For some reason I’m already thinking ahead to winter. Round by me, the singletrack turns to absolute slop from November to March, so I like to avoid off-road riding for the sake of the trails/my bike/my clothes/my washing machine. But that is so so so dull, and I always lose so much fitness over the winter, so…

I have an original series Cotic Roadrat which has mostly just seen commuting and pub duty, but which I still love. I’m considering turning it into a flat-bar gravel/bridleway/cx frankenthingy when the time comes to put the fat tyres away. I have 2 areas of uncertainty though:

Wheels – I have a set of 27.5″ 23mm Mavic rims on Pro2 hubs which I recently took off the full-sus.  Is it feasible to put a set of 40mm-ish cross tyres on those? They are mtb rims, and probably a bit heavy, but am I right in thinking that rim width is rim width irregardless[sic]?  If so, name me some likely tyres, please.

Am I likely to notice a difference in size between road tyres on 700c wheels and CX tyres on 650b?

Gearing – I could leave it singlesped, but should I want to put gears on it, is there anything special I need to consider? It must be flat bars, so that leads me to think that I can just chuck a handy spare SLX 1×10-speed setup on there. I have shifter and mech available (I can use this as an opportunity to stick 11-speed on the big bike). Anything wrong with this approach? Should I keep the cassette range the same as my normal one for the local hills?

Educate me, please.

I’ve got a mk1 roadrat currently in gravel bike configuration which I use for commuting and general knocking about with the kids, pub bike etc. It’s got drops, mechanical disks, tiagra 20spd drivetrain. I had 36c sammy slicks on it until recently on 700c rims and it was tight, especially with clearance to the seat tube and front mech clamp with the hub slid fully fwd in the horizontal dropouts – which I have to do to get enough engagement the with the dropouts to stop the hub sliding forward under braking due to position of the mounting of the calliper (chain tugs don’t work).

now I’ve got 32c’s on which gives a bit more clearance, enough to fit full mudguards. So moving to 650b rims would be a good move if you wanted wider tyres on as you’d dtruggle with much wider than 42’s on 700c rims.

but other than the the conversion to gears is simple and works well. It rides lovely.

Good to hear. The switch to 650b is really just because those are the wheels I’ve got lying around.

Re: the dropouts – are you on a QR skewer? Do you think bolt-on hubs would resist the braking force? Did you try chain tugs on both sides?

Impressed you’ve converted to drop bars – I think I remember that the Mk2 came in short/long varieties because they couldn’t get the original long version to play well with drops.  If you don’t mind me asking, what size are you and the frame, and how long is your stem?

Its a long frame (was originally on flat bars when I bought it) and i’ve got a short stem on (50mm I think) and the reach is still about 30mm longer than my road bike, so it is a long frame, but is comfortable and handles beautifully and is bang on trend – I guess it could be considered as a Longshot Roadrat! Its a medium frame and I’m 5’9″ with 31″ inside leg. Compared to my road bike the aero position is not as ‘racy’ when using the drops due to the additional reach, but this makes it a lot more comfy to ride on the drops as I’m a bit more stretched out, so maybe not as aero, but a lot more comfy. I ride on the drops a lot. I do  feel a little too stretched out when riding on the hoods though.

I am on QR hubs and I’ve tried allsorts to prevent the hub slipping issue as I wanted to put wider tyres on than the 36C’s I had previously so that would have required me to slide the hub back in the drop outs, but couldn’t find a solution. Tugs don’t work as the hub is being slid in the opposite direction. In the end I decided to go with the narrower tyre as I wanted to fit full mudguards on too for those wet commutes, so needed the clearance with the seat tube so that put paid to the wider tyre plan.

Even without QR hubs the slippage is still an issue. A mate has a MK1 Roadrat too with Alfine so a bolted hub and disk brakes, and he was having similar issues so he just solved it by using a longer spanner to tighten the nuts up super tight. He’s be screwed if he had to fix a puncture on the roadside the bolts are torqued up so much, but not an issue for him as it’s really just a pub bike so never goes further away than about 6 miles from his home.

That slippage problem is interesting- I’ve never noticed it, either using qr or a 10mm ‘thru’ axle. I’m pretty sure I’ve had nanos in there with the wheel fully forward too, but I wouldn’t swear to it. No mudguards though.

Mine has spent most of its life as a singlespeed, but gets gears to go touring. Originally I ran it with flat bars but ended up sticking woodchippers on. In its flat bar days a gear conversion was just a case of sticking on a mech and shifter as you say. Drops make that a little faffier.

I think mine is a short version but I’d have to check. It was a nice length with flats but is just a tad long with the same (100mm) stem and drops, so I’ve got the saddle a bit further forwards. I should really buy a shorter stem.

I’d love to try it with big 650b slicks so I’d say go for it