ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 03-30-2013, 10:44 PM   #1
Bluethumb OP
Gnarly Adventurer
 
Joined: Aug 2012
Location: Texas Hill Country
Oddometer: 125
Higher final drive for a G/S - ST Options?

What can I do to lower r.p.m.'s of a ST? At hiway speeds of 70 m.p.h., the engine is spinning about 1,000 more r.p.m.'s then my R100. I know of two ways to change the ratio of the final drive on a G/S - ST. One is with the higher 5th gear and the other is the optional final drive. The higher 5th gear is expensive from what I've read, the cost of the gear plus the time and expense of a rebuild. I thinK I've read it drops r.p.m.'s by 400-500. The optional final drive is NLA I believe, but if it is still available I'm guessing it's unbelievably expensive and I'm not sure how much it drops r.p.m.'s.

Is there another option? Is it possible to use a different FD and re-lace the rear hub to a ST rim?

Any other way to replace the final drive with another to drop engine speeds?
Bluethumb is offline   Reply With Quote
Old 03-30-2013, 11:43 PM   #2
R-dubb
Dubbious Adventurer
 
R-dubb's Avatar
 
Joined: Aug 2001
Location: San Francisco
Oddometer: 4,800
Quote:
Originally Posted by Bluethumb View Post
What can I do to lower r.p.m.'s of a ST? At hiway speeds of 70 m.p.h., the engine is spinning about 1,000 more r.p.m.'s then my R100. I know of two ways to change the ratio of the final drive on a G/S - ST. One is with the higher 5th gear and the other is the optional final drive. The higher 5th gear is expensive from what I've read, the cost of the gear plus the time and expense of a rebuild. I thinK I've read it drops r.p.m.'s by 400-500. The optional final drive is NLA I believe, but if it is still available I'm guessing it's unbelievably expensive and I'm not sure how much it drops r.p.m.'s.

Is there another option? Is it possible to use a different FD and re-lace the rear hub to a ST rim?

Any other way to replace the final drive with another to drop engine speeds?
The issue is the three bolt hub. I dont think there is a spoke hub that will fit a four bolt FD with a higher ratio. You can't just change out the crown gear either, cause that's where the bolts fit.

By far, the best option is to add the tall 5th to the tranny. It's actually a very easy job. As I remember, its the low 1st that is a bitch because it goes into the intermediate shaft which requires many tons of force to press.
R-dubb is offline   Reply With Quote
Old 03-30-2013, 11:46 PM   #3
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,410
...or the higher 32:10 ratio 3 lug mono final drive is still available new. They're basically non-existent on the used market.
__________________
R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
Airhead Wrangler is offline   Reply With Quote
Old 03-31-2013, 05:44 AM   #4
Beemerboff
Beastly Adventurer
 
Joined: May 2005
Oddometer: 2,291
Most of the hi 5 th gears are 5% higher - on a decent running motor you wouldnt know the difference unless someone told you.

Just fork out for a new 32/10 as AW says, and sell the three stud 37/11 - they are hard to find and sell for reasonable money.
__________________
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST
Beemerboff is offline   Reply With Quote
Old 03-31-2013, 07:44 AM   #5
Clay Spinner
Woodfire or Bust
 
Clay Spinner's Avatar
 
Joined: Nov 2008
Location: Nova Scotia
Oddometer: 585
I concur with airhead wrangler.... I've been trying to find a 32:10 bevel for two years now... Not even a sniff. I've just had a higher 5th installed but if you are planning for only road use, Richie Moore of morespeed does a +10. Check out his site and email him.

Clay Spinner screwed with this post 03-31-2013 at 02:45 PM
Clay Spinner is offline   Reply With Quote
Old 03-31-2013, 09:38 AM   #6
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,410
Quote:
Originally Posted by Beemerboff View Post
Most of the hi 5 th gears are 5% higher - on a decent running motor you wouldnt know the difference unless someone told you.

Just fork out for a new 32/10 as AW says, and sell the three stud 37/11 - they are hard to find and sell for reasonable money.
Actually, I think the 32:10 works out to be about a 5% difference. It's 3-4 mph higher at 5000rpm. 78mph instead of 75mph. If you add a 5% taller 5th on top of that you'll get a 5th gear that's nearly identical to a R100GS final drive ratio, but the rest of your gears would be a bit lower.
__________________
R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
Airhead Wrangler is offline   Reply With Quote
Old 03-31-2013, 04:58 PM   #7
Bluethumb OP
Gnarly Adventurer
 
Joined: Aug 2012
Location: Texas Hill Country
Oddometer: 125
How do I track down Richie Moore? And hat do you mean by + 10?
Bluethumb is offline   Reply With Quote
Old 03-31-2013, 06:19 PM   #8
Beemerboff
Beastly Adventurer
 
Joined: May 2005
Oddometer: 2,291
AW -you are right on at five+ percent - somehow I had it in my head that 37/11 was 3.56 , but I just booted the Cray and you are correct.

BT, there is some tricky engineering in these gears - remember you are only changing one of a pair, so a change in gearing can only be accommodated in the size and profile of the tooth.

