Bicycle Tutor

I have an entry-level Rock Hopper that I bought roughly 10 years ago. Since then I've mountain biked once. I'm in reasonable biking distance to work so I'd like to ride more. I've got slicks on, but I'm really not happy with the speed of the bike. What's the difference between a mtn bike and a so-called commuter/asphalt bike like the Sanford by Haro?

I'm not a natural gearhead, but I've got some aptitude. Are there mods I can do make the mtn bike have some road bike characteristics?

Getting slicks on your MTB is the most practical way to increase the efficiency. If you get even narrower slicks it may help a bit more.

The main difference between mountain bikes and road/hybrid bikes like the Haro Sanford is the wheel size. MTBs have a 26" wheel size while road/hybrids have a 28" (called 700c). The larger wheel travels more distance for every rotation. Hope that helps!

Mountain bikes are also generally heavier, too. Mainly because they were made to be able to take some punishment (along with other design factors), for the off-road thing. Otherwise, road bikes are often made to be as light as the materials would allow one to get away with. All my project bikes I have on hand weigh around 40 pounds or more (all mountain bikes). It just makes them harder to pedal on flat blacktop roads. There's really nothing that can be done about that.

Of course, it might be worth checking to see if all the drive-train (chain, hubs, bottom bracket) is lubed and in good order. If it's not, it can cause you to do additional work to get the bike moving, and would lower your top speed as well. I noticed that on my riding bike lately, and will have some work ahead of me.
Also, favor lower gears and a higher cadence in your rides. That will always help in overall speed, as doing that will generate more power.

I don't know what the average fit person can do, but you might check and compare on it. For a MTB you might be doing very well, and the only way you can increase speed is to get a road bike.

Does your mtn bike have a suspension? Steel handlebars? I have removed steel parts and replaced them with light alloy parts. I have also added narrower wheels with the narrow tires on my mountain bikes. If you have a front shock replace it with regular forks that are cromoloy.

Drop bars (road bike style) also make a pretty big difference. Both because you're more aerodynamic, but also because you are in a better position to transfer power to the pedals. You can put drops on a mtn bike, but you do have to change brake levers and figure out where to put the shifters. Cutting an inch or two off the end of your flat bars and maybe getting a longer stem are an easier way to achieve some of the faster body position also.

On a 10 year old bike, I'd guess all the bearings need maintenance. This can have a big impact on how fast a bike is, especially if you've got any bad bearings that need replacing. A worn or badly lubed chain will also eat up a lot of your pedaling power.

Check that all the basic mechanical issues have been looked at before you drop a lot of money/time changing the bike around though. If you've got a bad hub, etc. slowing you down, it will still be there after you make all the other changes suggested.

I wouldn't be too quick to change the handlebars to the drop bars, depending on how your commute to work is like. If you are commuting through city traffic, I find that using the flat mountain bike type handle bars much better for giving you control weaving in and out of traffic. However, if you are commuting through more rural areas where traffic is not a concern, the drop bars would be better.

Another big thing about mountain bikes is that they run MUCH lower tire pressure, which is great for navigating rocky terrain, but bad for speed. road bike tires can easily run 100+ psi, and mountain bikes generally run under 50psi. take a look at your tires and see what that max pressure rating is, and run it at that. i run my current tires at about 40-50psi if i'm mainly commuting, but i'll drop the pressure down to about 30psi for off-road stuff. it makes a huge difference (the higher the pressure, the less rolling resistance the tire has.) i've never looked, but see if you can find a MTB tire that can run higher pressures. unlike you're running time trials or something, i personally think the width of the tire makes less of a difference than the air pressure for us regular folks. also, if you've got suspension forks, see if there's a lock-out. if it's got a lock-out, use it to "lock" the fork and keep it from moving vertically.

But as stated by others, i would imagine a complete takedown/cleaning/lubing of the bike would make a huge difference. my LBS charges about $100 for a total disassembly, cleaning and lube, and they check all the bearings as well.

If it has the Suspension (Shock) then you may wanna tighten them up for a rougher ride. Too bouncy will throw you out of cadence as well. For instance if you noticed that almost all Commuter/Road bikes have solid frames.

Higher pressure -> lower rolling resistance is wrong (or at least not completely correct) under "real" conditions (non-lab conditions). As the pressure of the tyre is increased, the amount of flex is decreased, that is correct. But at the same time, the tyre will not absorb small shocks any longer instead lifting the bike and dissipating the energy in the driver. While some of the energy that goes into tyre deformation is "put back" on the road, the potential energy that goes into lifting the bike is "lost". That is also the reason why full suspension bikes (that are set up correctly) are faster than rigids (see Bike-Magazin 01/2010). When plotting rolling resistance vs. pressure the curve decreases a bit as pressure is increased. At some pressure however, there is a sharp increase (slowtitch.com)

Interesting Joe, I figured that the extra bounce would be like a rubber band. Lol like I always say learn something new everyday

Oh and also note that for the same compound and carcass build (layers of fabric etc.) and pressure wider tyres have less rolling resistance than narrow tyres since the angle of deflection at the road contact point is smaller. Narrow tyres have less air drag, though this is only important when having an average speed greater than let's say 30km/h.

(Jan 4, 2010 07:19 AM)Joe_W Wrote:  Oh and also note that for the same compound and carcass build (layers of fabric etc.) and pressure wider tyres have less rolling resistance than narrow tyres since the angle of deflection at the road contact point is smaller. Narrow tyres have less air drag, though this is only important when having an average speed greater than let's say 30km/h.

Here is a picture of it, guess the part about the full suspension would not apply to this one lol....
http://www.nigelsecostore.com/blog/2007/04/

(Sep 19, 2008 09:52 PM)ptcommuter Wrote:  I have an entry-level Rock Hopper that I bought roughly 10 years ago. Since then I've mountain biked once. I'm in reasonable biking distance to work so I'd like to ride more. I've got slicks on, but I'm really not happy with the speed of the bike. What's the difference between a mtn bike and a so-called commuter/asphalt bike like the Sanford by Haro?

I'm not a natural gearhead, but I've got some aptitude. Are there mods I can do make the mtn bike have some road bike characteristics?

There are differences in the geometry and the gearing mostly. You can change the cranks for a larger ratio one, which will give you more speed. also you can change the geometry, raising the seat and lowering the handlebar to be more aerodynamic. but eventually if you want to go fast, you need a road bike.

Well, you cannot change the geometry of a bike. If you change the seat position on the MTB to match that of a road bike you'll end up with a bike that is probably very difficult to handle. This has something to do with the distribution of weight on the wheels and the position of your center of mass. Changing the gearing will not help if you're slow 'cause your seat position is not aerodynamic.