5″ Polyurethane Wheel Upgrade · Set of 3 · Lockable
Step up from the factory 2⅜″ hard-rubber casters — three 5″ polyurethane wheels with locking brakes roll smooth on driveways, garage floors, and indoor surfaces.
The JMI 5″ Wheel Upgrade swaps the factory 2⅜″ hard-rubber casters that ship with your Universal-style Wheeley Bar for three 5″ diameter polyurethane wheels. The bigger diameter rolls smoother over expansion joints and small obstacles, the polyurethane tread is gentler on finished concrete and garage epoxy than the standard casters, and each wheel has a full-locking brake — step on the lever and the wheel stops dead, keeping your leveled rig planted while you set up.
This is the middle-tier wheel upgrade in the JMI lineup. If you observe mostly on smooth, hard surfaces — driveway, garage, observatory floor, paved pad — the 5″ wheels are the right call. If you'll be rolling over grass, gravel, dirt, or rough ground, jump to the 10″ Pneumatic Wheel Upgrade instead. Made in the USA by JMI, part of the CXB Astro family.
Surface match matters. 5″ polyurethane wheels are designed for hard, smooth surfaces. They roll beautifully on concrete, asphalt, garage epoxy, and tile. They do not excel on grass, gravel, mulch, sand, or rough ground — the smaller diameter still catches on uneven terrain. For off-pavement observing, the 10″ pneumatic upgrade is the right tool.
Specifications
What's included
Three (3) 5″ diameter polyurethane wheels with locking brakes · all mounting hardware
Wheel material
Polyurethane tread — quieter and gentler on finished floors than the factory hard rubber, won't leave black scuff marks
Locking
Each wheel has a full-locking brake — the brake holds the wheel against rotation AND swivel, so the bar stays put once leveled
Ride height
Raises the mount 6⅜″ off the ground (manufacturer spec)
Tow handle status
Tow handle is not included — the 5″ wheel upgrade is wheels only. Add the standalone 1/2″ or 5/8″ Tow Handle separately if needed
Designed for
JMI Universal-style Wheeley Bars — Standard Medium, HD Medium, HD Large, HD Shorty, AP Pier Mount (size-agnostic, fits both 1/2″ and 5/8″ leveling-screw versions)
Best for
Driveway, garage, observatory floor, observatory pad, smooth pavement — anywhere the surface is hard and reasonably flat
NOT compatible with
Triangle Style Wheeley Bar (different frame — see the Triangle Style 5″ caster upgrade) · Sky Trekker series
Made in
USA by JMI · part of the CXB Astro family
5″ Polyurethane vs. 10″ Pneumatic: Which Upgrade?
Both upgrades replace the factory 2⅜″ hard-rubber casters but they're aimed at different surfaces and budgets:
5″ polyurethane ($149) — three wheels, no tow handle, polyurethane tread, full-locking brakes. Best on hard, smooth surfaces: driveway, garage, observatory floor.
10″ pneumatic ($364) — six wheels (dual-inboard rear) + tow handle included, air-cushioned all-terrain tires. Best on grass, gravel, dirt, mulch, sand. The price reflects the extra wheels, the tow handle, and the more capable tire.
If you observe on a mix of surfaces, the 10″ pneumatic is the more versatile pick. If you observe almost exclusively in a garage or driveway, the 5″ polyurethane saves $215 and rolls quieter on hard floors.
Triangle Style Wheeley Bar Instead?
The Triangle Style Wheeley Bar (for 8″/10″/12″ Dobsonians) uses a different frame and needs its own 5″ wheel upgrade. See the 5″ Lockable Caster Wheels Upgrade for Triangle Style ($149) — same wheels and locking design, sized for the Triangle Style frame.
Frequently Asked Questions
Will the 5″ wheels fit my Wheeley Bar regardless of leveling-screw size?
Yes — the 5″ wheel upgrade is size-agnostic. It fits all Universal-style Wheeley Bars regardless of whether they use 1/2″ or 5/8″ leveling screws. (Unlike the 10″ pneumatic upgrade, which includes a tow handle and therefore comes in two leveling-screw-specific versions.)
Why three wheels instead of four?
The Universal-style Wheeley Bar uses a 3-wheel layout: one wheel under each leg of the tripod or pier. Three wheels is the minimum for stable rolling, and it matches the bar's natural triangular footprint. The 10″ pneumatic upgrade uses 6 wheels because the rear has a dual-inboard design — not because four wheels are needed.
Does the lock actually keep the bar from moving?
Yes — each wheel has a full-locking brake that holds against both wheel rotation AND swivel (the caster's spinning motion). With all three brakes engaged, the bar stays put even on a slight slope. That's a meaningful upgrade from the factory casters, which on most Wheeley Bars are not lockable.
Will the polyurethane wheels mark my garage floor?
No. Polyurethane is the standard choice for indoor-rolling industrial equipment specifically because it doesn't leave black scuff marks the way standard hard-rubber casters do. Most observers see a noticeable difference in floor cleanliness after switching.
Can I add a tow handle to this setup?
Yes — the 5″ wheel upgrade doesn't include a tow handle, but you can add the standalone 1/2″ Tow Handle or 5/8″ Tow Handle (match to your leveling-screw size). Both standalone tow handles are designed for the 5″ caster setup.
Smooth surfaces only?
The 5″ polyurethane upgrade is the smart, quiet, affordable choice. Need off-pavement capability? See the 10″ pneumatic upgrade.
10″ pneumatic (1/2″) Shop accessories
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