hi,
i have ab31 with a 7 " front brake that i am considering swopping with a qd 8" front wheel and brake i have. However it has a wm1 rim which i have had no experience with and am asking if the handling would be off on a b31. Also what tyre size for a wm1 rim?
I swapped the 7" for the 8" single sided ally brake on my B31 and it was a huge improvement. You can keep the fork sliders as they are but you need the brake stay. I would not use the WM1 (is is a 21"?) but would swap to a WM2, they are easy to get 2nd hand. You may be able to use the existing spokes of perhaps only need half a set. The problems with the WM1 is that even if you fit a 3.25 or 3.5 tyre the narrow rim pulls it in so the tread is narrower.
I agree with limeyrob. Unless you go with 3.00 x19 (a size early GoldStars used) most modern tyres in the range you might fit are better with WM2. I have those on my Mongrel 600 and use Avon Roadriders 90/90-19 front and 100/90-19 rear. In fact Avon suggests WM3 for even 100/90 for best footprint. My DBD34 with alloy rims are both WM2 with same tyres. For trail tyre choice I committed heinous crime and put WM3 x 18 on rear of CB34 Competition to use 110/80x18 tyre.
The 7" front brake can be made tolerable with arcing of nice new Ferodo linings and I've kept mine on the greenlaner, but have been researching a TLS mod for it. I like the 8" brake but have Dow type TLS on both which means modern braking standards for modern tyres. Wheel building is not in my skill set so Mark at Anglia Wheels gets the job!
thanks for replies.
if a wm1 is not really suitable , i cant understand why someone went with an ally rim on one and not wm2.really wanted to avoid rebuilding and will have to use the 7 " with the upgraded forks i will use.
i have double damped qd b44 forks but i dont rate the damping or design much.
I forget where this came from but I think it's current.
Is the bike a road bike or green laner? Is it alloy rims front and rear at the moment?
I swapped my RR from WM2x19 steel over to WM2x19 ally by getting used rims form autojumbles. This was after agonising whether to go WM3x18 on the rear as there's much more tyre choice but a WM2x19 turned up first so that decided it.
I was surprised at the number of WM1x19 ally rims about, these must have been common, perhaps on scramblers?
The easiest B31 swap is the early A10 front wheel as the spindle is the same. I never got my 7" std B31 brake to do anything worthwhile, I think the drum is a a bit thin and its possible for the spokes to pull it out of round.
i dont find the qd 7 "front brake too bad , but the cable adjuster is part of the forks whereas the 8 " has a cable adjuster on the brake plate. and i want to swop over the forks as potholes are killing me.
regarding the chart martin. the tyre on there already [ tyre too old] is a 3.25 which is not covered by the chart. yet a 3.60 is ok? for a wm1 rim
Yes, I thought that was a bit odd.
I got into this mess fitting modern tyres to an old Land Rover. The "old" trye sizes 3.00 x 19 or for the Landy 7.00 x 16 are based on a circular tyre cross section so the dia and width are the same. Once you get to 2 numbers 3.60/90 or 215/85 the tyre is oval so there are two equivalents - rolling radius and rim size. A 3.60/90 is 3.25" high but 3.6 wide.
The trouble I ran into (in the end I bought new rims) was that fitting a modern oval section tyre on a narrower rim pinches it to a circular shape, this increases the rolling radius quite a bit and narrows the contact patch. The tyre is also less stable on the rim as its taller and narrower than it intended to be.
I can relate on the Landy. I fitted LWB rims to my 88 SW and fitted 225/70 16 Grabber ATs. Must be correct profile as my speedo is perfect (according to speed traps😂)
Hi,
Many years back when the Avon Road Runner tyre came out the 3.25 equivalent was a 3.60 and the 3.50 was a 4.10.
Today the 3.25 is a 90/90 and the 3.50 100/90.
Dave.
maybe i m missing something, but the metric equivalents' seem too wide
Quote from: EDDIE SIMPSON on 16 Feb, 2026, 20:16 maybe i m missing something, but the metric equivalents' seem too wide
The 90/90 front and 100/90 rear are correct and (IMO) the Avon Roadriders suit the BSA s/a frame very well, but you will need WM2 rims. IIRC I had 3.25 and 3.50 Skidmasters on my B31 with WM1 and WM2 rims but the front rim always seemed a bit narrow.
The 3.25 and 3.5 tyres are 100% so they are round, for 100% aspect ratio its not normally put on the tyre size. The 90/90 is 90mm wide (3 1/2") by 81mm high (3 3/16"), the 100/90 is 100mm wide (3 7/8") by 90mm wide (3 1/2")
The 90/90 should clear the mud guard and stays but a 100/90 may rub the stays or the chain guard if on the rear. The front mudguard stay between the sliders can be a bit close.
A 3" tyre for a WM1 would be around 80/90 (3 1/4" wide by 2 5/8" high) but these don't seem to come in a 19", mostly 17"
I have a 21" WM1 rim on my ZB32 with a 2.75" tyre which I think is correct for that rim..
I agree, I'm looking at something similar for the front my my Matchless G3CS. Is that a trials pattern tyre?
I have a ZB32 with a 21" front wheel with 7" brake. I recently bought a 3.00" trials pattern tyre and I'm glad I did as even the 3.00" looks small.
Quote from: limeyrob on 17 Feb, 2026, 11:01 I agree, I'm looking at something similar for the front my my Matchless G3CS. Is that a trials pattern tyre?
Yes, a Heidenau K67 (https://shop.heidenau.com/en/zweiradreifen/k67.html)