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Discussion Starter · #1 ·
Hey folks, I know there are some here that don't like the idea of wide tires on these "old style" bikes, but I'm in the category of those that do like them. I've seen some other RAT members conversions (and the vendors offerings) and like the idea of SuperMoto tire and rim sizes for these bikes.

So...I swapped rims on the rear yesterday and installed a Pirelli Diablo 180-55-ZR 17 on the back. The whole process took me all day, with a good deal of the time spent removing the rock-hard OEM rear Metzeler! What a bugger, with all those steel belts.

Anyway, since the rims are the same diameter I was able to re-use the OEM spokes and nipples. I went with a chromed Excel alloy rear, 5.5" x 17". The lacing and truing was fairly straight-forward. I covered the rim insides with masking tape, as it's easy to scratch them up with a pile of spokes flopping around inside the rim as you twist and turn them into position. Not an easy job, but I've done several wheels in the past, and I save myself a few hundred bucks over just buying it already done.

Here's a few pics of the finished installation:




Also, here's a link to a PicasaWeb album with a few more pics:
http://picasaweb.google.com/BKL93908/BigTireThruxton#

Still fine-tuning the wheel balance, and adjusting the offset a bit. The rim's a bit too close to the sprocket side of the bike, and adjusting it left (from the rear) a few mm will center it, making it just right. I did have to place a 1/8" spacer behind the front sprocket, and 6 of them behind the rear sprocket to clear the edge of the big tire. There is NO way a 190 will fit this bike. In hind-sight, a 170 (as others have mentioned) is probably a better match...I just wanted the 180.

The 180 will fit, it just takes extra fiddling with the chain clearance, and with the center-stand feet to clear. I think it looks cool on the bike...these modern twins are sort of the 'resto-mods' of the bike world. Old-world styling cues, punched up with modern hardware bits & pieces.

BTW, the bike rides, handles, steers, and stops just fine. No weird turn-in feelings or anything. I still need to break the tire in before I try anything too enthusiastic!

Let me know what you guys think! The front 17" x 120 is next...but I'll take a short break first.

Cheers!
BLIGHT
 

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Looks cool. But silly question: Apart from apperances, what's the advantage?
 

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Discussion Starter · #6 ·
Looks cool. But silly question: Apart from appearances, what's the advantage?
First off, thanks everyone! It was a lot of work, but I did it on a day off, so it was a good way to keep my idle hands busy. Besides... I like a good challenge.

TB-100, I have to say the aesthetics are the biggest plus for me, but I also like the idea of buying sticky sport-bike rubber in the now "standard" 17" front and rear sizes. Having 2 different diameters makes buying tires in 'packages' pretty tough. Besides, I haven't liked the choices in 18" fronts for this bike. I just got a new pair of Pirelli Diablo's 180 & 120 x 17" delivered for under $200 USD. Did the same thing for my VFR in Conti-Force's a coupla years ago for even less. Those are very good street tires too in my opinion. The 17" sport-bike rubber sizes are a very competitive class between manufacturers and dealers...seems like there are always bargains out there if you look around.

Another advantage to the wider tires is a slightly larger footprint (contact patch), front and rear, and that's good for cornering and braking grip. (Not too much of an issue in acceleration grip though with 70 hp!)

The larger sectional radius of the tires means more rubber is on the pavement vs. a tire with a smaller cross-section radius. Not a lot more rubber, mind you, but enough to make a big difference in maximum grip. The profiles are optimized for maximum grip when leaned over as well.

By the way, I just took the bike for a 50 mile ride, and I'm very pleased overall. Still 'babying' the rear until it goes through a few heat cycles, and scrubbing them in gradually. On one of my favorite twisty roads, it felt very stable when leaned over, and very good in initial turn-in. I still have a crappy front tire on the 19" rim, so it's not fair to judge the overall handling capabilities just yet, at least until I get the new 17" hoop on the front.

Feels great from these initial impressions though. I think the new rear rides smoother too (even @ 40 psi), absorbing bumps a lot better than the stock 'hard as a rock' Metzeler.

