crf250r wheel, sprocket, and disc fitment on crf250x

[savrvs]

Hey all!

I just picked up a new 2017 crf250x as my local bike shop was making room for their 2019 inventory to come in. I'm really looking forward to getting out and riding on the 650 square mile bombing range the USAF has parked behind my house (dont worry, its perfectly legal - thats where everyone in my town does their hunting every year), but in order to do so I have to drive down paved roads to go through a check station. So, because this bike will basically be a 60/40 dirt/paved road split, I would like to get set up with a second set of wheels and tires so that when I actually go to the nearby motocross track I can just slap back on the stock wheels and tires with the more aggressive tread pattern and they wont be completely chewed up from any paved usage. This leads me to my actual question - Will a 19x2.15 rear wheel from a crf250r accommodate a crf250x rear brake disc and drive sprocket? I know the wheel and accompanying tire will physically fit the rear swing arm - the only change from the crf250x stock size is a one inch diameter increase - but I'm concerned about a potential difference in bolt pattern / diameter for the brake disc or sprocket. I ask about this swap rather than just buying factory oem stuff online because I can get a steal of a deal here locally on the 250r hubs, spokes, and rims.

 

Thanks for any and all input guys

[Chuck.]

I had a complete early CRF250R rear wheel on my X and it was bolt on, don't know about the later R wheels.  You can check part fiche for rotors, rotor bolts, sprocket, sprocket bolts, and wheel bearing size.
Best tire selection is for the 18" rim. The 19" tires are about the same OD as the 18, just shorter sidewall for a little more stiffness. 

[mlatour]

One other difference is the R's 19" rim will likely be 1.85" wide rather than 2.15".

 

The latest trend in many 100/90-19 MX tires is having a lower profile than before, 

my recent experiences with some Bridgestone and Michelin on my YZ125's spare wheel set

show that these lower profile tire are overly stretched when mounted on a 2.15" rim.

 

You might need to experiment final gearing a bit if you ride both off-road and MX tracks,

keeping the same front sprocket and chain length might allow for only a 1 tooth difference between both wheel setups.

 

Stock final drive on the CRF250X is 14/53

I run 13/52 for off-roading (limited top speed, mostly crawling) and find it's also quite suitable for occasional recreational MX on a

relatively tight corner / short straigthaway MX track, you just corner one gear higher than usual and get use 5th gear more.

 

13/49 puts you about equal to the stock 14/53

a smaller rear diameter sprocket allows for better ground clearance and chain guide positioning,

the advantage to the 14T front sprocket is it's easier on the chain due to a larger turning radius but

in return requires a huge rear sprocket to achieve common ratios.

Edited August 19, 2018 by mlatour

[savrvs]

Thanks for the tip off on PartsFish, Chuck. I can't believe I didn't think to just cross reference the oem part numbers - it's been a while since I've failed to have my tech questions answered by a simple old google/forum search. I wound up using Bikebandit, but what I found was that the oem center hub assembly [part# 42635-KRN-710] (including bearings, etc) is the same for my 2017 crf250x as the center hub assembly on a 2013 crf250r . The 6x19 fasteners and 6mm nuts that hold on the brake disc, and the 8x31 fasteners and 8mm nuts that hold on the sprocket are also the same across both bikes. However, both the sprocket and brake disc themselves were different part numbers. I know that the number of teeth on the sprockets are different so it makes sense that they wont be the same part number, but given the fact that the hub and mounting hardware share a honda part # across the two bikes leaves me with the takeaway that at worst I'd have to change the sprocket and brake disk in order to run the 2013 crf250r rear wheel on my 250x.

 

As far as gear ratios Mlatour, I hadn't considered running anything but the stock 250x ratio - so that's also a very good consideration. I do plan to just run the stock ratio for now, but given my skill level and how frequently (read infrequently) I would realistically make it out to the dedicated track, if I were to change the ratio it would probably be to lower it in order to help myself out on the bottom end. I also hadn't considered the sidewall profile of the tires on a 19" wheel, but I do know that the rear in question is a 2.15 and has a dual sport tire already mounted on it.

 

So anyways, I plan to head out tomorrow and get these wheels and tires picked up and will report back. Apparently the wheels are in excellent condition and the tires have plenty of tread and the rubber is still plyable - if they weren't an hour away and entombed in bubble wrap, I'd probably have just bought them and tested the fit afterwards hah.

Thank you both again for all the pointers!

Edited August 19, 2018 by savrvs