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Discussion Starter · #1 ·
Hi All,

New to all this so be gentle!

I've got a 97 Triumph Sprint which i'm planning to chop about and turn into a café racer cross scrambler type affair (it makes sense in my head).

I'm happy with the stock rear sizes but want to go a bit bigger on the front.

Going to fit some knobbly tires so... (probably conti's)

Rear is 170/60 17
Front is 120/70 17

If I was just to upsize the front, how big could I go?

If I was to swap out the forks and go for a larger wheel is it just a case of wider yokes on the original headstock?

Sure this is grade school stuff but hey, gotta start somewhere!

Thanks in advance!
 

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Littering And...........
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The issue with just a tire would be tread width when at proper pressure compared to the width of the forks. Of course you'd have to measure the forks and find tread width sizes on google.

Or you could have a set of billet yokes made. Then have adapters made for whatever wheel you choose to be on the front. Lots of billet this way. But always a very nice look when completed. Lots of math. Gives me a headache. Can't function.


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watches you sleep.
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Hi and welcome to Custom fighters. If it were me I would take a look and see how much room youve got to work with now and how bad the sides of a wider tire might "crown" if installed on your current rim. If you wanna go real wide(like a 160 or something) than you're looking at modifying a rear wheel to use u front as well as having custom yokes made up. Not an cheap thing to get done.
 

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Discussion Starter · #4 ·
Hi and welcome to Custom fighters. If it were me I would take a look and see how much room youve got to work with now and how bad the sides of a wider tire might "crown" if installed on your current rim. If you wanna go real wide(like a 160 or something) than you're looking at modifying a rear wheel to use u front as well as having custom yokes made up. Not an cheap thing to get done.
Thanks for that.

I was only thinking of going up a couple of sizes, say a 140.

I suppose my question here is can the original wheel take a 140?

The other option was the rocket 3 front takes a stock 150 so could potentially use that front end. Although I am not keen on mis-matched wheels!
 

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I've actually been in the process of trying to find out if a 140 will work on my 92 GSX-R 750 as well. Got no help from Gixxer.com of course and was met with the most close minded ****** attitude I've ever seen from a forum before. Anyways yeha I not a fan of mis matched wheels myself but it might be work checking into to see how cheap a matching rear wheel is a what it would take to make that happen. I dont think it matter what you do man youre gonna have to put in quite a bit of work to make this happen if your current front end wont accept a 140 on its own with no mods.
 

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Generally speaking, you can use a tire about 10% bigger than what the rim was designed without any ill effects, assuming it fits in the fork or swingarm. More than that and you start to excessively "crown" the tire, meaning the curve of the tread is no longer even, it sharply curves down toward either edge. Bikes I've ridden with way oversized tires(only ever on the rear though) tend to have a somewhat nervous, twitchy feeling when really leaned over.

So I'd be comfortable going from the 120 to a 130 front. I suspect this would still fit in the forks without any modifications. 140 would be pushing it. If you get knobby tires, the knobs tend to poke out a little farther than the sidewall, so a 130 street tire may fit but maybe not a 130 knobby.

If you plan on riding this primarily on the road, you might want to reconsider knobby tires, or at least DOT knobbys(the knobs are close/shallow enough the tire never breaks contact). If you ride a dirt bike on pavement and make a corner, it feels like it's drifting toward the outside of the turn, they just won't hold a line. This is because at speed, there's a split second where the tire is actually off the ground, rolling off one nub before the next touches down. During this time the bike very slightly slips outward.
 

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Discussion Starter · #7 ·
If you plan on riding this primarily on the road, you might want to reconsider knobby tires, or at least DOT knobbys(the knobs are close/shallow enough the tire never breaks contact). .
Thanks mate, that's useful.

I was going to use some continentals - twinduro's - which are oem on the GS1200. They've just rebranded them so not sure of the new name just yet though...
 
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