Cafe Seat - Hoop or Straight Bar?

[Guest]

I bought this cafe seat, the fitment is good, but before I go off all sawzall-happy on the frame I'd like some advice:

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With the seat being so short could I brace the frame between the shocks with a piece of tubing rather than welding on a hoop to support the rear of the seat? Since the rear of the seat won't be supporting any rider weight, could the back end of the seat simply "float"? What are the pluses/minuses of each approach?

 

[Steve]

Not sure which might be better, but I would definitely be asking one question.

I am presuming there might be some sort of light(s) on the back. Where is it going to mount? :-k

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[Nessism]

I'd join the tubes together in some way to increase strength and allow mounting stuff to it. And speaking of mounting, please add a rear fender of some sort so your bike looks "finished" instead of hacked. Not to mention a rear fender, even a short one, will help reduce spray hitting your backside and provide a professional looking place to mount the license plate and tail light.

 

[Buffalo Bill]

Find a mo betta looking seat…

 

[Gorminrider]

i don't think there was much cross-support structure there in the first place, so if you wanted to bolt something across rather than weld it, you should be fine.

I see a couple of handy tabs right behind the seat to contrive something across...to mount a tail/brake light at the least! but you will want a licence plate too... as has been mentioned, without some sort of a fender, stuff mounted on it is probably going to get covered and beaten by crud.

Are you sure that seat will work out for you? You might discover that you are more comfortable sitting further aft. If you havent ridden the bike much, maybe ride it awhile and be sure before cutting length off.

 

[Guest]

Thanks for the feedback folks

Not sure which might be better, but I would definitely be asking one question.

I am presuming there might be some sort of light(s) on the back. Where is it going to mount?

Yes, I would have to add/fab/create some mount points and the hoop would provide those, but is that the only functional purpose of the hoop (i.e. - aesthetics aside)?

Google ?Suzuki GS650 cafe racer? for pics of what other people did & how it turned out.

I have, most folks cut the straight frame rails and weld in a hoop, but is that a structural requirement or just a preferred choice?

I'd join the tubes together in some way to increase strength and allow mounting stuff to it. And speaking of mounting, please add a rear fender of some sort so your bike looks "finished" instead of hacked. Not to mention a rear fender, even a short one, will help reduce spray hitting your backside and provide a professional looking place to mount the license plate and tail light.

Heh heh, yes a fender is coming, this is the planning phase

Find a mo betta looking seat?

helpful, cheers

i don't think there was much cross-support structure there in the first place, so if you wanted to bolt something across rather than weld it, you should be fine.

I see a couple of handy tabs right behind the seat to contrive something across...to mount a tail/brake light at the least! but you will want a licence plate too... as has been mentioned, without some sort of a fender, stuff mounted on it is probably going to get covered and beaten by crud.

Are you sure that seat will work out for you? You might discover that you are more comfortable sitting further aft. If you havent ridden the bike much, maybe ride it awhile and be sure before cutting length off.

My first thought was to fit/bolt a piece of tubular steel across for mounting lights etc. and seat support but now I'm curious how much lateral support the frame needs at that point? The stock hoop doesn't seem like much, but if it helps keep the bike tight then I'd want to preserve that functionality.

I haven't ridden with that seat so I'm not sure how it'll feel; with a dry fit and sit things felt ok but I'm sure time and fatigue will play a part. Comparing photos of the new and stock seat, the aft rise is about 2" forward of stock, I'll play with it a bit and see how things feel, but I'm with you on trying things out before cutting up the bike.

 

[LAB3]

I'd go with the hoop, it'll give you a much cleaner looking job when it's done.

 

[salty_monk]

Is the problem access to welding equipment? I would think that you could both bolt a cross brace and make a hoop that could be inserted into the frame tubes & through bolted for Fender / plate / light mounting duties.

The bikes that I've seen with the back hacked off (usually under the guise of "street fighter" have not found a good way of dealing with the exposed tube ends.

If you don't have a tube bender - fill the tube with fine sand & cap the ends with duck tape then bend it around a former. Flush it through at the end.

I like your seat (and the colourway). What colour are you finishing the paintwork? I think the browns always go best with torquisey blues and greens

 

[Guest]

Is the problem access to welding equipment? I would think that you could both bolt a cross brace and make a hoop that could be inserted into the frame tubes & through bolted for Fender / plate / light mounting duties.

The bikes that I've seen with the back hacked off (usually under the guise of "street fighter" have not found a good way of dealing with the exposed tube ends.

If you don't have a tube bender - fill the tube with fine sand & cap the ends with duck tape then bend it around a former. Flush it through at the end.

Access to a welder shouldn’t be a problem, but bolt-on does give some flexibility. The biggest concerns were whether a hoop/cross-brace was needed for lateral stability, and/or seat support. I was considering a cross-brace because the “floating seat” idea was interesting. Another thought was placing marker lights or led signals in the tube end to keep the crap out. Again, this is the planning stage, so even if the mechanics work, a hoop may find it’s way onto the bike after all.

I like your seat (and the colourway). What colour are you finishing the paintwork? I think the browns always go best with torquisey blues and greens

Initially, I was thinking of dying the seat black as I’m going to keep the gloss black tank and add matte black accent striping, but now I’m kind of digging the black & brown. The seat matched to some brown leather-wrapped grips might be pretty tight?

