Square wheels: Dr Pulley Variomatic Tuning

Dr Pulley Variomatik Tuning makes it possible: higher top speed at reduced engine speed – the ultimate dream in the variomatic tuning scene. The whole thing works with ‘SR castors’. The angular shape of the SR rollers results in a larger adjustment range for the Vario. “The achievable top speed increases, the speed at a certain speed is lower and driving with less fuel consumption is smoother,” argues Reinhold Harsch from RNH in Gießen, where the Dr Pulley Variomatik tuning rollers are available.
The Dr Pulley range has around 25 different dimensions from 15 x 12 to 30 x 20 for almost all scooters, CVT quads and ATVs. On top of that, each dimension is available in different weights, with which each vehicle can be optimally adapted to its use, because the roller weight of the Dr Pulley Variomatic Tuning sliding rollers can be selected around 10 to 15 percent less than the original rollers.

Dr Pulley Variomatic Tuning: SR sliding rollers on RNH quads

Reinhold Harsch from RNH-Quads in Giessen, who equips CVT quads and ATVs with the ‘square rollers’, has already thoroughly tested them. “The increase in performance is awesome,” says Reinhold. “I’ve just made a Kymco Maxxer 450, which now runs a strong 115 according to the speedometer.” It is important to find a workshop that has the Dr Pulley castors in stock, and that in a wide variety of dimensions and weight classes. “The choice of roller cannot be applied to all models across the board, but must be matched to the chassis – each quad and ATV is therefore individually tuned,” says Reinhold Harsch. After the conversion you should also drive a few kilometers, because the rollers have to be broken in first. With a balanced ratio of pulley weight and belt height, the Dr Pulley optimization takes effect.

The Dr Pulley in detail

The Dr Pulley SR Caster is made of self-lubricating polymer nylon. It glides smoothly, even when accelerating suddenly. According to Dr Pulley, the material used is very hard-wearing, and Reinhold Harsch schedules appropriate service intervals: “These things have been on the market for a long time, but you can drive 50,000 kilometers before the first inspection,” he says. The angular shape of the castor definitely results in a larger adjustment range for the Vario.

Decisive: the weight of the Dr Pulley castors

The first step in determining the optimal weight and size is to get the right information of the original rolls. A workshop, a brand forum or the Dr Pulley Variomatik Tuning Forum offers help. The choice of the optimal weight of the Dr Pulley wheels also depends on the rider’s weight, the route profile and personal wishes: Should the acceleration be increased or the top speed increased? With ATVs and quads, the different final gear ratios and the tire size are also important factors.
In addition to these parameters, the height of rise of the belt must also be taken into account, which ideally extends to the edge of the riser pulleys. As a check, Dr Pulley recommends the ‘edding pen test’: draw a vertical line with a pen in the ascending disc; after a few kilometers at full throttle you can determine where the belt hasn’t been: where the line is still visible.

Availability & costs

The Dr Pulley rollers are suitable for tuning varios from Dr. Pulley, Malossi and Polini. Here, in addition to the deviation in the roll size from the original, there can also be a deviation in terms of the sliders to be used. Compared to the sliding rollers, the sliding blocks are of lesser importance in the vario optimization. However, it makes sense to switch to Dr Pulley sliding blocks here as well, since these have the same service life as the pulleys due to their material properties, and both components should usually be replaced at the same time. According to Dr Pulley as the manufacturer, the tolerances of his sliders are lower, which is an advantage for a precisely working vario.
In any case, Reinhold Harsch says: “The installation of this system is better than some tuning.” Regarding the costs: Depending on the size and weight, the reel prices vary, with around 45 euros (VK) per reel you are usually there. The prices for the sliders are also different, on Dr Pulley’s bestseller list they range from a price of 10 euros. The shipping costs are added. chk

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