Topic: Dry weights for cb750 based road racers

[gschuld]

I've got pretty strong legs.  I can average 20mph for 40 mile loops on my ...umm, other road bike.

George

[scottly]

Hi there,

I weighted my bike just yesterday, 180 kg in full working condition (oil + fuel). I'm aiming to remove at least another 10 kg during the winter... let's see...

An LiFe battery of the "equivalent" capacity will weigh 1/3 of the lead-acid battery you are now using.

[scottly]

Don't overlook steel parts hidden from view; I replaced the steel hose barb with an aluminum version on the first diet, as well as the very heavy crimped fitting with a hose clamp. The hose itself was lighter than the stock hose with the braided covering.
The crimped sleeves weigh 29 grams each (there are 4), while the hose clamps only weigh 6.5 grams each. The steel hose barbs weigh about 35 grams each (there are 2), while the aluminum replacements are about 12 grams each.
The stock speedo drive, not counting the drive plate and cover plate is 204 grams; a plain aluminum spacer would be about 20 grams. The two stock rear wheel spacers total 287 grams on a K7 wheel; aluminum replacements would be 1/3 or less.

[slikwilli420]

Ok I'm reviving this one to get the juices flowing for me and anyone else interested in shedding pounds.

I weighed my race bike today using a digital bathroom scale that calibrates each time it turns on. The gas tank was off so I weighed separately adding the weight of 4 gallons of gas meaning wet weight for the bike ready to ride. I am at 393lb as of today. I was expecting a heavier bike considering things looks the heavy rear drum brake and stock gas tank.

In thinking about the next iteration,I know the rear wheel is ripe for improvement as is the steel gas tank. The stock air box will have to stay for now or at least until I can get an anti pod kit going.

Getting more intense,I will be trimming the cases of the engine I am building to get rid of the starter box and will cut the crank snout for the charging system. I already have a cut down kickstart shaft to help a bit more. Thinking about high grade aluminium engine hanger bolts as well.

Any other ideas, no matter how wild?

[Captain]

 Titanium........and lots of hard work got this down to 170 KG wet  (374 lb)

 Brent

[calj737]

Any other ideas, no matter how wild?

CroMo frame. That'll shave some serious weight.

[scottly]

Getting more intense,I will be trimming the cases of the engine I am building to get rid of the starter box

Not much weight savings in trimming the starter box, but you can shave 1/2 pound off the stock cam-cover, not counting the tach drive. Of course, there is a bit of welding required.
 

[PeWe]

Weight of the rider is one thing to adjust, right?  My bike has now 1005cc and I get flashbacks of how the bike felt with first RC 836 kit and more then 30kg slimmer rider (closer to 35kg), most of the weight over the seat.

Note! I'm not a racer guy, could not resist to comment the weight

[livefast_dieold]

Ok I'm reviving this one to get the juices flowing for me and anyone else interested in shedding pounds.

I weighed my race bike today using a digital bathroom scale that calibrates each time it turns on. The gas tank was off so I weighed separately adding the weight of 4 gallons of gas meaning wet weight for the bike ready to ride. I am at 393lb as of today. I was expecting a heavier bike considering things looks the heavy rear drum brake and stock gas tank.

In thinking about the next iteration,I know the rear wheel is ripe for improvement as is the steel gas tank. The stock air box will have to stay for now or at least until I can get an anti pod kit going.

Getting more intense,I will be trimming the cases of the engine I am building to get rid of the starter box and will cut the crank snout for the charging system. I already have a cut down kickstart shaft to help a bit more. Thinking about high grade aluminium engine hanger bolts as well.

Any other ideas, no matter how wild?

Hey Willi,

managed to get mine below 160 kg (352 pounds) with no fuel but with oil.

Picture for reference:



My frame was heavily modified, everything that wasn't needed was cutted down, or replaced with something lighter. The rear shock mount was cutted and relocated using a way lighter solution. I think I was able to get to 12 kg (26 pounds). Don't bother adding gussets or reinforcements, they are useless.

The engine weighs 68 kg (150 pounds), down from the original 90 kg. A LOT of weight come off by removing the alternator and the starting engine. Cutting the crankshaft let you save another 3+ kg. Cutting all unnecessary fins and supports let you save another kilogram.

Some other serious savings come from replacing the exhaust with a stainless steel one. Mine is an aftermarket exhaust for a CBR900 (heavily modified). My mechanic is now making them if you are interested (4 in 2 in 1). I think it weighs 3 or 4 kg. Same goes with the oil tank, replace it with an alu one.

The wheels also are quite heavy, especially the rear hub. If you have to keep spokes then you need to replace the hub, but to save even more find a pair of alloy wheels so you can remove also the inner tube (those are 0.7 kg each - rotating non suspended mass!).

My mechanic Silvio just finished a pair of Honda 650, bored to 750, for two friends of mine, those things weight 143 kg (315 pound) with oil and no fuel!!!!

[bwaller]

If you get similar results every time by weighing front/rear separately then at least you can track weight loss. If you can find a business with a forklift scale that will help, you'll be surprised at the difference in accuracy.

It's commendable to remove as much weight as possible during the build phase, but if your bike handles and stops well in your first season, be happy, that's the biggest goal. Further weight loss can be the focus during the off season.

All the suggestions are good. I think lighter wheels offer a couple advantages. Less unsprung weight sure, but as livefast_dieold mentions less rotating mass allows for faster turn in. It all contributes to an easier bike to ride fast. If you still have those Astralites, consider them. The Ron Muzzy rule begins to apply at some point though. 

