Hi,

I am new to cycling. I am trying to make my (prepare to laugh) 1986 Schwinn Sierra MTB into something fast and road-worthy for the winter. For two reasons, I won't be getting a true road bike until late next summer (travelling and money).

Thus far, I put a set of slicks onto the bike, I am waiting for a trekking bar (for more hand positions), I have replaced all the cables, and I replaced the brake pads. Now, I am wondering how to make the bike a touch faster at the top gears. With the current set up I can't get the bike over 30 mph, but I think that I have more in me to do so. I just can't get my cadence high enough. Here is my question: what can I replace to make the bike faster? My cassette has a couple of broken teeth. Should I replace that? Is that easy? How do I know which one will fit my current bike? How about the front chainrings?

Here are the 1986 specs:


Freewheel
Shimano Z 14/32 5 speed

Crank
SR SXC310 28/38/48

Rear Derailleur
Shimano 523 SGS

Front Derailleur
Shimano 204 GS

Shifter
Shimano AT50

Oh, and I should mention that I am willing to trade for a new or recently used Bianchi Vigorelli in good condition

Thanks!
Mike

If you can get that bike up to 30 mph on any reasonably flat road, you are a strong rider indeed. Given your gearing, that requires a cadence of 105 rpm and given the riding position, it requires pretty impressive wattage.

It is theoretically possible to regear this bike with a larger chainring say 52T in place of the 48T. A higher geared freewheel could also be used. An Ultra-6 13x28 used to be available from Sun Tour that's a direct replacement for your 5-speed and, depending on your dropout spacing, perhaps a 6 or 7-speed freewheel could be used.

However, economically it's isn't worth it. The bike is really obsolete and was a low line model to begin with so you will run into the "silk purse from a sow's ear" problem very quickly. If you change the freewheel and chainring, at the least you will ned a new chain and the "improvements" will get expensive rapidly, particularly if you have to pay a dealer to provide and install the parts.

Take the money you would spend on this bike and apply it to one that's newer and better suited to you needs.

Smaller cogs on the rear would help. So would a larger front chainring.

The problem with replacing cogs is that your bike likely does not have a 'cassette' - it has a 'freewheel.' A freehub type hub has the freewheel mechanism built in and the cogs slide on. A freewheel hub has a set of cogs with a built-in freewheel mechanism threaded on, and they are a lot less common these days, and you might have trouble finding one with considerable smaller gears. Modern cassettes are regularily found down to 11 teeth, which would help you out a lot, but you would need to replace your rear wheel, which is more expense than it is worth... unless your wheel is already bent or the bearings are shot.

If your crankset has bolted-on chainrings (many are riveted on) then you should be able to find larger replacements. MTBs from that era usually had cranks with 110mm bolt circle pattern, and this size has become very common again as it is used in modern 'compact' road cranks. Compact road cranks usually have two chainrings - 34-50 is common - but you could likely leave your 28 and 38 alone and just replace the 48 with a 50 or 52 without too much trouble. If you are using the same cadence as you have been to reach 30mph with your current setup, you could reach ~32 and 33 mph with a 50 and 52 tooth, respectively. If you can find a freewheel with a 13 tooth cog, your top speed with a 52 tooth chainring would be 35.5 mph.

(all speeds calculated with Sheldon Brown's Gear Calculator)

One more thing - if you are strong enough to get your bike up to 30mph the next step is to bring up your cadence... "spin to win" is the old saying.

ok, first of all that 30 mph is DOWNhill! So, I am not at all as impressive as that. I should have specified! To make it clearer, I ride something like a 12-14 mph average through a gently hilly 10+ mile course in my neighborhood. But on a couple of the downhills, I can get near 30. There actually is not much true flat ground, but on flat streets, I get to somewhere near 20 or so. Here again, though, I need another gear.

I am happy to learn that his bike is really not worth upgrading, though. I appreciate your detailed comments. I will look into it, but as you say, I can't make a silk purse from a sow's ear. I'll just save my money for the road bike and keep this one as my bad weather bike, or perhaps as a commuter eventually.

Thanks!!!

another excellent idea: 52 tooth chainrings are on ebay for $10!!! And it looks like these are mainly interchangeable (just by looking at the numbers of bolts). Is there anything else to look for as far as compatibility?

You need to match both the number of bolts (5 for your crank I'm pretty sure.) and the "bolt circle diameter" (BCD) which is most likely 110 mm on your crank. Finally, you have to be sure your chainrings really do bolt on and are not permanantly riveted. Many low cost cranks are riveted together and the chainrings can't be removed or changed.

Also, you will most likely need a new chain for the larger chainring and a putting new chain on an old freewheel is a sure way to get skipping on the cogs. So, plan on a new freewheel too. You are into way more than $10 at that point.

