As part of our series of articles about radio controlled model car wheels and tyres we have the following article about the Pegaso wheel and tyre combination that PMT produced for the large scale cars.
Many thanks to Alro Racing Systems for supplying the wheels and the tyres used in this article.
This article is split into two parts, with the both the wheels and the tyres in this first part. Pictures of the wheels and the tyres are covered in Part One.
Note: This article was originally written in 2001, but the Pegaso wheel sytem was still listed on the PMT website (December, 2008).
As far as I can see, the main body of the tyre is made just like any other, (the picture on the right is an artistic impression — the reinforcing may be different) but where the difference lays is with the spiral spring (blue) that is used as a bead on the tyre.
This spring serves two purposes, it controls centrifugal expansion of the tyre, and because it is covered by only a thin covering of rubber, it will also ‘bite’ into the plastic of the wheel to stop the tyre from spinning on the rim.
The image on the left shows a cross sectional view of a wheel to show how the PMT Pegaso wheel mounting system operates.
The inner plastic sleeve (blue) is sandwiched between the two outer wheel mouldings. The three parts, once fastened together with the supplied machine screws and nuts, compress the spiral springs to create an assembly that is rigid and reasonably light.
Assembly should begin by pushing the nuts into the recesses in the deeper inner wheel moulding. They are a nice press fit and this can be done with a flat ended punch or screwdriver, etc..
Continue by pressing the inside (deeper) part of the wheel mouldings into one side of the tyre and then align the outer (shallow) side of the wheel mouldings into the other side. Both these parts are a reassuringly tight fit. Although PMT have made a rather nicely machined assembly tool for the Pegaso wheel and tyre system, it is, apparently, relatively expensive.
Assembly Tip — A simple solution to assembly is to purchase some M2.5 x 12mm machine screws and either use three or four of these to hold the wheel assembly together while you put in the supplied M2.5 x 8mm screws in, or throw the supplied ones away and use 12mm long ones all the way round.
Please Note: The supplied screws are not high tensile (see note below) and you would be advised NOT to over-tighten the screws, instead, use some low strength threadlocking compound such as Loctite™.
Having had the Pegaso wheel system tyres and wheels in my possession, I can see why they have been such a success in the short space of time they have been available.
The low profile and stiff design is made all the better by being able to take the tyre off and reverse it if wear is becoming uneven.
Only time will tell if there are any problems with the design. I personally have only three concerns at this time;
1. The plastic is reasonably hard and could lead to problems with impact damage in colder climates, a problem which is compounded because the assembly is so stiff. It has to be mentioned that this problem affects almost all wheels though.
The outer rim is a little thin and could deform and allow the tyre to escape under some circumstances.
2. The use of M3 machine screws would have been better than the standard M2.5 screws, as M3 high tensile replacements cost a fraction of the cost of M2.5 ones at the fastener suppliers I have enquired at. The trivial extra weight would be worth the peace of mind they would bring, as well as allowing the use of inexpensive Nylock nuts.
An alternative is to drill the holes out to 3mm and put M3 allen cap screws in as the nylock nuts will pull into the plastic and be retained at the rear.
Many thanks to Rob Lochier at Alro Racing Systems for supplying the wheels and tyres used in this article.
Part One of this article
Wheel & Tyre Mounting Systems — Part 1
CHM file format PMT Tyre listing of the full range of wheels & tyres from 2001.