Mountain bike in triathlon? How much disadvantage?

I am competing in a triathlon and my only problem is the bike I have. It is a mountain bike and I've been told that I am at a great disadvantage by using this. How much is it going to disadvantage by ability to ride fast and well? I need answers and possible solutions as soon as possible.

A mountain bike isn't really ideal, but the real question is how well do you hope to perform? If you think you have a chance to be competitive, you should borrow a time trial bike or a road bike and go for it. On the other hand, if this is your first race, you are likely to have issues with your transitions, etc. and the bike probably won't make too much difference in your overall standing.

That said, here are some things you can do to make your mountain bike faster on the road.

First, get some lightweight, narrow, slick, high-pressure, 26" road tires. These will reduce the rotating mass of your wheels allowing you to accelerate more quickly. Also, they will reduce rolling resistance of the tires letting you go faster.

Secondly, get clip-on aero bars for your mountain bike. This will reduce wind drag helping you to go faster.

Thirdly, lock-out your fork so it doesn't absorb energy as you pedal. If you have a full-suspension bike lock out the frame shock, or set the "platform" to high, as well.

If you want to get really fancy, you can swap out your suspension fork for a rigid fork. Being lighter than even the best suspension forks, a rigid fork will save you a pound or two of weight. (Most bike shops have lots of rigid forks lying around because they have upgraded customers to suspension. They'll usually sell a rigid fork for $5-$10. If you don't know how to change a fork, the shop will charge $40-$50 to install it for you. Watch and get them to explain how they do it so you can do it yourself when it is time to put the suspension fork back on. BTW - You don't really need to have a fancy tool to remove and set the bearing race. A hammer, a flat head screwdriver and some care will suffice.)

If you enjoy the triathlon, you may find you want to get a tri-bike which will be somewhat lighter and more aerodynamic than your mountain bike.

Hope this helps and hope you have lots of fun.

it depends on your goals. my guess is that you arent out to win the race. you are doing this to push yourself and to finish. if that is so, you dont need some cutting edge time trial bike. yes, your mountain bike isnt as effecient on the roads, and will not be as fast as a road bike. you can limit the difference with street tires that are higher pressure and smoother. you can even clamp a set of areo bars on for that matter. no, it wont be as fast as what a road bike would be, but you arent out to win. you are out to see if you can do it and if you like it. if you do, you will tend to gravitate toward better equipment as your desire to do well in the sport grows.

Disadvantage is 20%. This is split between tire resistance caused by wide, rough tread tires and low pressure. Also, there are some gearing efficiencies that road bikes offer. Add in the aero aspects and Yes, 20% is a good number.

If you must use a MTB, replacing the tires with high pressure slicks, usually 1.5" width or narrower will help you tremendously. A set of tires and tubes is relatively cheap and it the single most effective upgrade you can do.

Here's one example: http://www.nashbar.com/profile.cfm?categ...
or
http://www.nashbar.com/profile.cfm?categ...

If the only bike you have to compete on is a mountain bike there are a few things you can do.
1) change your tires from the standard off-road tread to a road/slick tread. These tires roll very close to the same as the skinies that come on road bikes.
2) Mountain bikes have a lower tooth count on the large ring gear, 44t, on a road bike the big gear is 50t+, check with your local bike shop for what is available for your crank set.
(you still will have minor disadvantage gearing/wheel wise as you most likely have 26" tires and not 29"s, 29" compare very well with a road bikes 700cc rims.)
3) Standard mtn bike handle bars don't allow a very aerodynamic position, add a set of clip-on aerobars to get you in to a better aerodynamic position.
After these changes the difference was not all that great, for me the difference between my mtn bike and road bike was less than 3mph.(on the flat, going downhill the difference was greater)
At first I had only my mtn bike, but got tired of swapping parts from off-road to road and finally bought a road bike. If you are going to compete at this on a regular basis you might want to consider a road bike, or perhaps try X-Terra. (an off-road triathlon)

The difference is huge. H-U-G-E

If you can use a road bike. Borrow one. Rent one. Steal one ; ) . Only kidding. I love mtn biking and own two. But if I was in a race there is no way I'd even entertain for a millisecond using one for a race. I'd rather ride a junker road bike than my mtn bike.

To paraphrase a common answer in this thread - if you're in it to win it, find a road bike. You are at a big disadvantage on a mountain bike.

Even with road tires, you'd have to be a monster on the bike to keep up with roadies. The difference in the gearing between road and mtn bikes is the main (although not only) factor that'll put you at a disadvantage, and it's substantial. I've done a tri on a mtn bike and I've also done a few MS150's on a mtn bike and although the dynamics of those two events are entirely different (a race vs. a charity event), there was no way to keep up with those on road bikes.

That said, when you show up at a tri with 'substandard' gear, be it a mtn bike or a pair of lame running shoes or whatever, there will be a subset of participants who are going to look down there nose at you. Call them 'tri snobs' or posers or whatever. There's nothing better than finishing ahead of these people when it's all said and done.

Conversely, there are as many if not more participants who are stoked just to see someone they'd assume (based on your gear) is new to the sport and they're very encouraging when they see you "gut it out" on a mtn bike.

Along these lines, I'd advise you to go with the mtn bike, just for the fun and experience (I'm assuming that this is your first one). Afterward, if you find that you're scouring the web to find tri's to register for, then upgrade the bike (just don't become a tri-snob).

Do your training on the MTB. Borrow a road or tri-bike from a similar-sized friend for the race. Assuming this is not going to be a one-time-only event for you, you're going to hook up with a group or a club at some point, why not now? Most triathletes have several bikes hanging around in the garage. I've lost count of how many people have done their 1st tri on one of my bikes.

As for speed difference, I'll keep it simple. I run out of gears on my MTB at 27mph, on my tri-bike, 35mph. Don't worry too much about that, though. Regardless of your ride, you're not going to win first time out. Welcome to the sport, enjoy the experience.