[SOHC4 Cafe Racer Fan]

Wow 368-400 wet or dry is pretty impressive.

[slikwilli420]

I want to keep this going since I am a little crazy about the ideal of shedding weight. I will add ideas here but document the process in my build thread.

First is to use 7075 aluminum rod for the engine hanger bolts. The material is as strong as the steel they are replacing and since the engine doesn't really apply any shock to the bolts, the accumulated stress would not be near as big a factor as aluminum axles (not doing that by the way). There are two 10mm bolts and one 12mm one, and replacing the three largest bolts on the bike should be noticeable on the scale and cost will be reasonable, especially relative to titanium.

My second though is to replace the damping rods in the forks with ones made from 7075 aluminum. Again, just as strong and less than half the weight. This is also unsprung weight, so even more important to control.

I wish the wire wheel sealing kits were more reliable as that would allow me to run without tubes, but I have heard mixed reviews. I suppose they would be best on new rims so everything stuck as it was designed to.

[calj737]

Id be curious about the actual net weight differential with the hangar bolts? The steel ines don't really eight that much already.

Perhaps, hollow CroMo axles would be more advantageous in terms of net gain? You should be able to purchase some reasonably priced tubing in .120 wall and still have ample thread. I'd bet that would be far lighter.

[slikwilli420]

I am running cbr600 axles front and rear which are hollow and 0.143 wall. And the front is now 20mm instead of the stock 15mm.

The stock 10mm bolts weigh 200g each x2 and the 12mm one weighs 318g. That is 1.57lb without nuts. I should save 1lb by switching to aluminum for all three bolts.

[slikwilli420]

Alright, Im back at it! I weighed my bike last night just as I had done before, using a digital scale that calibrates each time it turns one, weighing each end 3 times and moving the scale around a bit to see if it varies (it didnt at all) and Im at 355.9 wet! Wet means 3.5q oil and around 3+ gallons of gas, enough for a race at Road America, so enough for any race I will do all season.

Changes from last year:
Aluminum damping rods in forks
Extra caliper bracket shaved off
New wheels front/rear
Lightened front rotor on lighter carrier
Titanium swing arm pivot shaft
7075 aluminum engine hanger bolts w Ti nuts
Shaved engine cases
Cycle X pork chop crank w/ alternator stub cut off
1/4" stator block off plate instead of 3/8"
New seat subframe
Aluminum top triple clamp nut and spanner nut
Aluminum fork caps
Lighter rear set brackets
Cut down kickstarter shaft/removed ratchet and replaced with aluminum spacer
Cut down clutch cover
Cut down oil pump gear
Lightened clutch basket

Thats all I had on my list but Im sure there is more. I still see a weight in the valve cover, shifter drum, seat upholstery and Im sure a bunch of other little spots.

[scottly]

Well done, Matt! How much weight at each end?

[slikwilli420]

Well done, Matt! How much weight at each end?

176.2 on the rear and 179.7 up front. Near perfect front to rear distribution with 49.5% out back and 50.5% up front.

[gschuld]

Well done buddy👍

That’s easily the lightest factory frame cb750 that I have ever heard of.

Now imagine yourself getting really skinny and your competition(family🙄) will start getting really nervous.

George

[slikwilli420]

Well done buddy👍

That’s easily the lightest factory frame cb750 that I have ever heard of.

Now imagine yourself getting really skinny and your competition(family🙄) will start getting really nervous.

George

Im back at it getting my body into a lighter state. The wife and I do these "challenges" through her gym and it motivates me to get into better shape. We are doing the next 8 weeks until out trip to Aruba. Gotta get those beach bodies!!

I really want to get the bike onto a known calibrated scale just to be sure. The method I used especially with a digital scale, is known to be quite accurate, but Id like to know for sure.

[simon#42]

you have got a lot of weight off the old girl then , dont agree with your idea of perfect weight distribution though , am working on a moto 2 frame at the moment and that will be
63% front 37% rear .

[slikwilli420]

you have got a lot of weight off the old girl then , dont agree with your idea of perfect weight distribution though , am working on a moto 2 frame at the moment and that will be
63% front 37% rear .

Dont I only want a little bias to the front? I always thought that 50/50 was ideal and that rider position could change that as needed. Given what it currently is, moving that much weight around on the bike is unlikely.

[754]

So I ask Willi and Scott... how much do you figure the street legal and charging parts accounts for.
 Having it would increase Willi,s weight, not having it would makes Scott's lighter.
 I am guessing 20 to 30ish lbs..

[slikwilli420]

Probably close Frank. That alternator and starter motor are substantial. I've also gone further that Scottly in many places which make up for the difference. Would not need to add much back to go street legal and kick start.

[bwaller]

You can ride these faster if you load the front with your body...instead of back in the seat.

[scottly]

I've got weights of all the parts scribbled down; I'm going to have to get them organized someday. After removing the end of the crank where the alternator mounts, it would be hard to go back to street legal, at least for any real distance, Matt.
BTW, I've recently been working again on my lightened valve cover; it started at 1645 grams bare, and is now at 1360.
On weight bias, my bike has always been heavier in the back. A week or so ago, I was riding at 65 MPH, on a rough road, with a bit of a crosswind, and the bike didn't feel right, until I shifted my weight forward..