jur

I'd like to re-open the discussion re Greenspeed Scorchers on the back of a Brompton.

I have seen any number of posts that repeat the limitation that the chainstay bridge/brace does not allow enough room for a wider tyre such as the Scorcher. While the front may be OK, the rear is not.

So I just had a quick look at my Brommie and it appears that there is loads of room for a fatter tyre in the back.



Am I missing something?

Dynocoaster 

Width wise it doesnt appear to.

fietsbob

Mudguards.. you are not using any?

1 1/2"greenspeeds are a wider tire than the Kojak, or the standard 1 3/8"/37mm

if a wider tire was needed the 305 rims,
on the other 16 " wheel bikes will be fatter.
and lower pressure..

bendembroski

The photo is taken looking "up" at the bottom of the bike. You can see the mudgaurd in the background.

chagzuki

That looks like around 12mm clearance to me; on my mark 3 with marathons there's only 3-4mm clearance. Perhaps Brompton moved the bridge sometime in the last couple of years?

invisiblehand

Jur,

It might help if you let us know the tire in the picture and its measured width.

I recall that the original message about the Scorcher was on BromptonTalk and the person mounted a Scorcher to discover the conflict.

jur

That's a Kojak, measuring 32mm wide.

jur

Just searched to Bromtontalk forum a bit; it is mentioned that the chainstay bridge is a problem along with the mudguards.

Well my chainstay bridge has about 13mm clearance on the Kojak an the closest chainstay about 5mm.

The mudguard has wide clearance all round except at the back - the screw that holds the flap would rub but that I believe is easily remedied. I am beginning to think Brompton has modified the design to accommodate wider tyres. So I am going to try a Scorcher.

chagzuki

Jur, to be sure why not measure the bridge position against the chainstay end and we'll compare stats.

jur

The distance from the centre of the rear axle to the edge of the chainstay bridge is 220mm. You can see in the photo that the bridge itself is indented even further by another 2-3mm, as is the closest chainstay. The gap at the closest chainstay to the tyre bulge is about 7mm. In fact, the indent on the chainstay is not opposite the Kojak bulge, but a bit further away, to coincide with a wider tyre's bulge.

chagzuki

What's the distance from chainstay tube end (near hinge) to bridge centre?

chagzuki

It's tricky for me to measure. I've not seated the rear axle fully into the dropouts, don't know why I've done that. I think it was something to do with a clearance issue when I was using an X-RF5 high-flange shell, but now I have an S-RF5 so it's pointless. Anyhow, it increases the length of the measurement from axle to bridge. It appears to be around 220 on my bike but if the axle were fully in the dropout that length would be shorter.

chagzuki

I make the distance from chainstay bridge to end of chainstay tube 61mm from centre of bridge and 50mm from end of bridge (avoiding the brazed filleted area).

jur

FWIW mine is 57mm, but I thought that would not be reliable across builds which is why I went to axle centre-line. I took a straight piece of metal and laid it on the chainstay, and marked the centre of axle off on it, then measured that. There could be 1-2mm error due to parallax.

fietsbob

could make up a C clamp like press, and make some serious indents in the tubes
to make more clearance.

re braze the bridge tube [Flatten it too?] a bit further away from the tire.

there is that indent low side of your picture, its on the Mk4 , but not the Mk2.

invisiblehand

Given your measurements, I'd expect the chainstays but not the bridge to be an issue. 5 mm of clearance is pretty good in my experience. But one or two mm typically results in rubbing during use.

chagzuki

That sounds consistent with the impression given by your pic, that your rear frame has an extra 4mm or so clearance which indeed ought to be enough for a scorcher to fit. You may have trouble with the bolt that affixes the mudguard flap, when I was looking into this it appeared that may be an issue.

jur

Yeah the mudguard flap bolt will rub but I think I can get past that one with a little persuasion.

Anyway the issue of getting another rear tyre has now been forced as my Kojak had a casing failure yesterday. It's not even close to being worn.

feijai

I wholly support this, if only because you'd be one of the few who could compare your experiences riding on both tires.

As Greenspeed is Australian, could you get a discount on the tires?

jur

Unfortunately Greenspeed charges locals even more. Every time I buy something there I come away feeling severely stung.

jur

Scorcher in hand, non-folding, $60. Also got a slightly narrower Primo Comet just in case, $40. Ouch.

As you can see, Greenspeed is quite close to work.

feijai

Scorchers are all non-folding. There's a kevlar belted version, but no kevlar beaded version.

jur

It fits! No interference with the frame. There is about 5mm to spare.

The mudguard stays need to be bent to maximise the distance or it rubs slightly. And when folding, the tyre presses firmly against the bottom bracket shell.

chagzuki

Is it just the nut on the flap that rubs? In which case I'd take the flap off temporarily or maybe flip the bolt so the nut is on top.
I had to bend the stays on the front to get the mudguard clearance at an acceptable level.

chagzuki

Oh, photos please!