Bicycle Mechanics - Parts of wheel affecting stiffness the most
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11-18-05, 02:17 PM
So there are the rims, spokes, nipples, and hub - which of these would have the most impact on lateral stiffness? Good rims on crappy spokes better or worse than crappy rims on great spokes, poor-made hub ruins any wheel, etc?
11-18-05, 02:38 PM
I believe lateral stiffness depends mostly on the number of spokes and the tension they're under (building), on the rim, plus possibly the distance of the hub flanges. Maybe on the kind of spokes used, and, on a rear wheel, the dishing. Damon Rinard did a big test series on lateral stiffness, sheldon's page hosts the results. Here ya go: http://www.sheldonbrown.com/rinard/wheel/index.htm
Spokes. Quantity, quality, and tension.
11-18-05, 05:16 PM
Spokes. Quantity, quality, and tension.
Quantity and cross-sectional area, I'd think. Quality and tension should not affect stiffness.
But doesn't Rinard's test show that the rim deforms into a taco shape? So that means the rim affects stiffness.
The bicycle wheel is complex; I'm not sure I have it all figured out.
Spokes, quantity and tension.
11-18-05, 06:31 PM
Spokes, lace pattern, hub type a little (high flange or low flange), quantity, tension.
11-18-05, 11:44 PM
Section #2 of Rinard's study sums it up:
"Most front wheels are stiffer than similar rear wheels. Structurally this is because front hub flanges are typically wider than rear hub flanges. Rear hub flange spacing is constrained by industry standard dimensions, such as cassette width, drop out spacing and symmetrical frames.
Most rear wheels I tested are between 40 and 60% more flexible than similar front wheels. Although it may be the case that stiffer front wheels have been developed intentionally for more stable handling, it is possible that many front wheels are simply overbuilt or many rear wheels are underbuilt.
Track wheels are an exception: rear hub flanges are often much wider than fronts, and therefore such wheels are slightly stiffer laterally than similar front wheels. Compare track wheels number 83 and 84 (below) for an example. "
No other variable he measured makes a 40-60% difference in stifness (besides extremely loose spokes).
Width of the flange makes the biggest difference in lateral stiffness. Actually, it's the angle of the spokes to the flange. The wider the flange the bigger the angle and the stiffer the wheel is laterally. Imagine a wheel with the flanges just 10mm apart. No matter how tight you make the spokes and no matter how many of them you use, the wheel will still be easy to flop back and forth.
Now imagine a weird hub that has the flanges far apart, like 1-foot, and the flanges were way tall, like as large in diameter as the rim itself. Then the spokes would pull in opposing directions; the left flange would pull the rim straight left and the right flange would pull the right straight right. This wheel would immensely stiff laterally as the spokes directly oppose lateral movement.
In practical terms, the wider the flanges are apart, the bigger the spoke angle and the stiffer the wheel. High-flange hubs also increase the spoke angle as well. That's why track bikes use high-flange hubs, for maximum stiffness.
Sorry Danno, your post looked like it had lots of big words, so I didn't read it. To those that dispute the importance of quality spokes, I'll point of that you can build a very stiff wheel with cheap straight gauge spokes. But if you want it to last, you need high quality stainless, DB or triple butted spokes, depending on the application.
It's all about the triangles, man. Which is why on my next frame I'l be having an offset rear end with 145mm spacing.
11-19-05, 11:06 AM
Yeah, I might have gotten a little winded. Going back to the OP's question of "the most impact on lateral stiffness? ", dooley's got it right on. The only thing that matters in lateral stiffness is the width of the flanges, more specifically the angle of the spokes, the wider they are, the stiffer. Surprizingly, spoke-tension doesn't matter unless it's really, really loose.
But the width of the flanges (spoke angle) is not something that I would think of as much of an option. A cyclist with a typical 8,9, or 10-speed bike will not normally have a selection of hubs to choose between that will make much difference in the spoke angle. How often do any of use choose wheels based on this variable?
11-20-05, 08:14 PM
...How often do any of use choose wheels based on this variable?It's certainly rare for sure because how often do people choose lateral-stiffness as a deciding factor in wheel-selection? The amounts of wheel-deflection is many times higher than frame-flex and contributes greatly to the solid feel of a bike in sprints. Due to a crash on Sat. I didn't have a front wheel for Sunday's race one time. So I bolted on the front wheel from my track bike. The difference in feel was definitely noticable, so I only use large-flange hubs for front wheels now.
I'm not even sure what the OP's purpose with this question is really. The vertical-stiffness of a wheel is what you notice most of the time since you're riding the bike upright. And in performance and handling terms, I like a rectangular cross-section rim for maximum lateral-stiffness with the most vertical compliance possible. This gives the best grip in cornering, especially on rough terrain.
11-20-05, 08:20 PM
In truth I only read the question. It is a combination of rim strength, spokes and dish. The rim, I think is the biggest factor. you can have crappy spokes and lopsided dish and still have a very stiff wheel if you have a strong rim(The spokes may not last long) You can have a fairly stong wheel with zero offset dish, but if the rim is flimsy it will still spoing with out much input. The spokes are lowman, if they are cheap they may break easy but the stiffness will still be up there. Except for the very thin spokes like the Revolutions, they are very springy and can let the rim move around a fair amount, another reason to use a good strong rim.
Correction, the hub is low man. I think it makes little difference, in most cases, which hub is chosen, with some super light weight exceptions.
See, I'd say rim strength is probably the least important.
11-21-05, 05:51 AM
Definitely so. Number and tension of the spokes is the main thing.
11-21-05, 08:57 AM
So a 36 spoke Open pro will be stiffer than a 28 spoke CXP33?
11-21-05, 11:12 AM
Do the same test that Damon Rinard did with weights hanging off the rim and measuring lateral rim-deflection. You'll want to modify this test to include bare rims. Perhaps you can lay a rim with 50% hanging off the edge of a bench and clamp the rest down. Repeat his hanging-weight test with the following:
1. bare 28-hole Open Pro
2. bare 36-hole Open Pro
3. built-up 28-hole Open Pro
4. built-up 36-hole Open Pro (same hub, same tension as previous)
You'll find that #1 & #2 will be identical. Both #3 and #4 will be SIGNIFICANTLY stiffer than bare rims and #4 will be stiffest. To bring #3 28-hole up to the same level as #4 36-hole, you'll need to increase spoke-tension by about 20%. This is why wheels with fewer spokes are built using higher tension and bigger spokes; to give the same load-carrying capacity.
Analyzing Damon's data-table (http://www.sheldonbrown.com/rinard/wheel/data.htm), you can see the effect of flange-width on wheels #94 and 95. Using radial lacing with the only difference of having the spokes coming from the inside or outside of the flange. This minor difference in width (wider triangular base) for the spacing the spokes further apart gives a 12% stiffer wheel using same hub, same spokes, same rim.
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