ET tyre size/chain run.

[imago]

What tyre size can you  go up to on an ET and maintain chain clearance? The swing arm's getting changed anyway, but I want to get some decent sized sticky 17" rubber under the throwback turbo. At the moment the most likely size I'll be aiming for will be 180/55 but I don't know what I can go up to with the stock engine sprocket position qand still maintain the chain run.

[Toecutter]

A 180 is doable, but chain run is tight to frame. A couple of mm at best. Can notch the frame to suit with good results. I've machined sprocket carrier a couple of mms to suit and 3/8 offset front sprocket what have you to line things up accordingly. You Can do all of that and also run a 170 tyre to be on the safe side. 180 tyres don't always measure true 180 depending on manufacturer when fitted. I've had some chains kiss the rear tyre and others not. Hence why I dropped to a 170. Albeit, 170 tyres limit your manufacturer/tyre options. 

[TonyGee]

2 minutes ago, Toecutter said:

A 180 is doable, but chain run is tight to frame. A couple of mm at best. Can notch the frame to suit with good results. I've machined sprocket carrier a couple of mms to suit and 3/8 offset front sprocket what have you to line things up accordingly. You Can do all of that and also run a 170 tyre to be on the safe side. 180 tyres don't always measure true 180 depending on manufacturer when fitted. I've had some chains kiss the rear tyre and others not. Hence why I dropped to a 170. Albeit, 170 tyres limit your manufacturer/tyre options. 

yeah had a 180 on mine, and bang on with the width of different makes of tyre, they do differ. 

[coombehouse]

Things get a little easier if you run a 520 chain. You gain a few precious mm's which will allow a 180 tyre subject to offsetting the front sprocket & machining the cush drive.

[imago]

Thanks gents. I want to use the Marchessini rims from a Do-Whaty on the draw through project as they have the right look. At least now I know I'll be close enough to make it work. 

The standard for the rear is a 180/55 so what I'll try and do is to get a rim with a tyre on it. Then I can do the trial fit and if I need to drop to 170 I can.

[Duckndive]

My old ET with blandit arm I ran a 170 using a 530 chain ...as mentioned not all 170s measure the same 

[imago]

As long as I'm in the ball park with the rims I can adjust tyre size to suit, drop to a 520 chain, maybe offset the sprocket a touch or a combination. Basically as long as they fit without notching the frame I'm happy.

I just like the style of those Marchessini cast rims (as below) as they have a similar look to the old magnesium race wheels but without the added "will it be today?" excitement and they not too bad price wise.

[Duckndive]

4 hours ago, Duckndive said:

My old ET with blandit arm I ran a 170 using a 530 chain ...as mentioned not all 170s measure the same 

Found a Pic ....

[TonyGee]

mine with a 180 and a 530 chain. their was 2mm from the frame to the chain and about the same on the tyre side. never had any contact with the frame as no paint was scratched off 

 

[coombehouse]

Numbers to consider & draw your own conclusions 

Swing arm width at pivot is 226mm inc caps

Tyre nominal width is 180mm.

With wheel on centre 226-180=46mm /2=23mm gap per side

A DID 530vx3 chain is 25.3mm wide across the pins. A non o ring DID chain is 22.55mm wide A DID 520vx3 chain is 18.69mm wide. 

[imago]

6 hours ago, coombehouse said:

Numbers to consider & draw your own conclusions 

Swing arm width at pivot is 226mm inc caps

Tyre nominal width is 180mm.

With wheel on centre 226-180=46mm /2=23mm gap per side

A DID 530vx3 chain is 25.3mm wide across the pins. A non o ring DID chain is 22.55mm wide A DID 520vx3 chain is 18.69mm wide. 

Thanks, that's the sort of useful info I needed. I just wanted to see if I was in the ballpark. That way tweaking things will make it work. 

