Triumphrat

speedybrit · 03-23-2008

Im about to widen my thrux rear end. Im looking at the excel rims through buchannan wheels in the US. Just want to make sure i can put a 5inch rim with a 170 tire on and not have to offset the rim from the hub or put spacers behind any sprockets..... Can anyone confirm this for me .. ??

I see buchannans does not offer a 'dimpled' 5inch wide excel rim. Does anyone know another rim supplier that does ????

thanks a lot

JG · 03-23-2008

I have been going through a similar process all winter, and have some info that might help a bit. It might be possible for you, but just barely. The 170 mm tire size is just nominal, and the actual mounted and inflated tire's width can vary from the listed nominal size. Most tires are actually several millimeters wider than their nominal width when mounted on their 'standard' width rim. A 170 mm tire mounted on a 4.5 inch rim will be significantly narrower than if mounted on a 5.5 inch rim. Most 170 mm tires have a 5 inch wheel as their standard rim.

In the process of installing a wide rear wheel and tire, I have very carefully measured my rear wheel and the position of the sprocket. From my own measurements (which could of course vary slightly from bike to bike), if you want a truly centered rear wheel (rim centered in the swingarm), while keeping the drive chain in its original position with no offset, you have about 172.7 mm to work with, meaning a centered tire of 172.7 mm width would be just starting to touch the drive chain. If you are willing have only about 1.3 mm of clearance (a little less than I would want) between the chain (DID 525VM, width: 0.904 in.) and tire, you might be able to use a rear tire with an actual width of no more than 170 mm. It will be a *very* close call for you. You might want to offset your front and rear sprockets a couple millimeters with spacers. Also, you might have to settle for a rear wheel that is offset a couple mm left of center. Or you could mount a 170 mm tire on a 4.5 inch or 4.75 inch rim, which would reduce its width a little bit. You might have to do a combination of these things.

I have found that a Dunlop Qualifier, sized 170/60/17, mounted on my 5.5 inch wide Carrozzeria rear wheel, is actually between 180 mm and 181 mm wide (measured with calipers) when inflated. To center my own rear wheel on the frame's backbone, I actually had to move it a little over 1 mm right of center in the swingarm, since my Thruxton's swingarm is a little bit 'tweaked' to the left - may have been built on a Monday or Friday. I have had to modify the wheel, cush drive, sprocket carrier, and sprocket in order to center this wheel/tire on the bike. My rear sprocket is offset about 8 mm to the right from the original stock position. The front sprocket is offset a little less than 8 mm. I also had to offset the chain slider on the swingarm. My chain clears the tire by a little over 2.5 mm, which is fairly close, but should be fine.

speedybrit · 03-24-2008

JG thanks a lot for that amazing reply ... a lot of the things you mentioned have also crossed my mind as regards the 170mm tire being influenced wider or slimmer depending on the rim. The measurements you have given are very helpful and at this point i think id be going for the 5inch rim with a carefully picked 170 tire.

I also thought about putting spacers (washers sanded to the same thickness) behind the front and rear sprockets, and although i have changed both to help lower the RPM's i dont remember what is behind them ??

i know the driveshaft is splined.. can you remember if a regular washer would fit behind there ? or would it have to be some impossibe to find spline washer ? how much space do you think can be made from using washers behind the sprockets ?

Whitehurst · 03-24-2008

A bridgstone battleaxe will work.

JG · 03-24-2008

For the front sprocket, the outer diameter of the splined shaft is 30 mm, so the inner diameter of the spacer should just fit over that. A splined spacer would not be needed. The outer diameter is not too important. The splined shaft has a sleeve around it that passes through the seal. The sprocket gets tightened against this sleeve, and the outer diameter of the sleeve is only 40 mm. So an outer diameter greater than 40 mm should be OK. There is only enough spline length to allow around 2 mm to 2.5 mm of spacer thickness and still leave enough spline left to engage the lock washer that keeps the sprocket nut tight. I got a larger offset by using a custom sprocket.

For the rear sprocket, you can use washers as spacers on the sprocket studs behind the sprocket. I would not space it out so much that the sprocket inner diameter no longer rested on the outer diameter of the support tabs on the sprocket carrier. So maybe 3 mm or so...

With only 2 or 3 mm offset on the sprockets, you should be able to avoid having to offset the chain slider on the swingarm.

MAR · 03-24-2008

I am running the Carrozzeria wheels on my thrux with the dunlap qualifiers without any issue. The rear is a 170 and there would have been room for a 180( not needed however). The front tire gently hit the fender bolt. I replaced the bolts with button head bolts and the problem is gone. I do not do anything about the offset and there is no issue with handling. A good place for information is South Bay Triumph. This is what Matt Capri is running on the bonneville racer.

Treehugger · 03-24-2008

speedy brit, I have wider rear and front wheels. Are you just planning on widening the rear? or both? I'm just debating returning to the original wheels. My bike came with the wider wheels, I'm not sure if I want it... might swap them out. let me find out just how big they are. I'll post some pics in the pics thread... check them out.

Baltobonneville · 03-24-2008

Is there any functional reason you want a fat rear tire? Or is it just for looks? I'm trying to figure out what exactly this fascination with fat tires means.

JG · 03-25-2008

I can't speak for anyone else, but for me, what I really was really after were the black anodized forged wheels themselves. Wide tires happen go along with them. I do think the wide tires look very good, better than narrow tires, but I would have probably chosen a 160 mm tire with a 4.5 inch rear wheel, had that been an option. The wide selection of 17 inch tubeless sport and sport touring tires on the market is also a bonus. After mounting the tubeless tires on the wheels, I was pleased with how simple it was, not having to mess with an inner tube. Before that, I had never mounted a tubeless tire myself, but I had heard it was a real nightmare - not so bad, actually.

MAR · 03-25-2008

I wasn't looking to install a fat rear tire. In fact i would have prefered a more narrow tire. However, I was looking to reduce the weight of the wheels and these wheels reduced weight by over 23 pounds.