AELmx

thanks for the replies

I bought the apidura Frame Pack Hydration Bladder (3L) to carry enough water.

Tycho Brahe 

Best of luck. I would not do the ride in August due to heat and because of the summer visitors to Big Bear. Otherwise, it is a nice ride. The rumble strips at the start are annoying, but disappear eventually.

diphthong

weekdays (mon-thurs). start at dawn from yucaipa or mentone. you wanna be over onyx summit by 11am. it is (iirc) the longest climb in socal at 33+ miles. stretch from angeles oaks to jenks lake is the sketchiest part. rock your blinkers and ride as fast as possible through this stretch. recommend checking the caltrans hwy website/phone number to verify road closures/construction before going. there have been more than a few times that roads got closed due to resurfacing/construction in the area (such as the 330) and the resulting, detoured traffic made riding very less than desirable. range got absolutely hammered with rain/snow this year so caltrans likely active along your potential route at some point.

AELmx

Hello guys

I did the ride to big bear last week, starting in Murrieta (Clinton Keith street).

Some notes:
Leon Rd (part was not fully paved, around 2.6km but seems will be paved soon)
Domenigoni Pkwy (from this point had shoulder and traffic was OK)

I started at 5am, weather was nice at that time and arrived to Yucaipa at 8:30am.
38 was fine too but it was closed around 10 miles after Angelus Oaks due to road washed out. Hopefully this will be fixed soon.

I had to go back and try by 330, which as mentioned here traffic is heavy and no shoulder. Not recommended to use it, and also at 2pm it was too hot, and no place to have a rest.
I was able to make it to Running Springs at 7pm and stayed night there. I did not used the option to go back on my bike, even as a descent is risky for me, I did not wanted to take the risk.

diphthong

ballsy. the 330, as you now know, is not the recommended climb into the range. any road but that one. there are a few turnouts which help a little. descend it if you must.
helluva run up to the 38. don't really like to start that far away from that main climb given the heat/traffic. many don't feel comfy taking the 18 (either direction) into the range or the 38. personally think the 138 is the best, low-traffic way in/up but has the steepest pitches for approx a mile. the 138 to the 173 is the back door, extra-credit way in. just have plenty of water, gearing and tires at least a '28 width. kudos.

all that said, still think climbing the 18 and heading sw from lucerne valley up to baldwin lake then onto big bear lake, cruising the north shore, then climbing out of big bear lake area, dropping past arrowbear and running springs, going past santa's village and the various turnoffs to the right to lake arrowhead/lake gregory and descending down into san berdoo is the best mountain stretch of road biking in socal. will require a non-holiday weekday, car shuttle, an overnite or cat 1/pro legs. can divert and head west into lake arrowhead/lake gregory and (mostly) descend the 138 to silverwood lake and cajon pass area with the scenery still being top-notch.

as mentioned in the socal forum before, the san berdoos have pretty good road cycling. many have only experienced with a big, organized ride. hit the area on a weekday in april or september and you just might be surprised. challenging for sure unless you're just flatty cruising around big bear lake. even that is worthy. north shore is super-chill.