Is the difference between the 3700 and 4500 substantial? I am considering upgrading, but don't want to spend $ on something that is not going to be a big jump in quality. I've compared the specs, of course, but being a newbie, am not sure of the difference in quality of the components.

A lot of it depends on what kind of riding you're going to be doing. The 3700 will be fine for a lot of people, then again the 4500 won't come close to handling what others ride on a regular basis.

I can tell you that I bought a 4300 (non-disc) about two months ago, and I have already outgrown it. I've been doing a lot of XC since that is what we have here in Florida. So far I bought Panaracer Fire XC tires which made all the difference in the world. I also outgrew the fork and just had a new one installed a couple days ago. I picked up an 105mm '04 Marzocchi MX Comp ETA to replace the stock 80mm RST Gila T5 which has made all the difference in the world. Then again, it cost almost as much as the stock bicycle, but now it's one heck of a setup for what I do on it.

The next thing to go will be the seatpost and I may eventually swap out the v-brakes for disc since we have loads of water we run through. Otherwise the v-brakes hold up just fine for the trails we have here. The rest of the components seem to work well for me. They aren't the best in the world and are already showing signs of wear, but they do their job.

I'm still relatively new, but I know if you tell everyone what kind of riding you do now, and what kind of plans and goals you have, the more experienced folks here can let you know what your best options are and where to put your money.

3700 is made in china and a very poor manufacture, Im not sure but the 45 MAY be produced in Taiwan, If so Id go 45, but not real sure, I have an 04 4300, and have replaced everything but the frame, derailuers and the handlebars, everything else that comes on it is caca. Id go for the better bike, you wont have to spend money in the future.

I ride XC. I'm in Kansas, so I don't need to worry about mountains I have signed up for a couple of races in Oklahoma and Kansas, for fun rather than glory. I already have the 3700 (bought last summer). Would I be better off upgrading it?

What is it that you don't like about the 3700, or are you just looking for something new?

I have seen a lot of people complaining about the components which come on the 4500, and $500-600 will get you a lot of new components to replace the pieces you don't like. You can get a pretty nice fork, bottom bracket, wheels, tires, disc brakes and upgrade the derailleurs for that price and get exactly what you want.

The 3700-4500 are all alpha aluminum frames and have the same geometry. The only advantage would be the quality of manufacture for the frame (my 4300 was made in Taiwan) which may or may not be an issue. My wife's 3700 is comparable in build quality to my 4300. Very nice welding jobs on all joints on both bikes.

I personally would upgrade the 3700, but like I said, I'm still relatively new to trail riding too. I also have a tendency to buy mid grade things and upgrade them as time goes on.

I would do this:
Tires to Panaracer Fire XC 2.1" - $35
Fork to Marzocchi MX Comp w/ETA - $239
Avid ball bearing disk brake (front and rear) - $140
Shimano LX hubs (or similar) $15 front + $30 rear
Wheels to WTB Dual Duty XC Rim - $80
Total $539

Figure in shipping and installation of everything if you're not up to it yourself or have a friend who can help out and you're probably looking at around the $600 MSRP for the 4500, but you'll have a lot more bike where I have found it really counts.

Like I said, I as a relative newbie would probably do the above, but I'm sure others will have more input.

Throwing $500 of upgrades at a $400 bike? No thanks.

Totally agree.

And snakehunter, can I have some of what you're smoking. Thanks.

Just out of curiosity (like I said, I'm still relatively new to this), why not throw $500-600 at a $400 bike which is a year old?

It seems to me that upgrading a cheaper existing bike would be more cost efficient than buying another bike, and you'd be getting exactly what you want. You could also potentially have more money left over to save for a full suspension down the road. I realize the derailleurs and shifters are going to be higher quality on a more expensive bike, but dollar for dollar upgrades seem like a better bang for your buck, especially when you're talking about what is essentially the same frame. When the stock components start wearing out, replace them with better stuff.

The 3700 is Alpha aluminum. The 4500 is Alpha SL aluminum, which is lighter. The Geometry is basically the same.

because for 1000 dollars you can get a bike better straight off the LBS' floor

Meaning you have a 3700 and are considering buying a 4500? I think you'll definitely notice an increase in quality, but if you really feel you've outgrown the 3700, you should probably consider spending the extra money on a 6500 or higher to make sure you have a ride that will fit your needs for several years. Also, if you are buying a new bike, remember there's other options besides Trek.

Sorry if I misunderstood the question.

Naaa Looks like you have a good handle on it. At least in my opinion

Nope, you understood perfectly. I hate to bother everyone with "which bike" questions, but here goes once again. I went back to the LBS, they have an '04 Trek 6700 that would cost me $480 with trade and a '04 4500 which would cost $250 with trade. Neither has disc brakes, they both have rockshox forks (the 6700 has the pilot the 4500 has the Judy. I rode the 6700 briefly (I was wearing dress-type shoes so didn't get to hit it hard

Is the 6700 something I'll keep and be happy with for a long while? As much fun as trading bikes in each year is, my wife will kill me.

I plan to go back and ride them both, but would appreciate your imput once again.

The 6700 is a worthy upgrade if you're into Treks and is worth upgrade with better parts as you see fit. I just thought it silly to throw $500 at a bike that was arounf $400 to start with

I think that sounds like a pretty good price and I do believe the 6700 will be good to you for several years. Living in Kansas, I'd say there's no need at all to worry about lack of disc brakes, especially for XC. Overall, you'll have a good frame with mid-level components that you can upgrade a couple years down the road if anything breaks or you want more. It's stock weight should be pretty decent for racing, as well. The 4500 is a little heavy for racing.

I don't know about that. Kansas mud isn't a picnic from what I'm told. Mechanical disc brakes (read Avid BB7's) might be something to consider down the road.

i say go with the trek 4500 . i own one and it fits me pefectly fine

Welcome to the party. You're only two months late