BTW...that back wheel on these twins IS a pain in the arse to get back on. Next time, I'm going to try some of those tips I just read in the 'rear wheel' thread!

Thanks again guys!
BLIGHT:motorbike:
 

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BTW...that back wheel on these twins IS a pain in the arse to get back on. Next time, I'm going to try some of those tips I just read in the 'rear wheel' thread!

Thanks again guys!
BLIGHT:motorbike:
That looks sweet!
And not to fire up the whole bike lift who-ha again,but this is really the only time I use that thing. I raise or lower the bike until all the holes line up. No lifting the tire or anything.A one minute job....
 

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Discussion Starter · #10 ·
That looks sweet!
And not to fire up the whole bike lift who-ha again,but this is really the only time I use that thing. I raise or lower the bike until all the holes line up. No lifting the tire or anything.A one minute job....
Thanks!...a bike lift is now on my birthday 'wish list'!

BLIGHT
 

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the diablo pattern looks really sweet on your thruxton....the big back tire made a big differance!
 

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Dammit Blight! Just after I was thinking that the end of the mod journey was in sight (after new cams, different rear suspension and perhaps a smaller instrument cluster...) you come along and stir up the imagination again. The 5.5 inch makes my OEM rear wheel look rather underwhelming

PS. nice job - looks great
 

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Discussion Starter · #14 ·
Dammit Blight! Just after I was thinking that the end of the mod journey was in sight (after new cams, different rear suspension and perhaps a smaller instrument cluster...) you come along and stir up the imagination again. The 5.5 inch makes my OEM rear wheel look rather underwhelming

PS. nice job - looks great
Thanks again guys! Every time I go in the garage now, I just have to stop, grab a beer from the garage fridge (after 12PM somewhere, eh?), and just admire the bike even more! It's a real beauty IMHO...

Mind you, this is not a 'cheap' conversion if you buy it 'ready-made' from the vendors...it's about $600 USD plus freight both ways, which means you also have to send in your "exchange" rear hub. That means you have to remove your rear tire and rim (or pay someone to) and remove all the spokes & nipples (I said 'nipples') to get down to the bare hub so you can send it to them.

You are also going to get "someone else's" hub on your new wheel, so you don't know if they were a 'grandma' or a 'drag racer'. It's probably not an issue, but I tend to lose sleep over even smaller issues.

So...paying the shipping back & forth with the big wheel assy. will likely be another $30-40 USD or so. Also, you won't get a chromed Excel aluminum rim for that price! The powder-coat black and silver anodized alloy rims they offer look pretty good too, but they're just not appropriate on my retro-mod bike.

I did the rim swap myself and even got a new Excel chromed alloy rim (usually $100 more) on ebay for about $230 USD including freight. I reused the OEM spokes & nipples (said it again!) and I will sell the OEM rim for $75, so my NET cost will be about $155 USD. I'm OK with that! I needed a new rear tire anyway, so that's a wash.

I highly recommend the swap...I know it's not for everyone, but if you like it, it just looks really cool on these bikes. Plus, it can improve the handling capabilities. If I were to do it again, I'd probably go with a 170 rear tire...you'll have zero concern with the chain clearance with the tire edge, and it will look 95% the same as the 180, and it will handle just as well. (As I said before, there is 'no way' a 190 will fit without extensive spacer work, custom sprockets, or offsetting the rim from the bike's centerline.)

With a little fiddling using some 1/8" sprocket spacers, I now have about 3/32" clearance between the inside chain rivets and the 180 tire edge. Not much, but jusssst enough! The tire is now dead center-line with the front wheel, no left-offset required for chain clearance!

Cheers,
BLIGHT:motorbike:

PS: I just watched an episode of the Teutel's 'American Chopper'...they put a 300mm (!) rear tire on one of their creations. I bet it doesn't want to turn very well...
 

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PS: I just watched an episode of the Teutel's 'American Chopper'...they put a 300mm (!) rear tire on one of their creations. I bet it doesn't want to turn very well...
Creations? More like abortions! I play a little game while I watch the show called "which parts would I keep if it were mine?" and I usually end up quitting after engine, trans, primary, carb, etc...
 

