You don’t need 27c wheels to be competitive in a triathlon – and you can certainly complete a short course event easily on converted MTB. Many of the top Japanese guys actually race on little frames with 26 inch wheels and totally kick butt.

I wouldn’t even bother swapping your bars out – if you want to optimize your riding position try working with what you’ve got on the MTB – inverting you stem will often give you a zero rise which will lower and spread you center of gravity – in effect reducing the pitch of the front diamonds angles.

You don’t need aero bars to adopt a aerodynamic riding position ! Just drop your forearms onto the top of your bars or place your thumbs over the top of your bars and clasp the stem with both palms and tuck your elbows in.( I’ve hit over 70 kph on sealed downhills on MTBs doing this). You don’t really have to put a lot of effort into controlling the bike in a triathlon – it’s pretty much point and shoot.

To convert to a rig that will really rock you will need a set of rigid forks, a new back wheel, chain, and a couple of biggish chain rings.

If you are a taller person you could try some longer cranks – jump up to175’s.

All these changes will totally depend on the size of your frame, the dish of your new rear wheel , your chain line and your bottom bracket dynamics – but if you can get these things dialed all at once by a good mechanic – there’s no need to splash the cash for a tri-bike just to hit up one or two events a year.

Don’t be put off by people telling you your MTB is too heavy. It won’t be. Now that you can draft in triathlons – who cares about weight?

Using narrow slic tires helps, also gearing is different, so you could change cassette and chain as well. I don’t know if you could even get a rigid fork so you could have a lighter bike.

But the wheels are smaller on a mtb (26″) vs something around 29″ for a road bike (yea yea, roadies use cc, but I think they’re similar sized to a 29″). This will probably make your bike easier to accelerate but slower in the long run. You would be running handicapped, IMHO.

Trying to change the bar& seat position will just mess you up.