Gdubeck

So, I could use some input. I just recently bought a Mongoose MTB. its in great shape, but, I want to make a few changes to it. my first thought is to switch from a straight bar set up, to a drop bar set up, switch the gearset from a 3 x 8 setup to a Shimano 105 2 x 12 set up. i'd like to keep the rims that are on the bike and swap the cassette to the Shimano 105 12spd. does this sound like a doable build?

alcjphil

You are going to have to wait at least 3 years to do this. Shimano has not yet brought out Dura Ace 2 x 12 which will be followed a year later by Ultegra and 105 the year after that
It is also likely that a road crank will not fit on your bike

Koyote

To be blunt, it sounds like you bought the wrong bike.

Maelochs

MTB bottom brackets tend to be 73 mm wide, I believe, while most road BBs are 68 .... except for the ridiculous range of press-fits .... but it is likely, as @alcjphil notes, that a road crank set might not fit. You might be able to find MTB crnaks with 48 teeth on the large ring, which will be pretty close to road set-ups.

Changing to drop bars is expensive, because brifters (integrated shift-brake levers) tens to be about ten times more expensive than straight-bar shifters.

There might be an issue with cable-pull---as far as I know, new Shimano MTB derailleurs pull a different amount of cable than do road shifters, which means the derailleur won't move precisely from cog to cog, but will land halfway. if you use a road cassette and derailleur that shouldn't be a problem.

My question is .... what's wrong with the bike you own, and is it really the bike you want. I have to agree with @Koyote, you might not have bought the best bike for the kind of riding you want to so. (By the way, I assume it is an older mongoose? What model is it , please?

If you wanted a gravel bike with a front shock ... I know Cannondale makes one, and I assume others do as well. As for changing from 3x8 to 2x12, why? You could get about the same number of usable ratios with either set-up, and if you went with say, a 48-38-28 chainring and a 10-32 cassette, you could have almost the same range of gears as a road 50-34x11-28, just a little extra low end for the softer soil or steeper climbs.

What do you want the bike to do>? How do you want to ride it? What can it not do now which you want it to?

I could offer advice if I understood the situation better.

Milton Keynes

I don't want to dampen your enthusiasm, but my question is why would you spend the money to upgrade a Walmart bike? Probably best to save that money and put toward a good road bike.

Phil_gretz

The original post cannot be serious.

Milton Keynes

And don't call me "Shirley." I don't know if they're serious or not, but putting upgraded components on a Mongoose is like putting lipstick on a pig. You'd have a cheap bike with a few expensive components, and you could easily spend more than the original cost of the bike on upgrades. Would it really be worth it after going through all that time, cost, and effort? Just keep the Mongoose around for a beater bike and save money to buy the bike you want to turn the Mongoose into.

And I admit, I have a Roadmaster bike which was given to me that I spent money to put new tires on, but that's as far as I'm going to "upgrade" it. It works well as a beater/gravel bike and if it falls apart, I'm not out much. But I realize that it's a cheap bike.

barakah

i will not worry about some negative comments on here! The important thing is the level of happiness you get on your bike, biking should be fun!!! Regardless which brand it is; I have a Walmart bike and I am more fit than most of the riders where I live that rides a 5 thousand dollar bike. I would recommend wheels, that would be the first I would swap.

a bike you could buy, a fit body and very good health is never for sale. Ride safe my good friend.

delbiker1 

I would not consider the posts as being negative. Nothing wrong with buying a low cost bike, or "upgrading" if that is how you wish to spend your money. In the end, it is almost always less expensive to purchase a bike, that fits and suits your needs, with the better components to start with. Even more so if non-compatible components are purchased. As stated, level of happiness, satisfaction, is important. If riding a $5000 dollar bike is what does it for you, it is your money. Ones fitness has nothing to do with the price or quality of the bike and components. I would also suggest doing some research on the components before purchasing the bike. Not being critical, stating opinion and trying to be helpful.

Thomas15

From the OP: "...does this sound like a doable build?"

I'm of the opinion that if you throw enough time and money at a problem, the problem goes away. So it might be doable to some degree as long as time/money isn't a concern.

This reminds me of a guy I knew when I was a kid. He crammed a Chevy big block motor into a Vega. He couldn't keep it road worthy but it did work.

Maelochs

I have the same thought as most posters here ---- Why spend many hundreds of dollars on a $200 bike which is never going to work very well no matter how much one invests?

If a person plans to spend a few hundred on wheels and a few hundred on brifters .... why not buy a $600 bike which is going to be much, much better than the Mongoose?

In my experience, the cheap bikes break too easily. Not all of them, always ... but I spent many years buying and riding cheap bikes and most of the Walmart-level bikes broke under hard use. I was constantly collecting old bikes and scavenging parts trying to keep ahead of parts failure.

I suppose the OP could buy a bunch of yard-sale bikes, or even a Walmart road bike, and swap parts around .... but why not just take all that money and buy a better bike which suits the OP's needs and desires? For $500-$600 one can get a very decent gravel bike off BikesDirect---well, once things are back in stock---which would do everything the OP apparently wants his bike to do. S/he could still have the Mongoose for tougher trails .....

