Tiny wheel improvement - thoughts & facts

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.

Many thanks to Peter de Leuw for the report How to make a „Birdy“ to „Your Birdy“

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…

According to Sapim their „Polyax“ nipples should be able to supply up to 9° of SRA.

A German special bike shop told about the disadvantage of „Polyax“ nipples:

Question to Sapim:

Interestingly, there is an alternative rim to the Alex DV 15, sold as spare part for the Birdy – the Alex Crostini M1.1.
The Crostini rims here

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
Wheel Fanatyk
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

Maybe anywhere, actually my Crostini rims of pedalkraft.de are NOT offset drilled (?).
I hope the pics will explain the measuring method.

“left” (unmarked eyelet) row of spoke holes on bottom

“right” (marked eyelet) row of spoke holes on bottom

No difference means no offset…

Polyax nipple angle estimation Alex Crostini. +/- ~ 10°

Estimated SRA for different spoke patterns:
(Wheel drawings created with Spoke Pattern Explorer of machinehead-software.co.uk)

16" 1 cross ~ 4°
16" 2 cross ~ 8,5° (nearby critical)

18" 2 cross ~ 7,5° (original 18" Strida 36 spoke pattern)
18" 3 cross ~ 9° (critical range border)

Caution, these angles are different to those of 24 spoke hubs, for example:

16" 1 cross ~ 6,5° (original 16" Strida 24 spoke pattern)
16" 2 cross ~ 10,5° (in critical range)

Factory sticker Alex DV15

Factory sticker Alex Crostini M1.1

One more word about original Strida wheels:

Have you ever looked behind your rim tape/band?

You might find unexplainable marks at the bottom of your 16" rims,

at 16" AND 18" rims most of the nipple’s screw grooves might be damaged,

it actually looks as if the nipple heads were partially drilled out (at 18" rims)?

So what?

Imagining a tool like this

an electric screwdriver and a sloppy wheelbuilder, I think these marks are no longer unexplainable.
That need not be!

For completeness, a roughly material cost estimation for the new building of a 36-spoked 16" or 18" wheel set (except freewheel and brake rotors):

2 hubs ~ 50 €
2 rims ~ 40 - 80 € (depending on the used rim size and type)
72 spokes ~ 36 € (estimated price of 0,50 € should include the nipples)
2 rim bands ~ 4 €
2 tubes ~ 15 €
2 tyres ~ 30 - 60 € (depending on the used tyre size and type)

165 - 245 € is not really cheap regarding that we have NO freewheel and NO rotors.

The above estimation is meant for private customers, who are willing and able to assemble the parts DIY.
I mean a skilled and helpful local bikestore/wheelbuilder anywhere in the world should be able to get some parts cheaper than normal people.
(And/Or assemble the wheel parts for users who won’t/can’t.)

The original 18" wheelset does include brake rotors, freewheel and mudguards (at Vanmoof), for 170 €.

So, dear reader, if you think that’s the better deal - you’re 100% right, but please, please do me a favour:

[size=150] Check your spokes’ tensions! [/size]

or let them be checked …

Might be continued…

above pics 1024x768

Thanks for posting - Fascinating info !! :smiley:

Jobst Brandt in his “The bicycle wheel” book recommends to … simply bend spokes in this case.
In the section “Correction the spoke line” it is advised to do it (bending spoke where it exits the nipple) either with pliers or with bare hands, when spokes are not yet tightened to maximum tension.

But of course specialized nipples are better approach.

Thanks, the mentioned book seems to be very interesting…

To be honest, even with the Polyax nipples the spokes will not stay completely straight under tension :confused:

And of course, it’s a thorn in the eye of a perfectionist :laughing:

For completeness:


Thanks Flo :smiley: