Just bought a new road bike and I'm thinking of tweaking my old bike to make it a more effective commuter. It's a 20 year old Trek carbon fiber road bike, triple chainring, original Rolf wheels, all Shimano 105, 23/25mm tires, etc. Aside from a wider tire, what else could/should I consider changing? Anyone done something similar?

Fenders. Lights. Something to put your lunch or a change of clothes in.

Can it handle a rack? I have done a lot of commuting and I find a rack to be essential. I hate carrying a ton of stuff in a back pack, and if I am going for a long day, where I might need a change of footwear, a couple sets of clothes, two meals, four bottles of water, plus whatever tools and accoutrements I would need to do what I need to do ... plus tools, spares, lights, lock, etc ... . that knapsack gets pretty darn large and heavy pretty quickly.

Also, you will need to decide if you are a fair-weather commuter---and what constitutes 'fair weather." Any cold-weather or rain gear will need to be stored on the bike or in your bag when not in use ... but you really can't leave it home because if you come out of work and it is pouring rain .... And cold-weather gear tends to go on thick and come off in layers as you ride.

Everythihng depends on everything else. What do you mean by "commute?" A 35-mile ride on good pavement twice a day, to a location where you could store a change of clothes/ Riding to and from work and stopping for errands on the way home> How much would you need to bring in terms of food, clothes, tools for work (could be wrenches, could be a laptop ... whatever you need to bring to do the job.)

Alos, unless your boss is really understanding, you will need to be able to fix pretty much anything on the side of the road. Broken chain, broken cable, flat, another flat, broken spoke .... I can tell you form experience your boss likely won't buy the "bike trouble, can't make it today" excuse more than about once. So you would need to keep the bike in really solid condition, and also be able to fix anything likely to be fixable roadside. For that you would need tools, tubes, pump, patches maybe, and maybe nitrile gloves. You could probably get an oversized saddle bag for most of that.

You might be able (depending on what you find to need (to get by with a big handlebar bag and seat bag and a frame bag.

No real reason you would definitely need wider tires, either, unless you were carrying huge loads or riding really bad pavement. A lot of people like fat-tired commuter bikes, i think, because they ride urban areas where pavement quality can be iffy, and can change from week to week as new road destruction projects are initiated. But your frame will probably limit what you can fit for tires anyway.

I would suggest a serious headlight if you plan to ride any time around dusk or later, and a coulee of tail lights. Those little watch-battery blinkies are great--- you can just run them non-stop for added safety and the batteries are cheap. An alternative is a good rechargeable headlight with a blink setting. They can make a difference sometimes even in daytime. And definitely get a really good main tail light--- a super bright one only costs about $35 and can help prevent all kinds of scary situations.

Having a rack is very convenient, even more if you put a trunk bag on top of it. Tool kit in the saddle bag, or just in the trunk bag if you get one.

Fenders are optional if you don't ride in the rain or wet streets but since it's your #2 bike and designated for commuting, I'd opt to have them and the same goes for the headlight. I don't know that it's beneficial to have different tires though. Depends on the route I guess, but if it's the same roads that you ride on, I just use the same tires that I like on the road bike. Only when winter rolls around, I'll change to something more durable, generally cheaper. Since winter conditions aren't conducive to speed and tend to wear the tires out.

I have never tried automotive fix-a-flat in a bike tuber (Don't try it with tubeless.)

Reese, have you used it successfully with a bike tube?

Didn't you still have to take the tire off to find out what caused the flat? A piece or radial wire would just keep punching through the tube ... no sure ho many time one application could seal a tube that was being poked through with every tire rotation.

Interesting if it did work though. Bulky, but if a rider had panniers anyway ....

You could also asking in https://www.bikeforums.net/commuting/ forum, where expert commuters trade information.