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Message started by JimFPU on Jun 17^th, 2008, 3:18pm

Title: Drive wheel ?
Post by JimFPU on Jun 17^th, 2008, 3:18pm

OK, not meaning to sound like a novice, but maybe it's true....

Does the size of the drive wheel really make a difference? Is it better to have a bigger wheel hooked to the sproket, or for a smaller one will it just translate to more peddling. Any math wizzes out there?

(Yes, I know that there are some that think size matters...but that's not part of this discussion...tying to keep it above a 14 year old level...LOL!)

Title: Re: Drive wheel ?
Post by Opus the Poet on Jun 17^th, 2008, 3:43pm

Gear inches=(Front sprocket/Rear Sprocket)Drive Wheel Diameter

So yes, size makes a difference. But if 2 bikes are geared to have the same gear inches, then they will go the same speed at the same crank cadence even if one has a 20" drive wheel and the other has a 27" wheel. The major thing about a big drive wheel is it gives a wider range of gear inches than a small wheel. Because cassettes can only go so big and so small you have a physical limitation on the gear inches at the wheel, and because the derailler has a limit on how many teeth it can compensate for it limits the use of larger front chainrings to compensate for the smaller drive wheels.

Opus

Title: Re: Drive wheel ?
Post by JimFPU on Jun 17^th, 2008, 5:02pm

Thanks Opus, so with the distance from the front to rear derailleur’s on my LWB Infinity, that may not be such a problem right? I'm thinking of putting on a smaller drive wheel so I can lay the seat back more and get a lower profile...make sense? I already went from 27 (skinny) to 26 MTB (wider=comfortable!).

Title: Re: Drive wheel ?
Post by evblazer on Jun 17^th, 2008, 5:58pm

There is neat little tool/calculator you can play with over at sheldon browns site. You can be your own math wiz 8-)
http://www.sheldonbrown.com/gears/ setting the "Gear units" to MPH @ the rpm you usually spin out can show the difference or at least that works for me..
if I used a 700c wheel with a 25 width tire these are the mph i'd get at 80 rpms depending on what front/rear combo I was in. Strikethrough on ones I avoid because of chain slack issues.
52 39 30
29.7 22.3 ~~17.1~~ 11
25.1 18.8 ~~14.5~~ 13
21.8 16.3 12.6 15
19.2 14.4 11.1 17
16.3 12.2 9.4 20
14.2 10.6 8.2 23
12.6 9.4 7.2 26
~~10.9~~ 8.2 6.3 30
~~9.6~~ 7.2 5.5 34

Same gearing but 26x1.25" (equivilent to 32 width)
27.5 20.6 ~~15.9~~
23.3 17.5 ~~13.4~~
20.2 15.1 11.6
17.8 13.4 10.3
15.1 11.4 8.7
13.2 9.9 7.6
11.6 8.7 6.7
~~10.1~~ 7.6 5.8
~~8.9~~ 6.7 5.1

The difference from 700c to 26" isn't that great. You can play with alot of tire sizes to see what diffences you'll get or change out your gearing to see if you can make up for it easily by changing the cassette.
This reminds me I gotta check my bike. Either i'm spinning slower then my cateye says I am or my RD isn't giveing me all my gears under pressure. I should be able to hit 40 at my top gear when I'm spinning 120 or so and the highest I've seen is around 32 which means I'm in 52x13. Edit: spinning at 120 in 52x13 is a very very short lived event.

Title: Re: Drive wheel ?
Post by Opus the Poet on Jun 18^th, 2008, 12:46am

JimFPU wrote:

The distance between deraillers is not the issue, the chainwrap capacity of the rear mech is. The rear derailler I have now has a capacity of 40 teeth, but with an 11-34 rear cassette and 24-34-48 front I exceeded that. Since there were very few hills I couldn't climb with the 34-34 combo I went with an 11-25 cassette when I bought the parts to replace the parts damaged in the explosion (don't ask, long story). Now I have a really low granny around 24" and can use all the cogs in the cassette no matter what chainring I'm using up front.

Title: Re: Drive wheel ?
Post by JimFPU on Jun 18^th, 2008, 8:12am

OK, (and now shows noviceness :-[) how do I tell what all those numbers are on my equipmment? Do I just count the teeth, or would it be stamped on there somewhere? This stuff is pretty old, as I think it came with the bike in the first place. Looks like I have a lot to learn about chains and cogs...they don't have this stuff on AF jets... :o

Title: Re: Drive wheel ?
Post by JimFPU on Jun 18^th, 2008, 8:12am

Thanks evblazer, I have his site bookmarked, just forgot about all the info that was there... ::)

Title: Re: Drive wheel ?
Post by Opus the Poet on Jun 18^th, 2008, 9:53am

JimFPU wrote:

Sometimes the numbers are stamped on the sprockets, usually on the older stuff they're not.The easy way is to just count the teeth. Since you claim a 14 YO bike I'm going to assume freewheel instead of freehub, and probably a 7 speed rear and a triple front. And the terminology for those sprockets is the rear ones are called cogs and the fronts are called either chainrings if they bolt to a carrier on the crank or chainwheels if they have a hole for the crank in the middle and another hole for the drive pin from the crank to engage. On the rear derailler the ability of the mechanisim to take up the slack in the chain when going from the biggest front and the biggest rear, to the smallest front and the smallest rear is called the capacity. Capacity is determined by adding the biggest front to the biggest rear and subtracting from that the smallest front and the smallest rear. The capacity of the rear mech can be found at the manufacturer's web site, except Campagnolo. Campy just tells you which of their parts combinations will work with which deraillers.

My bike is even older than yours being a 1983 model Stratus, so I know what it's like trying to get repair parts for consumable parts of the drivetrain. That's the reason why I went to a current manufacture 8/9 speed freehub, so I could get parts.

And this has gone too long.

Opus

Title: Re: Drive wheel ?
Post by JimFPU on Jun 18^th, 2008, 11:57am

Your shared knowledge is greatly appreciated Opus. Wasn't too long for me. ;D

Title: Re: Drive wheel ?
Post by FlyingLaZBoy on Jun 18^th, 2008, 1:47pm

Opus the Poet wrote:

....when going from the biggest front and the biggest rear, to the smallest front and the smallest rear....

I swore to myself I was not gonna go there.... it's just not prudent... :D

But that line DID remind me of this photo!

http://i53.photobucket.com/albums/g73/flyinglazboy/Advertisement.jpg