Taller gearing option for your bike

roger albert · 01-31-2007, 08:36 PM

OK, I know some of you who are much more into top-speed than me have played around to gear your bikes a bit taller.

Another option I've played around a bit with on older bikes is with tire aspect ratio.

Not been many options for rear bike sport rubber up until now. (and of course, the beemers are not easy to tweak gearing on)

Anyway, I noticed something that might be useful to you guys running rims >5.5" Pirelli now offers a 190/55 (normally, 190s are /50) If you really want to run a little faster, if not quicker, then this is one option to try.

Yes, your speedo will be off, but your odo too, and in a favorable direction

I bet we see more of these. MotoGP has already brought taller sections back (16.5 rims) over the last couple years, and are doing some tests with 16.0s this year.

Yup, the pendulum has swung, and thicker sidewalls are in again.

RoLoo · RoLoo's Garage

...well I have a 190/55, but I will switch back to a 190/50...
...don't like it at all, such a higher tire ; it's the handling thats different...

roger albert · 02-01-2007, 01:36 AM

Good point. I almost always like extra rideheight at the rear, and so didn't even think to mention that aspect. Worth keeping in mind.

And on tires, anyone layed hands on a set of BT-21s yet?

Fenring · 03:50 AM

This must be a gazillionth time that I read about speed gain with higher gearing and/or bigger wheels.

Any max speed gain will be only marginal and insignificant, unless the vehicle producer has somehow completely miscalculated the optimal gearing for top speed.

As I understand it, maximum speed is achieved when the energy output of the vehicle (at top speed) equals the energy waste that friction produces. You would expect therefore that a manufacturer of the vehicle would set the gearing so that the rpm of the engine is such that it produces max power when you are nearing the top speed (in top gear). When you set the gearing like that, there is no higher gearing or bigger wheels that will push you to a higher speed, simply because it would require the engine to produce even more power... but it can't... unless you turn on the nitro or something

[edit]
And when you do put a higher gearing, the maximum speed gain would be very small or none at all, but it would take the bike more time to get there, which is another negative aspect.

roger albert · 02-01-2007, 06:03 AM

This must be about the gazillionth post where someone who hasn't done something holds forth on the topic nonetheless.

Hmmm, you must not have done this on too terribly many bikes.
Bikes come in all flavors. I've seen bikes go both slower and faster with changes in gearing, as have most experienced builders. To think they all come optimally geared out of the crate is very naive in general (and not just about motorcycles, but about the various tradeoffs that are made in the manufacture and design of _anything_) and additionally neglects that many folks make mods that would throw that balance out the window even if it were true.

A few folks here have changed gearing with positive results.
For that matter, the first factory run (pre boxer cup) at Daytona did so too. Think they were making it up?

And what of the two options for gearing on the R12S (though I dont' know anyone that has actually seen both)? There are no motor changes, and yet the factory offers both. Why would that be?

Of course the bike would take more time to accelerate with taller gearing. I think most 4th graders who've played with a bicycle understand the effects of gearing. I doubt anyone would claim differently. I was merely pointing out that tinkerers have another option when tinkering now.

It can also help iron out a shift-point at a track, where being able to carry a gear longer, or pull another one sooner can make a big difference, even when the gearing difference itself is very small.

But one point you make is valid; the change is generally pretty small on an unmodified motor.

Personally, I dont' care as much for top speed in most situation (mini racing being an exception) and I tend to gear down, if anything, but there are guys (Dr Curve, any Daytona racer, any mileage-meister etc etc) that care about top-end or tall gearing.

Good to have options if you're actually building/modding something for some purpose

Deans BMW · 02-01-2007, 06:10 AM

Fenring, what you wrote is true with the exception on the current crop on BMW's like the K1200S, R1200S, and R1200ST, to name a few. The rev limiter is hit in top gear and then becomes the top speed limiting factor. My R1200ST ran 144 at Bonneville with a worn rear tire, at the revlimiter before the first mile marker, the K1200S that set a class record added a 5 or 6 MPH to its top speed at Bonneville after they found a taller tire in Salt Lake City. My ST runs 147-148 with a new stock sized tire, still at the rev limiter. We think it might hit 150-151 with a taller tire yet.

Fenring · 02-01-2007, 06:24 AM

Quote:

Originally posted by roger albert
This must be about the gazillionth post where someone who hasn't done something holds forth on the topic nonetheless.

Hmmm, you must not have done this on too terribly many bikes.

That is correct. I have never done this and probably never will. I know nothing of modding bikes, etc. I just know basic physics.

Why any manufacturer would leave a rev limiter a limiting factor of the top speed is beyond me. It would make more sense to me just to make last gear longer. That way the acceleration wouldn't be compromised (much) and you'd have your top speed where friction becomes ultimate limit.

Although I allow for existence of a good explanation for this situation.

Steve Carlton · 02-01-2007, 06:30 AM

Quote:

Originally posted by roger albert
And what of the two options for gearing on the R12S (though I dont' know anyone that has actually seen both)? There are no motor changes, and yet the factory offers both. Why would that be?

I heard there was a bulletin sent to the dealers saying there is actually only one ratio for the R1200S and won't be another. This may only apply to the US models.

Jc Slaton · 02-01-2007, 07:16 AM

Quote:

Originally posted by roger albert
This must be about the gazillionth post where someone who hasn't done something holds forth on the topic nonetheless.

Hmmm, you must not have done this on too terribly many bikes.
Bikes come in all flavors. I've seen bikes go both slower and faster with changes in gearing, as have most experienced builders. To think they all come optimally geared out of the crate is very naive in general (and not just about motorcycles, but about the various tradeoffs that are made in the manufacture and design of _anything_) and additionally neglects that many folks make mods that would throw that balance out the window even if it were true.

A few folks here have changed gearing with positive results.
For that matter, the first factory run (pre boxer cup) at Daytona did so too. Think they were making it up?

And what of the two options for gearing on the R12S (though I dont' know anyone that has actually seen both)? There are no motor changes, and yet the factory offers both. Why would that be?

Of course the bike would take more time to accelerate with taller gearing. I think most 4th graders who've played with a bicycle understand the effects of gearing. I doubt anyone would claim differently. I was merely pointing out that tinkerers have another option when tinkering now.

It can also help iron out a shift-point at a track, where being able to carry a gear longer, or pull another one sooner can make a big difference, even when the gearing difference itself is very small.

But one point you make is valid; the change is generally pretty small on an unmodified motor.

Personally, I dont' care as much for top speed in most situation (mini racing being an exception) and I tend to gear down, if anything, but there are guys (Dr Curve, any Daytona racer, any mileage-meister etc etc) that care about top-end or tall gearing.

Good to have options if you're actually building/modding something for some purpose

Roger

Two things! You are correct on both accounts, the R12S does have different gearing options. The other options is basicaly changing the final drive of it to the one of the R1200RT!! Taller gearing making it run faster top end and less off the bottom!! Now beaing an owner of one, this thing winds up fast in first and you find yourself dancing on the shift lever trying to get it into second because you bumped the rev limiter!!! But after spending time on it I find it like driving a diesel truck!!! You never use first gear unless you are starting or stopping!! The bike pulls hard in second and really no need to find first gear even on the slowest of corners!! Stick it in second and watch it climb the ladder as it rockets to the redline!! So bottom line is if you are looking for speed yes changing the FINAL drive is a simple way to squeeze some extra juice out of the bike!!!

Tires......well Roger I know you and I know the effects of different aspect ratio of tires and what they do to the performance of a motorcycle!! Simple fact I always liked to remeber!! If you are on a short tight tecnical track whereyou want the bike to change directions faster and steer quicker I would always run a narrower width tire and a taller ratio for example if your bike normally runs a 190/50 17 run a 180/55 17!! Two things are acomplished when you do that, like Roger said ride hieght is increased and less rolling mass!! Now say you are on a track that is very flowing and lots of long fast sweepers!!! I would be more inclined to run the 190/50 17 and if you can get away with it 190/55 17!!

Now everyday street use just keep your tires inflated to the correct pressure and don't go straying away from what the manafacture says the correct tire size is!!!

JC

roger albert · 02-01-2007, 07:26 AM

I suspect that is actually the case too Steve, which is why I put that caveat in.

> Why any manufacturer would leave a rev limiter a limiting factor of the top speed is beyond me.

It may well be beyond you, yet vevertheless, it is VERY common practice. It's not a coincident of convergent combustion chamber design that leads so many vehicles to be limited to 155mph (250kph). Can you pick up a car rag w/o finding at least one reference to the speed being goverend?

What we moron engineers learn, is that in the real world, there are all sorts of technical tradeoffs, and business/marketing/regulatory/convenience and public-policy issues which factor into a vehicle's (or chip or toaster or personal 'massager'-product's) design, specification, and manufacture. The purely theoretical (even when true) is best left to physicists. Darn, and people call _me_ a bookawitz.

> It would make more sense to me just to make last gear longer way the acceleration wouldn't be compromised (much) and you'd have your top speed where friction becomes ultimate limit.

In some cases, you are right, but that's not always optimal either. If you're _really_ gearing for top end, and a fairly high speed (where aero drag is a big factor) then you often can't afford to have the bigger gap between top and the gear below it It just won't pull it. In fact, if you look at _any_ transmission, you'll see the gap narrows between each subsequently higher gear-pair. Besides my own formal training in physics and engineering, in general, and as pertains to motorcycles in particular, it's something I've observed on the track as both a tuner and a rider repeatedly.

There are cases where what you call for is implemented, but normally for reasons of economy, rather than top speed. A great example is when the oilhead GS went from an 1100 to the 1150. They added 6th gear that year. Overall gearing for the bottom 5 gears were a tiny bit closer together and lower than previously, but 6th was a pretty big jump up from 5th. This makes perfect sense for the way GSs are often used (dirt roads etc, but often with long stretches of highway in between where a really tall top gear makes the low final ratio tolerable at triple digit highway speeds. Previous GSs were really spinning in that utilization.

OK, I'm done geeking out for a bit. Suffice to say that there are a ton of reasons for an involved owner to want to have more gearing options.
I know you're new to the board, but if you search before pulling the trigger (here or on any other forum) you'll find gearing can be a big topic and of real benefit. (though due to the cost and complexity of the change on belt and shaft drive bikes such as beemers, it's less a topic here than elsewhere.

hope that in someway adds a bit of clarity to a difficult topic
(I'll allow as how my writing can sometimes have the opposite effect)

roger albert · 02-01-2007, 07:33 AM

Hey Jc, have you actually seen different ratios.
There's been a lot of talk of it here in the past (before you joined???) but I don't know anyone that has physically seen both ratios (as opposed to their being 'on the system') I'm curious.
Some of the early adopters may be more up on this than me, but I have't seen it yet.

Dean makes a good point in recalling that BMW has been pretty fastidious, in the past, of choosing the top gearing for top speed. Far more so than most other manufacturers. But even then, by definition, as soon as you change _anything_ in the equation (shorter screen or smaller rider included, much less engine mods) then you're immediately rev limited, and a taller tire or a tooth less on the rear can bring up top end.

Jc Slaton · 02-01-2007, 08:07 AM

Well I have some insight on this but just ask Nate K. !!! They are using the final drive off of the R1200RT on there Race bike for more top end!!! Now BMW doesn't say its off of a R12RT but gear Ratio's are the same!!!

I would definatley like to hear what Nate has to say about it as he is the one who has actually ridden it for the purpose that it is suppose to be used for!!!

Deans BMW · 02-01-2007, 08:25 AM

JC, not to disparage N8, but your question would be better directed to Chris Hodgson, owner of San Jose BMW, clearly the worlds recognized preminent builder and feelder of racing and record setting BMW motorcycles from road racing, Bonneville record setting and other endovers. They are using F/D units from the R1200GS for tracks like Infineon to the R1200RT F/D units at Daytona. They are currently looking to (find) a taller unit yet.

Jc Slaton · 02-01-2007, 08:34 AM

I understand where you are coming from dean but.......that stuff generally is not available to the public for street use where the final drive we are talking about is!!! SJ BMW has always and will always build Bad A** stuff and I definitely agree with you on there R&D but N8 currently uses the gearing on weekly basis for just an extra jolt of top end!!!

