5″ Lockable Caster Wheels Upgrade for JMI Wheeley Bars, Triangle Style for 8″, 10″ & 12″ Dobsonians

Product Overview

This upgrade swaps the factory 2⅜″ casters on a JMI Triangle Style Wheeley Bar for three 5″ polyurethane wheels, each with a full-locking brake, on mounting plates cut for the Triangle Style frame. The larger diameter rolls over expansion joints and small obstacles that stop the small factory casters, the polyurethane tread runs quieter and leaves no black marks on finished concrete or garage epoxy, and the brakes hold the Dobsonian platform still at the eyepiece. The kit raises the platform 6⅝″ off the ground, weighs 9 lb, and is made in the USA by JMI, part of the CXB Astro family.

Who It's For

This is a good match if you roll a Triangle Style Wheeley Bar and its 8″, 10″ or 12″ Dobsonian across hard ground — a garage floor, a driveway, an observatory slab or smooth pavement — and the small factory casters catch on every joint and crack on the way out. It also suits you if you want the rocker box to stay exactly where you parked it while you nudge the scope by hand, including on a pad with a slight fall to it.

Key Features & Design

• 5″ wheels in place of 2⅜″: more than double the factory diameter, which is what lets the platform roll over expansion joints and small obstacles instead of stopping at them.
• Polyurethane tread: quieter and gentler on finished floors than the factory hard rubber, and it leaves no black scuff marks.
• Full-locking brakes: each wheel locks against both rotation and swivel, so three engaged brakes hold the platform on a slight slope.
• Triangle Style mounting plates: sized for the Dobsonian platform frame and supplied with all the mounting hardware.
• Ride height: raises the platform 6⅝″ off the ground, per JMI’s published figure.
• Kit weight: 9 lb.
• Made in the USA by JMI, part of the CXB Astro family.

Mechanical Design

Wheel diameter is the single variable that decides what a dolly can roll over. A wheel meets an edge at an angle set by the ratio of the obstacle height to the wheel radius, and the smaller that radius, the steeper the climb and the more of the push goes into lifting rather than moving. Going from 2⅜″ to 5″ more than doubles the radius, which flattens that angle considerably — an expansion joint or a lip at a garage door that the factory casters stall against becomes something the 5″ wheels roll through without the platform lurching. That matters more than it sounds, because every lurch is transmitted straight into a rocker box carrying a mirror.

The brake is the other half of the design. An ordinary caster brake stops the wheel turning but leaves the swivel free, so a braked dolly can still shuffle sideways when it is pushed. These are full-locking: the lever clamps the wheel and the swivel together, which removes both degrees of freedom at each corner. With all three engaged the platform is fixed rather than merely slowed, which is what a Dobsonian needs, since manual tracking means pushing on the scope all night long.

Recommended Uses

• Wheeling a 10″ or 12″ Dob from the garage to the driveway over a threshold and a couple of expansion joints.
• Moving a setup around an observatory slab or a club pad without lifting it.
• Parking the platform on a driveway with a slight fall and keeping it there through a session of manual tracking.
• Rolling across a finished garage floor where hard-rubber casters would leave marks.
• Building out a Triangle Style bar alongside the Triangle Style Leveling Screws and Hardware kit.

Compatibility and Accessory Notes

• Triangle Style only: the mounting plates are cut for the JMI Triangle Style Wheeley Bar and cover its whole range, which is a single size class carrying 8″, 10″ and 12″ Dobsonians.
• Universal-style bars take the Universal-style 5″ wheel upgrade. The wheels themselves are the same polyurethane locking design, but the plates do not interchange between the two frames.
• Sky Trekker models fall outside this fitment.
• Leveling screws are separate: this is the wheel upgrade, and the Triangle Style Leveling Screws and Hardware kit adds levelling to the same frame.
• The 6⅝″ ride height changes the eyepiece height accordingly, which is worth knowing if you observe seated at a fixed-height chair.

Tell us which Wheeley Bar and which Dobsonian you own and we’ll check the fit for you.

Good to Know Before You Order

• These wheels are made for hard, smooth ground. Concrete, asphalt, garage epoxy and tile are where 5″ polyurethane performs; grass, gravel, mulch and sand still catch the wheel at this diameter. Off-pavement use on a Triangle Style platform calls for larger pneumatic wheels, which are a special order through CXB Astro.
• The plates are frame-specific. A Universal-style bar takes the Universal version of this upgrade rather than this one.
• Leveling screws are not part of this kit. The Triangle Style leveling kit covers that separately.
• The platform sits 6⅝″ higher on these wheels than on the ground, which raises the eyepiece by the same amount.
• The kit weighs 9 lb and ships as one carton.

Frequently Asked Questions

Is it difficult to install?

No. The Triangle Style mounting plates bolt to the frame with the hardware supplied, and the casters attach to the plates. It is a hand-tool job with no drilling, and the instructions are in the box.

Will this fit a Universal-style Wheeley Bar?

No. The wheels are the same design as the Universal 5″ upgrade, but the mounting plates are sized for the Triangle Style frame. The Universal-style 5″ wheel upgrade is the right part for that bar.

Do the locks really hold the platform still?

Yes. Each brake holds against wheel rotation and caster swivel together, so with all three engaged the platform stays put even on a slight slope — which is what keeps the rocker box stationary while you track by hand.

Will the polyurethane wheels mark a garage floor?

No. Polyurethane is the usual tread for equipment rolled indoors precisely because it does not leave the black scuffing that hard-rubber casters do.

Can these be used on grass or gravel?

Not well. At 5″, a polyurethane wheel is a hard-surface wheel, and soft or broken ground catches it. For off-pavement observing on a Triangle Style platform, larger pneumatic wheels are a special order through CXB Astro — send us a note and we’ll look into it with them.

Bottom Line

In short: a USA-made 9 lb set of three 5″ locking polyurethane casters with Triangle Style mounting plates, replacing the factory 2⅜″ casters on a JMI Dobsonian Wheeley Bar and raising the platform 6⅝″. It rolls smoothly and quietly on hard floors and locks solid against rotation and swivel, and it pairs with the Triangle Style leveling kit.