Cycling UK Forum

I see that Shimano sell their MTB QR skewers in both 168mm and 173mm lengths.

Can anyone explain how to decide between the two sizes? It is for a 135mm O.L.D. rear hub, and a frame with dropouts of 8mm thickness (each side).

Thanks

The two different lengths are 168 for130mm road hubs,173 is for 135mm MTB hubs.
You need a 173mm qr skewer

My understanding is that the two sizes are to allow for different thicknesses of drop outs and vary depending upon the OLN:

173mm - 135mm OLN with thick drop outs (e.g. aluminium with a replaceable hanger).
168mm - either 135mm with thin drop outs, or 130mm OLN with thick drop outs
163mm - 130mm OLN with thin drop outs

I think that a 168mm skewer would be a better fit for an 8mm thick drop out.

Incidentally, SJS are selling T610 168mm skewers for £2.99, but when I bought a couple the ones I received were 173mm.

Thanks for the replies.

I have a feeling the 135mm O.L.D. and 8mm dropout combination might lie at the boundary between the two Shimano sizes.

8mm dropouts appear to be considered 'thick', so I'm tending towards the 173mm as being better suited.

In fact, if you look at the Halo Hex key skewers sizing info (I know these aren't QR), a 135mm O.L.D. & 8mm dropout combination would require the 'XL' version: https://www.halowheels.com/shop/components/skewers/xl-hex-key-skewers/ The 'standard' version will only support 135mm/6.5mm dropouts.

I'm surprised that QR manufacturers are not more specific about the capacity of a particular length of skewer, given the safety implications. It's quite a simple concept, and Halo to their credit have been very clear about it on their products. Just specifying '135mm' is too vague as it does not take into account the dropout thickness.

I have emailed SJS to pose the question - I will post back when I get a reponse.

I've just checked one of my bikes which has 8mm thick drop outs, and the XT skewer in that is 173mm. The end of the skewer is virtually flush with the nut. So my apologies for saying that I think you needed 168mm.

@slowster
Thanks for taking the time to measure yours. How did you measure it?

Morgano wrote:How did you measure it?

With a steel tape measure. I've just checked with a vernier caliper and they are a smidgen over 8mm.

NB With regard to those discounted skewers SJS I bought, they are probably a job lot of OEM stock which SJS was able to purchase for a song: they might all be 173mm, or they might be a mixture of 168mm and 173mm. In other words, although I received two 173mm skewers, don't be too confident of receiving the same length if you order one. (SJS probably ought to measure at least a few to see whether they need to change the website description to 173mm or check through them all and separate them if they find their stock contains both lengths).

Morgano wrote:
I'm surprised that QR manufacturers are not more specific about the capacity of a particular length of skewer, given the safety implications. It's quite a simple concept, and Halo to their credit have been very clear about it on their products. Just specifying '135mm' is too vague as it does not take into account the dropout thickness.

What safety implication?

@slowster

With a steel tape measure. I've just checked with a vernier caliper and they are a smidgen over 8mm.

I actually meant which part do you measure to determine the length i.e. to/from?

@alexharvey
If the skewer is too short it might not be possible to engage enough thread in the nut. For a 5mm diameter thread you ideally want at least 5mm engagement.

Three full turns is another rule of thumb.

I don't think I've ever had a QR that wasn't well engaged in its nut. Just wondering if this is theoretical or actuality.

Re skewer nuts; the steel insert inside the most common sort of nut is ~8-10mm long, and there is another ~6-8mm or so which is inside a plastic housing. It is beneficial if the skewer protrudes into the plastic part because it is draggy on the screw thread and it helps to ensure that the skewer stays in adjustment when the wheel is removed.

IME if the skewer doesn't engage with all the threads in the steel insert, this greatly increases the chances of thread damage/stripping.

The skewer length is conventionally measured from the shoulder to the end of the skewer.

cheers

Morgano wrote:I actually meant which part do you measure to determine the length i.e. to/from?

The measurements are, as per Brucey's comment, from the shoulder to the end of the skewer. In practice the shoulder is recessed ~3mm in the lever housing with the lever in the maximum open position (90 degrees to the shaft), so the exposed part of the the shaft measures ~170mm or ~165mm depending upon the skewer size.

@Brucey @slowster Thanks both. Now I can measure an existing skewer and based on that measurement I should be able to order the correct size.