Dear Strida friends,
via a searching machine you can find lots of articles, posts and how-tos about wheel building, lacing and trueing at the www (e. g. source list below).
Also simple to find: basic knowledge about wheel construction, spokes, hubs and rims –
but especially tiny wheels, as used on our Stridas or the Birdy, need special attention to some technical details, which I will try to illustrate here.
First, a few pics of original Strida wheels, here a detail of a 16“ wheel, there are 6 groups of 4 spokes in one cross (1x) lacing.
and here another group of 4 spokes at an 18“ wheel, 9 groups of 4 spokes, laced 2x.
Clearly visible is the bending of the spokes near the spoke nipples –
this should not be!
What happens here exactly?
The spoke nipple cannot supply the required spoke angle, for example 7°.
Commonly used spoke nipples will not allow more than around 3°, I guess.
For enhanced understanding some facts:
Theoretically, the best direction for a spoke to meet the rim would be in exact radial direction – technically impossible due to physical dimensions of the wheel parts.
Practically, the spokes meet the rim mostly not in radial direction, in relation to the radius there will be an angle, the nipple head seen as angular point.
These bad „spoke to rim angles“, furthermore called „SRA“, will appear, to be more exact,
in two layers, one layer in direction of the wheel‘s axis
and the other lateral to the wheel‘s axis.
It is possible to decrease the axial SRA by:
- decreasing the hub flanges’ width
- increasing the rim diameter
the lateral SRA will decrease by:
- decreasing the diameter of the spoke holes pitch circle in the hub
- reducing the number of spoke crossings
- increasing the rim diameter
[To give a dimension, the amount of lateral SRA on a Strida 18“ wheel, spoked two-cross, is around 7°.
The axial SRA of this wheel is lying between 7° and 9°, depending on the left or ride side of the wheel, seen in driving direction, - why that?
The middle of the rim does not meet the middle of the hub, which means (theoretically) that a Strida wheel does need different spoke lengths at the left and the right flange to supply the offset of ~ 3mm [front = rear = 16“ = 18“).]
At first sight there is no chance to improve something, but tiny wheels need very precise looking:
The rim diameter is given and not increasable, preconditioned that we want to keep the existing tyre size – is that true?
Yes, if the original Strida rims are used, the 18“ wheels have an ERD of ~332 mm.
No, if we used Alex DV15 rims, ERD ~343mm, due to a different cross section shape the inner diameter is bigger than that of the original rims, at nearly the same outer diameter.
Ok, 11 mm are not much, but it might help.
Back to the nipples…
A German special bike shop told about the disadvantage of „Polyax“ nipples:
Question to Sapim:
seem to be equipped with eyelets, on the other hand Crostinis are „offset“ drilled (according to the Alex website). „Offset“ means that the left and the right rows of nipple holes do not have the same distance to the middle of the rim.
By now I couldn’t figure out whether an offset drilled rim might be beneficial for a Strida wheel or not…
Sheldon Brown’s Spocalc
Edd, an easy to use spoke length calculator
spoke length calculator for bicycle wheels
Wheel Lacing Information
check spoke tension by ear/John S. Allen
The Framebuilders‘ Collective
Variation on 3-cross lacing for 36-spoke wheels
Wheelbuilding with Arup
Gaerlan Custom Cycles
Birdy – Simpson Cycles
United Bicycle Institute