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trek 3900 upgrade advice

bj639bj639 Posts: 76
edited September 2014 in MTB buying advice
Wonder if you wise folk could offer some advice. I recently upgraded my bike so passed on my old trek 3900 to my nephew whos just getting into the game.
This is the bike: ... /trek/3900

He wants to upgrade it over time.

As its v brakes he wants to upgrade to discs which looks like changing wheels and brakes at the same time.
Wheel wise hes looking at these ... -prod87466

And brakes these ... prod124958

I thought for his use the deore brakes would be plenty ( hes not even gone off road yet his main thing at present is just shedding some weight on roads and cycle paths.)

So two questions would these upgrades fit that bike (the fork does have the brake mounts) and if so are they a decent option?

While i know the basics the rear wheel cassette compatability was a concern


  • The RookieThe Rookie Posts: 27,748
    New wheels, possibly new frame (unless it has disc mounts on the rear which I can't see - although it says it does these specs are not always right), will also need new shifters as I think that has combined levers.

    Unless he's not riding it as a mountain bike, forks and tyres would be a better first upgrade, I wouldn't recommend crossrides anyway and (not sure here what options are available as the website is being obstructive) they aren't compatible with the centrelock discs in the photo.

    To be honest that's a lot to through at a 3900 which will still then be a 3900, be better placed selling it and putting the money into a better used bike with better everything else, if he wants discs then convert using used parts at more sensible prices and comparable to the rest of the bike.
  • bj639bj639 Posts: 76
    frame deffo has disc mounts as does the fork (hence the reason him doing fork later)

    Had a few say the treks were good frames anyway/.

    Hes a mechanic by trade so I think he quite likes the idea of building one himself s to speak.

    Any other recommendations for wheels then? He wants to upgarde the cassette etc down the line but would new wheels mean a new casette needed at the same time?
  • supersonicsupersonic Posts: 82,708 Lives Here
    You can put the old cassette on new wheels, but would be the last thing I 'upgraded'.

    The Rookie is right, your best bet is selling up and getting something new. Is not really worth the expenditure.
  • bj639bj639 Posts: 76
    So ignoring the components iand upgrade cost is the fra,e itself no good or just a case of buying a bike as a whole would be better value? Not sure he can do a big lump sum hence upgrading as he goes. For the price of wheels and brakes £300 ish? Is he going to get anything worthwhile long term at that price?
  • The RookieThe Rookie Posts: 27,748
    The frame is OK, but not really good.

    He'd be better off selling the bike and buying a better quality used one for £350-400 you can get some pretty nice used bikes or using used parts to upgrade much much cheaper and doing the forks which will make it nicer to ride, brakes won't make it nicer to ride, just stop easier in muddy conditions.
  • bj639bj639 Posts: 76
    If he changes the wheels he will have to do brakes at same time (unless hes fine using v brakes on any rims?)

    If he does the fork he has to do wheels a d brakes as well in one go whereas leaving fork does mean he can do he other two bits then the fork later as it has v brake and disc mounts so is more flexible.
    I will speak about selling the bike though he might be a bit miffed me selling it then him having to buy another so soon!
  • The RookieThe Rookie Posts: 27,748
    bj639 wrote:
    hes not even gone off road yet his main thing at present is just shedding some weight on roads and cycle paths.
    Alternatively do this, the brakes will add as much weight as the wheels will lose, some ideas
    1/ Better and lighter forks, good ones can be found used for circa £50-70, investment for the future as he can swap them onto any new bike. He could go disc only and get a cheap front wheel and mechanical disc brake to minimise cost, or get some V/Disk ones. E.g. I have some Manitou Scarab Elite, V and disc, cost me £56 delivered off ebay and weigh in at 1.5Kg (so over a 1Kg saving off his).
    2/ Decent quality (lighter) tubes and better (folding) tyres can save up to about 1Kg and roll faster with better grip
    3/ look elsewhere on the bike, aim for parts he can then swap later onto a newer and better bike, for example I looked at a Trek 3700 yesterday and it has steel bars, if his are steel then a pair of cheap alloy or carbon bars off ebay will save 250+g for about £6-7, or maybe a decent quality replacement crankset such as a Deore HT2 or even an older square taper.
  • bj639bj639 Posts: 76
    meant his body weight mainly but your points are still good. Tha bars,seatost etc are cast iron i think! so these would be upgraded along the lines too because they are pretty heavy and are relatively cheap to do.

    I guess the hard thing is the fact its v brakes and changing the fork affects that and then the wheels. I shall pass on your advice and see what he wants to do. Appreciate the help, might be back with more questions later!
  • The RookieThe Rookie Posts: 27,748
    A cheap disc front wheel and mechanical calliper off ebay or similar should be possible for £25-35 so he could get some decent disc only forks and use those as a stopgap.
  • bj639bj639 Posts: 76
    Yeah i did wonder about splitting the wheel and brake upgrades.
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