Topic: widest tire for a street/drag application (750k3)

[5thofhonda]

Looking to build a high performance street bike on a slightly more functional drag-style frame.  I was told the custom frame I'm wanting has no structure for a jackshaft, and the transmission shaft is a weak point, which may rule out offset sprockets.  I was hoping to run a 160.  Nothing crazy big.  As for power, I'm aiming for 95+.  Do I have any options here, or will I be stuck with stock size?

[Don R]

 The late engines and cush drives have the sprockets further out for the wider 17" tire they came with, I think CycleX has offset sprockets.
 My dragbike has a 16x5 M&H slick but I don't have the engine back in. It fits in the swingarm with the adjustment all the way back. The struts had to be made longer to fit the top of the tire between the fender mounts since it's a flat slick, (not rounded on the tread area)  I just got a 17" cb750A rim with a 130 shinko I may use just to make it look more like it did back when it was raced.

[5thofhonda]

I'm having a hard time deciding on a wheel and size. Sticky tires on a spoke wheel make me nervous, but I don't want to lose the nostalgia either.  I've thought about trying to fit a sport bike wheel with disc brakes, but not sure how it would work.  The frame will be a custom hard tail from Cycle One, so there isn't a swing arm and shock to consider.

[Don R]

That will open up a lot of space, check the dragbike builds in the project section and in the high performance section. Lots of more current info than mine.

[Retro Rocket]

4.5 inch rear rim with a 160 will fit, no problems using a 10mm {3/8} offset front sprocket on the 750. Look at 1988 GSXR750J and GSXR 1100 J rear wheels for a 4.5x17 {750J} or a 4.5X18 {1100J, these are both 3 spoke rims}}, they have plenty of meat on the sprocket carrier you can machine off to help line up the sprockets, combined with the offset front sprocket...

[Jerry Rxman Griffin aka MuthaF'er]

Perhaps also check with member Red Good at CycleOne Manufacturing (?). He does frames such as you mention and could probably put you in the right direction including a jack shaft.

[5thofhonda]

Perhaps also check with member Red Good at CycleOne Manufacturing (?). He does frames such as you mention and could probably put you in the right direction including a jack shaft.

They would be the ones building the frame. I've already emailed back and forth with Kate, which is where this concern is coming from.   I'm asking for 4" forward stretch and 4-6" rear stretch and -1" in the backbone with a gooseneck fitted with a modern GSXR front end.  She told me the rear will require more triangulation and will resemble a trike rear end.  They told me the jackshaft wasn't an option as there will be no structure for it and warned me that using offset sprockets would put stress on a notoriously weak transmission shaft.  If I had the frame in front of me, this would be easier, but it got put on hold as we found a house and are waiting to see how it plays out.  I'm trying to figure out what I can work with in the meantime so this is more streamlined when the time comes.  Hell, I'll probably have to sell my bike to piece this one together, lol

[Retro Rocket]

and warned me that using offset sprockets would put stress on a notoriously weak transmission shaft. 

Since when are the tranny shafts "notoriously weak"..? which shafts, there a a few differences in both shafts and bearings, and how much offset are they talking about..? Heaps of people successfully use offset sprockets on these bikes, quite a few people make them as well... Did you read my post ?, there's more than one way to do this, I already have a 17x4.5 suzuki rim fitted to a honda 750, it even shares the same size rear axle, you have to make spacers up but this isn't rocket science....

[mystic_1]

They may be thinking of the 750's reputation for breaking chains and throwing them into the engine cases for massive damage.  This was a problem with the earlier models and Honda made several changes related to this, including changing the final driven shaft and bearing designs.

Consensus on this board seems to be that the chains themselves were the real weakness and that modern chains are more than up to the task.

I don't know that I've heard of too many broken transmission shafts on 750's.

mystic_1

[Jerry Rxman Griffin aka MuthaF'er]

I had been talking with Red a few years back about a 240 rear with a jack shaft and it was do-able.

+1 about the tranny shafts. I see no problem there.

[5thofhonda]

Retro, I did read your post and I'll look into that.

It seemed odd when I heard it, so I wanted to ask to be sure.

[Retro Rocket]

Just as an example, the F2-F3, and K7-K8 all have a 10mm longer output shafts, so all adding a 3/8-10mm offset sprocket on an early K does, is match the length of the later output shafts, haven't heard of any of them breaking. A huge, unsupported offset sprocket would definitely be less safe, but its completely unnecessary..