Mountain Biking - Small Back Wheel good or bad idea?

I know I am in the mountain biking area and I really enjoy off-road riding but I wouldn't really consider my bike a mountain bike at least not any more. You see I put a 20 inch wheel on the back and I have a 26 inch wheel in the front of my bike (originally a 26 inch bike). While it has greatly increased accerlation it travels a shorter distance over time so I get exausted quicker than I normally would. Also my turning radius and ground clearance is decreased but my traction and off-road abilities are increased. So what do you think is this a good or a bad idea?

You tell me. Do you like it. I know I wouldn't. 20" is far to small for technical offroad for my style. 24" is pushing it but the bighit compensates with geometry changes for that size wheel. If you like, love it. Don't worry about what I think ;)...acceleration would be nice but you would be slower overall. Obstacles would suck but wheelie drops would be better. Manuals would improve.

Wierd... never heard of a 20 inch in the rear on a mountain bike. Could this be a new trend?! I remember when 24 inches in the rear was unheard of.

"Why would you want to LOWER your ground clearance?"

I can see it for stability reasons, but 20" is way too small for a mtb, 24" is the minimum.

Is there anything in between......Say a 22 inch perhaps?

Is there anything in between......Say a 22 inch perhaps?


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You're either crazy, or a pioneering genius. Not sure which quite yet? :p

Does it work though? The reason why I ask is because you are emulating the designs on climbing motorcycles. You know, those ones that compete to see who can get to the top of an incredibly steep dirt hill.

Some of those have long, long wheelbases and small radius rear wheels.

I can see how you can deliver much more torque up steep hills but you sacrifice balance since a small radius rear wheel doesn't have as much gyroscopic stability than a larger radius wheel. That's the reason why they invented the "cruiser class" of BMX (24 inch wheels) during the 80's for larger riders who wanted a better balanced bike.

In fact Gary Fisher is trying to push the 29'er (29 inch wheels).

But I'm not going to write off your invention quite yet, but you might want to try putting your front wheel down to a 24 since your front wheel will wheelie too easily doing climbs.

What of instead of making the front wheel smaller I made the back bigger but still keep it under 26inches

26 front and 24 rear is not common but it is around. It rides pretty well and is a good comprimise between the two.

You'd have to have some pretty smooth trails for that setup to work well. Changing wheel sizes is always going to be a trade-off, benefiting in some areas while hurting you in others. The main reason that smaller wheels (even 24") haven't caught on is that the trade-off you make in rolling over obstacles is too severe to be worth it.

Ever try riding your mountain bike up a small set of stairs? Air your tires up to a pretty high pressure to prevent pinch flatting, get some speed up and "ride light" when first hitting the stairs to make sure you don't pinch flat and you may be surprised to see that riding up a small set of stairs (5 or so) is really easy on a mountain bike. Try it on a bmx bike, or even a mountain bike with 20" tires front and rear if you want. It's nearly impossible, the smaller your tires are the larger the obstacle looks to it.

It's the same reason you always see mountain bikers dropping stairs and landing on them, you almost never see bmx'ers doing that because the landings are so tough with the smaller wheels.

At least have rear suspension if you're going to ride a bike with a smaller rear wheel so the rear suspension can help you roll over obstacles that the tire won't want to clear on it's own.

That's not to say that bigger is always better, if that were the case we'd all have 100" wheels on our bikes, but if smaller was always better we'd all have skateboard wheels on our bikes. Knowing it's a compromise figure out how it affects the terrain you ride on and decide for yourself. For the terrain most of us ride in 20" is too small.

What of instead of making the front wheel smaller I made the back bigger but still keep it under 26inches

As Maelstrom pointed out already, 24" rear/ 26" front is becoming more common especially for freeride bikes and hardtail dirtjumpers.

http://www.brodiebikes.com/2003/2003bikes/hardass/holeshot.php#

What of instead of making the front wheel smaller I made the back bigger but still keep it under 26inches


Just stop messing around with your bikes and leave it with 2 26"s.

I know I am in the mountain biking area and I really enjoy off-road riding but I wouldn't really consider my bike a mountain bike at least not any more. You see I put a 20 inch wheel on the back and I have a 26 inch wheel in the front of my bike (originally a 26 inch bike). While it has greatly increased accerlation it travels a shorter distance over time so I get exausted quicker than I normally would. Also my turning radius and ground clearance is decreased but my traction and off-road abilities are increased. So what do you think is this a good or a bad idea?

_First Post_

Charlie Cunningham (founder of WTB) made a bike like that around 1980 and showed it to the head of Suntour.
http://www.mtnbikehalloffame.com/inductees.cfm?page=99&mID=80

I found a 24 w\7 ( yes I only run 21 speed ) and i'm gonna try the little wheel adj- I put a smaller tire on my rear for something- oh ya -it seems to give me a bit more launch-power to the tire.? like 2.10 front 1.95 rear- it does make it feel dif? 20-26 is crazy- cool if it's a street cruiser.

didn't get to try the 24 inch rear today-really raining hard-went for a ride and my brakes made so much noise-had to go in and fix-got the wheel on though-

I own a Bighit so I have a 24" rear but I have also used 26" bikes many times. And on occasion bikes that come with 26" rear wheels but have been changed to 24".

The 24" gives me greater acceleration speed due to radius. The 20" would acceleraate even faster aswell. This also leads to a downfall. The top speed is reduced.

However, the bighit's geometry is designed around the 24" wheel, lot's of other bikes are not designed for this so it starts to become strange and lowers your clearance. The 20" would just destroy the angle parameters as they are for a 26" front and back.

Another problem is when you are on the trail the smaller the wheel the harder it is to get over an obstacle. This is why you don't see any full on downhill/freeride bikes with 20" wheels or even a 24" on the front, unless you include the Stinky JR which is designed for smaller people. However this problem is lessened by a certain degree by suspension.

Also the shorter the spoke length the stronger the wheel. This then means that smaller wheels, ie 20" should be stronger than 24" wheel, while this 24" wheel is stronger than a 26" wheel. So the 20" wheel has this advantage.

By looking at these factors, and I'm sure there are many others, I think that it would be preferable to leave the wheel alone. And if you must make a change, only put a 24" on so that the geometry isn't stuffed up too much. Anyway, now lot's of bikes are starting to incorporate the possability of putting in a 24" rear wheel in their designs so that they still run in the bikes optimal performance range.

BTW: I believe that the size of the wheel shouldn't be changed and that under almost no circumstances should the front wheel be changed on a bike that will be used offroad. This is because in my opinion it is more important for the front wheel to be able to roll over obstacles than the rear. And if you do change 24" should be the smallest you go.

I do agree with bentrim tho, you are either crazy, or a pioneering genius.

What you see a lot of these days is people running 24" wheels, but with HUGE tires. Up to 3" wide. A 3" tire on a 24" wheel is almost the same overall diameter as a 26" with a 2.1" tire. You see a lot of guys who do Urban and ride skateparks running 24" tires front and back!

L8R