[Dezza]

If they're wheels from a 749/999 the back can be either a 5.5 or a 6 inch rim. Most were 6 but some had 5.5 inch wheels. The sprocket carrier, as for most 'modern' bikes, also positions the chain way out from the rear tyre. I had a set a while back but can't remember what the construction of the sprocket carrier is like regarding the feasibility of having it machined for reduced chain/tyre clearance. Obtaining fancy 5.5 inch wheels now is pretty difficult unless you buy a new one for mega-bucks

[Duckndive]

14 minutes ago, Dezza said:

 Obtaining fancy 5.5 inch wheels now is pretty difficult unless you buy a new one for mega-bucks

dept on what you deam fancy 

GSXR 600 from 2014 shares the same skinny 3 spoke wheel style from the 750, & 1000 but has a 5.5 rear and they are very light   

[coombehouse]

2 minutes ago, Duckndive said:

dept on what you deam fancy 

GSXR 600 from 2014 shares the same skinny 3 spoke wheel style from the 750, & 1000 but has a 5.5 rear and they are very light   

Is the sprocket carrier on these wheels very narrow, like the k model wheels, making it difficult to get the offset?

[Duckndive]

13 minutes ago, coombehouse said:

Is the sprocket carrier on these wheels very narrow, like the k model wheels, making it difficult to get the offset?

yes they are narrow compared to slingshot and blandit stuff ..

i used one from a thou "as i had it" which needed a little machining to get it spot on ..

you do have to be carful with the modern stuff when buying bits as suzuki san used both 6 bolt and 5 bolt Cush drives so research is key to get matching bits  "breakers are lazy and just say there all the same mate"

when i bought the thou wheels they were complete units which made life easier 

 

[Dezza]

Don't Triumph 675s have 5.5 inch back wheels? They look really good in older bikes

[coombehouse]

24 minutes ago, Dezza said:

Don't Triumph 675s have 5.5 inch back wheels? They look really good in older bikes

They do but they are quite a fragile wheel. I've seen a few bent badly by potholes 

[imago]

There's a slight change of plan, I'm going for '09 on ZX6r wheels as the spoke pattern is closer to the look I want. They're also light, plentiful, reasonably priced and use a 5.5" rear. 

 

[coombehouse]

27 minutes ago, imago said:

There's a slight change of plan, I'm going for '09 on ZX6r wheels as the spoke pattern is closer to the look I want. They're also light, plentiful, reasonably priced and use a 5.5" rear. 

 

The sprocket carrier looks to be a better design for easy machining too.

[Dezza]

Probably a good idea to go with a 5.5. It will enable more flexibility. Putting a 6 inch race wheel in my project bike involved having a bespoke sprocket carrier machined from scratch. The original put the chain out too far as it was of such a design that it couldn't be machined enough so the chain would clear the frame.

Edited August 24, 2023 by Dezza

[TonyGee]

yeah i think a 180 is about the biggest you can go on our old bikes, any bigger then as dezza says lots of machining. 

[imago]

25 minutes ago, TonyGee said:

yeah i think a 180 is about the biggest you can go on our old bikes, any bigger then as dezza says lots of machining. 

I'm not too fussed about the big tyre thing tbh, my main concern is being able to get some sticky rubber on there and there's plenty of choice in the 160, 170 and 180 widths for 17" rims. So rather than try to squeeze the widest possible into it I'll probably compromise at 170/55 and save myself some work.

[TonyGee]

13 minutes ago, imago said:

I'm not too fussed about the big tyre thing tbh, my main concern is being able to get some sticky rubber on there and there's plenty of choice in the 160, 170 and 180 widths for 17" rims. So rather than try to squeeze the widest possible into it I'll probably compromise at 170/55 and save myself some work.

yeah i agree, but still better than the original skinny wheels  

[imago]

13 minutes ago, TonyGee said:

yeah i agree, but still better than the original skinny wheels  

Sticky rubber that's 40mm wider with far less sidewall flex is going to be a big improvement. Not to mention the 100% increase in braking surface. 

[Tony Nitrous]

18” back and front.

Cant remember the size but from memory they were early GSXR size. Tyres a bit close to the chain but never caused a problem.  As already mentioned the numbers aren’t everything, one tyre can be different to another even if the sizes are written the same.