Thorn Audax Mark III maximum tyre width?

[Vintagetourer]

Is the Thorn Audax Mark III maximum tyre width 28mm? Or could mine (about a 4 year old model) handle slightly wider tyres? Say 32mm?
When I bought the bike I vaguely recall that 28mm was the limit, but looking at the clearances I am wondering why. There appears to be enough space.
I have a light fork...the Reynolds 853 fitted...if this makes any difference. And Shimano Ultegra brakes are also fitted.

[Danneaux]

Hi Graham,

First, you'll need to determine if you have an Audax Mk3 or a Mk3R. Where yours is 4 years old, it is likely a Mk3 non-R.
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Going back through the archives of the Internet Wayback Machine to the 12April2014 Audax Mk3 (pre-R) brochure ( https://web.archive.org/web/20140412062013/http://www.sjscycles.com/thornpdf/Thorn_Audax_Mk3.pdf ), page 2 states....

Please note, the Mk3 frame and its steel forks will accept tyres which measure 28mm (i.e. some tyres labelled as 700 x 32c) with sufficient clearance for mudguards - the carbon forks will accept 28mm tyres - but not with mudguards. The carbon forks will only accept tyres which measure 25mm, with mudguard clearance.

On the last page of options on the order sheet, we see...

Schwalbe Marathon Supreme 32c folding Ultimate in reliability and longevity - still very quick. Actually measure 30mm - will fit the Mk3 frame, with mudguards using either of the steel forks. PLEASE NOTE these tyres need partial deflation to enable removal from the brake callipers - is this an issue for you?

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The latest Thorn Audax Mk3R brochure ( http://www.sjscycles.com/thornpdf/Thorn_Audax_Mk3.pdf ) states on page 2...

What changes did I make to the
Mk3 frames to create the Mk3R?

Our Audax Mk3 had a 12 year production run, we offered different colours at different times and we changed the decals a few years ago, nothing else was changed - we considered it to be perfect! Only 2 things were changed when we introduced the Mk3R. [1] The rear brake bridge has been raised by 1.5mm - the frame now takes tyres which measure 31mm with
mudguards (e.g. 32c Schwalbe Marathon Supreme or 32cPanaracer Pasela).

Please note the brochure is referring to "32C" tires which measure an actual 31mm. Not all tires' actual size matches their stated size when inflated and "aged" on the rim for awhile...they tend to get wider and taller.

Also on page 2...

Please note, the Mk3R frame and its steel forks will accept tyres which measure 28mm (Some tyres labelled as 700 x 32c actually only measure 28mm wide) with
sufficient clearance for mudguards - the carbon forks will accept 28mm tyres - but not with mudguards. The carbon forks will only accept tyres which measure 25mm, with mudguard clearance

On page 3...

...Schwalbe’s latest Marathon Supreme (HS469) in 32c, which are still pretty quick but tougher and longer lasting. There is enough clearance, for sporty riding with 32c Supremes and mudguards, for the mudguards to be an asset, rather than a liability.

As I recall, some Forum members have also had good luck fitting Continental Gatorskins labeled in wider sizes to their non-R Audax Mk3s, but you will need to check the Forum archives to confirm. I suspect a 32mm Gatorskin might actually measure a bit shy of the stated size when mounted but again, it would pay to check first before buying.



Best,

Dan.

[Vintagetourer]

Thanks Dan.
Perfect information. Brilliant.
Eureka moment.  Bing!

Now it’s clear to me it’s all about mudguard clearance. Not brake or fork clearance.
I am in Australia the world’s driest inhabited continent so mudguards are total non necessity for me.
So next tour, I will be trying out wider tyres on The Red Bike.

[Danneaux]

Now it’s clear to me it’s all about mudguard clearance...So next tour, I will be trying out wider tyres on The Red Bike.

Yay! Please let us know how you come out, Graham. All good wishes,

Dan.

[PH]

Now it’s clear to me it’s all about mudguard clearance. Not brake or fork clearance.

Well yes and no - it's the brake that restricts how high you can set the mudguard and the fork fitting which dictates the distance from crown to blocks. 
But yes, not having a mudguard in that space frees it up for more tyre!
A couple of other variables -
Where it becomes borderline, rim width will play a part in the tyre's shape.
Mudguard profile doesn't always maximise the space. 
Thorn's direct fitting gets the guard as high in the crown as possible, for anyone using a bracket some modification can sometimes help get it higher.
Peoples definition of "acceptable clearance" varies
Running your brakes wide can get an extra mm or two, use the deepest pads and have them no closer to the rims than needed (I do this anyway, IMO it offers better braking at the cost of more frequent adjustment)

My bike with those brakes has the blocks right at the bottom of the slots and takes a tyre measuring 30mm and guards or one measuring 35mm without.  That's with my definition of acceptable clearance which is more than others I've seen, but not enough to stop them getting clogged up on mucky lanes.

[lewis noble]

Brief reply from phone . . . 32 Scwalbe Supremes will fit, with mudguards, but v tight. They do give a more comfortable ride than the 28 gatorskins in my view, an important factor on the tarmacced but with large stone chunks rather than chips on some of the roads in the UK Peak District. Lewis

[Vintagetourer]

Thanks also PH and Lewis.

Behind my original question was the preference to fit either Schwalbe 700x32 Supremes or Contis, next time I tour with the Thorn Audax. Most of my tours are in S.E. Australia where rain is a rare event, so mudguards are not needed.
From your posts, I am confident that 32s will fit. There appears to be plenty of clearance around the brakes.

[lewis noble]

Yes, I would do the same if guards not needed. I have reverted to 32 Supremes because of poor road surfaces on my regular rides, will keep 28s for when on areas with better roads.