CRF300L Index page
Tubeless Wheel Conversion index page

Thinking of going tubeless on your CRF300L or Rally? This page might be a good read.

Since my 2008 XT660Z I’ve been converting nearly every project bike with spoked wheels to run tubeless tyres, using various methods. The main reason: ease of puncture repairs on a hot day in the middle of nowhere (like left, Mali), let alone the added bulk of tubes and levers. Bombing around outback Morocco isn’t always like a day ride on the TET with your chums.

I want the same for my 300L which I might keep for longer than normal. One annoyance is that even the rear 18 x 2.15 wheel (right) is not an MT type rim needed for a secure tubeless tyre seal. Up front, Jap OEM 21s are rarely MT, so it means new wheels all round.

In my CRF TL MT quest I learned that ‘250cc’ bike wheel widths – typically 21 x 1.60 and 18 x 2.15 – are below the size where MT rims are commonly offered, especially once you factor in the Honda’s spoke count of 32 rear / 36 front. I did the usual scan on ebay looking for used rims that might work, but for the rear couldn’t find anything in MT with the width and spoke numbers needed.

Buying used rims
For the front in 19 inch (see below) I found a couple of MT contenders at 2.50 wide with the right spoke count (holes) and diameter, but buying used you also might need to consider the drilling pattern in the rim. The angle that holes are drilled through a spoked rim relates to the line of a spoke hooking up to a hub. There must be some leeway as the nipple can pivot in its seat/socket and new rims are sold drilled with no bike model designation but, broadly speaking, a rim drilled for a big bike twin-disc hub won’t match the dinky 300L’s hub. So, on top of the cost of the hubs, that leaves the following choices:

• Slightly wider new Excel front 21 x 2.15 rim in MT, £170
• Or a new wide Excel 19 x 2.50 MT front. £220
• Same as above, used from £70
• A rear Excel 17 x 2.50 32H MT with a wider adv tyre choice than stock 18″. £220
• Wheelbuilding a the above rims onto new Honda hubs – £130+ each
• Optional Airtight sealing at CWC, £125 a wheel

That will mean slightly bigger tyres all round, but they’ll wear slower and lightness is regained by ditching tubes (I’ve already junked the rim lock). A mate who regularly experiments with his TTR wheels tells me a stock front 21 with tube weighs the same 10kg as an 18er in tubeless (left). And on a CRF there’s just enough clearance in the swingarm for fatter 130 rear tyre*. He tells me offsetting the rim away from a chain by 5mm is actually a thing in wheel building and says you won’t notice the slight wheel misalignment.

Shopping
A used 300L wheel goes online for over 400 quid from breakers – all to dismantle just for the hub. Best UK price I could find for a OEM rear hub was over 200 quid. Meanwhile on ebay, outlets from Thailand (left; where 300s are made) sell front and rear hub combos for £270 plus about £55 tax.

So I returned to Partzilla in the US who I used while repairing my XSR700 a couple of years back. US-sourced Jap OEM parts with shipping and UK tax can still be up to half the cost of UK, EU and even Thai prices, depending on the item.

OEM rear hub $120; front hub $60. Add another $80 of collars, bearings and seals (actually not needed; the hubs came fully assembled) + $80 air freight and it came in at £340 taxed on my doormat 10 days later, with a spare air filter for luck. So that’s the same as Thai hub combos but with a full set of spare bearings and an air filter for free. Mistakenly buying the bearings and collars was an annoyance; I assumed the OEM hubs were bare. But wheel bearings are consumables so it’s not a total waste. Fyi; CRF250L 2017-20 hubs are the same; there might be more chance of finding those used from a breakers.

That all potentially comes in at around £1200 for a tubeless, Airtight wheelset ready to roll on new tyres. A lot of money to save on a sweaty puncture repair. I could save £250 by laboriously sealing myself, as I successfully did on the AT (left). This DIY method is better than proprietary Airtight or BARTubeless smotherings, in that individual leaks can be isolated and repaired. I might get 500 quid for my stock wheels if I’m lucky. I’m not sure there’s a cheaper way of doing it.

Rally Raid UK do sell an Asian-built low wheel 17/19 wheelset for just £600. RR spell out the low-wheel rationale here, and I agree with what they say. But even though the front 19er is a slim 2.15, neither wheel is MT type. John at Rally Raid runs a mousse on the front of his 300L low wheeler. I’m not fully convinced by mousses (see below); or should I say tubeless is more suited to road speeds; it’s no big drama to fix when flat and pressures can be varied if needed.

I’d actually be interested in a low wheel 300L as a CRF has ground clearance to spare and a chunky bashplate when it hasn’t. I’d also be interested to try a do-it-all 19 on the front as the light 300L wanders about a bit on the road and, like many 21-inch bikes, won’t cut through road turns so sharply. A 19er would feel more planted on asphalt, mostly down to a fatter and heavier tyre than claimed reduced rotational forces from a smaller diameter. On an agile bike and the sorts of easy trails I ride, I can live without a 21 incher.

To go full tubeless on 19 means getting a 19 X 2.50 MT Excel rim. The 2.50 width would limit the fitting of slimmer 19 inch tyres which I’d prefer, but puncture-wise the bike would be bombproof.

Mousse-tubeless combo?
I had a thought: seal up the non-MT Rally Raid rims then stick a mousse in there for back-up, even at £120 + fitting aggro, added weight and lube issues.
That way I could run normal 25psi road pressures in the tiny air space which is way above a typical 15psi mousse rating, The mousse would keep the tyre bead on the rim in the event of a flat, like they’re supposed to do. Meanwhile, you’d hope at 25psi and a typically moderate 60mph max cruise on a 300L, there’d be less tyre flex to heat up and degrade a mousse. Of course that assumes cool conditions and light payloads.
Part of the reason mousses get hot, soften and crumble or even explode, is that they’re not psi rated for road riding. On the Dakar Rally they used to get changed every day (maybe still do). Low low psi in a tyre means much more heat at higher speeds as the carcass flexes and unflexes on each wheel revolution (the same reason we get hot exercising; muscles flexing). Higher pressures from a tubeless sealed wheel might limit flex, especially on a light and lightly loaded bike.

I could even glue the tyre in place for good measure. I know TL pushbikes use some bead breakable (non-permanent) glue and there is one for cars with rusty wheel too (right). Of course cars have TL wheels with bead-seating lips and I’m pretty sure TL pushbike rims have some sort of sealing lips too. Without that lip to retain the tyre bead, back-up from a mousse is important.
This TL/mousse/[glue] idea seems a better idea than just shoving a lubed-up mousse in there and hoping it will survive a long road stretch on a hot day. As always, if it plays up, just stick tubes in there and anyway, I rarely drop pressures below the low 20s on stony Moroccan trails. I prefer to get traction from a suitable tread pattern, not ultra-low psi which is more suited to competitive events, not travelling.
But thinking this mousse and tubeless idea over, it’s all a bit far-fetched for travelling when added to DIY rim sealing. Too many variables. Better to keep it simple stick with a tried and tested tubeless (DIY or proprietary) for what I do. Less weight, less expense, no mounting and lube aggro.

* Fyi: the CRF’s skinny stock 120/80 rear IRC is 117mm wide and has 22mm clearance on the chain guard side, over 30mm on the other side and about the same up to the front of the swingarm shock guard. So add 22mm each side means anything up to 160mm wide ought to fit and which sounds loads.
Then again, on the left JMo fitted a 130/80×17 Bridgestone AX41 on her 300L DIY converted to TL with not much room to spare. 130 sounds fine; the lighter the better for a measly 28hp to turn.