 

[salty_monk]

I like this blue/brown combo:

Brown black looks ok too though... I definitely wouldn't go black. You can tie the brown in with the grips and/or some other leather accessories...

 

[Grimly]

Consider that all the rear suspension loads are coming into the top part of the frame, right where there's little lateral bracing. Frames want to twist, every single one of them. You'll feel the difference if you take the bike out on the road and try some twisty backroads, then come back and weld in the rear hoop. I'd also add a decent tubular brace across / between the top mounting points.

 

[Gorminrider]

hmm...well, I suppose the original rear fender supplied what rigidity was there originally....but when I look at my 650 with it's plastic fender, I don't imagine there was much....to my eye, any twisting flex where the shocks attach or behind them, devolves forward on the frame, toward the engine -binding the two sides together at the back so they act in unison would seem to make little difference-(when would they not?) The tubing is not weak of it's own either....but a cross piece can't hurt and is practical for attachments as is a fender.

 

[wyly]

there are aftermarket hoops with LED tail light built right in.

 

[Grimly]

hmm...well, I suppose the original rear fender supplied what rigidity was there originally....but when I look at my 650 with it's plastic fender, I don't imagine there was much....to my eye, any twisting flex where the shocks attach or behind them, devolves forward on the frame, toward the engine -binding the two sides together at the back so they act in unison would seem to make little difference-(when would they not?) The tubing is not weak of it's own either....but a cross piece can't hurt and is practical for attachments as is a fender.

I know it looks that way, but consider what happens when the rear wheel is loaded sideways - every time you're cornering with some gusto.
That's trying to twist, and so are the top mountings. If the load were purely carried forwards equally, there would be no need for braced swinging arms, either.

 

[Gorminrider]

...mmm just BSing,Grimly...but how does tying them together help? Tying them together just stops them from spreading. .. .....any twisting or deforming of tstill levers against and thereby depends on their endpoints ...that is, joining single end cantilevers doesn't stop them being cantilevers..and, it'd be the swing arm to twist in the first place. Note that the shock springs would STILL allow "twist" however you tie these seat-and-fender-and-shock supports together. The shocks themselves can act independently, right? So it's the swing-arm itself that is the "issue" if twisting is a thing.

And, by the way, a hoop is not as effective for "unifying" as a straight bar would be...just because it's longer and thereby more flexible...to stop spread it'd be best "pulling" along the shortest length. A hoop might act as a kind of spring...sure- that's unlikely with a matching gauge of tube but still...

 

[salty_monk]

I think if you tie them together you would feel some difference.

Surely any twist from the swingarm goes up the shock and if tied it may then bring the other shock into play in compression too stiffening the whole assembly.

I should think it also helps with any flex both up and down and side to side from the riders weight movement.

Essentially the closer you can bring them to a mono-shock the better I would think.

Agreed that a straight tie across would be stronger than any hoop.

 

[timebombprod]

brown seat/grips with a black tank looks nice but its more of a lowkey style like you dont wanna pop out much, but at the same time ive seen so many blacked out motorcycles here where im at it seems everyone does that. i would definitely add the brown to give the bike more colour

 

[posplayr]

This well known frame bracing picture from OSS shows no standard bracing in the area behind the shock mounts. In other words adding metal back here does nothing for stiffness. The virtually the only purpose for the cross piece at the extreme end is to support the tailpiece with light. Most of the wheel loads acting through its axle go to twisting the swingarm and not the shocks. As mentioned previously the shocks are in fact (unless a hardtail) compliant.

The only reason for tail bracing for the OP is to support the seat. A cantilevered seat (as in the case of a straight cross bar) would flex depending upon the construction of the seat pan. A hoop provides the most support for a seat assuming it is stiff enough in center not to collapse from the riders weight.



http://oldskoolsuzuki.info/archives/category/modifications/frame-modification

 

[Guest]

Great feedback folks! I love the exchange of ideas without the automatic ney-saying of another users posts, it's hard to come by.

As a follow-up to my last post; I did another dry fit of the seat and as discussed the seat will need to be pushed back to prevent a cramped seating position. Essentially, my hips/butt need to be right around the top of the shocks which pushes the seat back around 3". The push back leaves a gap between seat-front and tank, not a huge deal but another piece to consider, i.e. different seat, or adding a storage compartment/seat padding etc.

At the same time I mocked up some positioning with the signal lights, tail lights and the stock fender to get a better idea where things might go in either (bar or hoop) configuration. If the seat is pushed back to cover the last set of mounting tabs (right above where the rear frame support ends), I should be able to put a bar (weld or bolt) in to accommodate the tail light/license plate, fender, & seat.

I can assure Posplayr that there is NO risk of seat collapse due to my weight, even if I was a little "enthusiastic" at the desert table over the holidays...

The only reason for tail bracing for the OP is to support the seat. A cantilevered seat (as in the case of a straight cross bar) would flex depending upon the construction of the seat pan. A hoop provides the most support for a seat assuming it is stiff enough in center not to collapse from the riders weight.

View attachment 60064

http://oldskoolsuzuki.info/archives/category/modifications/frame-modification

 

[Guest]

here's my 2 pence / cents worth. I had a brace welded across the rear of the frame rails, I plugged the tubes with a threaded insert and then had a tailpiece manufactured and it screws into the tube bracers the socket buttons I used are hidden by the number plate.