Originally Posted by
caloso
Is your commute mostly or only partly on a trail? If it's mostly on city streets, it's likely that it won't matter what you do; the limiting factor is probably traffic signals. My 4mi/6.5k commute takes me 19-22 minutes every day whether I ride my Tarmac or my old Rock Hopper with semi-knobbies. It's the stop lights.
+1
I commute 17km round trip on city streets. I have three different bikes, a light 1980s steel roadbike, a new mid-weight semi-touring road bike , and a very heavy 1990s hard tail Mountain bike with higher road gearing. All three run on smooth street tires (except the MTB in winter, then it's studded snows).
On street tires, all three average the same running time due to lights, etc. I have multiple routes of similar lengths and the one with the least number of lights is quicker by 5 minutes.
Normally I ride at a good clip, 21kph in (It's slightly downhill) and 18.5kph on the uphill ride home. Occasionally I get the urge to see how fast I can ride my commute. Pushing as hard as I can I can get my average speeds up by about 1.5kph. This usually translates into a total time savings of only 5 minutes.
For instance my average time riding home is 45-48 minutes. Pushing it as hard as I can means 38-43 minutes. And when you add time to shower and change (shower at home only) it is not worth it to me.
Based on what you described I would make the following suggestions for the most speed for the least money:
A)
Toe Clips with Straps. They probably work with the platform pedals you already have and they are not as good as clipless, but they are cheaper than buying and installing "Clipless" pedals which need clipless shoes, and with toe clips you can wear any shoes you want, like old sneakers, but probably not open toe sandals. Approx $12 a pair online.
B)
Smooth street tires. This alone made a 2.5 kph difference on my Mountain Bike Based Commuter. over knobby mountain bike tires. Without traffic, that's good for loosing almost 7.5 minutes without traffic (I think). If you don't need super tough puncture resistant tires these can be found on sale on line for less than $30 a pair. If you need more puncture resistance, try adding tire liners, like Mr. Tuffy's. $12 a pair or so, and then you can continue buying regular, less expensive tires.
C)
An aero bar or drop-bar-end add-ons. Even on a straight bar bike. I put an aero bar on my Mountain Bike Commuter to increase the number of hand positions I have, and away from traffic I gain a couple of kph. I don't like riding in the aero position too long. But I also have bar-ends I mounted inboard. They approximate riding on the drops and I am more tucked in than on the normal flat-bar grips. I bought mine for $30 a few years ago, and the bar ends were like $12. This was on sale at a local bike shop.
In fact, check with your LBS first...they may have deals on all of these things.
Good luck!
Here's a photo of my Mountain Bike based commuter: