Topic: Knee cuts & decreased tank capacity?

[grumpy]

For those w/ knee cuts in your tank...

How much less gas does the tank hold? 

I want to do cuts (using the BFH method) on my 750 but I'm a bit worried about the decreased tank capacity. I live far enough from work that I can make only 2 round trips per tank without tapping reserve...

[tortelvis]

Don't know but there was a famous incident at the Isle of Mann where there was suspicion of a rider with an oversize tank. As the scrutineers approached to check it the rider put a big dent in the tank with his fist. It passed inspection.

[Johnny5]

I have a 75 750 tank with knee dents and it didnt decrease volume all that much. Maybe 1/4 of a gallon.

[Toxic]

Now you have made me curious.

I have two tanks for my project, one with and one without dents.
The tanks are newly lined but have been sitting in the basement collecting dust.

Both need to be washed out so I will measure the volume differential.

More later.

[Geeto67]

it depends on a lot of factors - how deep the dents are, how big your tank is, etc. In decreasing your tank capacity you could lose up to 1/4 gallon banging it out which on a cb750 is about 10 miles range. If you are making your trips without getting into researve this may push you into reserve but I don't see it really being a problem of you running out of gas.

I don't recommend banging knee dents in a stock tank because some of the earlier tanks on the bottom are not fully welded and denting them can cause them to weep through the seams. If you have the tank lined I wouldn't worry about it but still.

Here is what I ask people when they start the knee dent conversation - Do you really need them? the original knee dents were because older brit bikes had rubber knee pads and over time the pads would get old and fall out and people just left them out.  On larger capacity racing tanks there was a need to clear the rider's legs while expanding capacity (by the 70s it took about 5 gallons to run the isle of man mountain course - most stock tanks were not that big). 

knee dents on an otherwise stock tank really don't do much in the way of function and really it only looks cool to the other cafe posuers, most of the race bike guys I know laugh at it because really why build a functional performance street motorcycle modeled after a race bike if you can;t ride it for very long.

There are plenty of tanks on the market, both specifically for the cb750 or off another bike, that would give you pronounced knee "dents" without compromising fuel capacity. I once saw a kz1300 tank modified to fit a cb750 - looked like a dunstall tank but held 7 gallons and had very pronounced knee indentations.

you could also do the old chopper trick of molding where you use bodyfiller to creaty body contors and lines. if doing this I would use a quality filler like marglass and not crappy bondo. A thin coat can go a long way to creating the illusion of knee dents. You could also use fiberglass and epoxy to change the shape of your tank.

there are lots of other options out there than the BFH.

[Johnny5]

I can say from experience that the roughly 1/2" on each side of the tank makes a nice difference in feel over the stock tank. Personal preference in style too.

[andy750]

knee dents on an otherwise stock tank really don't do much in the way of function and really it only looks cool to the other cafe posuers, most of the race bike guys I know laugh at it because really why build a functional performance street motorcycle modeled after a race bike if you can;t ride it for very long.

+1 

[climbingaz]

What is the "BFH method" you guys are talking about?

[d3buttz]

Big (add expletive that starts with F and ends with -ing) Hammer.

[Laminar]

you could also do the old chopper trick of molding where you use bodyfiller to creaty body contors and lines. if doing this I would use a quality filler like marglass and not crappy bondo. A thin coat can go a long way to creating the illusion of knee dents. You could also use fiberglass and epoxy to change the shape of your tank.

It's a work in progress.

[mlinder]

With dents that average 10inches long by 5 tall by 1 deep, you would lose .44 gallons.

[climbingaz]

Big (add expletive that starts with F and ends with -ing) Hammer.

    Thanks!

[Slayer]

knee dents on an otherwise stock tank really don't do much in the way of function and really it only looks cool to the other cafe posuers, most of the race bike guys I know laugh at it because really why build a functional performance street motorcycle modeled after a race bike if you can;t ride it for very long.

I am still pretty new but I plan on trying out the knee dents. I like the look. Curves look good to me. I can see why a purist would not approve but if it is your tank and it falls in line with what you want it to look like, and you gain experience and knowledge along the way then why not? Why would a cafe racer not be able to ride for very long? What is a "cafe posuer"? For that matter what is a true cafe racer? Is this some elitist thing? I am not trying to rock the boat here I am just trying to understand your point of view.

[Laminar]

Based on my understanding:

Why would a cafe racer not be able to ride for very long?

