Published 6/05, Copyright 2005,

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Here's a riddle for you:  What do cowboys, skiers, and city slickers all have in common?

Off-road wheels, that's what.  Whether you're crossing a pasture on your ranch, transferring into your monoski at a ski resort, or hopping curbs on your way to work in Manhattan, you may receive increased mobility with big, fat, honkin', off-road wheels on your ultralight manual wheelchair.  With wide, low PSI tires, stout rims, heavy-gauge spokes, and recessed hubs, off-road wheels can dramtically increase your ultralight wheelchair's traction, shock absorption, and durability. Still, not all off-road wheels are created equal, nor are off-road wheels for everyone's liking, so there are a few sage secrets toward getting the right match for your manual wheelchair and lifestyle.

Tempting Tires
When many think of off-road wheels, knobby tires come to mind.  And, indeed, tires are a practical starting point.  If you don't want to purchase complete off-road wheel assemblies, which cost around $300, both Primo and Kenda tire brands offer knobby tires to fit common wheelchair rims, specifically to replace 24"x1" (25-540), 24"x1-3/8" (37-540), and 25"x1" (20-559) tires.  The unquestionable benefit of simply purchasing tires is that, for under $40, you can add knobby tires to your existing wheels.  However, an additional benefit is that wheelchair knobby tires are grey - as opposed to black mountain bike tires commonly used on complete off-road wheel sets - so they won't leave black marks around your home.

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Knobby replacement tires, like those made by Primo and Kenda specifically for wheelchair 540s and other sizes, aren't entirely beneficial or plug-n-play.  For starters, knobby replacement tires only provide a minimal increase in performance over everyday 1-3/8"-wide tires, so traction and floatation doesn't equal that of a true 2"-wide off-road wheel assembly.  Also, while replacement knobby tires are of similar profile to an everyday tire 1-3/8-wide tire, they are notably taller and wider than a high-pressure, 1"-wide performance tire, so when replacing a low-profile tire with a knobby tire, you may need to adjust your brakes, wheel offset, caster barrels, and handrim stand-off.

Among the most common consumer questions is whether an off-the-shelf 24" knobby bicycle tire will work on a wheelchair rim?  The answer is usually, no, as 24" mountain bike wheel rims are typically standardized to a 507mm diameter, much smaller than the wheelchair industry's 24" wheel standard of a 540mm rim.  For this reason, a pair of 24" knobby mountain bike tires from Wal-Mart or a bike shop usually won't fit on 24" wheelchair rim.

Bigger is Better
Those looking for optimal performance roll up a notch complete off-road wheel sets, where bigger is better.  Based on mountain bike wheels - but with recessed wheelchair hubs and handrims - off-road wheel sets offer full-profile mountain bike rims and tires, providing widths of 2" or more.  Going from a 1-3/8"-wide wheelchair wheel assembly to a 2"-wide mountain bike wheel assembly may not read as impressive - but, the performance enhancement is striking.  The 2"-wide tires float over soft surfaces into which wheelchair wheels commonly sink; the wider footprint increases stability and traction on uneven terrain; the beefy rims and heavy-guage spokes dramatically increase wheel durability; and, the large, low-pressure tires provide a shock-absorbing ride.  From sand to snow to street, off-road wheels simply provide a wider, higher-traction footprint that noticeably improves a wheelchair's ability to negotiate the rough stuff, and stay atop softer surfaces.

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Still, despite the unquestionable benefits, off-road wheels are not for everyone.  Off-road wheels can weight three times more than performance wheels, and up to twice as much as an everyday wheel.  To put the weight difference in perspective, off-road wheels can add 6-pounds or more to a chair.  Off-road wheels also add considerable width to a chair, not only because of the extra " or more of width at each tire, but also because the wheels most often require extra offset spacing from the frame, so that the wheels don't rub on the back canes.  In off-road applications, the vast improvement in handling far outweighs any increases in weight and width; however, if you're living strictly on smooth, dry concrete, you may wish to think twice before adding the bulk and weight of off-road wheels to your chair.

Tricky Tuning
In mounting off-road wheels, there are some tricks of the trade.  When purchasing off-road wheels, make sure that the hub width, outer-bearings-to-outer-bearings, is the same as that of your existing wheels - this is vital if you want to use the existing quick-release axles of your chair.

Wheel offset, again, is vital to mounting off-road wheels.  If you plan on using off-road wheels full-time, your best bet is to readjust your axle sleeves, if needed, moving the wheels an appropriate distance from the back cane (typically allowing 1" between the tire and back cane).  

If you're switching between everyday wheels and off-road wheels, offset can prove complex in that you may not wish to permanently adjust your axle sleeves outward, inappropriately widening the chair when using everyday wheels.  One solution toward interchangeable off-road wheels is to use a 1" longer quick-release axle and a 1" spacer to offset the off-road wheel.  For example, if your everyday wheel setup is a 2" hub, 2" axle sleeve, and 4" axle, use an off-road wheel with a 2" hub, 5" axle engagement, and place a 1" spacer between the hub and axle sleeve to accomplish the necessary extra offset.  With the off-road wheel set having its own axles and spacers, you can then pop them on and off the chair as needed, switching between your everyday wheels without adjusting the axle sleeves.  (There are some very high-end off-road wheel sets that feature an offset hub, intrinsically moving the rim and tire portion away from the frame - this setup is a great configuration because it allows mounting wide wheels without adjusting the axle sleeves or requiring a longer axle.)

In diameter, most specifically-designed off-road wheels for wheelchairs are based on a 507mm mountain bike rim and high-profile tire, so the overall outer diameter remains close to an everyday 24" (540) wheel and tire.  Put simply, while a 507mm rim is smaller than a 540mm rim, placing a full profile mountain bike tire on a 507mm equals a diameter close enough to a wheelchair 24" (540) wheel's diameter that you usually don't need to readjust components like the caster barrels - yet another plus to going with a complete off-road wheel assembly instead of simply placing a knobby tire on a 540mm wheelchair rim.  For those looking for even greater terrain handling, 26" off-road wheel assemblies are available, but will require considerable adjustment to the chair if moving up from 24" or 25" wheels.  

In the area of handrims, tab mounts are common, and longer tabs that move the handrim outward, away from the wheel, help keep your hand away from aggressive tire treads that may rub your hands.  Some off-road wheels utilize a smaller diameter handrim, so that the handrim is well off the ground, taking less abuse when rolling over rocky terrain.

Propelling Paradise
Big, fat, honkin' off-road wheels - they're not for everyone.  However, if you're looking to dramatically increase your wheelchair's rugged performance - on the range, on the slopes, or in town - off-road wheels may prove as a sound investment toward your adventurous spirit.

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