Until we can actually start changing the final drive ratios, or the internal gearing in the actual transmission we are limited on what we can do!!! So we use whats available!!! Me I am staying with the stock gearing!!! I love it when the bike rips the front wheel of the ground in first because its pulling that hard!!! Second gear is great simply put.......just ride the grunt wave!!!!!!

Dr. Curve · 02-01-2007, 09:08 AM

R1200S............2.75 standard, 2.62 optional. R1100S 2.75 stock........2.53 can be built up and used. R100S 2.91 standard, 2.75 and 2.62 can be built up.

Chris is facing a problem we have all looked at........for now at least......2.62 is the tallest ratio we have for the new rear end like the hex heads all have..........perhaps BMW will help us soon as many of us know that a R1200S will run 170 plus..........if we just had the gearing.

Deans BMW · 02-01-2007, 09:10 AM

JC, I agree, N8 is using the same F/D selections on his bike. That is the only thing that can be done at present.

Sure do miss the Texas hill country, bought my first Beemer in early '72 from a dealer named William Walter in San Antonio, no longer there. I remember at the time that there was a a BMW/Moto Guzzi/Munch Mamoth dealer in Austin. I was living in Kerrville at the time.

JonyRR · 02-01-2007, 09:15 AM

It's a well-known tuner's trick to vary tire diameter to gear higher or lower.
it's surprisingly effective, witness 5-6 MPH on a K12S when sidewall height is changed. 5MPH is a LOT.
There's physics THEORY and there's emperical fact; there are times the theory runs right into the brick wall of objective reality..like helicopters:
'helicopters don't fly, they beat the air into submission'...regardless, they're in the sky.

So, a /55 tire instead of a /50 aspect ratio tire I would expect to get 2-3 MPH more out of, IF there's the power to push it.
BTW+3 MPH in a 2000 metre straight is a substantial lead going into the turn at the end of the straight.

Dr. Curve · 02-01-2007, 09:17 AM

At that time Dean, we used San Saba as a hill country base to depart from and ran wide open everywhere we went. R75/5s with low bars, 2.62 gearing if we could find it, simple wedge plex fairing that was barely 14'' wide and 12 inches high. All over the area, and especially in the Kerrville area, we had fun. Fast sweepers, some flat outs and endless ups and downs, ins and outs. I was living in the Oak Cliff section of Dallas at the time, and although I had got a 63 R69S in 1970.........the 1970 R75/5 I got in 1971 changed me forever. Great years. Fast years.

Steve Carlton · 02-01-2007, 09:26 AM

Quote:

Originally posted by Dr. Curve
R1200S............2.75 standard, 2.62 optional. R1100S 2.75 stock........2.53 can be built up and used. R100S 2.91 standard, 2.75 and 2.62 can be built up.

Chris is facing a problem we have all looked at........for now at least......2.62 is the tallest ratio we have for the new rear end like the hex heads all have..........perhaps BMW will help us soon as many of us know that a R1200S will run 170 plus..........if we just had the gearing.

2.75 is the "Alternative Rear Axle," which means you could consider the 2.62 "standard." As Roger said, I don't think anyone in the US has seen a bike with the 2.62 gearset, although I thought I might have seen you claim to have it. A dealer has told me he received a confidential sales bulletin that says all the bikes have the 2.75 and there never was a 2.62. Ask your dealer...

Fenring · 02-01-2007, 09:29 AM

Quote:

Originally posted by roger albert
It may well be beyond you, yet vevertheless, it is VERY common practice. It's not a coincident of convergent combustion chamber design that leads so many vehicles to be limited to 155mph (250kph). Can you pick up a car rag w/o finding at least one reference to the speed being goverend?

I have no idea what you just said, except that many vehicles are limited to 250kph, which is a common practice for german manufacturers of cars that can actually go faster than that, so they have, usually electronically, limited top speed. I just never thought that anyone in his right mind would do that to a bike.

So R12S with taller gearing can be quicker than stock, but given it's max output power and bad aerodynamics, how much faster can it really go?

BTW, whatever I wrote that made you call yourself a moron, I'm sorry, don't take it personal. It's just my inferiority complex that makes me bark at people when they can't see me.