Hi again,

Well, this could be a nice little project. So, now that I have good info on the compatibility of the chainring, what about the freewheel?

I now have a 5 speed free wheel. Shimano z 14/32. Can this be replaced by any 5 speed freewheel? Is this doable (yes these are just listings from ebay):
Shimano MF-Z015 5sp SIS Freewheel 14-28T
Shimano Freewheel SIS 5spd 14-28 gold

And, a new chain. Well, is a chain, a chain? I assume that I need a particular size/length...

Mike

I am with HillRider's first post SAVE YOUR MONEY. any part you replace on the drivetrain my have unwanted consequences.

just ride the bike like it is and save up for a cool Bianchi in the spring. also I am not sure how fast you think you should be able to go ona bike, but even on a Pro level bike and in peak fitness an average of 22mph is really good and hard to sustain for a solo rider.

is there hill in Queens high enough to get a bie going 30?

switching from a 14-32 to a 14-28 will not improve your 'top end' to do that you need a 13 - 23 or 12 - 19. as far as your bike is concerned any chain for a 5/6/7 spd drive will work. but chains come in a standard size and need to 'cut' or taylored to fit your bike.

restating what HillRider mentioned in one of his post. when you start replacing drivetrain parts you will have issues with other parts. just like a new chain can slip on old cogs it could slip on old worn chainrings.

OK, I definitely get it. Save the money and get the good bike...now do I save up for the vigonelli or do I go for the brava...

If you are not able to get you cadence high enough with your current gearing, changing cassettes to higher gearing wont help. A higher gear will just lower your cadence further. If you are spinning too fast on downhills and need another gear to slow down your cadence, then changing your gearing will help. If you have broken teeth, I would replace it with something.

that is a tough choice like choosing between a Cosmo and a Martini both are fabulous but which will you enjoy more....

i appreciate the help and commentary on the project. now i know both the instructions on how to do it -- and i know that doing it doesn't make the most sense for me. thanks again!!!

In reality, 30mph is pretty damn fast - you can't maintain that for long on flat ground so you are really only talking about limiting speed on downhills. You can have a lot of good long rides with a max pedalling speed of 30mph. And if you can bring your cadence up you will be faster when you eventually get a road bike.

So for now, consider training on your Schwinn and saving $$, spend only on necessary items, keep an eye on craigslist for a half decent road bike that will fit and that matches the money you have - be sure to budget for dedicated shoes and clipless pedals as they make a difference in performance on longer rides.

While a higher gear (bigger chainrings and/or smaller cassette) might help you exceed 30mph on a downhill, you'll find that you can do as well and sometimes better by developing an aerodynamic position and coasting. Why work when you don't have to.

An effective downhill position is pedals horizontal at 3 & 9 o'clock, knees in against the frame for stability, head and body low over the handle bars, and elbows in. If there's cornering involved the outer leg is extended and some weight transferred to the outer pedal. With effective downhill technique, you'll be able to coast past people who are pedaling (something that tends to annoy them to no end).

Yes, due to the exponential-increase in drag and power required to overcome that drag, the actual amount of power generated with furious pedaling doesn't give you much more speed on downhills above 30mph. For example, to go from 20mph to 40mph, you need to generate 8x more power; simply impossible to do if you're already giving it your all at 20mph.

The pull of gravity is a fixed amount as well, but is based upon your total weight. So what I sometime do is wear an empty backpack up a local hillclimb. Then at the top, I fill it with big rocks to add an additional 20-30 lbs to my weight for faster downhills. This gives gravity a stronger pull for the same amount of aero-drag. The more weight you add, the closer your downhill acceleration approaches the theoretical free-fall speed in a vacuum (drop a rock and feather at the same time from the same height, then compare to doing it in a vacuum).

So your best bet to increasing speed is to reduce aero-drag. Tuck in tightly with your knees and elbows in. Head as low as possible with straight flat. If you have the skill and practice, you can even place your hands together just on either side of the stem:



BTW - Craiglist, thrift-stores and garage-sales are great places to pick up used bikes at incredible deals. Due to the "newest is best" fads, there's tremendous depreciation. I've seen carbon-fibre race-bikes with Ultegra components go for $150-200. With Dura-ace at $200-300. A very nice basic steel/alloy bike with low to mid-range components can be had for around $100-150. I picked up a nice alloy MTB with suspension-fork and DeoreXT parts at a local police-auction for $40.

When you are using final gear on downhill might will help to exceed speed of 30mph.In realty 30mph is really fast speed for downhill you can not mainten the bike.This speed is really dangerous for handle the bike on downhill.You have to daily practice and some changes in you bike to do this thing.You need to match both the number of bolts and the "bolt circle diameter" which is most likely 110 mm on your crank

Keep an eye out for a 6spd wheel with a 13t small cog... should be able to find one for nix sooner or later.