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Nice looking upgrade! Excellent work...please give us a review of the rear / front combination after getting after the front rim. I'd be interested in hearing what the 17" front does for cornering clearance since you have the clip ons over the tree up front.

Cheers,

--Rich
 

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Discussion Starter · #18 ·
Nice looking upgrade! Excellent work...please give us a review of the rear / front combination after getting after the front rim. I'd be interested in hearing what the 17" front does for cornering clearance since you have the clip ons over the tree up front.
Cheers,--Rich
Thanks Rich, I appreciate all the kudos...I will post some pics when the front is done, and report on how the package works.

The new smaller front tire OD will throw off my speedo too. I wonder if the speedo drive for the Bonnie SE cast 17" front will fit the "old" style spoked hubs? Anybody know? It should be the correct ratio to bring the speedo back to a 'fairly' accurate range...at least as good as it was before? I'll be using the same size front tire as the SE.

I'm curious too as far as the handling...the rear tire is about 1" larger in circumference that the 140 I took off...whattzat, about 1/3" larger OD? That's only a 1/6" raise in the rear. The front is a bigger deal as you suggest. The OD on the old 18" Metz is 79"...the OD on the new 17" Diablo 120 is 74"! That's a 5" circumference difference, divided by 3.1415 (pi) yields a diameter difference of 1.59"!!

That means the front will drop half that, or about 0.80 inches. That's a lot! I haven't been dragging anything right now with the fork tubes pulled up 1", and I like the way it steers. But...jacking the rear, lowering the front, AND having raised tubes is going to be too much I'm afraid.

I will likely need to pull those forks back out and put the bars back under the upper triple. Poop! Being up on the top sure made for a more comfy ride position. Maybe I can find a set of VFR800 clipons. I believe they are 43mm too, they have a nice rise to them, and will raise the bars up about an inch from the stock Thruxton clip-ons. I'm sure I can sell the stock Thrux clip-on's easily on ebay!

One more thing I just thought of...the front fender is going to look goofy with all that air space under it. The radius is also wrong for the new tire. I think I can live with that, but I will need to lower the front fender bracket 0.80" to keep the same clearance I have now. One more thing to play with, right?

I have always wanted a chrome or polished alloy fender (instead of the OEM silver painted plastic) so maybe now is the time to do it. I can order the right radius hopefully... or possibly use the SE front fender and bracket. I think it's a plastic fender too, and the wrong color! I'm sure I'll find something I like.:eek:

Cheers,
BLIGHT
BLIGHT
 

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Maybe I can find a set of VFR800 clipons. I believe they are 43mm too, they have a nice rise to them, and will raise the bars up about an inch from the stock Thruxton clip-ons.
You meant 41mm, right? The LSL clip ons are also have a bit more rise than stock. Or you can get some CBR600F3 forks, which are 41 mm cartridge forks & are 1.3" longer than stock... :)

Yeah, you never get 'finished' with these bikes...

Cheers,

--Rich
 

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Discussion Starter · #20 ·
You meant 41mm, right? The LSL clip ons are also have a bit more rise than stock. Or you can get some CBR600F3 forks, which are 41 mm cartridge forks & are 1.3" longer than stock... :)

Yeah, you never get 'finished' with these bikes...

Cheers,

--Rich
I thought they were 43, but you're correct. Too many numbers in my head. I'll look into the CBR600F3 tubes. I think you also gain a damper adjustment screw IIRC.

I'm also been thinking about going to a flat handlebar conversion. I rode my old CB400F the other day (my other 'cafe' bike:rolleyes:) and man, I sure love that low flat bar they came with. It's 27" wide with only a 2" rise. It has very little bend or pull back. Just super comfy and still looks sporty. It was pretty radical in 1975, hehehe. If I just install a couple of 7/8" bar perches on the Thruxton's upper triple clamp then I can fit any bar I want! I took a few quick measurements and it looks like it would work.

If I do it I'll post some how-to pics if anybody else wants to try it. If it doesn't work, you won't hear from me, and I'll just hang some more spare parts on my wall.

Cheers!
BLIGHT
 
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