Well, for a normal mountain bike, possibly not (unless he is running some insane DH tires on it) - but given that he has a Walmart MTB, I reckon just going to a standard "brand" MTB with proper parts will get him a significant boost in speed.

i say wait until you can do ~15 mph before getting a road bike.

unless you're a senior citizen then just get one now.

i recently switched from a MTN bike to Road bike and there is quite a big difference when going downhill or with the wind. when going against the wind though the difference is smaller.

on the average i would guess you would gain about 10% speed.

Not more than double.

True, true - the real improvement is probably going to be a fair bit more than than a regular MTB -> Road bike, that's all I am saying.

Going from a bottom of the line Trek mountain bike mounted with 2.0" slicks to my Defy 2, it accelerates and handles noticeably better, but the biggest difference is definitely from the position change. Going into a headwind, I've notice about a 3 km/h difference with roughly equal effort

I occasionally ride my 29er MTB on the same roads where I train on my road bike. With non-knobby hardpack-oriented tires, and using the same effort, I average about 1.5 mph slower on the 29er than on my road bike.

Depending on what you mean by "a fair bit", I've seen a few day laborers who should join a pro tour team.

I agree it's pretty pathetic. Last night I ran 5.16 miles in 50 minutes. So I'm not in great shape, but I thought I should be able to ride much faster than I am.

I might be able to borrow a bike from someone to test. If not, it sounds like changing the tires may be the way to go.

Thanks for all of the help guys.

Meh, have fun and just try not to come in last. Keep riding. I GUESS you can keep running and swimming too :)

That's what i was thinking but didn't wanna embarrass the OP..

Why do you think I'm eager to blame it on the bike? :-)

It seems to me if you can run nearly the same distance in only 10 minutes more time (OK, it's .84 mi less, but I think you get the point), there is either something wrong with your bike, or you're doing something wrong on the bike. Are you talking about similar terrain and wind conditions?

As others have mentioned, is your tire pressure alright? Switching to slick tires will help out, but even on knobby tires I would expect a better result. Has the bike been checked for other issues? If you haven't ridden much, do you know how to shift properly?

I've ridden with people on MTB's who can hold 17-20mph for 5mi. or more and they are not dedicated riders. I think you can squeeze out 15mph on your MTB.

The bike ride had a little more elevation change, but I would say the conditions were pretty similar.

As for the condition of the bike . . . maybe I need to read up on proper bike maintenance. I haven't really done any besides filling the tires with air until they felt "tight."

And I guess I should read up on shifting too.

Honestly I have to believe that you calculated something very wrong when you figured out your pace/distance/time on the bike. Unless there was a ton of uphill you had to have gone faster than that?

Don't underestimate how slow some people can actually be. My office building is located right on a bike path (yes, literally) and the break room window looks out onto the path. I see many people pass very slowly by the window who look like they are actually working hard, on hybrid/mountain/commuter/cruiser type bikes. The whole cadence spectrum too, some doing like 25rpm weaving side-to-side as they try to push their highest gear at 10mph and some spinning furiously in their lowest gear and barely moving. One of these days I'll shoot some video, it's pretty funny.

Are you doing the tri just to finish or is time, personal or otherwise, a consideration. If you're doing the tri for the experience, and to see if you can finish one, good for you, but you should be fine in the mountain bike.

If you're going for a decent time, I think you need to buy a cheap, used but working, road bike. I see them being given away at yard sales pretty frequently, and on sale for dirt cheap, often sub $100 on Craigslist. Borrowing is a great idea, but it would be good if you could train on the bike that you plan to race on.

Please do

Well, I was looking at the results from last year thinking I could beat last place pretty easily. His times were 22:49, 1:06:08, 48:46 (swim/bike/run). Then I was looking at the pictures from the event and this guy is middle-aged, overweight and was walking.

I'm 29 and at a fairly good weight after loosing 25 lbs the last few months. So yeah, if I can't get my time below 1 hour that's going to be a hit on the self-esteem.

I pumped up my tires to 60 psi and I did 7.75 miles in 52 minutes. That's the same average speed, but I did a different route that's a little tougher, so I'll consider that a slight improvement. Still, I have a long way to go.

How are you measuring the distance? If you are using a wheel-sensor based computer, did you properly calibrate it?

Edit: Also, these are wide and knobby mountain bike tires, right?

You're more or less at your prime, which does not jibe at all with the results below:
There's something massively wrong here, have you checked that your brakes aren't rubbing, your watch is not running at double speed, and that your cyclocomputer is set to the proper wheel size?

I'm measuring the distance with Google Earth after I ride and I'm pretty sure the watch is right. These are wide, knobby tires.

Brakes? Um . . . yep, it seems the back brake is rubbing some. I'll have to fix that and see what kind of difference it makes.

It should be quite a big one, depending on how much the brake was rubbing

My two cents...

The difference between a walmart MTB and a decent roadie (or decent MTB) will be mostly the amount of energy you are using. You may see a slight gain in speed, but mostly it will feel easier to go fast. The amount of energy lost to the drive chain is significant, even on $5k bikes. If you've ever had a chance to try a decent fixed gear, you'll see what I mean. The shoddy components on a wal-mart special are just going to exacerbate those losses more than is necessary. That'll kinda make it feel like you're wearing bricks on the end of your feet. One other big loss is the silly mock suspension things they have on sale at walmart. They've got the resistance on the shocks so low that you spend almost as much energy bouncing up and down as going forward. If you have one of those, then the best thing you can do is to get something else as soon as possible, even if it's just a beater you got at a garage sale for $30.

Also, to improve your time right now, adjust your seat and watch your cadence. Most people I see ride with the seat so low their knees are in the way of the handlebars. You should raise it until you only have a slight bend in your knee at the bottom of the pedal stroke. That'll give you better leverage and body mechanics and probably make you hurt less. You also should be completing about one and a half full rotations of the pedals every second. That's a ball park figure, but it will make your energy output lower for the same speed. Lowest reasonable cadence is about 60 rpm, or 1 rotation per second.

wut

Drivetrain losses on chain-driven bikes are about 1-2%

Rolling resistance from wide knobby tires and aerodynamic drag from an upright position are going to waste far more energy than extra drivetrain losses with shoddy components.

when I weighed 240 starting out riding last year I would do 9 miles in 56 minutes using a 40 lb Iron Horse.... 2 months later on a Schwinn Peloton road bike I would do 10 in 45. I can't quantify the road bike itself helped more than the added 2 months, but I remember the placebo effect of the road bikes feel. With its stiffness, lightness and overall stability giving me the ambition to try harder for longer.

I rode a wal-mart bike for about a year back in the day. Seemed like I couldn't go more than a day or two without hearing a new noise, rubbing, squeaking, etc. coming from the drive train. I'm willing to bet a lot of energy was lost that way. It also felt like I was dragging the chain around it's circuit rather than driving the bike forward.

On fairly efficient bikes, yes. I'm willing to bet that friction on various parts of the drive chain will raise that to 5-7% on a walmart bike. Pretty significant, if not a life changer.

Yes, but that's already been covered pretty well in this thread.

+1 90% of changing to a road bike is the experience.

Make up your mind. We were talking about "The amount of energy lost to the drive chain is significant, even on $5k bikes".

I was making the point that there is some inescapable energy loss there, but cheaper components make it worse. Like I said, try a fixed gear that is set up correctly, and the energy loss drops enough to be noticeable. My bad for getting off topic in the middle of a paragraph, but geez, little jumpy are we?