This is normal gear cutting practice, of course, as the sum of the number of teeth in the pairs in a normal box is rarely the same for all pairs, but there is a limit to how far you can go with any given gear, and it seems that most folk are happiest at 5% difference from the stock OEM gear.
__________________
Adelaide Hills, Australia. 93 R100 GS, 77 R75/7 ,70 BSA B44VS, , 86 R80 G/S PD, 95 BMW Funduro F650 ST
Beemerboff is offline   Reply With Quote
Old 03-31-2013, 06:24 PM   #9
AntonLargiader
Beastly Adventurer
 
AntonLargiader's Avatar
 
Joined: Aug 2003
Location: Charlottesville, VA
Oddometer: 4,168
moorespeed.uk I think.

However, I would carefully consider your riding style before going to a drastically taller 5th gear. I personally like the "Four and a half speed" Airhead gearbox because it lets me downshift on the highway without changing the RPM all that much.

The ratio that I've seen that's higher than 5% involved all three helicals. I can get that gearset also, but I've only been asked for it one once.
__________________
Anton Largiader largiader.com BMWRA.org
AntonLargiader is offline   Reply With Quote
Old 04-01-2013, 12:38 AM   #10
Clay Spinner
Woodfire or Bust
 
Clay Spinner's Avatar
 
Joined: Nov 2008
Location: Nova Scotia
Oddometer: 585
Quote:
Originally Posted by AntonLargiader View Post
moorespeed.uk I think.
.

The ratio that I've seen that's higher than 5% involved all three helicals.
Correct anton... the +10 is a 3 cog jobbie and it alters the spread of the whole box. It is a specialist item and probably only really useful for someone who really needs it i.e. racing.
Clay Spinner is offline   Reply With Quote
Old 04-01-2013, 02:31 PM   #11
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,618
Looking at the forest and not the trees: Don't be tempted to gear your 800 like it is a 1000. If you want lower 1000cc rpms, get a 1000cc engine. 800's are geared for more rpm for a very good reason: Less power. The rpms compensate.
supershaft is offline   Reply With Quote
Old 04-01-2013, 03:07 PM   #12
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,410
Quote:
Originally Posted by supershaft View Post
Looking at the forest and not the trees: Don't be tempted to gear your 800 like it is a 1000. If you want lower 1000cc rpms, get a 1000cc engine. 800's are geared for more rpm for a very good reason: Less power. The rpms compensate.
They can go a LITTLE higher, but depending on the use, maybe shouldn't. Agreed, gearing it higher than a 32:10 is asking for a lifeless throttle in 5th. The decrease in revs probably wouldn't result in better gas mileage either as you'd need to have it wide open to push that taller gear.
__________________
R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
Airhead Wrangler is offline   Reply With Quote
Old 04-01-2013, 03:29 PM   #13
GapRunr
Gnarly Adventurer
 
GapRunr's Avatar
 
Joined: Oct 2005
Location: East TN / Smokies
Oddometer: 490
Taller 5th

I recently bought a taller 5th (5%) from Anton for my 81 R80 g/s and am happy with the results.

I just recently installed a tach so I have some numbers written down. Using a GPS for speed, the engine is turning at 4,000 rpm for 62 mph. Every 500 rpm's increase provides 8 mph. (4,500 is 70mph, 5,000 is 78mph, and at 6,000 rpm I was travelling.. no wait.. I would never break the speed limit so disregard that) .

It's enough of a difference that 5th now feels like an overdrive when loafing along the highway.
__________________
GapRunr
07 R1200GSA - 81 R80g/s - 88 Hawk GT - 06 TW200 SuperDuper Tenere
GapRunr is offline   Reply With Quote
Old 04-01-2013, 05:54 PM   #14
Rucksta
Chronic Noob
 
Rucksta's Avatar
 
Joined: Oct 2008
Location: Gold Coast
Oddometer: 2,631
Quote:
Originally Posted by GapRunr View Post
I recently bought a taller 5th (5%) from Anton for my 81 R80 g/s and am happy with the results.

I just recently installed a tach so I have some numbers written down. Using a GPS for speed, the engine is turning at 4,000 rpm for 62 mph. Every 500 rpm's increase provides 8 mph. (4,500 is 70mph, 5,000 is 78mph, and at 6,000 rpm I was travelling.. no wait.. I would never break the speed limit so disregard that) .

It's enough of a difference that 5th now feels like an overdrive when loafing along the highway.

100kph / 61.2 mph @4000 rpm is factory spec for an R80G/S with a 37/11 drive & 4:00 /18 tyre.
What rear tyre are you running?
Does the tacho need calibrating?
__________________
My bike is slow but the earth is patient.
Rucksta is offline   Reply With Quote
Old 04-01-2013, 06:48 PM   #15
GapRunr
Gnarly Adventurer
 
GapRunr's Avatar
 
Joined: Oct 2005
Location: East TN / Smokies
Oddometer: 490
Quote:
Originally Posted by Rucksta View Post
100kph / 61.2 mph @4000 rpm is factory spec for an R80G/S with a 37/11 drive & 4:00 /18 tyre.
What rear tyre are you running?
Does the tacho need calibrating?
Hmmm....

Perhaps the factory spec was for the OEM speedometer, which isn't accurate?

I'm running a Michelin Pilot Activ in a 4.00-18. If anything it looks big compared to the 4.00-18 Conti Go I had on there previously. As for the tach, it's a new digital tach designed for two cylinder dual fire ignitions. I would suspect it is pretty accurate. And I just checked to make sure and my g/s is a 37/11, so the previous owner hadn't changed it.
__________________
GapRunr
07 R1200GSA - 81 R80g/s - 88 Hawk GT - 06 TW200 SuperDuper Tenere
GapRunr is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 08:28 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014