A4 scale = 70%
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A4 scale = 70% |
EGGring Ovals page 6 ... Technical notes continued
An Oval feels like a larger round ring during the power-stroke and a smaller one at the dead-spots. You can calculate the sizes of these equivalent round rings as follows:
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equivalent large round chainring (L) = number of teeth × ( 1 + U ) |
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equivalent small round chainring (S) = number of teeth × ( 1 - U ) |
| where U = ovality 200 + ovality |
A larger capacity front mech is required than for round rings, since it must cope with both the largest diameter of the the largest Oval and the smallest diameter of the smallest one. The required capacity is found by subtracting 'S' for the small Oval from 'L' for the large Oval, as described above. Alternately your existing mech may have sufficient excess capacity, which can be estimated from the knowledge that each tooth will raise (or lower) the chain by 2mm.
| required capacity = (L - S) teeth |
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Oval EGGrings do not affect your rear mech's capacity. (You might imagine that the mech would swing backwards and forwards as you rotate your cranks, but it hardly does at all - which is why mild Ovals can be used with hub-gears and fixed-wheels where there is no chain tensioner at all.)
| © Chris Bell, 2004 |
continued on the next page... |
| HIGHPATH ENGINEERING Cornant, Cribyn, Lampeter, Ceredigion, SA48 7QW, Wales, UK phone / fax: +44 (0)1570 470035 (UK office hours only) email: 
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