I'm looking at converting an old T140V (1977) into a 'Trackmaster' replica ,but am a little confused on alloy rim sizes regarding what I can go up to without fouling issues - chain on tyre.
I want to keep the rear at 18" and front at 19" but not sure on the widths - WM2-3 etc. Been looking at charts but still not sure what will be best.
Has anyone else done this who can give me some advice?
Here is a pic of what I'm aiming for:
Hi Rob -- i have just had similar thoughts on this subject - the standard rear rim is WM3 which is 3 inches wide - I have a TT100 4-10 x 18 tyre on a std rim in a standard rear end set up -- the max width of the tyre measures 100mm or 4 inches -- this then has a distance from the tyre to the chain of 20mm --- so if you dont use a chain guard you could easily go to a tyre that is 120mm wide -- however if you want to go wider you can move the engine to the left by about 6mm if you dont use the left side front engine mount spacer , have the engine tight to the frame mount then adjust all the other engine mounts to suit (i think the TSX custom thing was done like this) - but then you will also need to space the rear sprocket off the hub by a similar amount to maintain the chainrun -- plus if you go bigger that 110 / 120 wide tyre you may have to go to a wider rim --- all the above is just swimming around in my head so dont take it as gospel true --- i already have an ali rear wheel with a WM3 so i will be staying with a 120 wide tyre on my project --- later model swing arms were stronger but i dont know if they gave more tyre clearance
"WM" is a (now obsolete) rim cross-section. Specifically with WM, the number is just that, a number, nothing more.
Otoh, the current motorcycle rim cross-section is MT. When this is followed by a number, this is the rim width in inches. The MT cross-section is so universal that it's frequently not used, especially where space is limited. So, if you look on tyre makers' websites for recommended rim widths, you'll frequently see just decimal numbers; they are the rim width(s) in inches.
The rim width is measured where the tyre seats. Specifically the WM3 is 2.15" wide.
Specific to the alloy wheels (as opposed to just alloy rims) that the Co-op fitted, the Co-op fitted only Lesters (6-hole front disc) to the T140D and Morris's (4- or 5-hole front disc) as an option on any late ('82-on?) twins. The Co-op quoted all four as WM3 rim width but that's certainly unlikely of the Morris - contemporary Kwaks used 'em so I believe they're far more likely to be MT cross-section.
As I say, the standard alloy wheel rim width is WM3/(MT)2.15. This is below any tyre makers' minimum width recommendation for a 120-width tyre; that is normally 2.50 (equivalent to WM4). I happen to know that, if you fit a 120/90x18 Roadrider on a 2.15/WM3 rim, the overall diameter increases sufficiently that you can't get the rear wheel off the ground using a standard Trident centrestand ...
Moreover, while the "max width" of a 4.10 TT100 might be "100mm or 4 inches", that happens to be pot-luck; width numbers moulded on tyre sidewalls are always the section width, never the overall width. Consulting something like http://www.avon-tyres.co.uk/motorcycle/roadrider shows "120" tyres vary from 120 mm. to 129 mm. overall, depending on section height.
no probs - post some pics as it progresses - i am intending to strengthen my frame and swing arm like the Big D race bikes -- if you find a small tank like in your pic for a sensible amount let me know
its not absolute cods that a WM3 is 3 inches wide -- my stick of inches proves it is -- just because the manufacturer chose to quote a measurement from a different place on the rim for their specifications does not change the fact that it measures 3 inches across its width - rim edge to rim edge -- but yes if you want to be pedantic my statement is wrong
My turn to be pedantic ;" a 120 roadrunner tyre on a WM3 doesnt clear the ground when on the centre stand on a Trident "-- in possibly one instance that you experienced - but what about wear in the stand pivots - or a bent stand - too many variables to make your statement valid for all Tridents (T150 or T160 ?) -- and anyway we are talking T140 not Trident - the geometry may be different - plus if the bike in question is to be a flat tracker it unlikely to have a centre stand
its not absolute cods that a WM3 is 3 inches wide
just because the manufacturer chose to quote a measurement from a different place on the rim for their specifications does not change the fact that it measures 3 inches across its width
A WM4 is not 4", a WM2 is not 2", a WM1 is not 1" and what do you suppose a WM0 is?
And it's not "a manufacturer"; that's the standard, that's where every tyre and wheel manufacturer measures any rim width. If you ask for a rim to replace a WM3, you will be sold a (MT)2.15.
That is not the point. The point is a 120-width tyre on a 2.15/WM3 rim is so badly deformed that its overall diameter is greater than it should be. Why will that be any good for the bike's handling or the tyre's longevity?
And, given the T140's original tyre is a 4.10x18 while a Trident's is 4.10x19, why would a T140 be any better-able to accommodate an oversize-diameter tyre?
a 120 roadrunner tyre on a WM3 doesnt clear the ground when on the centre stand on a Trident
what about wear in the stand pivots - or a bent stand - too many variables to make your statement valid for all Tridents
Really? After all I've posted about Tridents here, I wouldn't notice pivots so "worn" that the holes are bigger than the standard tubes, or the sides so "bent" they're broken?
By all means do dodgy stuff on your own bikes but, if you post it without any warnings, do you really expect everyone who knows it's dodgy to sit quietly?
OK - I have to own up - my previous post was intended to provoke the kind of "outburst" that you have so kindly given - you seem to take great pleasure in picking out the technical errors in advise given and then go all text book and at great length to provide the correct information as you see it
Your "outburst" - shows me that you are unable to handle any criticism of statements you make -- you cant always be right - or can you ?
I know the vast majority of your words are correct and very helpful but i think you need to calm down a bit in some of your rebuking responses
so now we come to dodgy stuff -- you have recently advised in another post the use of Mini Cooper brake pads on a T140 - i assume you have looked into this in great depth and can confirm that the compounds used are suitable - they appear to be half the price so why arnt we all using them - or maybe we are and we dont know it ---Stuart ; on this i am genuinely interested do you know for sure ?
I promise i wont "bait" you again
By the way - you must have missed the bit where i said in my first response "all this is just swimming in my head so dont take it as gospel true"
Ok, so now I've been looking at tyre choice - obviously not so great with 18" and 19" rims (compared to 17"). Something like Pirelli Mt60's - this is why I originally posted, to see if anyone had gone for this 'look', and what they'd found with rims and tyres.
Rob.
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