I installed RP 85w140 in my tranny in mid-'07 hopefully to quieten the clattering tranny that plaged these bikes before IDS came on the scene. It did help with the clattering and reduced shift clunking. I ran it through last winter and changed it two weeks ago, this time going to RP 75w90, thinking the reduced drag might increase gas mileage, which it didn't. The clunking increased, so I will be going back to the heavier oil soon.

I didn't know they made a 75w140, but if so that might be the better alternative for colder weather. I rarely ride when air temps are less than about 45°, and even that is iffy. In LA we ride year-round.

Edit: I just checked their site and they make six different gear oils, including 75w140 and 85w140.

Don't let the brand zealots sway you. Your question was whether or not the heavy fluid would cause problems in winter and you predictably got a barrage of "my oil is better than yours" replies. Unfortunately, this is typical of any oil thread, since for some reason oil is a product that has been elevated to religious status in this society.

Any high-quality synthetic oil (RP, M1, Redline, Amsoil, etc.), whether engine or gear oil, will give excellent service. Nobody can point to any objective data that shows one superior to another in all applications and scenarios, so IMO you should select based on price and availability. This is what you're doing and it isn't wrong. For most this will be M1, which is an excellent product that is available everywhere at excellent prices. I use RP because of long-term experience, its history in racing venues, and the fact that I get it from a distributor at dealer cost, who delivers it to my door. I do not proselytize and will never claim it is better than another product, even if I think it is--as I have no data to support such a claim. I ran RP in the engine and tranny of my '96 RK for 106k miles and the bike never had the heads removed, nor did I have tranny problems. Static compression and oil consumption remained unchanged in that time period, and it is still running today at >120k. Will [insert your favorite brand] cause the bike to last longer? Maybe, but who can say? Who can show objective data to support any such claim? No, the Amsoil White Paper isn't proof of anything, so please don't go there.

I would not hesitate to use any of these products in my tranny, although some are scarce locally. This brand-centric braggadocio ranges from "I use Acme Heavy-duty" to "If you don't use Acme Heavy-duty your bike will die within one year." When reading oil threads, skip over the brand-loyalty drivel and check out those who simply answer your question. Just my 2¢.

I use synthetic 75w140 made by Mopar (Dodge). I get it for free at work! Can you say "fringe benefits"? Seems great to me! I rode with it last winter, no problem here in my So. Cal 50 degree winter! Don't think brand is very important, but 75w140 is perfect. Ride on!!!

iclick makes a very good point. I would venture to say almost all the synthetics on the market today will work just fine in everyone's bike. I doubt many of us have had an engine failure due to the brand of oil that we put in our bikes. Some don't even keep their bikes long enough to wear out a set of tires much less have any engine problems due to using one oil over another ( I fall into this class... I like to change bikes, what can I say). Find yourself a readily available synthetic oil and use it and you will be fine !!

Don't listen to these guys, they're all full of malarkey, take it from me; I use Acme Heavy-duty, and if you don't use Acme Heavy-duty your bike will die within one year.

Cycle Gear now has Redline V-Twin Tranny Fluid (with Shockproof) in stock. $12.95. rated equivalent to 75W250 with the friction equivalent of 75W90. Awesome stuff.
Luckily there is a Cycle Gear shop here in Huntsville, AL. But they are online as are other sellers.

Heck, I'm using Mobil 1 V Twin in all 3 holes! And see no reason to use anything else!

just my 2c..... quality oils are very important, but CHANGING your oil regularly is the real key,

and ACME is the best:D

1st 1k service on my 09...
 

I have used Amsoil in all three holes but I am trying Red Line Heavy Duty on this bike for the transmission... I've never heard anything but good stuff about it and time will tell.

Tim

I'm running 75X90 Royal Purple now, works just fine, may change to Red Line next time.
As most have stated..regular maintenance is the key....change often, use what floats your boat.