTL - 20FTL is the increase in fork height (IFH)
IFH is 8cm. A 26" fork adds only 8cm.

That won't get you to NHN, you'll need 6cm more.
I would keep your fork as is and add the height by a stem or handlebars.

 

[mikeeebikey]

You need Voris Dixon monkey bars!

 

[Mattley]

Thank you again for your messages. I will give you an update next week.
HI Wildcat, I saw the bikes you built (Purple Puppy and Bulldog) Could you please give me some details about the frame size? Thank you
Best
Mattley

 

[K_50]

Why not just go with a taller handlebar?

 

[Wildcat]

The taller bars would be the simplist and cheapest way, and keep the geometry of the bike.

My two mini velos both are using 24" bike frames (old 10 speed road bikes) with 26" forks. They need that much fork to keep the pedals high enough off the ground with 20" wheels.