Milton Keynes

I don't mean to be negative about Walmart bikes, I have a Roadmaster I'm using as a beater and gravel bike. It's a bike I don't mind taking out on rough gravel roads and riding it hard. It's just that I don't see much benefit in outfitting a cheap bike with expensive components. But to each his/her own.

My hybrid was a $250 Vilano bike from Kohl's online. I rode the heck out of that bike and enjoyed it. Probably put 5,000 miles on it, did two centuries, dozens of half centuries, and several metric centuries on it. However, the bearings in both wheels started going bad, and I broke the rear axle. The bike shop guy said that it was a poor design, putting a lot of stress on one side of the rear axle. I would have to get a new wheel for it, which would have cost me around $170-$190 to upgrade the rear wheel to a better one. The front hub would also have had to have been replaced, probably at another $100. Since I only spent $250 on the bike, I couldn't see pouring any more money into it, especially since I was wanting a road bike. So I browsed the local online bicycle buy/sell/trade group and found a decent old Trek road bike for $125. I'm back on a bike at a cheaper cost, plus I have a better bike.

So for me it's really all about cost effectiveness, since I don't have a ton of money to throw around on bike repairs or upgrades. As much as I would like to get new wheels for my old bike, it would be a far better deal to get a new one. But having learned my lesson with cheap Chinese bikes, I'm not going to go down that path again. Just feels like throwing good money after bad.

wphamilton

Mongoose MTB doesn't really pin it down. There's cheap Target store Mongoose and there are Mongoose bikes every bit as good as the $500-800 online bikes people are talking about.

Replace cheap parts with better parts and you've eliminated the main thing wrong with cheap bikes. In fact, some of the things most often needing improvement are sometimes the cheapest. Wheels and tires can be an enormous improvement in the ride, and I'm talking a $40 wheel, not hundreds.

There is nothing unsound about that in general. But I think I wouldn't convert a Mongoose to a hybrid road bike. I think you might be fighting geometry. And if it's one of those where you really need to replace front suspension, headset and bottom bracket, it may start getting more expensive than was planned. With complications. You'd be better advised to stick with MTB configurations and upgrade those to a desirable level.

Ironfish653

I think, based on what I’ve observed here, and my own observations, is that most new cycling enthusiasts (as opposed to people who just own a bike) is how much the frame contributes, besides just as a place to hang parts, especially as you move up the price/ performance tiers.
There’s not a whole lot of difference between the frame on a $200 Tourney bike and a $500 Claris bike; 4130 vs hi-ten or 6061, marginally better fit and finish, but the difference in components will be really apparent.
Now, while the difference between Claris and 105 is even bigger, the construction and finishing kit of a $1200 bike is an even bigger jump, with more considerations given to performance than a ‘price point’ bike.

You might be able to throw enough parts at an aluminum Denali to make it into a reasonable approximation of a Trek FX, (although it probably wouldn’t save you any money)
Putting 105 and drop bars on it doesn’t make it into a Cannondale Synapse.

wphamilton

This at least I can speak with direct experience. The Denali (a hybrid IMO) has road geometry and drop bars already so it will never approximate a Trek FX, but I know what you're getting at. However, upgrade a Denali to altus and acera level including shifters, improve the wheels and the Trek FX won't have anything over it.

I think we tend to vastly overvalue the differences in these low end frames. The only real difference (except for the ridiculous ones) is maybe a pound of extra weight.

RiceAWay

The rear triangle spacing is probably incorrect for a 12 speed. Drop bars on a bike that has a suspension from end is not a good idea.. What it sounds like to me is that you're looking for a modern cyclocross bike.

2 x 8 is a pretty good setup. While the manufacturers have done a pretty good job of making you think that more gear are better, they aren't. 8 speeds are close to perfect. you only have to shift one gear at a time. with the tens and 11's you spend all of your time shifting many gears to get to the place you want to go. So your main gears turn out to be two gears below your fastest gear and the bottom two gears. Lance Armstrong requested that Shimano make him a 9-speed so that he could have his close ratio racing gears and one super-low climbing gears. Immediately everyone had to have what Lance had and they bought 9 speeds. So that worked so well they brought out a 10 speed and again everyone had to have a totally new group. Then 11. Now a 12. Since Shimano presently makes plenty of parts for 8 speeds keep it. Dump the triple and buy a new front derailleur unless you're riding off-road. Then don't change anything.

RiceAWay

The rear triangle spacing is wrong for more than 8 speeds. The wheels will not take more than probably an 8-speed cogset. The chain would have to be changed. Drop bars on a suspension bike is dangerous because of so much weight on the front. The problems are endless. But don't think that a Mongoose frame has any problems other than excess weight.

Milton Keynes

That's why I think it's better if they just save the money they'd spend trying to upgrade it and buy the bike they want it to be. Then keep the Mongoose around for a beater bike.

Maelochs

OP has yet to return and thus has not provided any more info about the actual bike he plans to heavily modify.