The low handlebars typical of Cafés make riding for an extended period of time uncomfortable.

What is a "cafe posuer"? For that matter what is a true cafe racer? Is this some elitist thing?

Probably. To be a true Café racer you had to have grown up in the '70s in England. Anyone that puts Clubmans, rearsets, and a single seat on their vintage bike is a "posuer."

[Slayer]

So the "true racers" don't tour on their racing bikes? Weird... Well I guess I would be uncomfortable with low bars if I was fifty years old too. I am going to enjoy riding as much as I can with what I like while I still can. 

[mlinder]

Geeto can be pretty opinionated, but most of his opinions are at least rooted in factual concerns or scientific reality.

I like tanks with the knee indents. Average indents will net you about 18 miles reduced traveling distance between fill ups.
I'm also building a race bike. I only have to go about 22 miles in the race, so it makes no difference one way or the other.

That being said, none of my tanks have indents that weren't stock (350f tank, for example, has stock indents, sorta.).
Not because I wanted bette rmileage, but jsut because I didn't care enough to actually go through with doing it. I may do it on the GS550, though, but they wont be pounded in, they'll e cut out, along with some of the pan.

[grumpy]

No apologies.
I like how they look & it's my bike.


but I'm w/ mlinder... I may never get off my lazy arse & actually do it. 

[Slayer]

I did not think I would ever try it until I realized I had to clean, reseal, and repaint the tank. Might as well go for it right?

[BobbyR]

I did not think I would ever try it until I realized I had to clean, reseal, and repaint the tank. Might as well go for it right?

If that is what you like and willing to do the work and have a solid belief you will be able to pull it off then go for it. If I had a good tank I would store it and dent one I picked up somewhere. This way you have a fall back in case it does not work out well or you change your mind.

[bucky katt]

the cx500 d (deluxe) has a rectangular looking tank with small "knee dents" in it the xs850g does as well.

http://cgi.ebay.com/ebaymotors/1977-81-Yamaha-XS750-XS850-Fuel-Gas-Tank-NOS-OEM-NEW_W0QQcmdZViewItemQQ_trksidZp3286Q2em20Q2el1116QQhashZitem413e500403QQitemZ280218305539QQptZMotorcyclesQ5fPartsQ5fAccessories

http://cgi.ebay.com/ebaymotors/Honda-CX-500-D-Gas-Tank-1979-Used-2128_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem4399b10026QQitemZ290341322790QQptZMotorcyclesQ5fPartsQ5fAccessories

[Geeto67]

the "cafe racer" name evolved to represent performance oriented vintage bikes (When I was growing up they were just used crappy bikes from the 60's and 70's that we wanted to go faster to try and keep up with the modern sportbikes).  Eventually cafe racer's evolved into the modern race replicas that the mfgs make today. Lately the genre has been backsliding into bikes that look the part but can't actually back it up, and that is kind of sad. The core ethos of a cafe racer is that the mods you do should improve your bike in the performance and handling department first and foremost.

If any of you are into hot rods a similar thing happened with prewar hot rods or the pro street movement - for a while functional built 32 fords gave way to easter egg colored show ground crusing things that were all sizzle and no steak. The same with pro street cars - street machines started showing up with real drag race parts until all you had was blown hemi's, gumball slicks, and smoothed firewalls on tubbed stock framed cars that spent most of their life at 5mph at a good guys meet. Well I would hate to see a genre of bike that I grew up with de-volve into that - a bunch of style monsters that can't get out of their own way.

There are certain parts and mods which I think do this: clubman bars on a stock seat and pegs, 16" rear rims, and knee dents - they don't add to the overall improvement of the bike and in some cases decrease performance. yet you will see people with these bikes claiming they are cafe racers cause they want to belong to the new hip bike trend now that choppers are fizzling out.

I am not anti-knee dent, actually I am working on a fiberglass version of the stock 69-76K K tank that has them added (should be available by christmas) but I think if you are going to do it you should try to increase the capacity of the tank.

As far as touring cafe bikes, I rode my dunstall 78 750 to mid ohio last year, and I think Andy 750 has ridden his to mid-ohio as well. That is pretty much an all day in the saddle ride. I used my dunstall 750 to ride everyday to work last year also, parking it on the street. What's the point in owning a bike if you don't use it. Do I park it in front of Bar Matchless or Starbucks every now and again to be admired ? sure. Is that it's only function in life? not in the slightest. I rode my modern cafe bike (Ducati sport 1000) to work today in the pouring rain - I would have taken the 750 but the dunstall tank is delaminating and needs to be redone (damn modern fuels).

[Johnny5]

I guess a nerve has been struck here...

I ride my "cafe racer" bike everyday the sunshine is out. I would ride it all day long if I could, which sometimes I do...but I have kids and wife that works nights. Makes it tough...


So to the hard core cafe guys, these things make me a poser:

1. I have drag bars on mine. So my bike is not a cafe racing bike.

2. I have crappy 30 year old shocks that suck on my bike, because well, I cant afford to get new shocks.

3. I have knee dents and probably lost 1/4 of a gallon. I can still go almost 200 miles before having to fill up again.

4. I love taking my bike to meets (if I ever get the chance too) and hang out with others that love riding and bikes.

5. Have pods installed and tuned, which by all the feedback on here, should diminish performance, thus another artifact of poserness.


Geesh, we have bikes to have fun with. Some have them to simply mod out and look cool. Well, good for them if that's their thing. I've never been a fan of cliques and I dont care what you ride. Let's just have fun with the time we have here on Earth.


Johnny5 (the ultimate poser) over and out

[BobbyR]

Nice article on the Cafe and the TON:

http://www.cycleworld.com/article.asp?section_id=3&article_id=94

[Brantley]

3. I have knee dents and probably lost 1/4 of a gallon. I can still go almost 200 miles before having to fill up again.

A shop owner/ greybeard buddy of mine said to me a few days ago "sometimes a small tank can be a blessing" after telling him I never even hit reserve on my last 700 mile round trip, cause I stopped a lot for gas, a smoke, some water, a leg stretch, and a look at a map while taking nothing but U.S. highways and state roads. Think real world: even if you average 70 mph, do you want to sit in the saddle for almost three hours at a time?

[Geeto67]

I guess a nerve has been struck here...

I ride my "cafe racer" bike everyday the sunshine is out. I would ride it all day long if I could, which sometimes I do...but I have kids and wife that works nights. Makes it tough...

.

You ride it as often as you can. It's the best you can do. No big deal. There are guys (here in NY and I am sure all over the country) who literally build or buy (mostly buy) "cafe bikes" and ride them as far as their nearest sunday morning bike/car gathering and that is all the use it gets. their bikes can get more use but honestly I am pretty sure once the parked coolness factor is used up the bike is useless to them.

So to the hard core cafe guys, these things make me a poser:

1. I have drag bars on mine. So my bike is not a cafe racing bike.

So do I, I like drag bars a lot. There is no one singular part that makes a bike a "cafe racer". The emphasis is on riding position, just throwing a pair of clubmans or clipons at a bike and calling it a cafe racer is pretty lame. The secret to a good bike is to have a well thought out riding poition, but all too many people just throw a set of clubamans at a stock bike and say that is it, I built a cafe racer, and then spend the rest of their time doing damage to their spines because the low bars and stock pegs combo can lead to interesting back curvature.

2. I have crappy 30 year old shocks that suck on my bike, because well, I cant afford to get new shocks.

 

eh. I am sure you can replace them when you can.

3. I have knee dents and probably lost 1/4 of a gallon. I can still go almost 200 miles before having to fill up again.

I am going to call bull#$%* on this because I have yet to see a SOHC 4 get even close to 200 miles on a tank, most are lucky if they cross 150 stock. It is you bike you can ruin it however way you want, but really do you care what others really think of your bike anyway. You know part of the thing that creates cafe poseur bikes is people caring about how others will perceive their bike in the first place - they just want it to look really cool. Ask yourself, if nobody ever saw this bike would I have still done the mod?  

4. I love taking my bike to meets (if I ever get the chance too) and hang out with others that love riding and bikes.

Who doesn't . Is it the ONLY use your bike gets? probably not.

5. Have pods installed and tuned, which by all the feedback on here, should diminish performance, thus another artifact of poserness.

well again, do you really care? personally I would care if my bike was loosing performance, but to some people that is not as big an issue as how cool they look.

Geesh, we have bikes to have fun with. Some have them to simply mod out and look cool. Well, good for them if that's their thing. I've never been a fan of cliques and I dont care what you ride. Let's just have fun with the time we have here on Earth.


Johnny5 (the ultimate poser) over and out

for someone who doesn't care about cliques you wrote a fair amount in defense of how you belong . Some of it makes sense, others, eh, not so much.